Hints & Kinksfor the Radio Amateur

Edited ByStuart Leland, W1JEC

The American Radio Relay League, Inc.Newington, CT 06111

Copyright © 1978 by

The American Radio Relay league, Inc.

Copyright secured under the Pan-AmericanConvention

International Copyright secured

This work is Publication No. 10 of the RadioAmateur's library, published by the league.All rights reserved. No part of this work maybe reproduced in any form except by writtenpermission of the publisher. All rights oftranslation are reserved.

Printed in USA

Quedan reservados toaos los derechos

Library of Congress Catalog Card Number:33-14685

$4.00 In USA$4.50 elsewhere

Foreword

How can you find a solution to a tricky problem in youramateur radio workshop or station? Has some otheramateur experienced a similar problem? Chances aresomeone has already grappled with a like problem andhas devised a workable solution. It shouldn't be surpris­ing. Inventiveness has always been an outstanding qualityof the radio amateur.

This booklet contains a collection of such tricks of thetrade, written by several hundred amateurs. Many of theirideas were published originally in 05T, the monthly jour­nal of the League.

A sincere effort has been made to touch upon a widearea of interests with the Intention of offering somethingfor everyone. And should you find your own experimentsproducing a handy answer to a common problem, send itto 05T. You may be among the authors of the nextvolume of Hints & Kinks for the Radio Amateur.

Richard L. Baldwin, W1RUGeneral Manager

Contents1 Aids for the Station

and ShopPage 7

2 Test Gear IdeasPage 21

3 Transmitting and ReceivingKinksPage 36

4 Hints for the Power SupplyPage 56

5 Antenna TidbitsPage 65

6 Thoughts for CW OperatorsPage 76

7 Portable and Mobile QuickiesPage 95

8 VH F Band·aids and TricksPage 108

9 Notions for Various ModesPage 118

10 Data for PC Boardsand Solid StatePage 126

IndexPage 133

- -------- --._...._.._--

Chapter 1

Aidsfor the Station and Shop

SOME IDEAS ON STATIONLAYOUT AND HELPFULACCESSORIES

Desk drawers with stops: "Second" or"reject" doors, finished and mounted onlegs, with flaws 'underneath, have comeinto common use as desks. Two-drawerfiling cabinets on each end, beside the legsOr in place of them, further extend theusefulness of the gimmick. There is a needfor more carpentry to make shallowdrawers for installation under the lengthof the front of the desk. An easy trick is touse shallow aluminum baking pans of thetype that are made with a rolled liparound the top. Strips of wood can begrooved, then glued and screwedunderneath the door. The pans are simplyslipped by the lip into the grooves. For anice finishing touch, varnished strips ofwood are secured to the front side of the"drawers." Both front and back slidestops are made by placing a stick-on rub­ber foot on the underside of the table. Forthe inside stop, simply reach inside theopen drawer at its intended maximumpull, and stick the stop in place.

Step-to-talk: For those who haven'tdiscovered the ease of using a foot switch,here's a quick application for a relay fromthe junkbox. Select one that will sit flat onthe floor, wire the push-to-talk circuitthrough a length of line cord to the con­tacts, and place the assembly on the floorunder your operating table. A mic on aboom makes for hands-off operation inthe absence of VOX as well as the profes­sional studio look for the station.

Centralize your switches: A friend ofmine, K9KXP, told me how he stops wor­rying about wearing out the switches in hisvarious units. He has them wired througha master control panel which can berigged to include master switch, fused cir­cuits and the individual circuit switches

labeled for various pieces of equipment.Wire such a unit with a three-wire systemfor maximum shock protection. The in­stallation might also include a voltage­monitor meter, and the position would be

\.l

This operating position features many of thehInts described, including a relay for the footswncn, power panel, boom mlc and Kleenexbox speaker cabinet 85 well as the custom­crafted baking pan drawers under the table.

a good place to put your SWR meters.Speakers the easy way: New poly­

planar foam cone speakers are beingmarketed by Lafayette Radio Electronicsin a 5 x 8-inch (127 X 203 mm) size andwill fit marvelously into a plastic Kleenextissue box, the oval opening serving as thecabinet sound exit. Drill four holes in thefront, spaced to fit the speaker mounts;mount the speaker with a double layer of

grill cloth, and drill two more holes inback, where you prefer, for hanging thespeaker cabinet on the wall.

Doorstop/bookend: I just can't bringmyself to throw out that old transformerthat burned out in my af amplifier. Itmakes a fine bookend or doorstop. Besure to put a strip of felt on the feet so youdon't mar the bookshelf. - HarrisonLeon Church, WeKXP

HOLDING LIGHTWEIGHTEQUIPMENT IN PLACE

Years ago, amateur equipment would stayput by sheer weight alone. Today, light­weight transceivers and the like will scootoff the desk with just a slight nudge.

I have found that a piece of indoor­outdoor carpeting will hold them in place.The equipment feet nestle down into thenap of the carpet. The rubber backingholds the carpet material firmly to thedesk top or other surface.

When stacking gear, put a piece ofcarpeting under the feet of the top unit.This should not be used on a ventedcabinet of course, but is great for solidones, such as speaker enclosures. ---:- EdHeubach, W9AO

BEWARE OF PROTECTIVEDIODES

A word of caution regarding the use ofprotective diodes across the antenna inputterminals of solid-state receivers is inorder_ If separate antennas are used fortransmitting and receiving, severe TVI canbe created by the diodes rectifying thetransmitted signals and reradiating themon many frequencies in the rf spectrum. Idiscovered this while experimenting withmy solid-state receiver. I was attemptingto see if the diodes really protected the

Aids 'or .he Station and Shop 7

HOTE'LEHGTH OF STRIPSWILL VARY WITH BOXLENGTH, THEY SHOULDBE FLUSH WITH INNERSURFACE.

An orange-crate transceiver stand.

ORANGE-CRATE STANDFor those who have a small operatingtable, a wooden orange crate makes an ex­cellent stand for a transceiver. One of thelong 'sides of the crate is removed to pro­vide a small storage space below. I have akeyer , bug, and small lamp storedunderneath with room to spare. If addi­tional support is desired, wooden stripsabout I X 1 X 12inches (25 X 25 X 305mm), attached as shown in the drawing,should. do nicely. - Robert Zagorac,WN9QYU

GROUNDING AC LINESHoward M. Berlin's (K3NEZ) "DangerLurks!" article in February, 1976, QSTwas excellent. Because of Berlin'sfamiliarity with the subject, I think hemay have overlooked supplying informa­tion which some hams do not have.

When a receptacle is properly mountedin a wall box, the pin hole GROUND is atthe bottom. The line ground (NEUTRAL)is at the left side of the two slots. It islarger than the hot side slot in some recep­tacles.

The GROUND pin hole is frequentlyconnected to the conduit or BX cable andlike many other "pipe" conductors, doesnot provide the most perfect ground. Innonmetallic sheathed cable (Romex) in­stallations, the ground is simply a barewire.

Modern two-lead (two connections)wiring devices will show different colors

LATCHING RELAY SOURCEFor your latching relay requirements, Ihave found VW electrical systems. a goodsource of supply. They use a latching relayto control high- and low-beam headlightswitching with a single pulse button. Mylast trip to the local junkyard netted mefour relays for two dollars. The quality isexcellent and the size is about l-inch cube.Older VWs are 6 V and newer ones are 12V. - Walter Lelioret, WA3VCY

BASE

~' · '\. , 7

2'8"

!:/ /fAPPROX.2' LEGS

® ):-

SCREWS GO IN ON UNDERSiDETO HOLD DOOR DOWN

of work. While not necessary, the ends ofthese pieces were curved to improve theappearance.

3) Place the 22-inch pieces (legs) over'these half-moon cuts and mark the legs sostarting holes can be made. Four a-inchNo. 14 wood screws should be sufficientto hold the legs in an upright, stationaryposition.

4) Next, place two 1 x e-incb piecesover the ends of the legs and drill fourstarting holes at the four positions. Securethe two I X 6 pieces with four No. 14wood screws. This completes the base forthe table.

5) Set a door or a sheet of plywood112- or 3/4-inch (13 to 19 mm) thick ontop. Drill two holes through the 1 X 6 at

, each end, so that they enter the top.Secure to top with 1-112 inch No. 14woodscrews. This completes the table.

6) A 2 X 4 is placed on the back side,about halfway down, to give the tablelateral stability and to support electricoutlets and cabling. A piece of plywood'will do very nicely, too.

7) A large shelf on top gives additionalroom for equipment. A 2 X 12 was usedhere. The end supports (also made from 2X 12 stock) for this shelf should becentered over the 4 X 4 legs of the table.L-shaped brackets hold the shelf together.

The overall dimensions used will makethe surface of the table about 28-1/4inches (717 mm) high, which is quite com­fortable for myself. The height can be ad­justed by making the legs differentlengths. The table can be disassembled in­to its basic components, if necessary. ­Mike Greenway, K4TBN

t",e"-EXACT LENGTHOF COOR BEING USED

SUPPORTSARE INSETA fEW IN-;,";:;."27':;V

'" '"""~\2J BE CURVEDDRILL AND COUNTERSINK HOLES AT EACH END

HAM SHACK TABLEFor about $30, a handsome desk that willsupport heavy equipment can be built byfollowing some simple steps. This infor­mation is offered as a guide for anyamateur interested in constructing his owntable (see drawing).

1) Two 4 X 4-inch, (102 X 102 mm)8-foot (2.44 m) lengths are cut into thefollowing dimensions: four pieces 22inches (558 mm) long, two pieces 33inches (838 mm) long.

2) Half-moon shaped cuts are made6-112 (615 mm) and 7-112 inches (190mm) from each end of the 33-inch-longpieces. These cuts should be 2 inches (51mm) deep. A jigsaw is handy for this type

2," 012,"

USE WOOD SCREWSAND COUNTERSiNK

12"

Plans for a homemade table that can be disassembled eaSily and Is large enough to handle mostof the equipment in one's shack. The builder can modify accordingly to suit his own needs.

front-end rf transistor stage by leaving thereceiver connected to its own antennawhile transmitting with a 3S0-watt rignearby. I was impolitely informed by theXYL that I was raising havoc with thetelevision set. As soon as the receiver wasdisconnected from its antenna, theproblem disappeared. If the same antennais used for transmitting and receiving,such a problem should not exist. - G/enBenskin, K6UH

GMT "HOUR HAND"A homemade "hour hand" of thin sheetmetal fixed to the same shaft as the hourhand of your clock, and set to the propernumber of hours ahead (or behind) willshow GMT, while the original hand willshow local time. - Tom Chaudou,WN9FLD

8 Chapter 1

NOTE :42.661.21-1152 MHz1152 +144 ·1296 MHz

+~T 15V

220 m

(Editor's Note: The circuit is similar to the modi~edPierce oscillator, which uses the crystal between gnd Iand grid 2 of a tetrode tube. Depending upon the reso­nant frequency of the output network of theoscillator, overtone or fundamental crystal-modeoperation can be obtained.]

DUAL-GATE MOSFET OFFERSAN UNUSUAL CRYSTAL·CONTROLLED OSCILLATORCONCEPTThis unusual crystal-controlled oscillatorcircuit offers some interesting possibilitiesfor application as the LO in vhf and uhfconverter design. No trimming or tuningis required to get the overtone frequency.Should the fundamental frequency of thecrystal be desired as the output, raise thevalue of RFCI to tOO ~H or replace it witha 1000·ohm resistor.

The stability of the oscillator is ex­cellent. Actually the circuit works wellwith as little as four volts applied to it. ­G. Tomassetti, I4BER

power for the IC. A switch should be in­stalled in the circuit to prevent running thebatterydown when the preamplifier is notin use. - Robert D. Shriner, WAIlUZO

1000 OUTPUT"':>,-<>--1 f-(---"1( 10 mW

L_+-l I AT~42.661MHZ

1000'2k4100

to the carbon element. Remove the carbonelement and install a dynamic element.One with approximately 500 ohms im­pedance is satisfactory; however. I havenot found any element that won't work.

Distribute the rest of the parts aroundthe inside of the microphone case. Prac­tically any pnp transistor will work in thiscircuit. Any of the' general replacementaudio types should do. A drop or two ofcement or liquid rubber will hold the partsin place. Connect points Band D to thedynamic element.

For use as a desk mic, add the Ie circuitshown. Connect the output of the Iepoints Band D to the input of the tran­sister circuit, points Band D. Connect thedynamic element to the input points Aand C.

The output waveform is clipped by the1N34A diodes to prevent overmodulation.Careful adjustment of the input and out­put potentiometers will result in adistortion-free signal. If the input level istoo high, severe clipping will occur. Ad­just the input so that normal voice levelwill just start clipping.

A small 6-volt battery supplies the

Schematic diagram of te pre-amp for use with desk microphone.

A ,10./Jf

'OkHi~M>C '> I rGAIN

~2 ~C

IO./Jf

5 U, '<, • 6 ~,6,V AMPLIfiERHEP <; GAINz/ ' 4lN34A lN34A

-i>+7~~ '"'6V

: 'MS'M

~~6V

+lllr

+~< "V

4'00 reo

,- 3300DYNAMICELEMENT 0 '+

PUTIING YOUR BUG ORPADDLE IN ITS PLACEAND KEEPING IT THEREI keep my bug in place by applying a smallamount of rubber cement on the feet andpressing the key down on the desired spoton the table. When I wish to move thekey, I just pry it loose from the table. Theold cement rubs off easily, leaving nomarks on the table. - M. CrosbyBartlett, K4EU

DUAL.PURPOSE CARBONMICROPHONE REPLACEMENTSome of the fm transceivers coming intoservice in the vhf amateur band still usecarbon microphones. A vast improvementin audio quality can be achieved by the useof a dynamic microphone replacementcartridge.

Shown is a simple transistor circuit thatcan be used to adapt a dynamic element toa carbon circuit. The voltage required Jarthe transistor is derived from the samesource that originally was used by the car­bon element. To make the adaptation,simply open up your microphone case anddetermine the positive and negative leads'

Standard circuit for 117·Vac receptacle,

GROUND, THIRDWIRE PIN

'NEUTRAL'LINE "---+f

GROUND

of metal at connections. The natural brassis' the HOT side. The light-colored con­nection (tinned, nickel, cadmium, etc.) isthe NEUTRAL (line ground) side. If thereis a third connection, as in plug recep­tacles, it is the ground connection, screwhead daubed bluish-green.

In devices with pigtails, the white lead isneutral ground. In ac power wiring, whiteis almost always neutral ground. It mustnever be broken with switches, fuses, etc.The hot lead is black or any color exceptwhite. - B. H. Hansen, W6HOZ

Schematic diagram of simple transistor adapterfor dynamic element to carbon microphone ctr-cult. A crystal-controlled oscillator with Interesting possibilities.

Aids lor Ihe Slelion end Shop 9

ADJUSTMENT OF POLAR RELAYSFORRTTY

Almost nobody uses polar relays thesedays in connection with amateur RTTYoperation, but there are still hundreds ofthem available as surplus, and at com­paratively low prices. They have manypossible uses besides RTTY. The mostcommon type is the Western Electric2SSA, and there are several equivalentsmanufactured by other companies. If youhave one of these relays that you wish toadjust. try this simple procedure. It isn'tas precise as you could do with a polar­relay test set, but is plenty good enoughfor most purposes. You will need anoscilloscope for finest adjustment,although fair results can be obtained usingonly a de voltmeter. A small nail or thepointed tip of a soldering aid can be usedfor the adjustment tool. A feeler gaugemight also be helpful.

The circuit for testing the relay is shownin the accompanying diagram. If you planto check relay adjustments frequently, thecircuit can be built into a 3 x 4 X 5-inch(76 x 102 x 127 mm) chassis box withinsulated binding posts provided for scopeor meter connections. With SI closed, thearmature (moving contacts) of the relaywill move back and forth between thefixed contacts 60 times per second. That'sjust a bit slower than you would get withan RTTY signal at 100 wpm. The outputfrom pin I (through the lOO-ohm resistor)will alternate in square-wave fashion, go­ing from + 1.5 V to -1.5 V.

Begin the adjustment by disconnectingthe ac power. Back off the contacts andthe pole pieces (those round-shaped thingsbelow the contacts) and check to see thatthe armature is centered inside the coilopening. If not, loosening some screws onthe bottom of the relay should allow youto position the coil for best alignment.After you get the coil set so the armatureis centered, tighten all screws. Adjust onecontact screw until it just makes contact.

A polar relay such as this may be adjusted bymeans of the test circuit shown below.

Use the de meter or watch for a shift in theposition of the baseline on the scope.After contact is made, back off thirtydegrees or 1/12 turn on the contact screw.This should give a .D02-inch clearance.Then adjust the other contact in the samemanner. You should end up with a sym­metric arrangement, with .002-inchclearance on either side of the armaturecontacts.

Now turn one pole piece until the arma­ture just touches the opposite contact.Then back off on the pole piece slightlyless than a half turn and tighten the ten­sion nut. Then adjust the second polepiece so that the armature stands midwaybetween the two pole pieces and tighten itstension nut. The armature should flip toeither contact and remain, or else return

to center, when moved manually. Slightreadjustment of the second pole pieceshould help if needed here.

Now apply ac power. Look at thewaveform on the scope, or use thevoltmeter set on a low-value de range.You should see a symmetric signal on thescope. It will not be a perfect square wave,because some time is required for thearmature contact to move from one sideto the other. During the travel time, youwill sec a small part of the waveformwhere the signal is neither positive nornegative. During contact, the signalshould be positive or negative 1.5 volts.Any nonsymmetry can be corrected by avery slight readjustment of the pole pieces(not the contacts). If you are using a meterfor indication, the meter should read zero.Slight pole-piece adjustment should bringthe reading' to zero, if needed. On theoscilloscope you may observe someamount of contact bounce, as a broken­up portion of the square wave. A veryslight readjustment of the contacts maycorrect this. You won't be able to detectany contact bounce using a meter only.

That's all there is to it. Just a word ofcaution: Once you apply the ac and makereadjustments, go very slowly and do notmake adjustments of more than a smallfraction of a turn. Usually with surplusrelays, if they can't be adjusted by veryslight trimming, something is defective inthe relay. Even if this is the case, com­promise settings can sometimes be foundwhich will give quite satisfactory relayoperation. - KITD

COLOR CODING CIRCUITDIAGRAMS

Numbered triangles showing connectionsbetween parts of a schematic clean up thediagram, but make it difficult to find thecompanion number of a pair. I color themaround the outside, using a different colorfor each pair. - Temple Nieter, W9YLD

Schematic diagram for adjusting polar relays. Resistances are In ohms.51 - Spst slide or toggle switch. shown with relay plugged In).T1 - Filament transformer, 6.3 V at 0.6 B'Tl, BT2 - 1.5·V penlight cells. A Key-

A (Halldorson 21F21 or eqvtv.). stone Electronics no. 140 or equlv.X1 - W. E. 255A relay socket Iclrcult battery holder may be used.

TV BACKDROP

With more amateurs using SSTV and fast(regular) scan television, the need for awhite backdrop becomes important forthe production of high-contrast pictures.The installation of a white roll-type win­dow shade hanging from the ceiling,mou~ted a few feet behind the subject,provides a suitable background for thispurpose. - Robert W. Gervenack,W7FEN

(Editor's Note: This is a handy hint for matching upsections of multifunction res.]

CATVTVI

This information should be of interest toany ham operating in a community orcondominium complex served by cabletelevision. After being informed that I was

OSCILLOSCOPE'00

,----"'-';----.,- - -- -15

6' I11 an +

-'-----o-C'---J t±---~h>---I-o.. :4 6T2...l:"

~'------'-i,-J I

L .J

w.E.2!55A

o

T1

O.!5A

10 Chep,er 1

A crystal oscillator for locating W1AW on 80meters.

A STABLE CAPACITORROTOR CONNECTIONElectrical connection to the rotor of 'anair-variable capacitor is usually madethrough the use of small brushes whichrub on the shaft or through contact be­tween the shaft and the bearings. Thereare times when corrosion or dirt will causethe connection to become intermittent.This becomes an important factor whenbuilding any circuit requiring good fre­quency stability, such as a tunableoscillator.

.~-­Modification of air-variable capacitor to make astable rotor connection.

pump, and an "armstrong" energy sourceapplied, I have a variable-velocity air jetthat is cheap and easy to build, which doesthe job very well. - Ben Fidler, W7PZ

A remedy is shown in the drawing. Firstdrill a hole through the shaft; then drill ahole at right angles into the shaft near thefront of the capacitor. Use a No. 34 toNo. 40 drill size depending on- the shaftdiameter. Fish a length of small-diameter,stranded copper wire (usually 27 gauge) /'into the hole in the end of the shaft andout through the egress hole. Solder thewire onto the shaft at the egress hole.Next, make a small brass bracket asshown in the drawing with a mountinghole and a soldering tab for a connection.Attach the bracket to the capacitor frameby means of a nut and screw. Solder the Iwire coming out of the shaft onto thebracket. This completes the installation.- Gene Pearson, W30Y

[Editor's Note: This type of connectio";"'should beused primarily with an air-variable capacitor with astop.l

ADDED SWITCH FORCONVENIENT OPERATIONOF HM-I02 WATTMETERI recently purchased a Heath HM·102wattmeter. and have noticed that it is easyto change the position of the sensitivitycontrol when pulling out and pushing inthe switch that selects forward and reverseindication. I replaced the 'original switchwith a miniature spdt toggle switch. If theswitch is centered on the panel just belowthe meter, it does not affect the ap­pearance of the instrument. - RobertWerner, W8BTD

WEATHERPROOFINGLOW·VOLTAGE CONNECTORSSalt finally corroded one of the taillightson the boat trailer. The price of a newlight was more than offset by discoveringthe trick that the manufacturer used toprevent the problem. The sockets for thebulbs were liberally smeared with grease,which effectively weatherproofed themetal parts, while not interfering with thepressure-contact electrical connectors.While a more suitable compound isrecommended (such as Dow CorningDC-4, which is also good at rf), the authorused ordinary marine grease (the kindused for pressure fittings and steeringlinkages) on the other lights, and withgood results. The method could be used toadvantage by amateurs where low-voltageconnectors may be exposed to moisture. Itdefinitely should not be used on ordinaryrubber, since reaction between the greaseand rubber will ruin the insulation.However, most modern plastics will notbe affected. - WI YNC

PLASTIC-BAG TIES MAKENEATER CABLE HARNESSESThe serrated plastic ties supplied withdisposable plastic bags are useful aroundthe shack and mobile installation to holdthe various cables together. Unlike thecommercial version, they may be un­fastened when a wire must be added orremoved. - Mack Beal, WIPNR

CERAMIC TUBE CLEANERI had a problem in trying to keep the lintand dust out of the cooling fins on theplates of the 8122 final amplifier lubes inmy linear. They are the ceramic types likethe 4CX250 family.

My solution was to solder anautomotive 'inner-tube valve stem to the4-inch spout of an oil can, using a l-inchsection of copper tubing as a coupler be­tween the two. The end of the spout hasan opening of about 1/16 inch and whenthis arrangement is connected to a tire

without holes could simply be glued to thebottom of the piece of equipment. - RayBass, W7YKN

Economical cable ties.

~----<l+,!lIOK

COLOR·BURST OSCILLATORCRYSTAL HELPS VISUALLYHANDICAPPED LOCATE WIAWEven when using a tOO-kHz calibrator, itis difficult to know what frequency areceiver is tuned to if you can't see thedial. The color-burst generator in a colortelevision set operates on approximately3.579 MHz, close to the WIAW bulletinand code practice frequency in the80-meter band. A color-burst crystal waspurchased from a local TV repairman for$2, and the circuit shown was constructed.Now my sightless friend can easily locateWIAW. - Steven A. Licht, WB2CZC

causing TVI on several occasions, someinvestigatory work seemed necessary. Theproblem stemmed from the loss of con­tinuity in the outer shield conductor onthe CATV feed line from their mainfeeder to the subscribers' sets. In eachcase, the connectors joining the feed lineto the main line had corroded to the pointwhere the resistance between the feederand the main line was on the order of40,000ohms. The subscribers still receivedreasonably good quality pictures, but igni­tion noise and other forms of interferencewere also present. The CATV people wereadvised of the situation and have beenmost cooperative in resolving the prob­lem. - Richard M. Purinton, WISXI4

KEY DOWNMaybe your XYL won't like you drillingholes in that maple operating desk so youcan mount your new electronic keyer pad­dle or "bug." Two-way carpet tape plac­ed on the bottom of the "keys" will holdthem quite well; also the tape is useful forwall maps and other items that requirehanging. - Larry Baine, W8GBR

RUBBER FEET FOR EQUIPMENTMany hobby shops stock a large supply ofrubber stoppers intended for use with testtubes and flasks. They come in many sizesand are usually slightly tapered. Somehave holes drilled through themlengthwise, which would facilitate mount­ing with sheet-metal screws. The type

Aids lor Ih. S,.,lon .nd Shop 11

A simple vector calculator.

CMU BIAS POT

C-105c+

1) Secure a copy of the manufacturer'sinstruction manual for the tuning pro­cedure and general information On theparticular piece of equipment to bemodified.

2) Obtain a crystal of the proper fun­damental frequency so that the unit can betuned up on 460.45 MHz, the originaldesign center frequency.

3) A power supply which will provide330 volts at 400 rnA, 330 volts regulated(for use with the oscillator) and -105volts for bias is required.

4) Remove the modulator-limiter tubesfrom their sockets.

5) Tune the "strip", as if for operationon 460 MHz; about Ig watts of 28.3-MHzenergy willbe required for proper mixing.Mixing can be accomplished by applyingthe 28.3-MHz signal to the 5894 grid orcathode circuit. The circuits at A showtwo methods for mixer input. The cathodecircuit is suggested since it is the easiest ofthe two methods.

6) Apply a 28.3-MHz signal as shownand readjust the output at 432 MHz. Astrip-line filter should-be used to attenuatethe unwanted mixer products. Under key­up conditions the 5894 output circuit isout of resonance since the plate tank cir­cuit is tuned to 432 MHz and the excita­tion to the tube is at 460 MHz. Tominimize damage to the strip (and forcooler operation) the circuit shown at Bprovides for the last three stages of thestrip to be biased to cutoff during key-upconditions.

The eMU-IS provided about 10 wattsof output power after the above modifica­tion was performed. This output power isused to drive a 4CX250B linear amplifierfor use with OSCAR 7. It has performedvery satisfactorily. Ben Stevenson.W2BXA

2N3635

28.3 MH21N914 (OR EQUlV.)

USING STiLLoCAMERA LENSESON SSTV CAMERASMany SSTV cameras are designed to uselenses having a "Cvmount." This type ofmount is used on many I6-mm motionpicture cameras, and dealers often stockadapters allowing various .ss-mm still­camera lenses to be fitted to a C-mount.In addition to allowing the use of lenseswhich may be already available, still­camera lenses are usually of higher opticalquality than those commonly supplied foruse on video cameras. - Bill Levy,WA2RODI5Z4Pl/VQ9BL

(AI

5694

AMSAT-oSCAR 7, MODE BOPERATION MADE EASIEROne way to generate a signal of any modeat 420 MHz is to high-level mix twosignals in the final amplifier stage of aMotorola, RCA, General Electric or anyof the other commercially manufactured460-MHz business-band equipment.These units are usually rated for aminimum output power of 15 watts, withthe final output stage operating in theClass C mode. A very cooperative unit fOT

conversion is the RCA CMU-IS whichuses a 5894 as the output tube.

Here is one procedure for convertingthis type of rig for use as a high-levelmixer:

base and fasten it to the operating table(rough side up of course) with a few piecesof wide masking tape. If the operatorwants to change the position of the key,

_he can simply move the sandpaper.The same system can be used to keep

the rotor control box, lamps, and otheritems from walking around the desk.WIFBY

eo- ¢":,

\

«I/

0II /

0f

0 rr I0 if / /0

/1//

/:;0 fT L-/0 [7, V '/- V -/

=1'!O2030 50607080901

e

,•

9

•7

90' 80' 70' 60"W

x

2 10",/

\ cZ\ /'

\ . /P~~~~E~E:'~OF~~IN-, __./ 1. FROM HYPOTENUSE OF TRIANGLE.

EXAMPLES: ~O.j. )~0·TO.7L'!~":~OO-)~90' 71~L-50'

Pl\RALLEL TO SERIES CONVERSION:

Z'Z~-)100 ZPARALLEL' 'iT+"Z2

~'0040'.1004-90"

• \00-1'100' --vY'v7r,O"o!.- 90' 00 -j50roo ~. 70,7L-'!5"

WB2NAG POLAR TORECTANGULAR CONVERTERWhen calculating ac circuit behavior, theuse of polar and rectangular formrepresentation of the vector relationshipsis almost indispensable. The "Impedance­triangle" relationship between X, R, Z,and the phase angle +can be worked outfrom the trigonometric relationships in anumber of ways. A picture is worth athousand words, so the Chinese say, andoften mathematical relations are clearerwhen expressed graphically as in the sim­ple vector calculator in the illustration.

The calculator can be fashioned fromposter board. Measure off the 10 XIo-cm grid into l-cm squares using a ruler.Set up the phase angles with a protractor.

Pin the rotating Z member to the bottomleft corner of the calculator with a thumb­tack. Flatten the protruding tip againstthe back and put a piece of masking tapeover it to flx it into place. Mark off the Zscale in I-em divisions. - John Carlini.WB2NAG

Circuits for converting the RCA CMU·15 460·MHz bustnees-bend.untt for OSCAR 7, mode B at 420MHz. Tuned and untuned cathode mixer inputs are Illustrated In A. Biasing Is provided by the cir-cuit at B. .

KEEPING THE KEY IN PLACEIf the operating table has a smooth suraface, keeping the key or paddle in placecan be a problem. Removing dust fromthe rubber feet often helps, but the heavy­fisted operator still might have problems.An easy cure is to cut a piece of fine­grained sandpaper to the size of the.keyer

lSI

1000

"100)JF +

2200.,2000

R1, C1 PROVIDE A TWOSECOND DEl.AY

-105VTO CMU

.250k

TO l.IMIT VOl.TAGEACROSS TRANSISTOR

12 Chapter 1

NAIL POLISHIN THE HAM SHACK

I) I use red nail polish to mark dialsand points on cabinets for rotaryswitches.

2) Red for the Hoff" button or switchon .all equipment so the XYL and har­monics will know what to push if I leavesomething on when I am out.

3) I use red and white (other colors areavailable) to identify mating male andfemale connectors as in the case of theleads on a stereo or tape deck.

4) If you have a screw or nut that tendsto work loose with vibration, a dab ofpolish under it will hold it solid.

5) Don't overlook nylon cord andrope; a little polish on the cut end stopsthe raveling.

6) Clear nail polish is ideal for water­proofing labels on equipment and elec­trical connections that tend to corrode. ­Max Pierce, K8DYI via DARA Bulletin

1M"3 tao,

~OFF

~ ~+9V9Vi ,1'

E~CEPT AS INDICATED, DECIMAL VALUES OF

CAPACITANCE ARE IN MICROFARADS ( JJF l ;OntERS ARE IN PICOFARADS (pF OR JJJJFl;

RES\STIINCES ARE IN OHMS;k' I 000, M'IOOO 000.

0'2N915

OR EQUIV.

.001

"-':>'1H~TPUT

~

low cost are achieved by using CMOSs in­tegrated circuits and a minimum numberof components.

Fm receivers and transmitters operatingin the vhf range are typically crystal con­trolled, and they use a small value trimmercapacitor to "net" the unit on thespecified channel. Without a frequencycounter f it is difficult to accomplish thisto any degree of accuracy. By using asecondary frequency standard withswitch-selectable outputs every 100, ,50,25, 20 and 10 kHz, it is possible to set thetransmitter or receiver on frequencyquickly.

The frequency standard uses twoCMOS quad 2-input NOR gates and a1000kHz crystal oscillator. The CD4017counter is wired in a divide-by-X. con­figuration by connecting two NOR gatesas an RS flip-flop to reset the counterafter X counts. The output level of thelO-kHz markers is on the order of 15 to 30~V at 150 MHz. - Alan D. Wilcox,W3DVX/WB4KRE

HINTS AND MORE HINTS

I've noticed quite a few hints on ways tokeep one's hand key from moving abouton the table. The best and least expensivemethod I've found is to use loops ofmasking tape between the key base andthe table. Two loops are formed withabout two inches of masking tape. Thetop half of each loop is secured to the baseof the key, and the key is then presseddown on the operating table. This methodkeeps the key firmly in place, yet it may beremoved without leaving any gummyresidue on the table.

I recently built a shelf for my operating

U3 - CMOS decade counter-dlvlder IC,type CD4017 or equlv.

"Rl l~OfJF

33 l~V

EXCEPT AS INDICATED, DECIMAL

VALUES Of CAPACITANCE ARE

1"1 MICROfARADS l JlF I ; OTHERS

ARE 1"1 PiCOFAFlADSl pI' DR JlJlFI;

RESISTANCES ARE 1"1 OHMS;

k -1000. M·IOOOOOO

spet contacts.Q1 - Darlington pair (Motorola HEP semi·

conductor).R1 - See text.81 _ Dpdt toggle or slide switch.S2 - Spst toggle or slide switch.T1 _ Audio transformer, 8-0 to 100

ratio.

isn't critical but the unit should be built ina metal enclosure to provide rf shielding.- Bill Radice, K20 WR

A secondary frequency standard.U1, U2 - CMOS quad 2·1nput NOR gate

ICs, type CD4001 or equtv.

VHF SECONDARY FREQUENCYSTANDARD IS INEXPENSIVEAND BATTERY OPERATED

The secondary frequency standard shownhere provides accurate calibrationmarkers for vhf fm channels in the 144- to225-MHz bands.' Battery operation and

'00

~'L S<A .

~ TO XMTR PTT L1"1E

Jl :> i 0Mit ,

"

Schematic diagram of the contest accessory.8n - 9·volt tranetstor-radlc battery

(RCA VS323 or equIvalent).C1 - See text.CR1, CR2 - Silicon diode (1N914or

equivalent).J1 - Connector to mate wIth station mlcro­

phone.J2 - RCA·type phOno Jack.K1 - Sensitive dc relay with B·volt coil and

CQCONTEST

Using a prerecorded tape to call CQ dur­ing a contest is nothing new, but many vhfrigs don't have VOX, and manuallyswitching the PTT line is tedious. This cir­cuit will automatically activate the PTTfunction of the transmitter. while the tapeis playing. Cl and RI determine the delay

. time before the relay drops OUt, and exactvalues will depend on the relay used. TI isconnected to step up the voltage beforeapplication to the voltage doubler. Sl isused to select the microphone or tape in­put. The TAPE IN connection is made tothe speaker of the tape recorder. Layout

Aida 'or Iha Slalion and Shop 13

RUBBER;'BANO

RECYCLED BATTERIES

Used film packs from Polaroid SX-70cameras contain a flat-plate, Ray-O-Vac,e-volt battery that is still good even aftertaking ten pictures with the camera. Thebattery is enclosed in a cardboard andplastic envelope which measures 3-1/2 X4-1/2 X 1/8 inches. These batteries canbe connected in series, parallel or series­parallel to provide a variety of voltagesand ampere-hour ratings, and thus areideal for powering portable, low-powerequipment. Removal of the battery iseasy. Simply break off the plastic end ofthe container and slip the battery out ofthe case. Individuals should pay attentionto the warning stamped on the battery: Donot cut, take apart or burn the battery. Sodon't throw those SX-70 film-pack bat­teries away - recycle them! - R. W.Johnson, W6MUR

SEALANTS FOR AMATEUR USE

Many radio amateurs will find uses forone-part silicone rubber sealer that is soldunder such' names as RTV, Silastic, andbathtub and tile sealer. On exposure to theair, the material forms a waterproof rub­bery substance. This type of sealer hasbeen used at WB6GNM for over twoyears, and no deterioration of the materialis apparent.

One use of the material is to seal anten­na connectors. I have also used it to formnon-skid feet for a keyer-paddle base.Clean the base with alcohol to remove anygrease or oil; then put a dab of the siliconerubber on a sheet of waxed paper andallow to cure or set overnight. - PaulZander, WB6GNM

SOLDERING VISEFOR SMALL PARTSA spring-type wooden clothespin makes ahandy vise for soldering small work.Mount it in a vertical position on theworkbench. - K1ZZ

This ruined the tip for other uses, butsoldering-iron tips are relatively inexpen­sive to replace. - Julian N. Jablin,W91WI

A film-pack battery.

Long-nose pliers work nicely as a heatsink when soldering solid-state devices.Simply clamp the jaws of the pliers overthe pigtail of the transistor, diode, or Ie(between the point to be soldered and thebody of the semiconductor) before doingthe soldering. (This idea was borrowedfrom the Heath HW-lOl manual.) ­WNlLZQ

Long-nose pliers used as a clamp.

A TIP ON SOLDERING-IRONTIPS .

The tip on my so-wan soldering ironnever seemed too massive until I triedsoldering a 24-pin IC socket to a circuitboard. The old trick of wrapping a pieceof copper wire on the tip as a thin exten­sion was an unwieldy arrangement. Iremoved the tip from the soldering iron,chucked it in my electric drill and"turned" the tip down against a file. Thebest shape for my purpose was a thin sec­tion, terminating in a long tapering point.

pulses getting into the chip and upsettingits normal operation. The following pro-­cedure was used with success to solve thisproblem in six different clocks:

1) Bypass each of the set and holdswitches (pins 13, 14 and 15 of the clockchip) to ground with a .Ol-I'!' diskcapacitor.

2) Bypass each side of the ac line toground with a .OI-I4F capacitor.

3) Parallel a .OOI-~F and a .01'~F diskcapacitor and place this combinationacross the SOO-I4F filter capacitor in thepower supply. Your clock should then beessentially noise immune and a nice assetto the ham shack. - Leland R. Shultz,KORAB

THAT OFT·NEEDED"THIRD HAND"It can be frustrating when trying to solderseveral leads together at one time. If onlysomeone 'were near at hand to hold thoseelusive wires together until they weresoldered! Well, here's a simple remedy forthe problem. Simply encircle the handlesof your long-nose pliers with a goodsturdy rubber band, then grip the leads tobe soldered with the tips of the jaws, thusfreeing one of your hands.

WIRE SOURCEA handy source for No. 14 through No.6solid copper wire is the wire sold for housewiring. Most hardware and Sears storesstock two-conductor plastic covered wireand it can be purchased in any length re­quired. - WlICP

MM~"14

CLOCK ~'''". --'

CHIP 15p-- ---.J

table to hold all my equipment about sixinches above the surface of the table. Thispermits me to store my hand key, bug andkeyer in the space beneath the shelf. Withthe keyer under the shelf, I am no longerable to see the indicator knob for ad­justing keyer speed. I cemented a smallpiece of plastic to the knob, to protrudeabove the edge of the knob. By locatingthe position of the plastic with my fingers,I am able to determine the setting of thespeed control, and thus control keyerspeed without looking at the knob. Thismight be a useful accessory for sightlesshams.

I have always envied owners oftransceivers equipped with "spinner"knobs on the VFO. After seeing the fre­quency control knob on the Heath SB­104, I considered purchasing such a knobfrom Heath. Instead, I found a buttonwith a recessed center in my XYL's sewingbox, and cemented it to the edge of theknob on my SB-102. The button wasselected to provide a good fit to my finger­tip, and also to match the color of my rig.I can now shift effortlessly from one endof the band to the other. - Stu Levens.WB60GK

CAPACITANCE IN MICROfARAOS

MORE ON DIGITAL CLOCKSFOR THE AMATEUR STATION

For those who may have constructed thedigital clock described in the November,1974, issue of QST (by Bert Kelly,K4EEU) using the 6O-Hz time base, youmay have found to your dismay that itgained time radically. This is due to noise

Adding capacitors as shown reduces digital·clock noise problems.

14 Chapter 1

MORE ON SILICONE SEALANTSIn "Hints and Kinks" for May, 1976.WB6GNM described several uses for one­part silicone rubber sealants. If sealantsare to be used near electronic componentsor connections in an enclosed area, thesealant used should be one that gives offalcohol, rather than a corrosive substanceas it cures. One alcohol-cure sealant Ihave used successfully is Dow-Corning738, available from their distributors. ­Roger Halstead. K8ZKF

CIRCUIT·BOARD HOLDER

After only a brief exposure to workingwith circuit boards and the problems ofsupporting these unwieldy lightweights, itbecame obvious that some holding devicewas an absolute. must. The commerciallyavailable clamps are beautiful, but theyare expensive, and who needs all thoseuniversal joints?

The device I use was built from parts­readily available and simple enough for aone-evening project. My unit has a widthcapacity of 6 inches, but this can be in­creased by using longer threaded rods.For the ham with limited working space,this clamp has the advantage of beingstored easily when not in use, freeing theoperating position or kitchen table forother uses.

The 1-1/2 X 1-1/2 X 6-inch (38 X 38

x I S2 mm) aluminum tubing used as abase for the clamp is available - usuallyas scrap - from any aluminum-awningfabricator. The material I found had awall thickness heavy enough to be tappedfor the No. 6-32 screws that hold theplastic jaws. Wooden blocks could besubstituted for the aluminum tubing atsome sacrifice in weight and appearance.

The screws, nuts, washers, and thread­ed rod are available at any hardware store.The 1/4-inch rod comes in 36-inch lengthsat about 60 cents per length, so your totalinvestment should not be more than acouple of dollars. The plastic jaws werecut from 3/16-inch sheet stock (2 pieces 1X 5 inches) (25 X 127 mm). However,there is nothing sacred about these dimen­sions. The tapered clamping edge shouldbe worked with care to obtain a truestraightedge and a uniform taper fromend to end. This is not as difficult as itsounds. Place a sheet of sandpaper on aperfectly flat surface and hand lap theedge while checking at intervals with aknown straightedge.

The holes in the aluminum tubing topass the 1/4-inch rods should be drilledfor minimum clearance. This will permitsmooth adjustment while avoiding sloppyaction at the jaws. With a little effort andminimum expense you can roll your owncircuit-board clamp for near-perfectworking conditions on that next solid­state project. - Dave Adams. W6DRM

USE COIL DOPE ORAIRPLANE GLUE TOSHIM UP ANDTIGHTEN SLUG

~~"-COTTON SEWINGTHREAD WRAPPEDAROUND SCREWTHREADS

Two ways to tighten coli slugs.

TWO METHODS FORTIGHTENING LOOSESLUG-TUNED COILS

Here is a way to solve a minor problem. Ifyou should have a loose iron core in a coil,two methods for tightening it again areshown. I have used both methods and itsaves a lot of trouble when critical tuningis necessary. One word ofcaution; use theglue carefully-andavoid getting any on thecoil turns; it may affect coil Q. ­Franklin Rosenberg. W6NYG

REPLACEMENTSOLDERING·IRON TIP

Unable to locate a tip for my Ungar no.403S soldering iron, I used a copper boatnail that is threaded with a no. 5-32 die. ­J. Edward Goervey, WA2VTG

Printed circuit-board rig. Wooden blocks can be used Instead of aluminum tubing.

[Editor's Note; Ferrite material obtained fromhorizontal output transformers and loop antennasfrom portable radios may be usable up to 10 MHz.One particular ferrite sample tested gave good perfor­mance up to 7 MHz. In general, these ferrite cores canbe used in equipment that covers the 160- through4O-meter bands.)

SOURCES OF FERRITEMATERIAL FOR CHOKESAND COILS

If you plan on winding your own rf chokeor coil and the design calls for the use offerrite as core material, where can it befound? One source of ferrite cores is olderportable radios. These radios usually haveferrite rod antennas. The existing wire canbe either unwound or cut off. Anothersource of ferrite cores is the horizontaloutput (flyback) transformer in televisionreceivers. Use a hacksaw to remove thewindings.

Many of the cores, whether from televi­sion sets or radios, are approximately 1/2inch (13 mm) in diameter. This dimensionis satisfactory for most bifitar chokedesigns, but sometimes a smaller diameteris required. These cores can be cut andground to size, but caution must be exer­cised since they are brittle. If breakagedoes occur, not all is lost. These cores canbe glued or taped together. - WarrenMacDowell. W2AOO

1-114" 00 WASHER

t·V2'x l-tl2'x 6" AL.UM. TU8E (2)

3/16" PLASTIC STOCK (2)

PL.ASTICCL.AMPINGSURFACES

6-32 x 3/8" FH SCREWS (6)

\

Aids for the Ststlon snd Shop .15

BRAIDED SOLDEREDFOIL SI,DE

Connecting coaxial cable to a wafer switch issimplified by the method described below.

WIRING COAXIAL CABLETO A WAFER SWITCHHere is a useful way of getting rid of thehorrible mess that occurs when trying towire up a 3-pole, 3-position, rotary switchwith RG-S8/U coaxial cable. Cut a smallpiece of copper-clad, phenolic' board more)orless in the shape of the switch wafer.Orilla couple of holes in it to match thedistance between the screws 'that hold theswitch assembly together. Then with thefoil side of the board facing away fromthe switch, drill three holes which will ac­commodate the shields of the cable (a No.30 drill is about right.) Then solder thecenter conductors to the appropriate lugs,and the shields to the copper-clad board..This scheme results in a very neat jog, andalso provides a good ground for the braidthrough the frame of the switch. - M.Crosby Bartlett, W9MCIWB40BF

COILED CORDFOR THE SOLDERING IRONThere must be a special section ofMurphy's Law covering soldering irons.No matter how carefully you set the irondown, you always end up burning holes inits cord - or the schematic that you areworking on. One cure is to replace the pre­sent cord on your soldering iron with onecif the coiled appliance cords available atelectrical supply houses. The cords stretchout to five feet, but coil up to about nineinches when the iron is not in use. ­WIKLK

REVITALIZING NICADBAITERIESNickle-cadmium batteries of the kind usedin Motorola P-33 hand-carried fmtransceivers are prone to becomingrelatively lifeless after a few rears ofcharging and discharging. Though the oldbatteries will take a charge, the capacity ofthe units is very small. A tired battery willreveal its condition by allowing only a fewminutes of transmitting time after beingfully charged. However, the receiver wiIlperform fine under the same conditions,mainly because the de-to-de converter

16 Chepter 1

which supplies operating voltage to thetransmitter strip consumes considerablecurrent.

Those wishing to renew battery life canplace a pellet of industrial potassiumhydroxide (ACS pellets) in each cell bankof the batteries, after removing the plugs.The chemical carries the number FW­S6.11, and sells for approximately $1 perpound in most areas of the USA. ­WIFB

NON-SLIP D1P-SOCKET IDEAOf several methods suggested for securingDIP IC sockets to perfboard for wirewrapping (with a drop of glue, by bendingone pin, etc.} WA3LLJ seems to havefound the most convenient.

Electrical tape prevents an Iechip from shift­Ing or falling.

Asdepicted in the photograph, apply apiece of black vinyl electrician's tape tothe top of the perfboard, sticky sidedown. Then simply push the socket pinsthrough the tape and the perfboard holesfrom the top of the board. The tape willkeep the socket from shifting position orfalling off the board during wiring. Thesocket can be removed easily or reposi­tioned. - Edward Kalin, WAIJZC

ETCHING ALUMINUM

Recently, I built a version of McCoy'sTransmatch. Un fo rtun at ely , thealuminum shows scratches and finger­prints. So, I etched the material in a solu­tion of washing soda and hot water. I usedtwo tablespoons of sal soda per gallon.The aluminum to be etched must be clean.Immerse the parts in the solution for threeto five minutes, then remove and drythem. - Geoffrey S. Vore, W9QBJIWA9MZH

REMOVING SOLDERFROM TERMINAL STRIPSAND PC BOARDS

Although commercially manufacturedtools are available for the purpose, themethod shown is handy when removing

SOLDERINGIRON

A syringe for removing solder.

components from either pc boards or ter­minal strips. Cut the tip off a smallsyringe and insert a short length of Teflontubing into the end. It should be approxi­mately 2 inches (S I mm) long and1/16-inch (l.S mm) 00. If Teflon tubing

.is unavailable; the metal insert' from aball-point pen could be substituted. Wrapthe metal part that goes into the syringewith masking tape to prevent burning;The only difficulty with using a metal tubeis that solder tends to stick to the wallsand will have to be drilled out after a fewoperations.

Heat the terminal strip and squeeze thesyringe before the solder starts to melt.When the solder starts to flow, bring thetip of the tube up to the joint and releasethe pressure on the bulb quickly. Themolten solder will flow up into the bulb,leaving the terminal relatively free. ­WINPG

SOLDER PLATING - CHEAPIMany experimenters have told me thatthey are tired of looking at their work sit­ting on ugly old oxidized copper circuitboards. The general comment is, "Surewould be nice to either tin or silver plateour circuit boards, but who can affordsilver powder or a solder-flow pot?" Thesolution to this problem is simple. Oneneed not look any further than his solder­ing iron.

Hand tinning is really nothing new; itjust seems to be one of those things that isnot often passed on to others. Previously,I sent out all my board work to be tindipped and did so at great expense. As thebills mounted up, I decided it was time tofind a less expensive solution. The one Ifinally came up with was hand tinning.

Hand tinning requires only some goodrosin-core solder, a. flat-tipped 6O-wattsoldering iron, and for best results ­some liquid solder flux. Superior no. 30 orequivalent will do nicely. The liquid fluxaids the flow of solder onto the copper.

In the case of double- or single-sidedboards, apply a generous amount ofsolder onto the board. Next, hold the cir­cuit board upright with some pliers andslowly run the excess solder off the board

with the soldering-iron tip. Once the ex­cess solder has been removed, the boardmay be cleaned. Freon TMC or isopropylalcohol and a small brush will do the job.

Small wattage soldering irons should beused and care should be taken so as not toliftthe copper off the board. The excesssolder may be removed by the samemethod as before, or it can be done moresafely by using a solder-wick. Rememberthat on small surface areas it is easy todestroy the bond between epoxy and cop­per with too much heat.

After you have practiced this a fewtimes, you will not only get more profi­cient (and lessdestructive), but will proba­bly find ways of improving on this techni­que to suit your own needs. - RickOlsen, IVA 7CNP

STEEL PIPE SIZESAND STRENGTHSIn "Hints and Kinks," May, 1976, QST,page 36, W5LW describes a good fold­over tower he built from galvanized steelpipe. Hams wishing to duplicate the towermay misinterpret the pipe sizes. For exam­ple, standard pipe, referred to as being of2·inch size, has an actual outside,diameterof 2.375 inches (6 mm), and an insidediameter of 2.067 inches (52.5 mm), Stan­dard I-I/4-inch pipe is 1.66 inches (42mm) in outside diameter, with an insidediameter of 1.3g inches (35 mm). Schedule80 or extra-strong pipe may be used foradded load-bearing capability and windresistance. This heavier pipe has the sameoutside diameter as the standard grade,but has a thicker wall, resulting in insidediameters of 1.939 inches (49 mm) for2-inch pipe, and 1.278 inches (32.5 mm)for 1-1/4-inch pipe. I also suggest thatconsideration be given to the pipe fittings.Cast-iron fittings often crack under stress,while malleable iron fittings have atendency to stretch. A better choice wouldbe cast steel or the more expensive forged­steel fittings. The fitiings used should bethe extra-heavy type, as opposed to thestandard strength. Either size,fitting willaccept both standard and extra-strongpipe sizes. - Henry Spang

RESTORING NICAD CELLSAND BATTERY HOLDERSThe failure mode in NiCad cells is causedby fine conducting whiskers which growbetween the electrodes and prevent the cellfrom accumulating a charge. A momen­tary high-current through the cell willsometimes disintegrate the whiskers,allowing the cell to charge normally.

I have successfully restored several cellsby charging a 3S,OOO-J,fF capacitor from a12-volt supply and discharging thecapacitor across the cell. After twodischarges of the capacitor, each cell wasrecharged according to the manufac­turer's recommendations.

The spring clips in battery holders losetheir gripping ability after about a yearand should be replaced. A poor connec­tion will result in a small resistance inseries with each cell, causing a significantvoltage drop when current is drawn fromthe battery pack. - Ed Piller, W2KPQ

GROUNDING STRAPSUBSTITUTECopper-plated pipe-clamping strips, soldin hardware stores, make cheap and stur­dy ground straps for the shack. - LeoFinkelstein, Jr., WA4AOL/WB40NY

F connector becomes a BNC.

TWE-F TO BNC ADAPTERS

It is often necessary to adapt from a type­F connector to a BNC fitting. Adaptersfrom type-F female connectors to BNCmale or female connectors may be easilymade from type-F chassis female conec­tors available from TV sales stores andany of the BNC variety of connectors withbodies threaded to receive 3/8-32 clamp.ing nuts'. Before assembling, trim thesolder lug on the type-F connector toallow the center pin of the BNC connectorto just contact the lug when the connec­tors are assembled. It is only necessary tosolder the pin and lug together andreassemble the pair (see photo). - HaroldS. Eisley, W3NET

EXTRACTING HARD-TO-REACHTUBESIn my Collins 7SA3 receiver, one of thetubes, a 6BA6 (V-5), defies extraction. Itis located where only the tips of thefingers can touch the top of the tube, andunless one risks damage to the tube byusing a pad type of instrument reaching tothe bottom, removal for testing orreplacement of the tube is virtually im­possible.

The problem was solved with the use ofair-conditioning "duct" tape. The tape ismade of heavy cloth and has an adhesivethat grips well to most anything it

touches. Cut two strips of duet tape 1/4X 3-inChes (6 X 76 mm), Have a coffeestirrer (wood or plastic) or any stiff sliverof wood handy. Lower the tape stripalongside the tube, leaving enough of thetape above the top of the tube to allow theends to be pressed together. Do this toboth sides of the tube, using the stirrer togently press the tape to the sides of thetube. An easy pull on the strips will releasethe tube from its socket. Leave the tape inplace on the tube until after the tube hasbeen replaced in the receiver. Using thesame coffee stirrer, pry the adhesive awayfrom the tube. Although this techniquewas used on my receiver, it could be ap­plied to any piece of equipment whichuses tubes. - Mack O. Santer, W2ZPW

REMOVING HARD-TO-REACHPA TUBESIn many modern transmitters andtransceivers, it is difficult to grasp thefinal amplifier tubes to remove them fromtheir sockets, due to the tight compart­ment surrounding the tubes. A modernversion of the Chinese finger grip,manufactured. by the Kellems Division,Harvey Hubbell Inc., of Stonington" cr,greatly" simplifies tube removal. Thedevice, used- for industrial applications, iscompressed slightly and" pushed - downover the tube. When pulled up, the braidcompresses around the tube envelope,allowing the tube to be removed from itssocket. The braid may be removed fromthe tube by compressing it once again. ­David Higgins, KIBCG

ALUMINUM TAPEFOR SHIELDINGIn the 1950swe learned that extreme filter­ing and shielding of our communicationsequipment was required to avoid creatingTV!. Yet today we see manufactured andhomemade gear housed in non-metallic orpoorly shielded metal enclosures.

The author has found a heavy-gaugealuminum tape manufactured by SpartanPlastics, Inc., P. O. Box 67, Holt, MI48842, very helpful in fabricating easy andconvenient shielding. It is sold under the.name "Trim Brite Custom Trim Metal­Mend Tape no. 11822," and is intendedprimarily for repair of auto bodies. Theauthor bought a 3-3/4-inch (95 mm) by5-foot (1.524 m) roll for $1.37 in a localauto shop. It should not be confused withMylar tapes which appear metallized, butare realty plastic.

As far as the author knows, theadhesive used is nonconducting, so thisshould be taken into account in anyshielding project. Seams should be closedwith metal-to-metal covering or 3MScotch tape no. X-1I70, an RFI tapewhich does have conductive adhesive. Thelatter is designed for the purpose, but may

Aida lor the Station and Shop 17

DIA. IN MILS

Correlation TableTOROIDAL COIL FORMSFROM PLASTIC TUBINGIn situations where a low-Q toroidal in­ductor is desired, it is practical to cut asection of plastic tubing for use as a coilform. Acrylic and polystyrene tubing arebetter than nylon or vinyl, due to the highrf losses of the latter two. I found that3/4-inch (19 mm) diameter tubing, cut toa height of 1I4-inch (6 mm) and woundwith No. 20 wire, yielded coils with a Q of40 to 50 for a 2- to 5-~H inductor. Someplastic supply houses may give away smallscraps of tubing. - Don Lawson,WB9CYY

SPAGHETTIYour local hospital is an excellent sourceof spaghetti tubing. For medical applica­tions, the tubing can only be used once. Arequest to a doctor or nurse will usuallybring you enough plastic tubing of varioussizes to provide a lifetime supply for hampurposes. - WIKLK

STRAIGHTENING ANDREALIGNING DIP IC PINSHere is a four-step procedure using onlyfingers and a t6-pin dual-in-line socket tobend the pins of the Ie into correct align­ment: (I) Use the tip of a finger on the endof each bent pin to put the pins approxi­mately in line with each other. Ooly theends need be in alignment since the nextstep should straighten the shanks of thepins. (2) Insert one row of pins fully intothe socket as shown in the drawing. Verylittle force should be required for the in­sertion of the pins. Remove the IC fromthe socket and insert the second row ofpins as described above. (3) Place the ICon the socket and visually check the pinalignment. If the two rows of pins are toofar apart, or' otherwise misaligned,reinsert one row of pins in the socket as instep two. (4) Hold the IC by its body anduse the socket to bend the pins until therow spacing is correct, and insert the ICall the way into the socket in the normalmanner. The socket will be easier tohandle if it is mounted on a three or four­cm square base made of pc board. - D.F. Zawada. W9MJG

The second of four steps in straightening andrealigning DIP Ie pins. See text.

pin

No. 26 wire

.016

.051No. 16 wire

No. 24 wire

.020No. 22 wire.025

.062 "Flea"clips 8, F, G &H pattern

.064No. 14 wire

.032 No. 20wtre-Morex pin

No. 18 wire.040042 P patter!"). hole.045 DP socket

.015

Tolerances 14-16pin DP rc

1/16" drill .0625

No. 51 drill .067

No. 65 drill .035

No. 60 drillNo. 58 drill

No. 56 drlll .046

No. 55 drill .052

No. 72 drill

BONDING ALUMINUMWITH SOLDER AND FLUX

Several times in the past there has proba­bly been a need to bond something madeof aluminum to some other metal used ina home-built project. Alpha Metals offersa solder and flux package called"Depend-Adsond" that does the jobquite well. Several repair jobs have beendone using the Alpha Metals product withfavorable results. A tOO-inch coil and0.3S-fluidounce package are available as acombination from most hardware storesfor approximately $2. - WA6GVCII

Drttl-blt correlation table.

PC drills - wire size - Motex pins - DPsockets, etc.

Paper capacitor small no. 21 .0281f4-walt resistor no. 19.0361/2·watt resistor no. 18 .0401· or z-wett resistor no. 17 .045

WIRE-WRAPPING TOOLA dried-out ball-point pen refill may beconverted into a wire-wrap tool by cuttingoff the tip just above the ball, and filingor sawing a small notch in the metal. Besure the refill is dry before cutting the tip!- Chas. C. Whysall, K4WZ

TABLE SIMPLIFIES SELECfIONOF PROPER DRILL BITA copy of this table, showing the nearest,numbered drill bit for the lead diameter ofa component, when posted at theworkbench, speeds the drilling of holes inprinted-circuit boards. - Charles E_Terry. W4FZX

TEST POINTSIn planning the construction of equipmentit is desirable to give consideration to pro­viding useful test points for measuringvoltages. Small loops of tinned wire maybe soldered to appropriate points in cir­cuits to serve as test-probe connections. ­Carlos H. Daniels, WB4FlR

CLEANING CAPACITANCE­ACfIVATED KEVER PADDLESCapacitance-activated keyer paddles, suchas the Data Engineering ElectronicFeather Touch, become erratic in opera­tion when dirt and oxide build up on themetal grid. The dirt may be removed witha soft cloth moistened with denaturedalcohol. - Wayne E. Whitman, W9HFR

~lOOP FOR PROBE TIPNO. 20 OR 22 TINNED

SOLDER TO WIREPC BOARD -.....

Small loops of tinned wire are soldered to ap­propriate poInts In the receiver clrcultry toserve as test-probe connections.

RESISTOR ADDED TO S-CENTTRANSISTOR TESTER MAVSAVE TIlE LIFE OF AN FETA 100000hm resistor in series with the bat­tery of the five-cent transistor tester(Brophy, "A S-Cent Transistor Tester,"QST for November, 1975, page 24) mayprevent accidental destruction of a field­effect transistor, should the battery leadsbe improperly polarized when connectedto the transistor. - Franklin Swan,W9SIA

SLIPPING DIAL DRIVEI had an old receiver in which the dial cordon the tuner was slipping. I tried a varietyof things to put some traction into theline, and finally tried alum. A simple wet­ting of thumb and forefinger on the alumand running the fingers along the line didthe trick.

That was twelve years ago and that wasthe end of the trouble; it has not slippedsince. - A. P. McMonigal, WB8VZW

not be obtained as easily as the Spartanproduct, especially in the greater width,Obviously, the wider tape should be usedfor large areas, and the narrow X-Il70with conductive adhesive should be usedfor corners, seams, etc.

The author has used both tapes inshielding a transistor rig in a partly plasticcase, as well as a uhf converter in a plasticcase, both of which caused TVI beforetreatment. - Edward F. Erickson.W2CVW

18 Chapter 1

INSULATING ALLIGATOR CLIPSHere is a simple method to add insulation.(sleeving) to alligator clips that alreadyhave wires attached to them. Use a lengthof shrinkable tubing about 1-1/2 timeslonger than the clip being used and largeenough to slip over the closed clip. Mosttubing will shrink to about one-half itsdiameter, so when heat is applied to thefar end only, it will usually shrink farenough to keep it from sliding off thefront end. If you like a loose sleeve, thejob is done.

My preference is for a sleeve that doesnot slip back, and that is done easily bytying a knot in the wire behind the tubingor by building up the wire with tape. Theexperimenter wilt doubtlessly discovermany variations to suit his particularneeds. - James A. Herb, W3SHP

Aids lor Ihe Slelion end Shop 19

fields are converted to closed loops withinthe toroidal geometry, and a self-shieldingcharacteristic results.

Byemploying core materials which havespecific permeability factors, the numberof turns for a given value of inductancecan be reduced, as can the mass of theassembly. However, one can use a varietyof materials for constructing a toroidcore, provided the dielectric property ofthe substance used is suitable for the fre­quency of operation.

The photo shows three homemadetoroidal inductors for vhf use. Each unitis.wound for operation at 144 MHz (0.12,...:H), to resonate in the band with a shuntcapacitance of 10 pF. The toroid on theleft is made from a slice of 1/2-inchdiameter plexiglas rod with a hole drilledin the center. The unloaded Q measured150. The center toroid is wound on apolystyrene washer, and is measure Qchecked out at 160. The smallest toroid(far right) was fashioned from a piece of1/4-inch (6 mm) diameter Teflon rod. TheQ measured 130.

Proof of the self-shielding properties ofthe inductors came when a dip meter wasused to check the resonant frequencies ofthe coils (lO-pF capacitor across the wind­ings). No dip could be obtained, and thisis characteristic of any toroidal inductor.

Test inductors were made using vhftoroid cores (ferrite) of commercialorigin. Using the same L-C ratio, unload­ed Qs between 70 and 90 resulted. Stillpretty good, but fewer turns were neededto provide a like amount of inductance tothat of the homemade units. The fewerthe turns, the more difficult it is to findthe precise tap point on a coil whenmatching impedances. Therefore, thenonferramic cores may be preferred atvhf.

Those wishing to lessen the need forshielding in vhf solid-state transmittersand receivers, or to cut down on the sizeof the tuned circuits, may be interested inthis information. - WIFB

Homemade toroidal inductors for vhf.

HOMEMADE VHF TOROIDALINDUCTORSThe self-shielding property of a toroidal­wound inductor, whether it's air-woundor contained' on a toroid core of somevariety, can be beneficial in circuits whereunwanted interstage coupling is to beavoided. Some amateurs believe that inorder to qualify as a toroidal-wound in­ductor the coil must be wrapped around adoughnut-shaped object made of ferrite,powdered iron, or some other materialthan has an mu factor, Not so, for bybringing,the ends of any solenoid-type coiltogether (by bending the coil into a cir­cular configuration) the ends of the induc­tor, each being of opposite polarity, arenow in close proximity. Thus the magnetic

the modification kit for my FT-IO!. Thecolor code is the same as the one forresistors and capacitors as tabulated inThe Radio Amateur's. Handbook. Thedrawing indicates how to interpret themarkings on the Japanese components.The values are in ohms, microhenries and"picofarads.

For example, an inductor markedbrown, red and black would be 12 X 10",or 12-JlH. A ceramic capacitor marked30lK5 would be 300 pF, IO-percenttolerance, and 500 volts. In general, theworking voltage for ceramic capacitors is500 unless otherwise noted. - Noel B.Eaton, VE3CJ

/WOOD

CIRCUITBOARQ

INDUCTOR

FIRST SECONODIGIT DIGIT

"dYLTIPLIER

A

SECONDDIGIT

FIRSUxTIPLIER

""R

DISK CERAMIC

MYLAR

SECOND

MULTlPLIERfit""DIGIT

FIRSTDIGIT

CERAMICCAPAC ITOR

FIRST SECONDD

A

TOLERANCE

RESISTOR

SECONDDIGIT

FIRST MULTIPLIERDIGIT TOLERANCE

CIRCUIT·BOARD HOLDERThe holder for small-pc boards, as shownin the Heath HD-1250 manual, is also ex­cellent for holding small cables whilesoldering. - Dr. J. H. Grant, K4HHR

Markings on Japanese components are Inter­preted according to this chart.

ANOTHER SOURCEOF EQUIPMENT FEETA handy source of supply for equipmentfeet is the local automobile tire shop. It isgeneral practice when mounting or chang­ing tires, to replace the rubber valve stem.This is usually done by tearing the oldvalve out of the rim. The nub which heldthe valve in the rim is dropped on thefloor. The limit to the number of feet thatmay be obtained is only how busy the tireshop is. - WICW

DETERMINING THE VALUESOF JAPANESE COMPONENTSSome months ago we had fun trying tofigure out the coding on Japanese com­ponents. A copy of the code was found in

PINCHERCLOTHESPIN

A clothespin pc board and cable holder.

.-"

TOWARD BETTER·LOOKINGPANEL LABELS

Few of us have access to engraving toolsand silk-screen equipment for makingprofessional-looking labels on our equip­ment panels. Yet, most of us feel that apiece of homemade gear that works welldeserves to look nice if it is to become apermanent part of the ham station.

Having grown weary of battling withwater-transfer and press-on decals overthe years (to say little of trying to keep afresh supply on hand at all times), ] turn­ed to the more common practice of usingDyrno tape labels. I recalled the rathertired and "hammy" look that I had ob­tained when using them in the past, andthen decided to try a better approach thanbefore: I painted the panel a color thatwould match the available label-tapecolors. The results were considerablymore impressive than when] had put, say,black labels on a red panel, blue labels ona black panel, etc. By selecting paint andlabel colors that were matched closely, thelettering on the labels predominated sothat the main body of the labels did notstand out as grotesque rectangles on thepanel.

A further improvement came when Itrimmed the ends of the labels to an arc bymeans of scissors. Getting rid of the right­angle corners imparted a more profes­sional look. A pair of fingernail clippersturned out to be a useful tool for that job.- Doug Detdaw, 8P6EU

Another homemade adapter.

Screw a few threads of the adapter intothe PL·259. Next, place the outer shell ofthe second PL-259 over the wire and insertthe free end of the wire into the center pinof second connector. Screw the secondPL-259 onto the adapter snug against thefirst PL-259. Solder the two connectorstogether; then solder the remaining centerpin. Snip off any excess wire protrudingfrom the center pin. - Mac Bruington,W4NJE

ANOTHER HOMEMADEADAPTER

Many times the need arises to connect theoutput of a transmitter to a low-pass filteror coaxial relay. An adapter will enableyou to connect two SO-239 female con­nectors together as shown in the accom­panying photograph. All that is needed istwo PL-259 connectors, a UG-175 reduc­ing adapter and a short length of insulatedwire.

Saw off the "shoulder" on the UG-17Sreducing adapter. Thread the wirethrough the UG-175 and then through theouter shell of the PL-259 into the centerpin. Solder the wire to the center pin.

CHEAP·AND·EASY. PANEL TRIM

Adding a stripe of color to the panel of apiece of homemade radio equipment willoften impart a professional appearancethat might otherwise be lacking. Thoseubiquitous gray Hammertone rack panelscertainly need something to dress themup, and the technique described here doesthe job rather well.

Select a roll of masking tape that ismade to the width you prefer for a stripeof panel trim. (The writer has rolls of tapein various widths to meet various designrequirements.) Remove from the roll alength of tape somewhat in excess of whatwill be needed. Next, affix one end of thetape to a solid object. Hold the free end inone hand, and spray paint thenonadhesive side of the strip your favoritecolor. White, black, or red contrasts nice­ly with gray panels. After the paint hasdried, the strip can be applied to thepanel, and the free ends of excess materialsliced off with a razor blade.

White decals do not stand out wellagainst a gray panel. A strip of paintedmasking tape can be attached to the panel,fulJ length, above and below the row ofcontrols. White press-on decals placed onthe trim strip will be easy to read. Alter­natively, black decals can be installed on awhite or yellow strip.

Though the writer has not tried to useMystic Tape (available at most hardwarestores and supermarts), it should servenicely as trim. - WIFB

ju~t cut offtJietop'seetion and leave the ' " '.,bo~tom,section,orus~inTounting: ~th:a

small screw. 7" Stan J. Zuchora. waQKU

Handy homemade adapters.

ANOTHER SOURCEFOR COIL FORMS

For those fellows who like to wind theirown coils, another source for formmaterial may be your local coin dealer.Clear plastic tubes are used by collectorsfor storing their coins. There are six sizesof "coin tubes" ranging from the one­cent to the silver-dollar diameter. To usethe coin tubes, cut off the top and bottomsections with a fine-bladed hacksaw, or

HANDY HOMEMADEADAPTERSThe two adapters shown in the accom­panying photograph are simple to assem­ble and useful for hams using their2-meter rigs for both base and mobileoperation. The adapter at the top is forconnecting one chassis jack to another.Two male phono plugs (RCA type) and a2-inch piece of No. 16 wire are all that arenecessary. Place the plugs back to back.Run the piece of wire through both maleplugs, and solder the wire to plug tips. Besure the backs are touching one another,then solder them together.

For the other adapter, drill out the holein the reducing adapter (UG.175) to aO.242-inch diameter, using a letter "C"size drill. Remove the nut and washersfrom the chassis jack. Solder one end of a3-inch long, No. 16 wire to the center ter­minal of the chassis jack and the reducingadapter with a pair of pliers and threadthe jack all the way into the 0.242-inchdiameter hole.

Some resistance will be encounteredbecause the steel chassis jack is cutting itsown threads into the brass adapter. Thereason for assembling these two pieces inthis manner is that the chassis jack has a1/4-32 thread and a tap for this thread isnot readily available to the average ham.Solder the other end of the No. 16 wire tothe center terminal of the PL~2S9 and trimoff the excess wire. - Wayne L. Jung,WB9IQC

20 Chapter 1

Chapter 2

Test Gear Ideas

ECONOMICAL FET VOLTMETER

Circuit-board pattern for the FET voltmeter. The metal between the copper pads can be removedby means of a hobby tool and cutting bit.

"

\RB(ARM)

RB(LOW)

TO R7 R7s i (LOW) (HIGH)

BTl, (MINUS

TERM.)

FOILSIDE

TO SCALE

+2VR4 DC VOLTMETER'M C2., ,L01 R6

R1 R2 R5

°'0'

10M 'OM i00k+20 M'

S 0-100R7

R3 '0'1M ZERO

-GNO.~R'330 BTl., .V

~ON

U -111*5'

R'O'0'

G 5 0

Circuit for the FET voltmeter. Ftxec-value resistors are 1/4-or 1/2-W composition. C1 and C2 aredisk ceramic. M1 is a100-IlA dc meter. Q1 is a Motorola MPF102 or HEP102 or HEP602. R7 and ASare pc-board-mount composition controls.

Many amateurs may consider building thissimple voltmeter which uses one activedevice - a JFET. It will provide two de­voltage ranges, 0 to 2 and 0 to 20 volts.For most amateur solid-state experimenta­tion, it will not be necessary to measure delevels greater than 20. The accuracy of theinstrument is sufficient for all- but themost exacting applications.

Ml is a lOO-~ meter. Some current willflow in Ql even when no de voltage is ap­plied to the gate. Therefore, control R7 isadjusted to provide a zero reading on Ml.R8 is tweaked to provide a full-scale meterreading when two volts of de are appliedthrough R4. It may be necessary to read­just R7 and R8 a few times to achieve finalcalibration. It is best to calibrate thevoltmeter after it has been on for oneminute. Later, when the meter is to beused for voltage measurements, a one­minute warm-up period will assure properzeroing of the meter.

Isolated pads were formed on the cir­cuit board by means of a Moto Tool andcutting bit. It may be convenient to mountR7 and R8 on the front panel of thevoltmeter case. This will permit easyrecalihration. For greatest accuracy, Rlthrough R4, inclusive, should be i-percentunits. However, 5-percent resistors willsuffice for most amateur work.

Readout on Ml will be linear. Full-scaledeflection will represent 2 or 20 volts,depending on the range in use. Midscalereadings will equal I and 10 volts, respec­tively. It may be helpful to draw a newmeter scale having two ranges represented- 0 to 2, and 0 to 20 volts. - BP6EU

Te.t aeer Idee. 21

(

~-OHMLOAD

ToJ2,J4

ce~o.OO!l

To 51(FWD.)

J2

(matched pair recommended).RFCl - 1-mH rf choke (Millen J300-1oo0 or

equlv.).Sl - Spdt toggle.T1 - 60 turns no. 28 enam. wire, close wound on

Amidon T-68·2 toroid core (secondary). Pri­mary is 2 turns of small-diameter hookup wireover T1 secondary."

-Amidon Associates, 12033 Otsego St., N.Hollywood, CA 91607.

T<PRI.

SEC.

R2 "'aa "

ca~S.M.

REF. FWD.

st

",mSENS

To • .-----i~'\\\!i\\Xil\\'J1,J3

Schematic diagram of the aRP power meter.Cl, C2 - 0.5- to 5-pF trimmer (see text).C3 - 330-pF sliver mica.C4, C5 - Disk ceramic.01,02 - Germanium diode, 1N34A or equlv.Jl, J2 - Phono jack.J3, J4 - SO-239 type connector, or coax fitting

of builder's choice.M1 - 50-.uA panel meter (see text).R1 - Linear-taper 1/4- or 1/2-watt, 25,000-ohm

control.R2, R3 - aa-otrm. 1/2-W composition resistor

TRANS.

EKCEPT AS INDICATED, DECIMAL VALUES OF

CAPACITANCE ARE IN toUCROFARADS I J.lf I ;OTHERS ARE IN PICOFARADS I pF OR jljlFI;

RESISTANCES ARE IN OHMS;.'1000, hI.tOCO 000.

S.M.' SILVER MICA

An rf power meterlSWR indicator designed foruse with QRP equipment.

areult InformationThe circuit for the instrument is based

on the classic Bruene designI and wasmentioned in an earlier QST article. 2 It is

A QRP MAN'S RF POWER METERThere are a lot of pint-size hf-band signalsbeing transmitted nowadays, and this up­surge in QRP enthusiasm suggests a needfor some specializedtest equipment. An rfpower meter/SWR indicator is certainlyone piece of apparatus that all operatorshave frequent need for, but most in­struments that have been described inamateur journals are keyed to the QRO(high) power level. Rigs with less than fivewatts of output barely move the needleson medium- or high-power wattmeters orSWR indicators. Some kinds of indicators- the Monimatch for one - are frequen­cy sensitive, making it impractical for theuser to establish meaningful rf power'calibration for so-called all-band use (3through 30 MHz). .

Because of the writer's interest in QRPwork, it was decided to fill a personalneed with respect to owning a low-powermeasuring device. The circuit describedhere.satisfies the requirement, and can becalibrated for 0 to 5 watts, and is suitablefor operation from 80 through 10 meters.It is not "frequency conscious." so it willprovide the same meter deflection perwatt on all of the bands mentioned.

With the sensitivity control set at maxi­mum, only one watt of rf energy is re­quired to provide a full-scale meterreading. The user may wish to calibratethe instrument for some range other thanfive watts full scale. If so, he need onlyfollow the calibration procedure discussedlater, but set the sensitivity control at theappropriate point to provide the desiredrange.

Foil Side(Full Scale)

'Bruene, "An Inside Picture of Directional Watt­meters," QST, April, 1959.

lDeMaw, "In-Line RF Power Metering," QST,December, 1969. Scale template of QRP power meter pc board.

22 Chapter 2

2

Rf wattage can then be found by

E rms = VW X R

= 2W100SO=10'

SO

W=

W=

If the builder has an rf ammeter ormilliammeter he can do the calibration byusing the formula W = PR. Thus, if 0.2A of rf current is flowing through the50-ohm load, the power equals 2 watts(.04 X SO = 2). Be sure the rf ammeter israted for reasonable accuracy at theoperating frequency.

Some Final Remarks

The power meter can be used for ad­justing an antenna for minimum SWR, orin tuning a Transmatch.' Place SI in theREFLECTED position and make the re­quired adjustments to provide a meterreading of zero.

If a' zero reading can't be obtainedwhile adjusting a Transmatch or antenna,it is likely that the transmitter has an ab­normal amount of harmonic energy in itsoutput. A resonant load will not acceptthe harmonic current, causing it toregister on the SWR indicator as reflectedpower, even though the SWR at thedesired frequency may actually be I. Aharmonic filter can be installed betweenthe transmitter and the power meter toreduce the harmonic output, thereby mak­ing measurements more accurate.' ­W/FB

·DeMaw. "A Transmatch for QRP Rigs," QST.February, 1973.

'McCoy, "Getting Rid of Low-Frequency Har­monics," QST. April, 1968.

across the 50-ohm load, then convertingthe value to rms volts

Example: To find the rms voltage across50 ohms for I watt,

E,m, = 1/ I X SO = 7.07 V

Epk_pk X 0.707

It wilt be necessary to vary the transmitteroutput power by means of the drive con­trol, or by detuning the tank circuit of oneof the early stages, to obtain the rmsvoltage across the load that correspondsto the desired full-scale reading versus rfwatts. Calibration points on the meterscale can be selected by adjusting the rfvoltage across the load to a known valueversus power. then noting the meterreading and preparing a chart. The re- .quired voltage can be determined by

'Construction information on rf probes is givenin the chapter on measurements, ARRL RadioAmateur's Handbook. all recent editions.

desired by the writer and need not beemployed if just one type of fitting isperferred.

Most of the small components of thecircuit are contained on a pc board. It isimportant that all of the components inthe rf portion of the circuit be mountedwith the least amount of lead length. Thiswill assure minimum inductive andcapacitive reactance, thereby making thejob of nulling the bridge much easier.

A 1-II2-inch square Simpson meter isshown in the photograph of the completedinstrument. Any meter with a 0- to 50-JAAmovement will suffice. For power levels inexcess of 2 walls a 0- to IOO-~ meter willbe suitable. Those wishing to avoid the ex­penditure connected with purchasing ameter can use an existing YOM or VTVMfor visual indication. Simply install a pairof test jacks to permit connection of anexternal indicator to the existing meteringcircuit. Use one of the low-voltage rangeson the VTVM for your measurements.

AdjustmentIt will be necessary to have a nonreac­

tive 50-ohm dummy ioad for initial ad­justment of the power meter. A HeathCantenna was used by the author, but a2-watt 51-ohm composition resistor (5percenter) will work fine if the leads arekept short, and if no more than 5 watts ofrf power are applied during any lO-secondperiod.

Connect the dummy load to one port ofthe instrument and apply rf power to theremaining port. SI should now be thrownback and forth to determine which posi­tion gives the highest meter reading. Thiswill be the FORWARD position. Adjustthe sensitivity control for full-scalereading of the meter. Now, move theswitch to the opposite (REFLECTED)position and adjust the trimmer nearestthe transmitter input port for a null in themeter reading. The needle should drop tozero. It is recommended that these ad­justments be made in the 10- or 15-meterband. Next, reverse the transmitter andload cables and repeat the nulling pro­cedure while adjusting the trimmer on theopposite side of the pc board. Repeatthese steps until a perfect null is obtainedin both directions. The switch and thecoax connectors can now be labeled,TRANSMITTER, LOAD, FORWARDand REFLECTED, as appropriate.

Meter calibration can be effected at anyfrequency from 80 through 10 meters. Itwill be necessary to measure rms voltageacross the SO-ohm load by means of an rfprobe and a VTVM.) Those having accessto a wide-band scope can do thecalibrating by reading pk-pk rf voltage

•._11. '\f

not arranged (physically) for operationabove, say, 25 watts. At the higher levelsof rf power there is not enough isolationbetween the various parts of the circuit toensure a complete null when setting up thebridge circuit. The null will, however. becomplete at 25 watts or less. Those desir­ing to build a small power meter that willwork well from 25 to 1000 watts shouldconsider constructing one of the unitsdescribed in the article referenced by foot­note 2.

A toroidal transformer, TI, is used inthe rf-sampling circuit. A two-turn linkassures sufficient pickup to provide full­scale meter deflection (Tl primary). Thetwo trimmer capacitors, Cl and C2, incombination with C3 constitute the net­work for nulling the bridge. A pair ofsurplus 5-pF glass piston trimmers wasused in the author's model. Subminiatureair-dielectric variable capacitors can besubstituted, provided the minimumcapacitance is 1.5 pF or less. Alternative­ly, one can substitute a piece of double­dad' pc board, 1/4 x 3/4 inch in size, foreach of the trimmer capacitors. Each sideof the board then becomes a plate for thehomemade capacitor. A bus-wire lead issoldered to each plate near one end. Thecapacitor is adjusted by snipping off a bitof the board, continuing the process untila null is obtained (a piece of glass-epoxypc board of the foregoing dimensions ex­hibits approximately 6 pF of capacitance).

ConstructionThe QRP power meter is housed in a 4

x 4 x 2-inch utility box. Other types ofenclosures can be used if desired. Phonojacks are connected in parallel withSO-239 type jacks on each side of the in­strument. This was a convenience feature

This is an interior view of the OAP powermeter. Visible at the lower left are the pistontrimmers used for nUlling the bridge. Toroidaltransformer, T1, is located between the trim­mers. The pc board is mounted on the bottomplate of the utility box by means of two t-tnoh­high metal standoff posts which are attachedto the ground fall of the board.

Test Ge.r Ide.s 23

TOOSCIt.LOSCOPE

A high-impedance test probe can be assembl­ed from an old j·f transformer, or from a shield­ed Inductor and capacitor. C2 should be lessthan the normal value for resonance with L1, tocompensate for the capacitance of the cableand input circuitry of the oscilloscope. Seetext for a discussion of obtaining a value forC1 and C2.

A LOW I-F TEST PROBEA high-impedance test probe may beassembled from an old i-f transformert orfrom a shielded inductor and capacitor.Used with an oscilloscope, this probeenables one to look at the i-f signalamplitude without appreciably affectingor loading an rf circuit. When alignmentand repair work are completed. the probemay be removed without detuning the cir­cuit.

The probe is built from, an i-f trans­former and RG58/U coaxial cable. C1should be 10 pF or less if the oscilloscopeto be used is sensitive. Ten pF at 455 kHzrepresents a capacitive reactance of 3S kG.This high impedance, together with thehigh impedance of the tuned circuit, pro­vides a probe with very little loading. C2should be less than the normal value forresonance with Ll to compensate for thecapacitance of the cable and input cir­cuitry of the oscilloscope. The value of C2may be calculated by adding 30 pF/ft. ofRG58/U and the input capacitance of theoscilloscope, then subtracting this fromthe value that is needed for resonance at455 kHz. For example three feet ofRG58/U is 90 pF, plus 30 pF. A 7()()-~H

inductor for L1 requires 180 pF; thus 180- 120 gives a value of 60 pF for C2.

Tune the probe by feeding a 455-kHzsignal at CI and peaking LI for maximumsignal as observed on the oscilloscope. ­Carlos H. Daniels, WB4FIR

EMERGENCY CONTINUITYTESTER .

A simple continuity test can be con­structed with a receiver and two test leads.One test lead is connected to the receiverantenna terminal and the other is con­nected to the antenna. With such connec­tions, continuity can be easily detected bythe increase in gain in the receiver.Ronald J. Finger, WN9VCH

A F1VE-eENT TRANSISTORTESTERDo you own a collection of unmarked,untested diodes and transistors? Plenty of

24 Chnplnr 2

semiconductor assortments are bought forbargain prices on today's market, butfinding out which are the good or baddevices can be perplexing!

A conventional transistor tester can beused to grade out the defective units or toidentify the leads of diodes and tran­sistors, but the same process is possible byusing a simple ohmmeter and a singleresistor. Interested? Read on.

One five-cent resistor and an ohmmeterare all that's needed to determine the baseconnections of unmarked transistors, tellnpn from pnp types, distinguish betweensilicon and germanium devices, and evenmeasure the current gain of junction tran­sistors. For an additional 10cents you alsocan measure the transconductance ofFETs.

The ohmmeter function in either aYOM or VTVM involves an internal bat­tery and a current-indicating meter.Almost any ohmmeter type is satisfactoryif it has a range with a center scale readingof 500 or 1000 ohms. First, determinewhich test prod is positive when the YOMor VTVM is used as an ohmmeter.Measure the voltage between prods withanother voltmeter or open the case andtrace the circuit. Also, it's helpful to knowthe voltage of the internal battery, whichis often either 1.5 or 3.0 volts.

Identifying Diode and TransistorTypes

A semiconductor pn junction such as adiode rectifier or the emitter-base junctionand base-collector junction in a transistorhave a low resistance in the forward direc­tion when the p-type side is positive withrespect to the n-type side. Therefore,when you connect the positive test prod ofthe ohmmeter to the p-type side and thenegative prod to the n-type side, the ohm­meter indicates a low resistance. Reversingthe test prods should result in a very highresistance reading. Thus, you candistinguish the anode and cathode ter­minals of unmarked semiconductordiodes and rectifiers. A convenient way torelate the anode and cathode terminalswith n-type and p-type regions and withthe polarity for forward bias is illustrated.

- +14N p

Diagram of a Junction diode indicating nand pregions. If the ohmmeter probes are connectedwith the polarity shown, the diode will be tor­ward biased and a low resistance reading willoccur.

In this way you can identify the leads ofan unmarked junction transistor and tellwhether it is a pnp type or an npn type.

Find the common lead which shows low­resistance forward conduction with bothother leads, and you have discovered thebase terminal. The polarity of the testprod touching the base lead is negative fora pnp transistor and positive for an npntype. It is easiest to find this by connectingone ohmmeter test prod to any transistorlead and touching the other prod to eachof the remaining two leads in turn. Repeatfor the other leads, each time watching theohmmeter reading. If none results in a lowresistance between both of the other twoleads, reverse the test prods and startover. There is only one successful com­bination (since there is only one baselead), unless the transistor is open orshorted.

In the process of identifying the baselead, an indication of whether or not thetransistor is made of germanium or ofsilicon can be obtained also. This is oftenuseful information in connection withtransistor-bias design, particularly indirect-coupled Circuits, and for operating­temperature considerations.

The properties of semiconductors aresuch that pn junctions of germaniumusually have a lower forward resistancethan the silicon type at the same forwardvoltage. The exact resistance readingnoted on an ohmmeter depends somewhatupon the range scale and the internal bat­tery voltage. Typical ohmmeter readingsare .about 200 ohms for germaniumdevices compared with 800 ohms forsilicon units when using a WOO-ohmcenter scale (VTVM ohmmeter) with a1.5-volt internal battery. The same unitsindicate about 100 ohms and 200 ohmsrespectively (YOM type of ohmmeter)with a SOO-ohm center scale and a 3-voltinternal battery. These differences inreadings using the two meters are expectedbecause of the nonlinear properties of pnjunctions. Also, there is some variationbetween different devices of the samegeneral type, such as would result fromtheir internal design for maximumcurrent-carrying capacity and other fac­tors.

+

R.OHMMETER

100k

Testing a bipolar transistor with the ohmmeter.For npn transistors highest gain occurs whenconnected in this fashion. Conversely, thenegative prod is at the collector terminal forpnp units.

Measuring the Current Galn

The next step is to determine the collec­tor and emitter leads of the transistor and

100,000R

to get a general idea of its current gain.Excluding the base lead, clip one ohm­meter test prod to one transistor lead andthe other test prod to the remaining leadof the unknown transistor. The ohmmeterwill indicate a very large resistance sinceone of the junctions is under, reverse bias.Now connect a resistor (an inexpensive100-kO carbon type is quite satisfactory)from the base lead to the positive test prodif the transistor is an npn type. Connectthe base lead to the negative test prod inthe case of a pnp type. This biases theemitter junction in the forward direction,which results in collector current and adeflection on the ohmmeter. In effect, thetransistor is now operating as a deamplifier.

The transistor base-collector currentgain is approximately the ratio of thebase-bias resistor to the ohmmeter readingR or

Rbp=-=. RThe reading is now repeated after theohmmeter test prods are reversed. The ar­rangement producing the greatest currentgain determines which of the leads is theemitter lead and which is the collectorlead.

The exact value of current gain deter­mined by this simple circuit dependssomewhat On properties of the ohmmeterused. Consequently, the results should beviewed as indicative of transistorparameters. Actually, measurements of aselection of transistors in a typical assort­ment showed gains ranging from 20 to400. All units that looked alike had ap­proximately the same current gain,although there were occasional exceptionswhich produced significantly lowervalues. Good correlation between gainsmeasured with the tester and tabulatedvalues for several known transistors wasobserved also.

+

-I ;::-:::::::1OHMMETER

I"\--.~+t

An ohmmeter and a battery can be used to testa junction FET.

The scheme works best for small-signaltransistors, although most power tran­sistors can be tested as well. Power unitsdo not seem to yield particularly reliablevalues for gain. However, the test does in­dicate clearly whether or not a device isoperational. Incidentally, for conveniencein testing different kinds of transistorswith a variety of base and lead ar-

rangements, it proves convenient to attachan alligator clip to each end of theresistor. Thus the ohmmeter prods andthe resistor are simply clipped to the tran­sistor leads and interchanging connectionsis easy.

Testlag FET.A technique similar to that used for

bipolar transistors is applicable to junc­tion FETs as well. First, identify the.drainand source leads of the FET by finding thepair of leads that indicates the sameresistance when the test prod connectionsare interchanged. The resistance betweendrain and source in an FET arises simplyfrom the channel resistance, so it is thesame for either direction of current flow.A typical value is 200 ohms. You can tellwhether the FET is an n-channel or ap-channel type by noting the polarity ofthe test prods for forward conduction be­tween the gate lead (the third lead) andeither the drain or source lead. Ann-channel FET shows 'a low resistancereading when the positive test prod is con­nected to the gate in conformity withprevious tests.

The gain of an FET is measured by itstransconductance, which is the change indrain current resulting from a change ingate voltage. Notice that an FET is avoltage-controlled amplifier in contrast toa junction transistor which is current con­trolled. Therefore, in order to test FETs,you need a small battery to use as a biassource.

Connect the ohmmeter between thesource and drain leads as determinedpreviously. Short the gate to the negativeohmmeter prod in the case of ana-channel unit, or to the positive prod fora p-channel FET. The reciprocal of theohmmeter reading is the zero-bias channelconductance, Go. Now connect the gate asshown for an n-channel FET to thenegative terminal of the penlight battery(the gate is connected to the positive bat­tery terminal for a p-channel FET). Thereverse bias at the gate in either casecauses the channel resistance reading toincrease, which shows that the FET isoperating. The reciprocal of this reading iscalled Gb, and the transconductance, gm'is proportional, to the difference: Go ­Gb• Here, again, the actual value dependssomewhat upon the ohmmeter properties,but the test is indicative enough for mostexperimental purposes. - James Brophy

METER CASES FROM COCOABOXES

A neat looking serviceable meter box orcase may be made from a discarded cocoabox. (See photo.) First the ancestry of thebox is hidden by application of a coat ofpaint. Then the meter hole is cut with asmall knife in the pasteboard side. of the

box. Rubber grommets may be used toprotect wires passing into the metal case.Removal of the cocoa-box lid provides ac­cess to the meter terminals. - Arthus S.Gillespie, Jr., K4TP

A meter enclosure made from a cocoa box.

BATIERY REPLACEMENTCIRCUIT NOTES

The "Battery-Replacement Circuit forthe VTVM," described by K5LZT/9("Hints and Kinks," QST for January,1976) is a fine addition to most VTVMs.However, those contemplating makingthe change should be aware of some(usually minor) shortcomings observedwhile bench testing similar circuits prior toinstalling one in my Heath VTVM:

I) The regulator draws about 145 rnAfrom the transformer which also supplies450 rnA to the pilot lamp and tubefilaments. The added load will decreasethe heater voltage approximately 0.5 V.Replacing the 6-V pilot lamp with a lampacross the 1l7-V ac line will keep thetransformer output voltage at its formerlevel.

2) When the ohmmeter probes are usedto measure the small resistance, theregulator output willdrop by a few tenthsof a volt. This causes a measurement errorof about 20 percent at 10 ohms and about3 percent at 20 ohms.

3) Even with a I()(X)-~F capacitor in thesupply, there is an appreciable amount ofripple in the output of the regulator. Or­dinarily it will have no effect on ameasurement, but it is well to know it isthere.

I recommend two additional changeswhich have proven useful over the years:Bring out the (nominal) l.5 V to a ter­minal on the front of the meter so that de­volts calibration can be readily checked atany time, and drill two holes in the side orback of the cabinet so that ac and de voltscan be recalibrated without taking theVTVM apart. The latter change may re­

,quire relocating the calibration controls insome models. Donald F. Zawada,W9MJG

T••t O••r Id... 26

A circuit for testing power diodes. Because of the voltages used, precautions m~ntioned belowmust be observed carefully. 01 and 02 are silicon rectifiers, type 1N4007 or equlvetent.

ETC ETCETERA

curate and stable reference since the fourmajor television networks all userubidium "reference oscillators to generatethe 3.SS-MHz color reference signals.Every color TV receiver phase locks tothose references.

The calibration process is carried out bycoupling the input of the counter, througha low-capacitance probe, to the plate ofthe tube or the collector of the transistorused to regenerate the color subcarriersignal in the TV receiver. .

White the TV set is tuned to a stationbroadcasting a color program, set thecalibration adjustment in the counter sothat the frequency indicated is exactly3.579545MHz. When the counter probe isconnected to the color oscillator in the TVset, be sure to view the screen to verifythat the picture is still in color sync. Arainbow of color bars floating through thepicture indicates a loss of color sync. Ifthis should happen decrease the loading ofthe probe with a series resistor until thescreen has a normal color picture.Stephen Pawlowicz, WAJSDV

Easy Transistor Checker Evaluating Tran­sistors for Every Radio Amateur

Now, with that out of the way, here arethe "specs". . . ETC can not competewith a Tektronix 576 Curve Tracer but itwill do the following

1) Indicate the type of transistor (pnpor npn).

2) Show whether the transistor is openor shorted.

3) Indicate the approximate gain.Sl is positioned to pnp or npn, both

positions to be tried if the transistor typeis unknown. Actuating S2 (Ref) checksthe battery supply and lights DSI, giving avisual degree of illumination for com­parison with DS2. S3 (Xl), S4 (XIO) andS5 (Xloo) are actuated sequentially - thegain of the transistor overcoming the bias-

The ETC transistor checker. The two penlightbatteries can be seen through the plasticenclosure. At the right of the npnJpnp switchare the test switch and two indicating lightS.

15k +C1

DC VOLTAGE MEASUREMENTSOrdinary VOMs (volt-ohm-milliammeter)are suitable for much of the routine workdone in the amateur lab. Some of thesmall imported instruments can be pur­chased for less money than one wouldspend to build a cemparable tester fromscratch. The primary limitation of mostVOMs is, however, that of loading the cir­cuit under test. A typical VOM will ex­hibit a characteristic of 1000' to perhaps5000 ohms per volt when applied to a cir­cuit test point. Loading of this variety willsometimes cause incorrect readings (lowerthan normal). A more practical voltmeteris one which has a high input resistance,such as a VTVM (vacuum-tube voltmeter)or a solid-state equivalent. The latter canoften be built at a cost lower than that of afactory-assembled unit or commercial kit.The complexity of a homemade instru­ment will depend upon the accuracydesired. - Staff

another diode section. With a little prac­tice, you will find that this system worksextremely well in locating those strangeelectronic devices known as •'dye-odes"- R. K. Dye, W8YLN

AN ACCURATE STANDARDFOR CALIBRATING FREQUENCYMETERS

Digital frequency meters are graduallybecoming more common pieces of testequipment for the radio amateur and ex­perimenters. Precise calibration of fre­quency meters, especially those in kitform, can be a problem since an accurateand stable frequency source is usually notavailable to the average experimenter. Thecrystal-controlled secondary frequencystandard available to the amateur is notstable enough for precise calibration pur­poses because they tend to drift slightlywith temperature changes.

If a color television receiver is availablethe crystal reference oscillator in the fre­quency meter can be calibrated by com­paring its frequency to that of the color­reference signal broadcast by the majortelevision networks. A TV set tuned to anetwork .color program is a highly ac-

D1 D2 R1I H.V. RECTIFIER

'---~----_--4_~""'-2"i..'Ff"E2 DIODE SECTION

I UNDER TEST

VARIAC

TESTING "DYE·ODES"Power diodes are not always what theyappear to be - that is, although failureseldom results from excessivecurrent, notall "new" diodes will "hold-off" theirrated reverse voltage when placed in thecircuit.

This startling fact was revealed after mylinear amplifier final high-voltage diode­rectifier stack partially blew itself severaltimes in an erratic fashion. Indication wasthat there should be some dynamicmethod (other than the usual coldresistance check on a VOM) of evaluatingthese components before they give up theghost during a QSO.

Most diodes used in amateur and com­mercial power circuits are rated in severalamperes forward current with a reversevoltage rating of 1000 volts. With thisstatement in mind, I decided to design acircuit which would permit each diode sec­tion to be tested to the full voltage. Thecircuit is shown above.

With SI in the ON position and testleads EI and E2 clipped across the diodesection under test, the Variac setting is in­creased from zero until Cl is charged toexactly 1000volts through RI as indicatedby the de voltmeter.

Assuming CR3 and C2 are good com­ponents, the discharge path of CI is onlythrough the meter and R2. If any addi­tional resistance appears in parallel withthese resistances (such as a defective diodeor capacitor in the section under test), thevoltage indication on the meter will readlower because of the extra voltage lossacross RI.

After the initial setup has been made ona "good" section, just flip SI to theOFF position. Watch the meter readingdecrease from 1000 volts to zero (as CIdischarges through the meter and R2),move EI and E2 to the next diode section,turn SI on, and watch for the meter toreturn to the "goodt'reading of exactly1000volts. If the meter reads anything ex­cept 1000 volts, you have a bad compo­nent (usually a diode) in that section.

When using this procedure, pleaseremember that you are working withlethal voltages. Be certain the transmitterpower supply is disconnected from themains and the rectifier stack is lifted fromthe load; also, be certain the de voltmeterfalls to zero before moving the test clips to

28 Chepter 2

+3V

~os,

6 sl REf.

;;-;;

: REF.

II

.s: 1$1 ~ OS,1 GAIN

1 .s.! Sl

~' ( _\.

9X1~ ~d"o -;

S.i- t 'TRANSISTOR, ~2A SOCKET

XIO 306cr:L " R3"

X1O'i 6200

During this measurement a two-toneaudio signal is supplied to the speechamplifier of the transmitter. The primarylimitation in using a scope is that thedisplay-tube face is too small to provide awell-defined voltage reading (resolution).As an example, 2-kW PEP signal is ap­plied to a 50-ohm load, resulting in a pk­pk voltage reading on the CR-tube face of632.45. The accuracy of such a measure­ment would be rather absurd, therebyleading to possible unlawful operation.Furthermore, most scopes aren't set up tomeasure voltages of that magnitude. Thelower drawing shows the methods forvoltage-resistance power measurement. ­WIFB

051,052 - Panel lamp. type GE 338 or equiv.51 - DP3T (center off) miniature toggle switch

Raytheon type MST205P or equiv.52-55, inel. - Momentary contact mlcroswitch,

any type suitable for this application.

ing of RI, R2 and R3 to illuminate OS2.Depending on the characteristics of thetransistor, if OS2 lights to one-half thebrilliance of OSI when S4 (X10) ispressed, it is a good transistor. If DS2lights above a dim glow when S5 (XlOO) ispressed, the transistor is exceptionallygood. If OS2 lights without actuating S3,S4 or S5, the transistor is shorted. If OS2does not light when pressing S3 (XI), thetransistor is open.

R3 was selected to give a dim glow withan average good transistor, when 8.5 is ac­tuated. S2 through S5 should be pressedwith the tip of your fingernail.

I claim no originality for the circuit, asa variety of these have appeared from timeto time. I just wanted something compact,reliable, and quick, etc. - Howard L.Findlay. K6BYC

Delco 137-8864-9-512 lamp holder and Keystonebattery holder, type for holding two penlightcells, and a suitable chassis are recom­mended.

measure the rf voltage across the load.Multiply the computed power (in watts)by 2 to obtain PEP.

An oscilloscope can be used to read pk­pk (peak-to-peak) rf voltage across theload, However, the instrument must becapable of full response at the operatingfrequency of the transmitter (verticalamplifier bandwidth) and the instrumentmust be capable of being calibrated toread the displayed waveform in pk-pkvoltage. A scope is able to respond to in­stantaneous voltage peaks (unlike a decurrent or voltmeter), so PEP can bedetermined by the scope reading if theresistance of the dummy load is known.To obtain PEP in watts see the drawing.

1000 HzTONE

CALIBRATING A DC YTVMORFETVOM

A YTYM or FET YOM can measurevoltages quite accurately primarilybecause their input impedance is veryhigh, which allows only a small amount ofcurrent to flow through them. In mostcases they present such a light load to thecircuit being measured that the voltagethey indicate is almost the same as the ac­tual voltage which would be present in thecircuit without the added load of themeter. To take advantage of this accuracythe meter calibration should be checkedperiodically.

The usual methods for checking thecalibration of these instruments are bycomparison with another meter of knownaccuracy or by comparison with a sourceof emf whose potential is known. Thestandard of comparison should have anerror which is appreciably less than that ofthe instrument to be calibrated. For exam­ple, the de ranges of a YTYM with an in­herent accuracy of ± 2 percent should be

Rf power output can be measured by means of an rf probe, known-value resistive load and VTVM(A). A scope, as shown at B, will provide a pk-pk voltage reading but suffers the limitationsdiscussed In the text.

fi-1300Hz'2 ·1800 Hz WIDE-BAND

SCOPE

(A)

XMTR

XMTR

MEASURING POWER OUTPUTA method which can be used to measureoutput power is to determine the rfvoltage across a dummy load of knownresistance. An rf probe can be used incombination with a VTVM to measure therms voltage present across the load'resistance. In this instance W = EZR. Ac­curacy will be within ± 10 percent if the rfprobe described in the, measurementschapter of the Handbook is used with aYTYM which has a to-megohm inputcharacteristic. The waveform of the rfenergy being measured must be pure if ac­curacy is to be expected. Cw power outputcan be measured by applying a steady car­rier to the dummy load. For ssb power­output measurements, apply a tOOO-Hzsingle audio tone to the modulator and

Test Ge.r Ide.s 27

calibrated with a cell whose potential isknown to within ± I percent, if notcloser. Errors may accumulate, so theoverall accuracy of the instrument wouldthen be ± 3 percent. It would be within± 2.25 percent if the cell voltage wasknown to be within 0.25 percent.

Few batteries, however, can be trustedto be within I percent of their nominalvoltage, and most hams do not have ac­cess to another meter much less one theyknow to be accurate to within one or twopercent! The calibration instructions forHeathkit's popular VTVMs call for set­ting the meter to a point on the scale cor­responding to 1.55 volts while measuring afresh, size-C flashlight battery. But theubiquitous flashlight or transistor batteryis one of the least stable sources of emf.These types of batteries may present anopen-circuit voltage between 1.5 and 1.68volts. This is a possible variation of -3.4percent or' + 8.4 percent from thenominal 1.55 volts of a fresh battery. Ofcourse high accuracy laboratory standardsare available, but they are prohibitivelyexpensive sources for some amateurs.

Probably the best readily availablevoltage source for calibrating the deranges on a VTVM or FET YOM is thepopular PX-13. These batteries are com­monly used in photographic exposuremeters and. cameras. Most photographicstores stock them and ought to have areasonably fresh supply .since they are sowidely used. The open-circuit voltage ofan unused PX-I3 is nominally 1.35 volts,and in fact about 85 percent of the bat­teries tested in one manufacturer'slaboratories had a potential of 1.35 volts.The rest of the units ranged from 1.34volts to 1.36 volts. But even this variation(exhibited by only 15 percent of the bat­teries tested) is only ± 0.74 percent. Thetests included batteries just off the pro­duction line as well as ones which hadbeen stored up to a year.

To calibrate the de ranges of yourVTVM or FET YOM, use onlya new bat­tery - one which has never been sub­jected to any appreciable load. Check themeter to make sure the mechanical zero isadjusted correctly, then turn the instru­ment on and allow it to warm up untilstabilized. If there is a front-panel "zeroadjust," set it so that the meter readszero. Hold the probe tips to the PX-13and adjust the de-calibration poten­tiometer so the meter needle reads 1.35volts on the range which gives the greatestneedle deflection at that potential (usuallythe 1.5-volt scale). Remove the probes andzero the meter if necessary, and thenrepeat the calibration procedure.Daniel A. Gomez-Ibanez, WB9ICI

BATTERY TEST AID

Here is a simple device for use in measur­ing a battery current drain. It is a piece of

28 Chapter 2

double-sided pc board tapered at one end,allowing the board to slide in between twobatteries (or a battery and its terminal)easily.Tor measuring current being drawnby the equipment in which the battery isemployed. Insert the probe, connect amilliammeter to -the terminals on the pcboard, turn the device on and measure thecurrent being drawn. Plug a batterycharger into the equipment and if currentindication reverses, read the net charge.- Ralph H. Janowsky, W1RPO

A milliameter connected to this probe in­dicates battery drain when load is applied.

A UNIVERSAL TRANSISTORTESTER

,Most hams who do solid-state construc­tion quickly learn one thing about tran­sistors - the devices are easy to destroyand may.give no warning when they fail.The result: They must be tested for qualityoften, in and out of a circuit. However,many transistor testers on the market areexpensive and somewhat cumbersome touse.

This article describes a simple low-costtransistor tester that was designed to solvethese problems. It will test all kinds ofdevices in or out of their circuits, and itwill give a good relative indication ofnoise figure andlor gain (beta). A ham ac­customed to fishing cw signals out ofQRM can probably tell more about therelative gain or noise figure of several ran­dom production units of the same typedevice with this gadget than he couldusing a tester with an _expensive metermovement or curve tracer.

For someone building anything fromuhf preamplifiers to a regulated de powersupply, these test functions are extremelyuseful. Most hams should be able toduplicate this tester in one evening with alow-cost collection of parts, even ifeverything is purchased new.

This tester produces an audible tonewhen connected to any .conventional tran­sistor, JFET, MOSFET, Darlington-pairIC and so on, if the transistor is capable ofamplifying a signal. Among similar JFETsor MOSFETs, those producing the lowestpitch of audible tone have the lowest noise

figure. And among similar devices of anytype, those producing the loudest audiotone have the highest gain. For a ham whohas ten 2N5245 JFETs in his junk box andwants to install the best one in his144-MHz preamp, this is valuable infor­mation.

Circuit Description

The transistor tester inductively feedsback an audio signal through twotransformers to create sustained oscilla­tion when any device capable of amplify­ing is attached to the proper terminals. S1is used to apply either positive or negativevoltage through an audio-output trans­former, T2, to the device under test. T2feeds a signal to the 8·ohm speaker and toTI, another similar audio transformer.Positive feedback from Tl is applied tothe device under test through Cl or C2,sustaining oscillation only if the device hasgain. C3 and C4 must be non polarizedelectrolytics because the current-limitingresistors Rl and R2 may produce either apositive or negative voltage in relation toground, depending on the type deviceunder test.

Construction Details

Mount Tl and T2 on a 3 x 4-1/2-inch(7.5 x 11.5 em) copper-clad circuitboard. Then install three terminal stripsfor component wiring. All componentsare placed on the upper side and intercon­nected with flexible insulated wire. Sincethere is so little circuitry, etching a circuitboard is not necessary.

The pc board, speaker and battery aremounted in the 6-1/4 X 3-3/4 X 2-inch(15.9 x 9:5 X 5 em) plastic case, asshown in the photograph. The simplestway to proceed from here is to mount theseven post terminals shown in the diagram

The wiring of the top panel and circuit board isshown here. A variety of sockets is wired toconform to various pin configurations in com.man use. To simplify the circuit wiring, allcomponents are attached to a series of ter­minal strips soldered to a one-sided, copper.clad board. All of the sockets could beeliminated and clip leads could be used for alltesting, it the builder wishes.

How to Use tbe Tester

When testing various devices, anaudio note between 1000 and 5000 Hzshould be heard. A note above 10,000Hz indicates that the device has somegain but will not meet its specifica­tions or may have been connected tothe tester incorrectly. If there is noaudible tone, the device is defectiveand should be discarded.

JFETs are tested in the same man­ner as bipolar transistors with the ex­ception that the drain and source areinterchangeable in the tester, and maybe connected either way as long as thegate is attached to its designated ter­minal (gate one). When testingMOSFETs, the source and substrateare both connected to the source ter­minal post. However, gate one andgate two on dual-gate MOSFETsmust be attached properly (note themanufacturer's lead configuration).

As pointed out earlier, the relativenoise figure of" similar JFETs orMOSFETs can be compared, withthose producing the lowest pitch be­ing best. Among production units ofmost types, there are significantvariations in both gain and noisefigure, so this type of test is essentialfor anyone seeking high performancein a uhf preamplifier, for instance.

Of course, the tester will also iden­tify whether an unknown device is ofthe pnp or npn type. It will onlyoscillate with the polarity switch inthe proper position, and an incorrectsetting 'of this switch will not damageany device except possibly anondiode-protected MOSFET. Thus,MOSFETs should not be tested unlesstheir polarity .and lead configurationis known.

Certain "programmable" tran­sistors (unijunctions, for example)will produce an audio note of varyingfrequency. This is normal and doesnot indicate a defect in the device..

Devices with a current-carryingcapability above to amperes usuallywill not oscillate in this circuit andtherefore cannot be tested. A builderwho wishes to test such devicesshould add a double-pole double-throwswitch so R3 (the forward-bias resis­tor in the base lead) can be variedfrom the designated value of 22,000 ohmsto about 5000 ohms. However, low­current devices may be damaged iftested with this switch in the 5000-ohmposition.

Almost every amateur ownssomething that uses some of the solid­state devices this unit is designed totest. The tester's ability to indicatequickly and simply whether a tran­sistor is working - usually withoutremoving it from its circuit - makesit one of' the most basic pieces of test

."Rl;J::~tBO lSV

D

6BOkaa

"m s

.C<R2,.L2S.llF68 1SV

caO.22.oF

Circuit diagram and parts information for theTransistor Tester. Not shown Is the wiring ofthe various transistor sockets, which isdescribed In the text.C3, C4 - Nonpotartzed electrolytic.S1 - Two-pole switch, on-ott-on, (Radio Shack

no. 757-(1247 or 757-0301).T'f, T2 - Audio-output transformer, pri. imp:

12000 red and green, sec. Imp: B 0 whiteand blue (Calectro transformer no. 01-724.

s"

Bottom view of the socket panel. All socketsare wired to the terminals corresponding totheir pin configurations (collector, base andemitter for bipolar transistors, source,substrate, gate one, gate two, and drain).

primary or secondary leads of either. transformer (but not both).

S G, SNO

, I ,,,0.... ,,0, PVOCp D G, D S G' D, G2 Gl D Gl Gl D

0 '0/ '0" 0--0 8

~-¥/ -, / -, / ,

O~OED s s S s s,,., 0 0 0

S G' G2 D

Testing tbe TesterOnce all wiring is completed and

carefully checked, attach a bipolartransistor of known quality to the col­lector, base and emitter terminals.Switch the polarity selector to theproper position (an incorrect settingwill not damage the device). A toneshould be heard in the speaker, in­dicating sustained feedback. If thereis no tone, double check the polarityswitch and circuit wiring. If there isstill no oscillation, Tl may be feedingback out of phase. To change itsphase relationship to T2, reverse the

Here an rf power transistor capable of deliver­ing 10 watts of output at 1296 MHz is beingtested. The tester will reveal the sad newsquickly to a uhf enthusiast if he has just blownup his prized device.

Almost all devices can be tested withoutremoving them from their circuits, as shownhere. A set of smalt clip leads is needed to testa device Installed In a pc board.

(collector, base, emitter, drain. gate two,gate one and source/substrate) on the topplate and wire them to the circuit board asshown.

If the builder wishes to include a seriesof transistor sockets to match the morepopular lead configurations as the authordid, this can be done. Simply wire allsocket terminals to their correspondingpost terminals. Alternatively. slip leadscan be used eliminating the need forsocket wiring.

Test Geer Idees 29

f

o---~.-- --o,

A diode harmonic generator.

A SIMPLE FIELD-STRENGTHMETER

installing another switch contact at anyunused position on the front of wafer 3.An insulated jumper wire should be con­nected between the new contact and eithercontact 11 or 12. If no new contact isavailable, remove either contact 11 or 12by carefully drilling out the rivet andreplacing the contact in any unused posi­tion on wafer 3. A similar problemresulting from contact spacing on the rearof wafer 3 may be corrected by movingeither contact I or 2 to any unused posi­tion. - David Kraeuter

Few amateur stations, fixed state ormobile, are without need of a field­strength meter. An instrument of thattype serves many useful purposes duringantenna experiments and adjustments.Extreme meter sensitivity is not always arequisite, and for hf-band near-fieldchecks this circuit should be fine.Amateurs desiring to make far-fieldchecks (several wavelengths from theantenna under test) may wish to build theinstrument described in an earlier issue ofQST'.

The unit described here has ample sen­sitivity for most amateur work. The largerthe pickup antenna, the greater the sen­sitivity. Far-field measurements can bemade by using the alternative input circuitshown in the diagram. In that applicationa reference dipole, cut for the frequencyof interest, is connected to the input link.Alternatively, a one-quarter wavelengthwire can be used as a far-field pickupantenna. The polarization of the twoantennas involved in a test should be thesame if meaningful results are to be ob­tained.

Most of the simple field-strength metersused by amateurs are capable of recordingonly relative signal levels, and suchreadings are useful in a number of tests.However, knowing the approximate dBincrease resulting from antenna ad­justments can be helpful in evaluationwork with matching networks, loading in­ductors, and the like. Reasonable ac­curacy can be had with the circuit asshown.

lIZ-inch copper pipe coupling.Construction requires minor modifica­

tion of the pipe coupling. As the insidediameter is slightly larger than the thread­ed portion of the PL-259, the end of thecoupling should be "rolled" in by lightlytapping the edge of the fitting with a ham­mer while rotating the coupling until aproper fit is achieved. Then the couplingshould be slotted as shown in thephotograph. After cleaning. assemble theplug and position it, with the cable ex­tending vertically at the top. It is solderedeasily with the aid of a propane torch androsin-core solder. Finally, fit the workingend of the quick connector to an SO-239connector by slightly squeezing the copperadjacent to the slots with a pair of pliers.

The cable attachment is conventional,with the only difference being that thecable is soldered to the reducing bushingonly; then. the bushing is screwed into theplug and snugged down tightly.

The 6-dB hf-band attenuator pad,shown in the photograph, is constructedfrom a short length of lIZ-inch copperpipe and two end caps. BNC connectorsare used for convenience; however, anycoaxial type of connector of small sizewould work. Construction requires theappropriate resistor values be used. In thiscase a T pad was used. First, the resistorsare soldered together and then to the endof one of the BNC connectors. Then theassembly is slid into the pipe and solderedto the other BNe connector. It is impor­tant to allow just enough lead length atthe second end to facilitate soldering,because a necessary amount of slack is in­troduced when telescoping the unittogether. This slack should be as small aspossible. Secure the caps to the body bydrilling a small hole and installing smallsheet-metal screws. - John Bipes,K9YQX.

RECEIVERRFC2 INPUT

\N34

AF INPUTFROM GENERATOR

TEST AIDS

Here are a couple of test aids for usearound the shop. Both are constructed ofstandard lIZ-inch copper plumbing fit­tings. The modified coaxial plug, whichslips on or off the popular SO-239 uhfchassis connector, is just a standardPL-259 cable plug with the threaded shellremoved. The shell is replaced with a

equipment needed in any ham shack.- Wilson E. Anderson, WB6RIV

HARMONIC GENERATORFOR CALIBRATION WORK

It is often difficult to hear the high-orderharmonics of a signal generator whendoing calibration work in a frequencyrange that is far removed from the fun­damental frequency of the oscillator. Insuch cases a simple harmonic generator,such as that shown, can be used to providea stronger "signal" in the desired range.An 1N34 crystal diode is used to rectifysome of the output of the signalgenerator. The rectification generates har­monics throughout the spectrum. ­Russell O. Deck, Jr., DL40M, W9JVI

[Editor's Note: We queried the author about the termnoise figure as used in this article. Here is his reply:"As used in this article, the term does indeed refer tothat characteristic of FETs that iscommonly known asnoise figure or noisejactor, i.e., the amount of inter­nally generated noise in the device.

You wondered whether the tester will discern therelative noise figure of 10 FETs of the same type andmake, when all 10 are between 1.5- and 2.0-dB noisefactor at 450 MHz. In our experience, the answer isyes....

Obviously, this tester provides only an indirect in­dication of noise figure. But because a number ofdevicescan be tested quickly and easily with this unit,its audible indication of noise figure is an excellentpreliminary test. . ."J

Test cable equipped slip-on connectors.

A G·dS tit-band attenuetor pad, useful as a testaid.

HEATH IM-I04 VOM MODm·CATION PREVENTS METERPEGGING

The critical spacing between contacts 11and 12 on the front of range switch wafer3 may result in a momentary open circuitresulting in meter needle pegging when theinstrument is switched between ohmmeterranges. The pegging may be eliminated by

Circuit Highlights

In this model the tuned circuit, Ll , CI,C2 and C3, was selected for the 160-meteroperation. The constants can be changed.for the amateur bands from 80 through 10meters. Table I lists -the inductance andcapacitance values needed.

The capacitive divider (C2 and C3) is

'McCoy, "A Linear Field-Strength Meter," QSTfor January, 1973, p. 18.

30 Chapter 2

~-- ~~------------

all measurements. Meter calibration is ef­fected at three settings of the sensitivitycontrol, R1. This is done because themeter readings versus field strength in dBwill vary somewhat as the ohmic value ofRl is changed. The greater the amount ofresistance, the more linear the meterresponse.

During calibration, R2 is adjusted formidscale response ofM I at each of thesettings of R1. Maximum sensitivity willoccur when RI is set at maximumresistance (position I). Position 2(moderate sensitivity) is established by us­ing an ohmmeter to locate a position ofthe Rl arm that places 8000 ohms ofresistance between the high end of RI andMl. Position 3 (low sensitivity) isestablished when the arm of Rl is posi­tioned to provide ·16,000 ohms ofresistance between the high end of R1 andMl.

Decibel reference points are found forthe three preselected settings of the sen:sitivity control by varying the voltage toCRI and CR2 by means of R2. In each in-

Rear view of the meter cabinet showing thecalibration chart in dB. Ranges 1, 2 and 3 arediscussed in the text,

10 M

0.5 (Nom.)10474303

15 M

1.3 (Nom.)10474403

20 M2,2 (Nom.)15664404

large meters! For far-field observationsone can use a telescope or field glasses 'toread the meter scale.

Component wiring inside the instru­ment box can be of the builder's choosing,provided all rf leads are kept as short anddirect as practical. Although metal knobsare shown in the photographs, they aren'tnecessarily the most ideal kind to use.Touching them will affect the meterreadings markedly if the meter case is notconnected to an earth ground. Plasticknobs are, therefore, recommended,

CalibrationA simple technique for obtaining

calibration of Ml in dB is shown in thesecond diagram. 01 and 02 are used asrectifiers, but the tuned circuit of the firstdiagram is disconnected from them. T 1,R2 and C4 are used temporarily to providelow-level 6O-Hz voltage for calibrating theinstrument. It is necessary to install C4and C5 (electrolytic capacitors) for 60-Hzwork. The capacitance values shown aresuitable for low reactance at this frequen­cy.

Tl and R2 are used in combination witha YOM or YTYM to supply and monitor6O-Hz energy between 0.1 and 1 volt.Midscale (25) on MI represents zero dB.All readings below 25 are minus dB, andthe readings above 25 are plus dB. Thus,midscale, or 25, is the reference point for

40M10 (Nom.)15664406

80M25 (Nom.)251004407

160 M

100 (Nom.)251004409

Table 1

BandL1 ",H)C2(pF)C3(pFIMillerCoil

Component values for the various amateur bands in which the tteld-strenqth meter will be used.Miller coils can be ordered by mail from J. W. Miller Co., 19070 Reyes Ave., P. O. Box 5825,Compton, CA 90224.

used to provide a low-impedance connec­tion point for the voltage doubler,CRl/CR2. Since the rectifier diodeswould otherwise load down the tuned cir­cuit and spoil the Q - assuming they wereconnected at the high-impedance end ofLl - the capacitive divider is employed.Because CRI and CR2 provide a square­law response as rectifiers, the meterdeflection (respective to changes in signal­input level) will be nonlinear. Addition ofthe 1O,OOO-ohm resistor between CR2 andR1 helps to linearize the meter response,but it also reduces the sensitivity of the in­strument somewhat. This design trade-offis acceptable for most amateur work.

ConstructionIt makes little difference what the size

or shape of the enclosure is. It should bemade of metal to prevent rf energy fromentering the tuned circuit by any path thanthat of the pickup antenna. A 4-112-inchmeter was used in the model shown here.primarily because it was at hand in thewriter's "goodie cache." Physicallysmaller meters are quite acceptable, butthe builder should use a 50-JolA instrumentif good sensitivity is desired. Large-formatmeters are more suitable for viewing froma distance, and with advancing age it isnot uncommon for some of us to sufferthe "tired-eyes syndrome," which can beoffset considerably through the use of

ANTENNA

, "...>r--I,.-r--,I "t" -''(

',.1-- - ~ __,

ALT;RNATlVE L_"INPUT _l._METHOD I I ,

C2ae

02 '0' M\0-50

R1 +C3 0' 0.01 25''DO SEN S

CONNECT ACVOLTMETERHERE(;V SCALE)

Schematic diagram of the simple tletd-strenqth meter. Ptxed-value capacitors are disk ceramicunless otherwise noted. Fixed-value resistors are 1!2·W composition. C1 is a small 100·pFvariable. 01 and 02 are 1N34A germanium diodes, or equivalents. Jl is an antenna connector ofthe builder's choice, L1, C2 and C3 are selected values (see Table 1). Ml Is a 50-J>lA meter, and Rlis a 25,OOO-ohm, ttnear-taper composition control.

Schematic illustration of a suitable circuit forcalibrating the instrument in dB (see text). T1is a smaIl6,3·V filament transformer. C4 andC5 are electrolytic capacitors.

T••t G••r Id... 31

stance the value of ac voltage at zeroreference is recorded. Then the setting ofR2 is changed until the meter readingdrops or increases to the next numberedpoint - 30,35,40 and so on, or 20, 15, 10and downward. The change in dB for eachchange in meter reading can be computedby

which tells us that working in the oppositedirection our answer would be in minusdB.

A rear-panel view of the author's in­strument is shown photographically. Ifthe first circuit is used, the calibrationpoints visible in the picture will be validfor SO-JlA meters. - Doug DeMaw,WIFB

where E2 = ac voltage at zero reference(25 on the meter scale), and El = thevoltage above or below zero reference.Thus, if El was 0.9 volt, and E2 was 0.2volt, the increase in dB would equal 13.Example

dB = ~:~ = 20 X log 4.5

= 20 x 0.6532 = 13new parts. Accuracy should be better than0.5 percent. By taking advantage of thesurplus market, a comparable unit couldbe built for less than $20. Accuracy ofbetter than om percent should be ob­tainable if a calibrated laboratory bridgeis available for tailoring resistors.Multiturn potentiometers could besubstituted for resistors R2, R3, R4, R5and R6. Rule of thumb suggests that thestandard should have an accuracy four

L----o BATT.

Basic Wheatstone bridge circuit.A1/R2 = R314A1 - Unknown R.A2 - Unknown R,R3 - Variable R (known value).R4 - Variable A (known value).

the range of the instrument. In the bridgecircuit to be described, R4 remains cons­tant at 10,000 ohms and R3 is varied indecade steps. R4 could be varied in decadesteps if better resolution were desired atthe high and low extremes, or if rangesabove and below those given here weredesired.

There are at least two disadvantagesassociated with most commercial. bridgesas far as the amateur is concerned. Thelow-resistance galvanometers normallyemployed require considerable loop cur­rent. Second is the expense. The commer­cial units are very costly considering therelatively low use they would get aroundthe ham shack. In the inexpensive bridgesthat the author has used, R2 and R4 arereplaced with a potentiometer, the wiperserving as the junction. This results in awildly nonlinear scale. Dial calibration ona pseudo-log scale can compensate forthis; however, with the tolerance normallyavailable, the erratic linearity, and thepoor reset accuracy of carbon poten­tiometers, the accuracy is no better thanthat of a good YOM. The application ofac to these instruments may render themuseless for some measurements.

The CircuitThe bridge described here can be con­

structed for about SSO when employing

El= 20 log E2dB

or better.R6 - Precision resistor, 10·k ohm, 1 percent or

better.R7 - Precision tn-turn potentiometer, 100·k

ohm (see text).S1 - Spet push-button switch, normally open.S2 - Spdt push-button switch.S3 - Rotary switch, 2 pole, 5 position,

ceramic.

A WHEATSTONE BRIDGEFOR ACCURACY

The Wheatstone bridge named for SirCharles Wheatstone, a noted physicist ofthe mid·1800s, is a nearly indispensableinstrument in most electrical andchemistry labs. In its most familiar form itis a simple bridge used for measuringresistance. Because of its accuracy andalmost infinitesimal resolution, it canfacilitate measurements far beyond theability of most other resistance-measuringdevices.

Shown in the illustration is the basicbridge circuit. In operation, when Rl/R2= R3/R4, the bridge is said to be bal­anced and no current will flow throughthe galvanometer. Rl represents theunknown resistance, R2 the knownresistance, and R3 and R4 are variableresistances of predetermined and' knownvalues. These resistors are changed to vary

Shown here is the schematic diagram of the Wheatstone bridge. Battery information is given inthe text.M1 - See text.A1 - Sensitivity potentiometer, 5000 ohms.R2 - Precision resistor, 100 ohms, 1 percent

or better.R3 - Precision resistor, 1000 ohms, 1 percent

or better.R4 - Precision resistor, 10·k ohm, 1 percent

or better.RS - Precision resistor, 1000·k ohm, 1 percent

32 Chepler 2

-------

The Wheatstone bridge as assembled by the author. The large object mounted on the aluminumbracket is the precision potentiometer.

R1

METER

CR2

CR'SWITCH

Basic capacltance-measurtnq circuit.

READING CAPACITANCEWITH A YOMGot a lot of mica and ceramic capacitorsin your junkbox that you don't knowwhat to do with? Wish you could readthem so that you could complete that pro­ject that has been sitting on the shelf forthe past year? Well, this is your lucky day- here is a simple circuit that will allowyou to convert your YOM so that it readscapacitance, for only around $22(probably less with a healthy junkboxl).

Circuit TheoryEveryone knows (even the Novice ­

right?) the relationship that says:capacitance times voltage = charge. If wekeep this relationship in mind and use thebasic measurement circuit shown, we seethat our unknown capacitor C, is chargedthrough Rl and CRI when the switch isopen. When the switch is closed, theunknown capacitor is discharged throughthe switch, CR2, and the meter.

Now replace the switch, static-powersupply, and Rl with a T'TLederived,square-wave generator. When thewaveform is high, the capacitor C; ischarged to a value of approximately 3.5volts and when low it discharges as before.

The frequency at which the generator

+

high degree of accuracy.In use, always start with the sensitivity

control at ,minimum" With both buttonsdepressed; 'advance the, sensitlvity controluntil' a meter reading is obtained. Ifpolarities have been' observed in con­structing the, instrument, turning the, dialto the right, will result in" galvanometerdeflection to the right and,vice versa. .Zerothe needle and 'advance 'the sensitivitytoward maximum and re-zero thegalvanometer. The final readirig should befound by alternately pressing PB·2 with

. PB-I depressed and re-zeroing with thedial until no change is noted on the meter.Measure meter movements in the samemanner, being careful not to "pin" eitherthe meter under test or the galvanometer.This bridge, incidentally, is best used in ahorizontal position to minimize anytendency of the meter to stick near zero.Carefully constructed, this instrumentshould be a valuable asset to any hamshack. - Sidney Gilstrap

Using the InstrumentA few uses for the bridge include

measurement of meter-movement'resistance (meters as sensitive as 25 IJAhave been measured with no damage tothe movement), matching resistors, deter­mining cable length, locatingshorts, ortailoring resistors for meter repair or con­struction. In fact, it is useful anytime thatit is necessary to measure resistance with a

galvanometer. In as nearly a dust-free en­vironment as possible, remove the move­ment from the housing. Three screwsaround the case are usually all that hold itin. Sealed meters are not normally usable.Remove the meter face carefully, clean theback with solvent and spray paint it flatwhite. Apply suitable dial markings, spraywith clear enamel, and replace the face onthe movement. Displace the front andback spring levers an equal amount tobring the needle to center zero. Do thiscarefully as the meter adjustment screw isnot normally usable after this operation.Linearity of the meter may not be exact,but this is not important as a centerreading is all that is required. Commer­ciallyavailable meters may be used but arequite expensive especially for the betterquality units. A flexible drive from thedial assembly to the potentiometer is anecessity. A dual flexible coupling wasused in this meter. Calibration of the in­strument is best performed with alaboratory bridge. However, quite ac­curate results may be obtained by using anumber of 1 percent or better resistorsand setting the dial to the mean readingson the various ranges. Keep in mind thateven a l-percent, lOO~kn resistor may vary1000ohms either side of its lOO-kO value.With off-the-shelf parts used in construe­tion, and assuming a 0.5 percent ac­curacy, this could be as much as 1500ohms each way. This looks good sincemost YOMs and YTYMs operate at ap­proximately 5-percent accuracy.

The cabinet was constructed from1/4~inch thick Masonite panels usingepoxy resin and glue strips at the corners.This method worked well; however, ametal cabinet would be better.

times that of the desired measurement.Thus, if the standard bridge has an ac­curacy of 0.001 percent, the measurementcan be considered accurate at 0.004 per­cent. In this unit, the absolute accuracy ofthe 10- turn potentiometer (knownelement) is of less importance than thelinearity. This potentiometer and the dialwill probably be the most expensive com­ponents in the instrument.

In this bridge the known element (R7) isa Borg Model 205, which has a linearityaccuracy of 0.1 percent. The battery is anine-volt transistor-radio type. A22-I/4-volt battery could be substituted toimprove resolution at the high end of theR X IO<X> scale. However, this bridge wasdesigned primarily with a range of 10ohms up to about half a megohm in mind.As stated previously, better resolutionmay also be obtained by switching inother decade resistors at R6. Do notsubstitute a supply with high currentcapability (more than a few rnA). Currentmust be limited, as the known element iseasily destroyed. One of the best ways tolimit the current is through the internalresistance of the supply.

ConstructionIt is vitally necessary to avoid erratic

contacts or resistances. Special attentionmust be paid to all soldered connections.The rotary switch should have silver- orgold-plated contacts and the push-buttonswitches should be the snap-action type toavoid possible changes in contactresistance. On S·2 the normally closedcontacts are used to short out thegalvanometer and damp the meter move­ment when transporting. It is notnecessary to run the conductors exactly asshown in the pictures. This does not repre­sent the only way, or possibly even thebest way, to wire the unit. The dial is anAmphenol Type 1350which boasts an in­dexing accuracy of 1O<X>: I. As the ultimateaccuracy is a function of the dial andpotentiometer combination, don't skimp.

The meter is a surplus 0- to lOO-$iA unitwhich was modified for zero-center use.

. This is a fairly simple operation andresults in an excellent and inexpensive

Test Gear Ideas 33

1N34A

DIVIDER CHAIN

( 0

( 0VOM OUT

""ML-+----<3VOM " ":

L-+-_-I-----<

(

(

117VAC

READ Cx.-------,- ---,

52 I I I

OSCILLATOR

+'V

"runs determines the discharge currentthrough the meter.

since Q ::::CxVnQ = nCxV

The capacitance checker is shown beneath theHeath YOM.

Schematic diagram of capacitance checker. Unless otherwise specified, resistors are 1/4·wattcomposition and capacitors are disk ceramic.CR1·CR4, Incl. - Mallory PTC 401 slllcon-

diode bridge rectifier. T1 - Filament transformer, 6.3 V ac -StancorR1 - Control, Mallory MLC13L. P·6465 or equtv.j.

'i·

but nQ = charge stored per secondnQ = dQ/dt = i (average current)

i :::: nCxV

where: Q = charge supplied to C, perpulse.

C, :::: unknown capacitancen :::: number of pulses per second

(frequency of generator)

The most sensitive scale of my YOM is150 ,.A (Heath MM-I) so the followingcalculation was made to determine thefree-running frequency of the generatorfor 150 pF at full scale.

n = i/CxV= 150 x 10-'/(150 x 10-")(3.5)= 285 kHz

Larger values of capacitance can be readby decreasing the frequency which is ob­tained digitally through decade division(7490s). The power supply is straightfor­ward and many 'different types may beemployed (batteries, LM335, ,.A723). Thesimple Zener circuit shown was used bythe author with a total current drain of 90rnA.

Construction and Calibration

The instrument was built on a 1-3/4 x3-1/2-inch single-sided, printed-circuitboard and mounted into a 6 X 3-1/2 XI-7I8-inch black plastic case. The physical,layout is left to the builder since nothing iscritical to actual circuit operation. The

unit could use a higher frequencyoscillator to extend its range down tolower capacitances and employ a se1f­contained meter. Example: A 50~A meterand a 571-kHz oscillator should give a25-pF full-scale reading. Dream up yourown variation!

The author calibrated his instrument bysetting 51 to the 150-pF full-scale positionand placing a tOO.pF I-percent silver-micacapacitor across the C, terminals. Thecalibrate control was then adjusted for thecapacitance value indicated. If no forwardreading is obtainable, then check the 7402oscillator for output either at pin 4, I J or13. The other scales are checked with cor-

Bottom view of the tester.

responding larger capacitors. The func­tion of 82 is to disable the power supplywhen using the YOM in normal opera­tions. - Kenneth H. Carcey, W6YOR

USING BC RECEIVERSAS MAKESHIFf TEST GEAR

Not all of us are fortunate enough to ownan rf signal generator for use in aligningand calibrating homebuilt receiving gear,but almost anyone can scare up a sparebroadcast set. Here are several methodsfor using the be receiver as a substitute.

To align the i-f section of a receiverwhich has a BFO for 456 kHz or 465 kHz,attach a couple of feet of antenna wire tothe BFO and run it near the broadcastreceiver. Tune the bc set to the secondharmonic of. the BFO (912 kHz or 930kHz) and adjust the BFO until a beat noteis heard. Finding frequencies in the broad­cast band is simplified by the fact that thecarriers are spaced at to-kHz intervalsthrough the band. The frequency of yourlocal station is usually published with thedaily program schedules, and otherpublications are available with listings ofall stations. For a 456-kHz i-f, try to finda station on 910 kHz. The 2-kHz dif-

34 Ch8pter 2

_._-------------_._.--------

is the approximate i-f of the first receiver.- JamesB. Bamberg, W80PX

A USEFUL RF PROBEAn rf probe can be built for use with avoltmeter. It will be useful when deter­mining relative rms values of rf voltagefrom 50 kHz to at least 148 MHz. It canbe used with numerous commercialVTVMs to provide accurate rms voltagemeasurements, provided the voltmeterwith which it is used has a lO-megohm in­put characteristic. The internal 4.7megohm is chosen to change. the peak rfvoltage response of the probe to an rmsvalue compatible with voltmeters whichhave the IO-megohm characteristic.

Signal tracing and relative rf voltagereadings can be taken during circuitdevelopment or trouble-shooting. Whenused with a lO-megohm instrument, bestaccuracy will result when the waveformunder test is a pure sine wave. Distortedwaveforms will change the voltagereadings significantly.

The probe is made from a short lengthof copper tubing (3/8 or 1/2 inch indiameter). Wooden end plugs are installedto fit snugly inside the tubing. The probetip can be made from a small nail or apiece of brazing rod which has beensharpened to a point on one end. CRl isan IN34A. An IN914A silicon diode issuitable also. - Doug DeMaw, WIFB

ference beat note can be estimated, butmake sure that the BFO harmonic ishigher in frequency that the be station. Aslight tuning of the be receiver dial willdetermine this. Then, without disturbingthe "antenna" on the BFO, align the i-famplifier by peaking it on noise, not onthe signal. This method is accurateenough for any receiver except one whichuses a crystal filter. The third harmonicsof the 456 kHz and 465 kHz also fallwithin the broadcast band, and can beused, but they will not fall directly on anybe station frequency.

The spare be set can also be used forband-edge calibration of another receiver.The hf oscillator in most be sets can betuned to lOOO kHz. In some instances itmay be necessary to add a very smallamount of tuning capacity to theoscillator circuit, but in most cases thiscan be done merely by screwing down thepadding capacitor a couple of turns. At­tach a couple of feet of wire to theoscillator tuning capacitor in the bc setand place one end of it near the receiverbeing calibrated. Tune the bc set to thelow-frequency end of the tuning range sothat the harmonic of the oscillator beatswith WWV. Then, without disturbing thebe receiver or the temporary antenna, thecommunications receiver can be tuned topick up harmonics of the be set oscillatorat IOOO-kHz intervals through a large partof the spectrum. It should be possible topick up this signal at 4 MHz, 7 MHz, 14MHz and perhaps at higher frequencies.

If the exact i-f of the bc set is known,the hf oscillator may be used for approxi­mate calibration of a receiver between theHX)O-kHz points mentioned above. Theoscillator frequency will usually be higherthan the dial frequency by the i-f. Thus, ifthe bc set is tuned to a station at 700 kHzand the i-f is 465 kHz, the oscillator willbe tuned to 1165 kHz. Harmonics of thisfrequency can be used to obtain addi-

CATH~OE

'STRIPE

C 14 A

Details of the rf test probe.

tional calibration points. It should beremembered, however, that only when the"generator" can be tuned to beat theWWV or some other frequency standard,can the calibration points be considered asexact.

To determine the i-f of a receiver whichhas a broadcast band, tune the receiver toa bc station of known frequency near thelow-frequency limit of the band. With asecond be set, tune higher in frequencyuntil a beat note is heard. In my area wehave be stations at 850 kHz and 1300kHz,just 6 kHz less than 456 kHz apart. Therequired 6-kHz beat note can beestimated, and a slight retuning of the sec­ond receiver will tell whether the i-f is 6kHz higher or lower than 450 kHz. If thehf oscillator of the receiver being checkedis lower in frequency than the mixer, theset being 'checked will have to be tuned toa station at the high-frequency end of thebe band while the auxiliary set willhave tobe tuned lower.

To determine an unknown i-f in setswhich do not have broadcast bandcoverage, the same principles describedabove are used, with the receiver beingchecked tuned to any station of knownfrequency. Tune an auxiliary receiverwitha calibrated dial until the oscillator of thefirst receiver is heard. The difference be­tween the frequency of the known stationand the dial reading of the second receiver

COAX• +\:: TO FETVOLTMETER

Teet aee. Idee. 35

Chapter 3

Transmittingand Receiving Kinks

PLUS OR MINUS 600 KHz FORTHE HW-2011

To make my Heathkit HW-2021 2-meterhand-held transceiver more versatile Idecided to modify the unit for either aplus or minus 600 kHz offset. Thetransceiver is supplied with a 6OO-kHz off­set crystal (YS -10.1 MHz). There is nointernal provision for a + 6OO-kHzcrystal, other than removing V8 andinserting a 11.3-MHz crystal, 1 which is notsupplied as original equipment. Themodification was accomplished for under$10 and within 90 minutes.

SW3 (offset switch) was removed andreplaced by a double-pole, three-position,subminiature slide switch.' I cut 1/8 inchfrom each mounting ear on the newswitch. In order for the switch to be in­serted, I/S inch of plastic had to beremoved from the inside flange of themounting slot. Plastic also had to beremoved from the external slot to allowfor the extra position on the new SW3.

Locating a ground point on the printed­circuit board was the next step. The

'The 11.3 MHz crystal may be ordded from the In­ternational Crystal Manufacturing Co., Inc., 10North Lee, Oklahoma City, OK 73102.

'SW3 is a double-pole, three-position, subminiatureslide switch available from Circuit Specialists Co..Box 3047, Scottsdale, AZ 8.52.57. Catalog no. 1239.

'3JJUMPER~"'Gcrr"N_ G . SNEW

CRYSTAL c::::J n.e, 0 0---,11.3 MHz1 2 ..L

P'N/'"" !~77MH' :f'~~'MH'

An additional crystal provides + or - 600 kHzoffset for the HW·2021 transceiver.

38 Chapter 3

chosen point was the printed-circuit boardmounting screw located behind thesquelch control. A two-inch piece of wirewas connected from this screw to one ofthe two pin sockets.' The schematicdiagram illustrates the remaining connec­tions to be made.

The Il.3-MHz crystal was then insertedin the two-pin sockets and the crystal andsockets were wrapped in electrical tapeand laid over the grounding screw.Because there was insufficient roomavailable to mount the crystal on the pcboard, it had to be positioned in this m~n·ner.

When SW3 is wired properly. the lowerposition is for the -6OO-kHz offset, thecenter position for simplex and the upperposition for + 600 kHz offset. Amateurswho plan to make a similar modificationshould remember to order local-oscillatorcrystals cut for the receive frequency.whether for 146- or 147-MHz repeateroperation. . William C. Boyer,WA3YOX

"The two pin sockets for the crystal are available fromthe Heath Company, Benton Harbor. Ml 49022.Part no. 432-878.

CHANGES FOR THEWILSON 1401SM

A useful improvement for the Wilson1402SM hand-held transceiver is toreplace the type F antenna connector witha BNC connector. which may be installedvery easily. Only three connections needto be lifted; the inner conductor, the outerconductor and a ground strap. Be carefulnot to melt the dielectric of the coaxialcable!

Another change I made was to move theinternal microphone from the bottom of .the case to the upper right-hand corner of

the speaker grille. A convenient hole isprovided as well as a little insulatingblock. A square of black tape covered thehole at the bottom.

Because the Wilson manual did notdescribe the pin configuration for the newround microphone connector, I turned toWA9FRC for assistance. He explainedthat looking from the top, the pin connec­tions are identified as: no. I, microphone;no. 2, speaker; no. 3, PTT lead; no. 4,ground; no. 5, + 12 V and no. 6, n.c. ­Peter Wang, WB9PLI

HERRlNGBONEPATTERNFROM SB·303In performing TVI checks while using myHeathkit 8B-303/8B-401 combination, itwas observed that a herringbone patternwould appear on the channel 8 picturewhenever the equipment was set for 20meters. Further checking indicated thatthe 8B-401 was not the source of the in­terference but rather the problemoriginated in the SB-303. Evidence of theharmonic would disappear when the HFOcable was removed from the '303.

I presumed that the undesired harmonicsignal was the eighth multiple of the22.S95-MHz crystal oscillator, although

HFO~OUTPUT», G~~O ~SPARE

CONNECT COAX"TO 58401 HERE(HET OSC.)

A harmonic suppressor for SB-303JSB-401elimInates TVI.

A circuit modification for Improving receiver recovery in Heath transceivers.

'Kirsch, "The 2 & 2 Dial for the HW-IOO," CQ,March, 1969.

'Abbott, "Variable A.F. Bandwidth for the HW­100," CQ, June, 1970.

'Modification Kit Model S8M·IOO·I. The HeathCompany. Benton Harbor, MI49022.

of the HW-lOO, with signal readings in­'creasing approximately three S units onthe high bands after removing the shunt.If, however, the meter seems too generousfor some individuals, various shunt valuescan be tried until a satisfactory level isreached. This modification will also causeale readings to increase during thetransmit mode, giving a better indicationof modulation peaks.

Improved cw operation of the SB-200linear can be obtained by reducing the"key-up" plate current to zero (Class Boperation instead of Class AB). Themodification will substantially increasetube life, increase the amplifier outputsomewhat and reduce "key-up" idlingpower from about 200 watts to zero. Itcan be accomplished by inserting a250-ohm, lO-watt resistor in series withthe antenna-relay lead. The resistor maybe mounted externally or internally. Aswitch to short out the 250-ohm resistorfor ssb work will facilitate moving fromphone to cw and vice versa.

By adding the 250-ohm resistor, thegrid-bias voltage is increased. It normallyis taken across a 33-ohm resistor. For­tunately, the resulting reduced current isstill adequate for operating the antennarelay that is in series with the negativegrid-bias supply output.

Owners of the HW-100 are referred topast issues of CQ magazine!" for addi­tional modifications on that particulartransceiver. In addition, Heath has pro­vided a kit which compensates for Miller­effect detuning of their transceivers."Heath also recommends retuningtransformer Tl for maximum output ob­tainable. The slug should be adjusted atthe top of the coil instead of the bottom,providing a more balanced modulatoroutput on all bands. - John Abbott,K6YB

ONE FOR THE HALLICRAFTERSSR-4GOAMy Hallicrafters SR-400A transceiverdeveloped a malady that was disconcert­ing. After 30 to 45 minutes of operation,the rf output would drop to about 30watts PEP (depending upon the band andfrequency). Efforts to retune the finalamplifier produced no improvement.Could there by an alignment problem?Fortunately, the solution was simple. Idiscovered that the heterodyne oscillator,V12, was not firmly seated in the tubesocket. Removing and reinserting it in thesocket cleared the problem: Power outputwas restored to normal. - John F.Marthens, WA 7YRQ

Tranamllling and Receiving Klnka 37

Ave

ALe

V,6AU6

Rl02lOOk

on cw because of the greater duty cycle ascompared with ssb operation. This causesthe 572Bs to go soft, which require fre­quent replacement.

My solution for each of these problemsis relatively simple. The receiver recoveryproblem is caused by V2, the 6AU6 isola­tion amplifier. When transmitting, thisamplifier couples the output of thebalanced modulator to the crystal filter in­put. In the receive mode it is still coupledto the filter, but no input is fed to the tubewhile the grid is at a high impedance withrespect to ground.

The modified circuit shows the grid­bias lead of V2 connected to V3 per­manently instead of only during thetransmitting periods. This places anegative ave grid bias on V2 when thetransceiver is in the receive mode. The ef­fect of this is to cut off V2 immediatelyupon returning to the receive mode,thereby eliminating the slow receiverrecovery phenomenon. V2 is not used inthe receive mode. Therefore, there is nodisadvantage in having it cut off.

To implement the change, the ale line isdisconnected from R22 (I megohm) onthe circuit board near V2. The lead istaped and stowed. A new wire is thensoldered to R22. This new lead is routedthrough the chassis-wall grommets, pastthe crystal filter, and is connected to R102(100 kilohms), There, the ale line connectsto the circuit board near V3. The wireneed not be shielded.

The S-meter problem is quickly solvedby removing the S-meter shunt, R115. Noreplacement seemed necessary in the case

R929 RIOl2000 lOOk

ADDED WIRE

R221M

R214700

C2:J,

Cl:L

K2 TX ';"'-o~--_......JRX

DISCONNECTED'--'" ' .. ~ALC LINE 11

FROMBALANCEDMODULATOR

IMPROVED RECOVERY FORHEATH TRANSCEIVER ANDA MODIDCATION FOR THESB-200 LINEAR AMPLIFIER

The popular Heathkit transceivers (HW­\ 100, HW-IOI, SB-lOO, SB-101 or SB-102)and the SB-200 kW linear-amplifier com-bination are used by many amateurs onphone and cw. Some have found thatrecovery in the receiving section of thetransceivers is slow after a long transmis­sion. This seems more prevalent whenoperating on cw and on the higher fre­quency bands where the MICICW controlmust be advanced for adequate drive. Thetransceiver S-meter in some instancesshows extremely "Scotch" readings, par­ticularly on 10 and IS meters where an 55signal may not move the Scmeter. TheSB-200 linear amplifier tends to overheat

ISOLATIONAMPLIFIER

the second harmonic would fall squarelyon the 45.790-MHz i-f of the TV set.

An effective attenuation of the har­monic signal was achieved by connecting a6800-ohm, I-watt resistor wrapped witheight turns of No. 24 wire from theSB-303 HFO connector to a nearby spareconnector. Also, enclosing this trap in asmall Minibox inserted between the HFOconnector and the coaxial line to theSB-401 is helpful. Although it would beexpected that the HFO output would besomewhat reduced, there is still adequateexcitation for the SB-401 to reach full out­put on all bands. - John W. Hartung,W7THY

The Kenwood TR·7400A"rouch-Tcne-pad socketconnections as seen from the transceiver ex­tetter.

cy from the Drake receiver directly intothe HFO input of the 5B-650. Also applya 5645-kHz signal to the LMO input ofthe 8B-650. This signal can be derivedfrom an rf signal generator or anoscillator constructed for that purpose.The 5645-kHz signal must be very ac­curate.

Such an arrangement may be used withmany receivers. If, for instance, the localoscillator is 4SS kHz above the incomingfrequency, build a 455-kHz oscillator. Iused such an approach to update an SX­101. If one remembers that the counterwill display the difference between theHFO, LMO and BFO inputs, othersystems can be designed. - Nenad Down­ing, WB4SLO

FREQUENCY STANDARD FORl-METERFMA simple synthesized frequency standardfor z-meter fm (and possibly ssb use) isavailable to those amateurs who have aGLB model 4OO-B· Channelizer, or haveaccess to this unit. I have found that theChannelizer is rich in harmonics well intothe 2-meter region. Inmy application, theGLB and discriminator meter are tied intoan IC-22A through a single socket in theback of the rig. I disconnect the PTT linebetween the Channelizer and the IC22A.12-Y dc is then applied to the transceiverand Channelizer, followed by dialing thedesired frequency. The PTT line must notbe connected to the transceiver during thisoperation: By doing so, the transmitterwill be activated when grounded at thesynthesizer. The GLB 400-B provides afull-quieting signal when placed near thetransceiver. This makes a handy meansfor frequency checking and spotting.Daniel L. Steinhoff, WA 7UPP

THE WATTSIT

Almost every amateur is interested inknowing the line voltage in his,shack. The"Wattsit" will tell the story. The diagramshows the simple series circuit consistingof a diode, resistor and a recording levelmeter. The resistor value should be suchthat the indicator of the meter rests on ared mark on the meter face when the ap­plied voltage is 120 V. A VTVM is re­quired to measure the line voltage whilechoosing the proper resistor value. ­Wade Rogers, W4EN and Bill Richards,WB4WYG

A simple line-voltage indicator circuit.

-,Editor's Note: It is a matter of good practice to havean earth ground connected to the chassis of theHW_7].

After trying every possible way I couldthink of, I still was unable to rid my HW-7of a terrible hum, particularly whenoperating on the 4O-meter band. Con­sidered were such ideas as adding morefilter capacitors to the power supply orusing batteries permanently!

While moving the equipment around inthe shack, a different ac outlet was used.The hum disappeared. After checking theold outlet, I found that the ground leadwas broken inside the wall! In summary,be sure the ac outlet to be used for theHW -7 power supply has a three­conductor receptacle on which the groundterminal is effectively grounded.· ­Bruce Ault, WA4UVG

Connecting O.001·,..F capacitors across the117·Vac line eliminates hum in the ,HW-7.

F1 Sl

readable. The tape can be removedwithout harm to the set whenever mylicense is upgraded or I decide to sell theequipment. Builders might like to knowthat glossy, matt and metallic tapes arealso available: They may be used to givethat final professional trim to homemadeequipment. - Gary Wilson, WB2BOO

REDUCING HUM IN THE HW·7The hum problem encountered by manyamateurs using the Heathkit HW-7powered by an ac-operated supply can insome instances be eliminated by simplybypassing the primary leads of the powertransformer to chassis ground with two0.001-~F capacitors. This may avoid theneed for an external ground" which someoperators say is a "must." After this sim­ple modification my HW-7 sounded asthough it were running on battery power.- Lee M. Clark, WB4SYC

USING THE SB-650 FREQUENCYCOUNTER ON THEDRAKE R-4AIB/C

To use the Heath 5B-650 frequencycounter with a Drake R-4A, R-4B orR-4C, simply apply the injection frequen-

12V DC(FILTEREDjONTINUOUSLY

TT (GROUNDFOR PTTl

of~~J~ 0600 OHMS

AN UPDATE ON THE KENWOODTR·7400A TRANSCEIVERThe latest modification to the KenwoodTR-7400A 2-meter fm transceiver is areplacement of the Touch-Tone-pad inputjack. The old miniature phone jack pro­vided for audio input and ground only.The new jack is a DIN type wired foraudio input, 9-Y dc on transmit only, andground. While this is an improvement,there are still two main drawbacks. The9-Y de is supplied only on transmit.Touch-Tone-pads with built-in PTT linekeying circuits do not work with this setbecause no power is applied. The otherproblem is that there is no PTT line con­nection at the jack (apparently an over­sight in manufacturing).

These problems may be resolved bymaking the following changes. Locate thegray wire from the TT pad socket to thetie bar near e64. This gray wire is the B+lead. Remove the wire from the tie bar,feed it through the chassis and connect itto pin 6 of RLI. This provides 12-V decontinuously at the IT pad socket. Com­plete the change by connecting a wirefrom the unused pin on the TT pad socketto pin B of RLI. This is the PIT linewhich functions when grounded.Murray Lampert, VE3FXA

MARKING THE NOVICE BANDS

As a holder of a Technician-class license,I'm a newcomer to the low bands. SinceI'm restricted tothe Novice subbands, Ihave found that I was constantly referringback and forth between my VFO dial,receiver dial, and frequency chart to makesure my operation was legal. The solutionto this inconvenience was to mark theNovice subbands right on the dials. Doingthat neatly was difficult.

I then discovered a transparent graphicstape, manufactured by Chart Pak andothers, in an art supply store. The tape isavailable in many colors and widths at acost of about $1.30 for 24 feet. It enabledme to mark the Novice ranges on the dialswith liB-inch wide tape of suitable length.Amateurs with more privileges could useother colors to identify their bandsegments such as cw, phone and Extra.

With backlit translucent dials, theNovice subbands show up quite easilywith original frequency numbering still

38 Chapter 3

REPLACEMENT FORTRANSCEIVER CONTROL BELTS

After much use the plastic or rubber beltsin many transceivers may become brittleand come apart. I found an ordinary pieceof insulating spaghetti threaded aroundthe pulleys and then tied into a knotmakes a satisfactory replacement in manycases. The spaghetti should be pulled tightwhen making the knot. Trim any looseends. There will be some give as thespaghetti warms but for most plate andloading controls the backlash is nottroublesome. In six months of use thereplacement has served the purpose well.- Joseph Gregor. WA3WRN

A SIMPLE MODULATOR FOR THEARRL IO-WATT TRANSMITTER

A young man in my neighborhood hasvisited my station many times and ap­parently was bitten by the "ham bug. U Hepassed his Novice examination and thenthe General. On another visit he asked if Ihad a circuit for a low-power transmitter.Knowing that I had an over-flowing junkbox, we decided to build the small W-wattcw transmitter described in a recent edi­tion of The Radio Amateur's Handbook.I thought it would be fun to add amodulator to this little transmitter.

In my collection of miscellany was thiscircuit, but I must admit that I do notknow to whom I should give credit for thedesign. Scrounging again in the parts boxbrought forth a Stancor A-287l modula­tion transformer. well suited for this pur­pose. A small chassis would serve formounting the' rf section and themodulator. We wound plug-in coils andeven found an illuminated milliammeter... talk about class! The power supplyused an old Elmac M-1070, which provid­ed the 250- to 3()()-V de needed. Since thepower unit was designed for a 12-V fila­ment circuit, we simply connected the two6T9 tubes in series.

We finished the project with en­thusiasm, delighted with the beautiful,crispy clear audio produced by this two­tube modulator. In our opinion, thiswould make a dandy beginning projectfor any club helping people just starting inour wonderful hobby. - Harry E.Stewart. W8PSV

A CONNECTOR FOR THEKW-l000

Amateurs who have the KW ElectronicsKW·l000 linear amplifier may have ex­perienced difficulty with the two femalepins which connect the T-R relay to thetransceiver VOX relay. A solution to this

annoying situation is to use a five-pin plugsuch as the ones found on eight-track tapeplayers. Drill out three pins, leaving thetwo wide-spaced pins, nos. 3 and 4. Themodified plug fits the receptacle perfectly.- Ron Pierce. WB6EFG

GETTING YOUR FOOT INTOTHE ACT

There is no need to fret over someone ask­ing you to send next with your left footwhen using this idea! This one is for cwoperators and comes from an old-timer.Send-receive switching is facilitated byusing a foot switch.

For receiving, the foot switch is open.This releases a relay which controls thescreen voltage of the buffer amplifier.With differential keying the oscillator isoff when the key is open. To spot a fre­quency, simply operate the key and tunethe VFO to zero beat by means of thereceiver BFO. Use appropriate bypassingof the screen leads to reduce rf leakage.

To transmit, the foot switch is actuated,closing the screen relay. The rig is ready tobe keyed normally. The operation is sosimple and useful that I am surprisedtransmitter manufacturers have never in­corporated this idea in their equipment.- George Seyffert, K4IG. ex-4CA.ex-W3CD

PARASITIC CHOICE

AMP.7 TURNS NO. 16 WIRE FINAL. 1.8 -14MHzosc. COIL A'I1r.0.001 0.002 o.ooe

1 Ic:::J XTAL 6TO a 36.

" 4 2.~rnH1mH B

3039' 10krLS

• e '7'0.002

~O.O1

~'EY 0;: •10

"

~O.O1

100

0.00!5 470kBLUE

GREEN

0.001

MIKE 470k 4 B

27011;

470k e 0

'70 RED YELLOW

~'!5

ONl 1200

+12V

S.M._SILVER MICAB+

25O-300V

Circuit for a modulator to be added to the 6T9 transmitter described in The Radio Amateur's Handbook for 1972. Coli information for the separatecoils used in the final amplifier: 160 meters - 48 turns No. 24, 32 turns-per-inch, 1 inch dia. (B&W Mtntductcr 3016).80 meters - 43 turns No. 20,16 turns-per-inch, 314 inch dla. (B&WMiniductor 3011). 40 meters - 30 turns No. 20, 16 turns-per-inch, 314 Inch dis. (B&W Miniductor 3011). 20meters - 19 turns No. 18, 8 tums-per-tncn, 314 inch dis. (S&W Miniductor 3010).

Tr.n.mlttlnll .nd R_lvlnll Kink. 38

~ ~'-20"1, 1-.A,f''-''v-+--FH,.70k I

'* IN6"19 IIIII______ "- ....J

VARACTOR DIODE(A)

-t30VBIAS

"120k R112W "17k

ea'M

C2

""-ecv

DC BIASING(B)

was added to eliminate the ripple that af­fected the VFO. Increasing the values ofRll and RI2 from those shown wouldreduce the current drain on the -130 Vsupply. Except for these changes, all othercomponents are the same as thosespecified in the original article byW6KVD. For ssb operation, the new cir­cuit has the added benefit of providingoffset tuning - desirable for use at a netcontrol station. - Jim Themig, WA6MSI

WWV ON THE DRAKE R-4C

AQ extra crystal is not needed to receivethe 5-MHz signals from WWV on theDrake R-4C. Tune to 3632.5 kHz. Detunethe preselector to the 4O-meter band.Reception is adequate for most purposes.By placing the function switch in thecalibrate position, the calibrationoscillator may be accurately set to zero­beat with WWV. The mode switch shouldbe in the a-m position. - Lou Phillips,K9SPD

that my TR-4 had only one set of contactson the antenna-changeover relay, KI. InDr. Sheller's modification the extra set ofcontacts operate the receiver mute func­tion by breaking the de path to ground viaRFC7.

An alternative to the approach used byDr. Sheller may be easily accomplished in15 minutes by following this two-step con­version. First, the coaxial cable that isconnected to T9 should be removed fromS4 (TCVR-RCVR). Insert a O.OOI-~F

ceramic capacitor in series with the switchand cable. This provides de isolation fromground for the RCVR muting jack via T9.

Next, solder a jumper across all threecontacts of the spdt switch, 54, renderingit nonfunctional. This parallels the TR-4receiver and the outboard receiver inputs.At the same time the receiver mute featureis allowed to function normally. Neitherof these steps require any harmful drillingor physical changes that could spoil theappearance of the TR-4. Restoration ofthe circuit requires another 15 minutes atresale time. - William P. Winter, Jr.,WB8JCQILUIAKO

w

,,:V,MUTE

ReVR.MUTE

I ANT.

I ANT.

O'O~""~ANT.

0.00.5

TO L9 +"Q...-J

OUTPUT

TO L9 +"O--JOuTPUT

MODIFICATION:

ITO T9

~ADDED CAPACITORceo-./ADOED JUMPER

~ o.co-~ 54 ~RCVR.

~ANT.

ORIGINAL TR4 CHANGEOVER CIRCUIT:TO T9

Use of the TGVA-ACVR switch on the DrakeTR-4C is eliminated by means of the modttlca­ucn shown here, a helpful change whenoperating with an outboard receiver.

REDUCING MUFFIN·FAN NOISE

While an extra 24-watt muffin fanmounted on the back of transmittingequipment is useful in extending the life ofcomponents and reducing VFO heat drift,the air turbulence created by the fan pro­duces noise. My method of lowering thenoise factor defies engineering principlesof limits for synchronous-motor slippageand starting torque, but it works. A4O-watt bulb connected in series with themuffin fan does the trick. The series bulbarrangement should be used only on add­ed fans - not on fans originally installedin the equipment. - A. H. "Ted"Heavens, VE7CHE

MORE ON THE DRAKE TR-4OUTBOARD MODIFICATION

When I decided to try the TR-4 outboardreceiver modification .described by Dr.J.R: Sheller, WA8ZDF, in the February,1977, issue of QST, I found, unhappily,

ERRATIC EQUIPMENTPERFORMANCE

All of the tubes in tube-type or hybridequipment should be removed from tubesockets periodically to clean any possiblecorrosion build-up that may occur on tubepins or socket contacts. This should be ofparticular interest to radio amateurs orany user of tube-type electronic deviceslocated in areas of high humidity,such asseacoasts or islands. This corrosion build­up acts as a partial insulator and maycause erratic functioning or failure ofequipment. - John Marthens, WA 7YRQ

lN976

"2m.ae4.7M

OFFSET VARIATION(e)

SOLUTION TO KEY CLICKS

My HW-lOl produced key clicks 15 kHzup from the transmitting frequency aftermaking the offset-tuning modificationsdescribed in QST for March, 1975. The'offset-switching transistor apparently wasturning on momentarily as the key wasreleased. The fact that I used a pnpHEP-52 from the junk box instead of theprescribed 2N2907A may have had somebearing on the problem.

I solved the matter by keying the offsettuning through the T-R relay, and insteadof using the cw-keying line to supply de tothe varacror, I used the -J30 V bias cir­cuit. This provided the required -55 V bymeans of a voltage divider.

To obtain more or less offset tuningrange, Cl may be varied as needed. C2

Offset tuning is provided for the HW·101 withthese circuit modifications.

40 Chaptar 3

------

Schematic diagram of the modified section of the HW-7 where incremental tuning has been add­ed. Numbered components not appearing In this caption are so identified for text discussion pur­poses only. New fixed-value resistors are 114-W composition or larger. A103 is a 250-ohm, linear­taper, miniature control, Allen Bradley no. WA2G056S251UA used by author. C101 is a diskceramic. Components not bearing an asterisk are new parts required for the modification.

I-WATT MODIFICATIONFOR THE CLEGG FM-27B

Here is a $3 modification for the CleggFM-27B that avoids wasted rf or excessiveTVI when the unit is operated' in theI-watt position. Furthermore, there is stillplenty of power in the 25·watt position.

Remove the RGI74/U coaxial cable be­tween the pc board and the poweramplifier assembly. Drill a hole for aminiature dpdt toggle switch on the backplate beside the 50-239 receptacle. Solder

the Zener-diede voltage because of thebase-emitter voltage drop.

The switching circuit is built on a smallpiece of Vectorbord and mounted on theside of the chassis. The transistors usedare not critical of specifications, but theyshould be npn silicon types with betagreater than 100, and a breakdownvoltage greater than 15. When lifting theground end of RFCI, drill a small hole inthe circuit board just beyond the groundpad and run the wire from RFC I throughit. Connect bypass capacitor CIOI directlyto ground at this point. The rest of the cir­cuit operates at de and can be wired inwhatever neat manner the user desires.The 250-ohm potentiometer is mounted inthe screw hole that originally held the leftside of the front panel in place. Theemitter-follower voltage regulator is con­structed on the main circuit board in thespace formerly occupied by R25.

Operation

By listening to the HW-7 VFO outputwith an additional receiver, the RIT con­trol can be adjusted so that zero beat isobtained under both key-up and key­down conditions. This position can bemarked on the front panel for each band.When receiving a signal, adjust the HW· 7main tuning for a zero beat while the RITcontrol is set at its marked position forthat band. Then, turn the RIT control forbest copy. Answering a CQ on the samefrequency can do wonders for increasingthe number of stations responding to you,especially while operating QRPI

This circuit provides a maximum fre­quency shift of 1.4 kHz on 40 meters, 2.4kHz on 20, and 3.4 kHz on IS. Tuningwith the RIT is easier than with the maintuning dial. On-the-air tests indicate thatthis circuit doesn't cause any chirp on theHW-7 signal.

The modification described here, alongwith some of those of previous articles,make the HW-7 into a more versatile per­former. The author's unit has operatedadmirably under extreme conditions,from the top of 14,()()()"foot peaks in theSierra Nevadas, and in the depths of theGrand Canyon. If anyone can modify theHW-7 for operation on 80 meters, I'd surelike to hear abou t it. - JohnGrebenkemper, WA6BVA

R106

'"

R10!5'0.

+13V DC

TO 03•

.oM

.=ORIG. HEATH PARTS

HW-1SWITCH *SECTION

Q',6

R{043900

R1014100

During key-down periods a fixed-value120-ohm resistor is used, and during thekey-up condition a 250-ohm poten­tiometer serves the purpose. Theseresistors are switched in and out by meansof transistors QIOI and Q102. Both tran­sistors are saturated and have a voltagedrop across them of less than 0.1 volt.Transistor switch Q101 is driven directlyfrom the keyed 13-volt line. QI03 invertsthe signal of the keyed line to drive switchQ102. As a consequence, either Q101 orQlO2 is always conducting. (An earlierversion of this circuit used a second relayin parallel with the transmit/receive one todo the switching, but it was discardedbecause of its higher current drairi.)

On 40 meters the potentiometer cannotprovide a sufficiently wide frequencyswing. To increase the bias available onthis band, additional current is fedthrough the potentiometer by connectinga 3900-ohm resistor from the positive sup­ply to the cold side of RFCI. Since thesemodifications make the VFO more sen­sitive to supply voltage changes, the drainof the oscillator, Q2, is regulated at 10volts by using QI04 and VRIOI in anemitter-follower voltage regulator. Thiscircuit was chosen because its currentdrain is lower than when using a Zenerdiode alone. The regulated voltage at theemitter of QI04 will be 0.6 volt less than

OlD'2N3!56~

TO KEYED +13V DCKEYEO

STAGES

C23 Ii

'~'~L'000.L13

C21 *1200

EXCEPT AS INDICATED, DECIMAL.VALUES OF CAPACITANCE AREIN MICROFARADS (.l'F); DT'1ERS

ARE IN PICDFARADS{pF OR .l'.l'F\;RESISTANCES ARE IN OHMS; Rl0l

k -1000. M.t 000 000 _"'''''--1--1"

KIT FOR THE HW-7

This article describes a receiverincremental-tuning (RIT) that can be in­corporated in the HW-7 for only a fewdollars. It will allow the receiver to betuned independently several kHz eitherside of the transmitter frequency.

The original design of the HW-7 includ­ed no circuit to offset the transmitting andreceiving frequencies from each other. In­stead, Heath depended on the change inloading of the subsequent stages to pullthe VFO frequency between key-up andkey-down conditions. In the author'stransceiver, which uses a regulated powersupply, the offsets were measured as 20Hz on 40 meters, 600 Hz on 20, and 400Hz on IS. An offset of 400 to 1000 Hzprovides suitable copy with the HW-7.

The Circuit

The HW-7 VFO uses a JFET (Q2) in aColpitts oscillator circuit. The frequencyof the oscillator can be shifted by varyingthe bias voltage across the gate junction ofthe JFET. As the bias is decreased, thecapacitance of the junction increases,thereby lowering the frequency of theoscillator. A bias change of I volt will pro­duce a frequency shift of 1.5 kHz on 40meters, and more on the higher bands. Toobtain the bias, a resistor is inserted in thesource lead of the JFET oscillator, Q2.

Transmitting and Receiving Kinks 41

a IOOO-ohm, five-percent, liZ-wattresistor across one end of the switch.Short the terminals on the other end of theswitch. Install a new length of RG 174/Uto the center terminals of the dpdt switchfrom the pc board drive stage. Then use anew length of RG I74/U to connect theswitch terminals (shunted by the resistor)with the power amplifier. This replacesthe RG 174/U which was removed. Thecoaxial line braid should be grounded tothe chassis at both ends. - Ted Lucas,K3TNH

THE GTX·200 ANDINTERMODULATION

When I tried to make a few contacts in aJune VHF QSO party using the GTX-200,I found that the front end was being rat­tled by the strong local signals to the pointwhere we were losing contacts. The in­stallation of a 22-element beam at 50 feetdidn't help this problem. Obviously,something had to be done to relieve theproblem..

In looking at the circuit, I noted that

Genave built the rig with no rf stage. Thebandpass filter and bipolar first mixerwere not quite enough for the averageham operator, so Genave added a preampusing an MPFlOZ. This does reduce thenoise figure, but it adds enough gain thatthe first mixer overloads with carriersaway from the tuned frequency. I have agreat respect for the higher inherentdynamic range of FETs soI decided itwould take very little effort to try one inthe Genave. I did not want to have to per­form major surgery, however.

What resulted is shown in the accompa­nying diagram. The only thing that re­quires a little care is the correct CBE toDGS placement in going from the tran­sistor to the FETj they are not always ar­ranged in the same sequence. The manualhas a rather complicated procedure foraligning the bandpass filter between thepreamp and the mixer. I found that it wasmuch easier to peak ClOl at 146.0, ClO2at 146.94 and ClO3 at 147.9. This has tobe repeated several times, but most peopledon't have access to the equipment calledfor in the manual. I did not notice anychange when I tried moving the oscillator

coupling capacitor, C107, to the top ofthe receiver oscillator tank. No L designa­tion was given for this coil.

I am pleased with the change. I candetect no difference on overall sensitivityand have not been able to hear any of theinterrnodulation which was so prevalentbefore the change was made. The simplici­ty and the benefits derived from thischange should make it good reading forfellow owners of the Genave GTX-200. ­Richard Frey. WIFCC/3

IMPROVING VOX RELAYRESPONSE DURING CW OPERA·TION OF THE HEATH HW·IOITRANSCEIVER

When attempting to key the HW-lOI atspeeds over 20 wpm, the VOX relay willnot actuate quickly enough, causing theloss of the first dit sent. Replacing R328, a470-kO resistor, with a 330·kO resistor in­creases the drive to the VOX amplifiertube, V17A. V17A is turned on sooner,and the VOX relay is actuated more rapid­ly. - Ed Solov, WA2DIW

ORIGINAL FRONT END CIRCUITT101

.2

FIRST I-F

CHO.2

MIXER

'2V

C107

RECEIVER OSC.F~----,

C102 C104

L101r--~-;11.27 .27C10f C1026 6 L102

TX

CHANGED CIRCUIT

No major surgery Is required for this Simple modification of the Genave GTX-200. II effectively reduces Intermodulation.

42 Chapter 3

LINEAR AMPLIFIER21 MHz TUNING TEMPLATE

EXCITER21 MHz TUNING TEMPLATE PLATE BAND LOAD

ANT.PLATE LOAD

C5"'Ocw- 21050558-21300

cw- 21050558-21300

oGRIDcD

'--- I

_______1

(Al (8)

These templates make frequency Changes quick and easy. An exciter template is at the left and at the right ;5 a template for a linear amplifier.

TOI TRANSMATCH

CRl 330pF'oN34A

resistance of SO ohms. Four 1/2-watt com­position resistors safely dissipate the out­put of my transmitter when 51 is in theTUNE position. Meter MI indicatesrelative power applied to this load. Theantenna is connected (through aTransmatch) and the antenna tuner is ad­justed for minimum deflection on SI, orlowest SWR. R5 acts as an attenuator andeffectively isolates the transmitter fromthe antenna, preventing possible damageto the output transistor of the rig. Whenthe 5WR has been reduced to itsminimum, 51 is placed in the OPERATEposition. MI now indicates relative poweroutput into the antenna. CRt may beanygermanium signal diode; Cl is either aceramic-disc or silver-mica capacitor. 51should be a ceramic rotary switch (dpdt),although a phenolic rotary switch or aslide switch is adequate for use on theSO-meter band - Albert S. Woodhull,WIGSJ

6OPERATE>r-<A--o-....:::TO

TRANSMITTER I

diode connected to the cathode of theother. The back-to-back diodes should beconnected between the wiper arm of R6and the offset switch, SI. - GlenCarlson, W6KVD

SIMPLIFIED OUTPUT METERINGPROTECfS QRP TRANSMITfERSAfter destroying a few transistors whiletuning QRP transistors into a mismatchedload, I decided I needed some way to in­dicate proper transmitter adjustment, andthen protect the rig while the antennatuner was adjusted. An adaptation of thesimple resistive 5WR bridge described inthe ARRL Handbook provides me with adummy load, relative power-output in­dicator and a safe method of tuning thetransmitter.

As shown in the schematic diagram, theinput divider (RI-R4) has a total

TEMPLATES FOR QUICK TUNINGThe problem of changing transmitting fre­quencies from high- to low-frequency por­tions of a band. or from phone to cw, hasbeen a chore to me because I have aseparate receiver and transmitter. Bothare transceivers and tune quite sharply.To simplify frequency changes withoutthe need to consult a table of dial settings,I devised a set of tuning templates for mytransmitter and linear amplifier.

I made templates for each amateurband, using manila file folders formaterial. Two or more settings are in­dicated for each band, the markings beingmade after careful and precise tune-up. Itis then an easy matter of placing thetemplates against the front panels and inseconds setting the transmitter and linear­amplifier dials.

This system for quick retuning can beused with almost any make of transmitter,amplifier or transceiver. The time and ef­fort expended in making a set of templateswill payoff in the satisfaction experiencedin rapid band changes. - David J.Gaeda, s-; WBRI

HW·IOI MODmCATION UPDATESeveral hams have reported to me aftermaking the offset tuning and keyingmodifications described in March, 1975QST, that their transmitters had key clickswhen operated in the offset mode.Although I was not aware of the problem,a close inspection of my transmitted signalrevealed that I had key clicks also. Thefollowing changes were made to correctthis problem. Connect a one-megohmresistor from the base of Ql to ground.Prepare two silicon diodes by connectingthem in parallel, with the anode of one Protective circuit for QAP transmitters.

Tranamlttlng and Rae.lvlng Kinks 43

4

10

TOB11 TO

B7

TO'9

TO

••

V,SEW6

OF

~GW

0"

''"Wi""

e

V,.1/2 6EA6

HETERODYNEMIXER

Partial schematic diagram of the HW-16 showing the addition of a 100-pF capacitor across the rf·stage ptate-tuning coil.

Sketch showing approximate location of the20·meter tap on l12.

Partial schematic diagram of the HW-16 driver plate circuit. A 20·pF capacitor must be connectedin parallel with 19.

Transmitter modification involveschanging the tap on L12. Unsolder thefour wires which connect to LI2,remembering where each of them wasconnected. Unscrew the two 6-32 hex nutswhich secure the coil to the chassis, set thenuts and lock washers aside, and removethe coil. The IS-meter tap is located 7turns from the bottom of the coil (chassisend). Use a pair of pliers to remove theloop that forms this tap. From the bottomof the coil, count up II turns (half waybetween the IS- and 4O-meter taps) andgrip the wire at this new position with apair of pliers. Twist the wire to form anew loop. This will retighten the turns onthe coil form. Scrape away the insulationon the loop and solder a one-inch piece ofbare wire to the new tap. This wire isnecessary to reach from the new tap to thewire coming from the band switch.Replace L12 and resolder the four wireswhich were previously removed. Solder a20-pF mica capacitor across the two ter­minals of L9, the driver-plate coil. Thiscompletes the transmitter modifications.Refer to the transmitter alignment sectionof the instruction manual and perform theIS-meter alignment procedure. Use4O-meter crystals or 4O-meter VFO outputfor 20-meter operation.

Replace the bottom plate and top coverand the job is finished. It might be well tomake a small label, "14.0" and tape itover the u21.0" lettering on the frontpanel. The HW-16 can be returned toIS-meter service by reversing the forego­ing procedure. - Llewellyn P. Rose,G5BGA

AN IN AND AN OUT FOR A CWFILTER WITH THE TS-520

After installing a cw filter in my TS-520transceiver, I found (to my dismay) that Iwas tuning right past several weak (andnot so weak) DX stations because of thesharp characteristics of the filter. Placingthe mode switch in usb and Isb provided

C10100pF

RFC10.5mH

C14,.L0.005

--- ---,L'r--- ---1 :

I I II I ...1..AOOEO

I I T 20 PF

I I II I'L J :

____ .J

chassis, carefully unsolder the crystal pinconnections while pulling on the crystalfrom the top side of the board. Replacethe old crystal with the 19.54S-MH, unit.Resolder the pins and the ground wire ontop of the crystal.

Power was applied to the HW-16, andweak 20-meter signals were received. Acheck of the L1 and C41 resonant fre­quency showed that the circuit tuned from17 to 25 MHz. A l00-pF mica capacitorwas soldered across L1. The circuit nowtunes from 12 to 19 MHz. Refer to thereceiver alignment instructions on pages42 and 43 in the instruction manual. Per­form the 21-MHz alignment procedure,bearing in mind that you are actuallyaligning the receiver for 20-meter opera­tion. Remember that the transceiver nowtunes from 14.0 to 14.2S0 when the bandswitch is placed in the IS-meter position.At this point the received signals will besomewhat weak. This is because thetransmitter pi-network output circuitserves also as the receiver antenna circuit,which has not been adjusted for 20-meteroperation thus far.

0'1000"""iW

C12

rJ:0 0 PF

10,--------.!..'Ili, ~".L_ -----,

o e 40

uor------,I II I

Cl1 I I36PF1 I

I IL __ . __ --.J

L"r r r : -----,

, II II II II II IL .J

10

MODIFYING THE HW-16 FOR20 METERSThe HW-16 transceiver performed ad­mirably on the 40- and SO-meter bandsdespite the European broadcast in­terference. There never seemed to bemuch activity on the IS-meter band attimes when I could operate. As a result.the instruction manual was inspected tosee how difficult it would be to convertthe transceiver for 20-meter operation.Surprisingly, it was a simple operation. re­quiring one new crystal and twocapacitors along with an easy alignmentprocedure. The following steps explainthe conversion.

Simple arithmetic and reference to thecircuit description (pages S4-S6 in theHW-I6 manual) show that substitution ofa 19.54S-MHz crystal for the 26.S4S-MH,crystal will put the 6EA8 heterodyneoscillator on the correct frequency for20-meter receiver coverage. Remove thechassis bottom plate and the top cover.Unsolder the ground wire from the top ofthe 26.S4S-MHz crystal and push the wireaside temporarily. From underneath the

51

44 Ch8pt8r 3

ease in tuning, but when returning to cwthe station would be lost because of theslight offset between modes.

Problem: How to switch between cwwithout the filter and cw with the filter,using a convenient, accessible switch. Theswitch would have to be mounted in sucha fashion that the front panel would notbe marred.

Solution: Since I operate strictly VFOand have no need for the fixed-channelcapability offered with the CH. SELECTswitch, I decided to press this switch into"filter-in, filter-out" service. I believethat most users of the TS-520 do not usethis switch, so this suggestion is offered.

Procedure: Remove the top cover of thetransceiver. Locate the Fixed Channel­AVR Board. Disconnect the wires fromterminal C, I and 2. Now locate the i-fboard and the ssb and cw filters. Discon­nect the brown wire which is connected tothe i-f board cw terminal. Connect thislead to the wire disconnected from ter­minal C of the fixed channel board. Thisis the wire moved during the installationof the cw filter in sets where the filter wasnot installed at the factory). Connect thewire disconnected from terminal 1 of thefixed channel board to the ssb terminal ofthe i-f board and connect the wire discon­nected from terminal 2 of the fixed chan­nel board to the cw terminal of the i-fboard. Insulate all wiring splices and putthe top cover back on the transceiver.

Final results will be worth the 15minutes of work necessary to make thismini-modification. With the CH.SELECT switch in position 1, the unitworks just as it did before the cw filter wasinstalled, with nice broadband-width totune in the weak ones. When a station istuned in properly, switch to position 2.This cuts the filter in (simplicity itself!). Ifyou decide to return your unit to the fac­tory configuration it will take another ISminutes: You will have not.even scratchedthe front panel! - Patrick Bailey,K7KBN

After much frustration from being unableto obtain a match to my 80-meter antennaand two attempts to raise WIAW on 3580kHz, it dawned on me - I wasn'ttransmitting anywhere near 3580 kHz.The signal was probably outside theamateur bands entirely.

If a plate-tuning capacitor rotates 360degrees it is very easy to replace a knobthe wrong way. Also, one should makesure that the dip in plate current occurswhen this control is set for the correctband. The results of little mistakes likethese could be disastrous. - StanGibilisco. WAIIOKV

,ELECTRONIC BIAS SWITCHINGREVISITED

I wanted to incorporate electronic biasswitching in my home build 4-250 linearamplifier. I It occurred to me that the pro­tective measures and high-power tran­sistors used in the original QST articlewere not needed if the bias were applied tothe grid instead of the cathode. I lifted thecontrol grid from ground and applied 80volts of bias from a voltage divider acrossa small power supply. The two O.OI-~F

mica capacitors keep the grid at rf groundpotential. I opted to use a slower-actingsystem like that described by W6VFR.' Ifthe bias circuit fails, either the high biasremains on the tube and the amplifierwon't operate, or the grid will be at deground potential, resulting in very highplate current with no drive. In either case,there is no danger of high voltage appear­ing anywhere in the bias circuit as is thesituation when the bias is applied to thecathode. The SENSITIVITY control is setjust above the point where ambient noiseand hum in the exciter activate the biasswitch. - Barry Boothe, W9UCW

'Bryant, "Electronics Bias Switching for RF PowerAmplifiers." QST, May. 1974.

. 'Gonsior, "Electronic Bias Switching for LinearAmplifiers," Ham Radio. March. 1975.

04

REC.LEVEL

XMITBUS

Zener diode improves battery charger.

IMPROVED BATTERY-CHARGEINDICATOR FOR THE WILSON1402 TRANSCEIVER

The addition of a Zener diode, as shownin the schematic diagram, provides a bet­ter indication of battery charge in theWilson unit. A 9- or In-volt Zener diodewill drop the supply voltage sufficientlythat VR7 may be readjusted to providefull-scale meter deflection when the bat­tery is fully charged. There will be nodeflection when the battery is depleted. ­Steve Hope, WA5YCG

TONE PAD CONNECTION FORTHE HW·202A quick glance at the inside of the HeathHW-202 might give the impression thatthere just isn't enough room to connectthe rig up for Touch-Tone use, particular­ly is a tone-burst encoder has already beeninstalled. It is not as hard as it might ap­pear; just follow these steps. On thetransmitter board, locate connector pinsAB. U and AD. These are the same pinsused to connect the HWA-202-2 encoder.Take a length of RG 174/U cable, solderthe inner conductor to pin AD and theshield to pin U. Take a length of strandedinsulated wire and solder to pin AD. Runthese wires along the edge of the poweramplifier board and pass them through

An electronic bias switching circuit.

ee

EXCEPT AS INDICATED, DECI~AL VAWES OF

CAPACITANCE ARE IN ~ICROFARAOS I j.lF I ;OTHERS ARE IN PICOFARADS (pF OR j.lj.lFl·,

RESISTANCES ARE IN OH~S;

k'IOOO, ~.IOOO 000.

-l~OV

lOOk

.~ 2000

REPLACE WITH CARE ORSPURIOUS YOU MIGHT AIR

With many transmitters or transceivers itis possible to transmit on spurious fre­quencies because of improper adjustmentof the final-amplifier tuning or preselectorcontrols. This past weekend the PA tun­ing knob fell off my FPM-300 transmitter.I replaced it while the rig was properlytuned for operation on the 4O-meterband.However, the capacitor rotates a full 360degrees, and I just happened to replacethe knob 180degrees from its proper posi­tion' Therefore, although giving a correctindication for 40 meters, the referencenumbers on the panel were reversed forthe other bands. Setting the control to the"10" position actually resulted in its beingset correctly for 80 meters, and vice-versa.

Tr.n.mlltlng .nd R.c.lvIng Kink. 45

the slot provided for the de voltage line.Secure them witha cable clamp fastenedto one of the rear-apron machine screws.

You will find the l l-volts de providedby pin AD superior to a 9·volt battery andalways "fresh. tt Should the tone pad loadthe microphone input circuit, you shouldprovide a means for switching the tonepad out of the circuit when not in use. ­J. P. Taylor, W4CWB

PROTECTING TRANSISTORS INTHE HW·:101Two-meter fm operators using the HeathHW-202 transceiver should be mindfulthat while the rf output transistor is rathertolerant of operator mistakes, the audiooutput stages are not so forgiving. Keepthe audio output properly loaded into aspeaker or earphones. You will save moretransistors that way. - Hilary McDonald,W5UNFl6

A CW MONITOR FOR THESWAN 170The ability to hear what one is sending oncw transmissions is usually a great aid. Ifyou are one of the many owners of theSwan 260, 270, 270B, or for that matter,any transceiver that doesn't have a built­in sidetone, here is a simple, inexpensiveaudio oscillator, built on a homemade pcboard that has more than ample power todrive my headphones and sufficient powerto drive my built-in speaker when theroom is quiet.

••

(AI

-,C

_ AF

OUTPUT

8

lMTG.HOLE (4) IB)

A sidetone circuit for the Swan 270.

48 Ch.pl.r 3

The circuit IS an adaptation of onefound in the 1973 Handbook, p, 12. Ituses an NE555 IC timer chip. But insteadof a battery, I made a simple rf voltagesupply. The output is very clean, and canbe varied in both tone and volume to suityour personal preferences.

Because] didn't want to, or was notable to, key the ground side of thespeaker, as is shown in the Handbook, ]resorted to keying the voltage on and off.I had reservations about this, wondering ifI might not get a chirpy note, but to mysurprise the output is nice and crisp.

The printed-circuit board shown washomemade from a scrap of copper-cladboard, about I x 1-1/2 inches (25.4 mmX 38.1 mm). I have found that one of thebest etch-resistant lacquers available is or­dinary fingernail polish. It is cheap, readi­ly available, has a built-in applicator, andis easily removed.

The other components on the boardwere all from the junk box, but even ifpurchased new they shouldn't be over $3.The NE555 cost 99 cents. RI, CI and R2determine the pitch, and R3 the volume. ]used a miniature slide switch (mounted onthe back panel) to break the voltage leadto the monitor, so it wouldn't "talk"while I was using ssb.

The value of Rs will have to be deter­mined experimentally if a rig of a differentpower level is used. The 1200·ohm resistorused here sampled enough power that,after rectification by DI, gave about 25volts with no load. When the IC startsoscillating, the voltage drops rapidly.However, it is still in the vicinity of 6volts, more than enough to power themonitor.

The board is small enough to be placedin any convenient spot. I ran leads to theswitch on the rear panel and to the toneand volume controls which] mounted inthe ventilation holes, so no other holeswere necessary.

This monitor has certainly made cwoperation more pleasant for me, and hasimproved my cw, It is very easy to con­struct, and gives one a small idea as to thewizardry contained in just one IC. ­Jerry Arnold, WA6MBP

OVERCURRENT RELAY MODIFI­CATION FOR THE HENRY RADIO1K-4 AMPLmERIn the present arrangement of the 2K-4amplifier there exists a possible danger. Iffor some reason the overcurrent delayengages, causing the amplifier to shut off,there is a chance of damaging the tubes.When the amplifier has been shut off, theexciter can still feed power to the grids,making it possible to destroy the tubes. Asimple change in the wiring of one ter­minal strip will eliminate the possibility.In the power supply upper deck, onterminal-barrier TBIOI. remove the

yellow wire from terminal no. 2 that goesto pin 4 of socket SK-I. Remove enoughyellow wire from the cable harness so thatIt will reach the unused. normally closerterminal of relay RYIOIA. Connect a newwire from the unused common terminal ofRYIOIA back to terminal no. 20fTBIOI.This change provides automatic disablingof the antenna reJaywhen the overcurrentrelay is activated; thus the exciter rfbypasses the amplifier, going directly tothe antenna when this overcurrent condi­tion exists. - Dave Porter, K2BPP

OSCAR RECEPTION WITHTHE SB-IOIOwners of SB-lOls or SBlO2s might ex­perience some difficulty when trying toreceive the OSCAR lO-meter output fre­quencies, 29.45 to 29.55 MHz, because ofthe band-switching arrangement in theHeath gear. By replacing the 38.395-MHzcrystal (in the heterodyne oscillator cir­cuit) with a 38.295-MHz crystal, the29.5-to 30·MHz position becomes 29.4 to29.9 MHz. The only retuning required isthat of L608, the plate coil for V19.Randall Smith, VE2BYG

THE SB-IOI ANDA SEPARATE RECEIVERThe wiring of the receive antenna jack ofthe SB·IOI can be modified to accom­modate an auxiliary receiver. This is doneby bending contact 4 at the socket of relay1 and soldering it to contact 3. To preventrf from reaching the front end of the out­board receiver when the antenna switch isin the COMMON position, disconnectone side of the switch AK. Now theauxiliary receiver has the same antenna asthe transceiver and can be used forseparate receive and transmit operation.- Timothy J. Brown, WB2ARGI6

,-..,----f'1--r<RCVR'-----''-----., ANT.

,

BLACK-YELLOWr----,

i II Ii '.'M',I TRAP

I II iL--f.J

S8·101 separate receiver modification.

47~Hr-----

rYYYl I

I.o'I )

I AC INPUTFROM AC I TO CIRCUIT

LINE CORD I ~~Al~~10347,uH 0> I

I(METER CASU

L ____

Filter connected to the ac input of the HeathIM-103 voltage monitor eliminates rf problem.

KEEPING RF OUT OF THEHEATH IM·103 LINE-VOLTAGEMONITORI noticed an apparent line-voltage increasewhenever I keyed my transmitter anddetermined that rf was being rectified byDl in the Heath monitor. A power-linefilter was constructed and installed in theunit. As shown in the schematic, the in­ductors were Nytronics no. RFC-S-47, butany value of rf choke greater than 45 fJHmay be used, as long as the de resistanceof the coil is less than 5 ohms. My thanksto Tom Baustert, W2HEO, who assistedme in correcting the problem. - A/an W.McCormick, WA2GTT

ELIMtNATING AC BUZZ INTHE HEATHKIT SB-102T'iANSCEIVERM" Heathkit SB-102 produced an annoy­ini: ac buzz at low volume settings. Myhorrebrew power supply was suspected,but , check made with a Heath HP-23power supply at a local Heath store gavethe same problem. The problem wassolved by connecting a nine-inch length ofcoaxial c hie from point C on the audiocircuit board, directly to the AF GAINpotentiom iter, R930, and the cable shieldwas gr'.:"1 rded at both ends. The originalshielded wire (red band) was cut at thepoints where it emerged from the wiringharness. Apparently, its long, circuitousroute through the harness, and poorshielding properties allowed the buzz tole-ak into the cable, because with the newRu58 cable installed, the buzz wasalmost completely eliminated. - JoeMartorelli. WA6BUV/WA2TCE

HUM IN THE SB-102

A slight but annoying ac hum in thereceiver audio amplifier has beencharacteristic of some SB-102s, includingmy own. The hum is mosf~oticeable withthe af gain at minimum. -Conventionalmethods, such as tightening circuit-boardscrews, adding capacitance across the B+line, and so forth, were tried unsuccessful­lyon my own receiver. A simple remedywas discovered however, which has work­ed for me and at least one other owner.

Disconnect the red harness cable frombetween C308 and the af gain control, and

run either the same cable (out of theharness) or another well-shielded cabledirectly between the two points, ground­ing the shields at both ends. This com­pletely eliminates that particular source ofhum pickup, which is apparently from theadjacent filament lines in the harness.Before performing the alteration, thissource can be confirmed by a simple test.Using a short screwdriver, alternatelyshort to chassis ground each end of thecable (both ends are protected by deblocking capacitors). The hum will remainwhen the audio-control side of the cable isgrounded, but will disappear when thenear side is grounded. - John Sims,WB6NGF

CURING SLIPPAGE ANDBACKLASH OF HEATH VFO DIALSSome Heath equipment owners complainof tuning-dial slippage and backlash onthe transceivers, receivers and transmit­ters. The referenced dial-drive assembly isidentified as their part no. 100-450. Hereis a simple modification to the dial-drivepulley, part no. 100-444, which will solvethis problem.

The drawing shows the details.Disassemble part no. 100-444, the dial­drive pulley assembly, noting the positionof pulley wheels in relation to each other.Now replace the first pulley wheel in itsoriginal position on shaft. Hold it firmlyagainst the shoulder and solder it to theshaft through 360 degrees. Be careful notto allow solder to flow back along shaft.Next, replace the spacer on shaft and thenreplace the second drive pulley. At thispoint a new part is added. Use a spring­tension washer, sometimes referred to as adished washer, under the screw headwhich is now screwed into position. Thiscompletes the modification. When install­ing the dial-drive bushing in the keyholeslot, note whether the dial-drive pulleyengages with the circular drive ring on thecircular dial. It may not seat deep enough,in which case file out the keyhold slot topermit better grip. - T. C. Galbreath,W2AXX

SOLDER

L_ -~o~)~/ 'SPRING

SOLDER WASHER

Anti-slippage modification of Heath dial drive.

.

10pH

INPUTOF~72O-METER20-METER --- NTENNA

CONVERTER S.M. . JACK

S.M.-SILVER MICA

A trap to eliminate interband QRM in theDream Receiver.

ELIMINATING 4O·METER SIGNALLEAKAGE IN THE MINI-MISER'SDREAM RECEIVERWhen using the Mini-Miser's DreamReceiver (DeMaw, llThe Mini-Miser'sDream Receiver," QST, September, 1976,page 20) on 20 meters, I noticed thatsignals on the 4O-meter band were leakingaround the 20-meter converter. To correctthis problem, a simple trap was con­structed and installed as shown in theschematic diagram. The IO-~H inductor isavailable from Radio Shack stores (RadioShack no. 273-101). - John Lawson,K5lRK

MORE OUTPUT FROM HG-10SERJESVFO

Users of the Heath HG-1O and -lOB VFOwith other than Heath transmitters mayhave encountered problems with low out­put. The HG-IO is rated at 5 volts rms,and this just wasn't enough to provideadequate grid drive for my hundred­watter, using two 6CL6s as buffer anddriver. No amount of work with tubeoperating conditions, tuned circuits, orimproved coupling did any good. Theproblem was solved by changing theoscillator plate choke to one with a valueof I millihenry. This change was all thatwas needed to yield ample drive on allbands. - Jon G. Harder, WIGVN

IMPROVED LOCAL.QSCILLATORPERFORMANCE IN THE K9UJF2-METER TRANSVERTERThe K9UIF transverter, which appears inThe Radio Amateur's VHF Manual/is oneof the most popular and effective designsin existence. One consistent difficulty hasbeen the instability of the local oscillator.The oscillator may drift during warm-up,and its frequency will shift when theoscillator is tuned. The high drive levelsrequired also may result in instability, as aresult of the subsequent high crystal cur­rent. An OX oscillator module and EXcrystal provide an excellent substitute forthe oscillator. They are available from In­ternational Crystal Co., 10 N. Lee,Oklahoma City, OK 73102. The module ismounted in a small Minibox, and al000-pF ceramic feedthrough capacitor isused to bypass the 6-volt supply to theoscillator. The oscillator output is con-

Transmitting and Receiving Kinks 47

nected to a phono connector, and smalldiameter coaxial cable joins the output ofthe module to the grid of the tube former­ly usedas the oscillator. If the lOO-kll gridresistor was connected across the crystalsocket, it should now be connected direct­ly from the grid pin of the tube to ground.Since the module requires a 6-volt supply,two IOOO-ohm resistors are connected as avoltage divider across the 12-volt supply inthe transverter, - Dr. Ralph E. Taggart,WB8DQT

QUICK CURE FOR AN R-4B VFOPROBLEM

After several years of use, some owners ofthe Drake R-4Bs may experience intermit­tently low VFO level, or find the equip­ment develops a vibrating, warbling quali­ty, Before digging into the VFO, short theforward and center lugs of each pole ofslide switch S-4, located on the left side ofthe receiver. This switch allows fixed fre­quency, crystal-controlled operation ofthe receiver. When the contacts of theswitch become loose from wear, the prob­lem mentioned occurs. - Marty Wotl,WB6VZI

RECEIVING NOAA WEATHERREPORTS ON 1-METERFM RIGS

Most two-meter fm transceivers are suffi­ciently broadbanded to allow reception ofNOAA weather reports on either 162.40or 162.55 MHz by installing the properreceiver oscillator crystal. If the operatortravels, it might be useful to have crystalsfor both frequencies installed. in the rig,allowing one to receive current weather in­formation while in transit. - BobMigliorino, K2YFE

FASTER RELAY RESPONSE INTHE SB-401

I am a cw traffic handler. and was disturb­ed by the slow response of the VOX relayin my S8-401. ] connected a to-kG resistorin parallel with R135, the cathode resistorfor V12B. VOX relay response is nowmuch faster. - Andrew Teetzel,WB8KVU

converted two Swan model 350transceivers and found considerable im­provement with both units. The 89508 notonly run cooler, the plates show no color,than the 6HF5s, but also provide moreoutput. It is possible to load the finalamplifier to approximately 450 watts ofinput.

The same 12-pin Compactron socket isused for both types of tubes so socketchanges are not necessary. The only con­nections that are common to both tubetypes, however, are the control grid leads:therefore do not remove anything that isconnected to the socket pins no. 5 and no.9 of either tube.

The "hot" heater lead on the rearsocket should be moved from pin no. Jand connected to pin no. 12; then groundpin no. I. This change is all that isnecessary to apply 12 volts to each tube.The 8950 tubes require 12 volts for heateroperation, whereas the 6HF5 tubes re­quired only six volts.

Carefully remove the ends of allresistors and capacitors that are connectedto the remaining pins on both sockets, asthese components can all be used in theconversion. In some cases the one-ohmone-watt cathode resistors will have to bereplaced with a 2-watt resistor. In somemodel 350 transceivers, we have found2-watt resistors already installed in thecathode circuit, in which case they can bereused.

Leave the two copper straps connectedbetween both sockets in place: One is inthe control-grid circuit; the other is left inplace and both pins no. 4 and no. 10 oneach socket grounded with the shortestpossible leads. These are the beam­forming plate leads. Reposition the twolOO-ohm screen-grid dropping resistorsunder the copper straps so that one con­nects to pin no. 11 of the rear socket andthe other to pin. no. 3 of the front socket.Wire pins no. 3 and no. 11 together oneach socket. Wire pin no. 2 to pin. no. 6on each socket; then connect the cathodes

of both tubes together by running a barewire from pin no. 6 of one tube socket topin no. 6 of the other socket.

Making all leads as short as possible,bypass pins no. 2, 6, 11 and 12on the rearsocket, and pins no. 2, 3 and 6 on thefront socket to ground with the 0.01 NFdisk-ceramic capacitors previously remov­ed. Pin no. 3 of the rear socket and pinno. lIon the. front socket should bebypassed to ground using the two 0.002NF disk-ceramic capacitors previously re­moved.

Resistors R405 and R406 in the cathodecircuit should be connected to the centerof the bare wiring running from pin no. 6of one socket to pin no. 6 of the othersocket. The 2-watt, l-ohm cathoderesistors should be connected from pinno. 2 of each socket to ground. It is im­perative that all leads be kept as short aspossible, particularly the ground leads.This completes rewiring of the tubesockets necessary for the conversion.

It will be necessary to touch up thedriver tuning due to the change reflectedfrom the amplifier tuning and loading.Neutralization will also have to be read­justed. See your Swan 350 manual forthe details of tuning and neutralizationprocedures. I strongly suggest a thoroughstudy of the manual, remembering thetimely warning about the tune-up tim-elimit of thirty seconds. Do not forget Itomake notes in the instruction manr ~al

regarding the changes you have rnacre.correcting the PA stage of the diagvamand the heater wiring circuit. The .tubelineup on page two should be corrected,the voltage chart on page 14 arid thetrouble-shooting guide on the sante page.

The type 8950 tubes, alth- .ugh notavailable everywhere, can be obtained inmatched pairs from Slep ElectronicsCompany at P.O. Box 100, ('~,H), NC28763, on the East Coast, and fromSwan Electronics, 305 Airport Road,Oceanside, CA 92054, on the West Coast,- Carl Coleman, K4WJ

The Swan 350 may be converted for use of the type 8950 linear amplifierlrt output beam pentooeswith this circuit modification.

PIN SKi

R406

SCREENVOLTAGE~

FIL.BIAS

R40S

.002 INPUT

t------------+----+--------+---jL.J-, FROMr--'-' DRIVER

UPDATING THE SWAN 350The original Swan 350 transceivers use apair of 6HF5 beam-power pentodes,designed for use as TV horizontal­deflection amplifiers in the rf outputstage. It is a reasonably easy task to con­vert this final stage 'to use the GeneralElectric type 8950 beam pentode which isactually designed for linear amplifier andrf power-output applications. We have

48 Chlpter 3

assembly manual. There are six harnesswires from the transmitter board and sixfrom the receiver board connected to theselector switches. They have pc-boardconnectors. These are lifted and carefullytaped out of the way. New wires, ter­minated in pc-board connectors, are in­stalled and brought out to the eight­contact Jones plug as shown in the dia­gram. Note the ferrite beads at the trans­mitter board. I do not have a tone burstencoder so I brought out a siz-wire cablethrough one of the four holes for that unitin the chassis. If the encoder were in­stalled, another access hole would have tobe made. A third pair of contacts is in­serted in the power connector housings.These provide connection to a phono plugat the external speaker socket.

The transceiver is mounted in the sup­plied gimbal bracket. This is fastenedsideways (by means of self-tappingscrews) to the wall at the front of thetrunk compartment near the top. I cutnew slots in the bracket to limit motion ofthe case. With this installation theHW-202 is easily removable, although it isnecessary to climb into the trunk tounplug it. For operation in the house I usea test lead to ground one of the Jones plugcontacts for channel selection. For mobileoperation the squelch is set to quiet an idlechannel, and the volume is adjusted for aweak signal with the dashboard volumecontrol wide open.

Incidentally. I found that theS/S.wavelength whip makes an excellentantenna for the car broadcast receiver.The broadcast antenna cable was transfer­red to a relay box to share the whip. Turn­ing on the HW-202 switches the antenna.This makes the broadcast antennasurplus. - Erwin AymoT, W3SU

Mle1 PLUG

FUSE

,,,,,,,Mle

CABLE

12V

MleCABLE

MleSOCKET

~==~2

,--------.". OUT

'XT~SPKRJACK

POWER PLUGS

TOUCHTONE

SOCKET

F

I-~=~J.....,>-~~:--<~ IN5'LED'l

,o

K L N

HW-202 REMOTE CONTROL PANEL

c

CHANNELSELECTOR

SWITCH

•ARECEIVERCIRCUIT BOARD

TRANSMITTER G HCIRCUIT BOARD

a-CONTACT' -- -- -- -- -- -- ---,JONES PLUG. 1 2 3 4 5 6 7 B I

(MALE) I I I~ J

FERRITE BEADS I

ORANGE

(YELLOW

: GREEN

BLUE

VIOLET

GRAY

a-CONDUCTORCABLE

RED YELLOW BLUE GRAYBROWN ORANGE GREEN VIOLET

B-CONDUCTOR CABLE

HW-202 REMOTE CONTROL CONNECTIONS

A remote control system for the Heath HW·202 transceiver is shown in this diagram.

REMOTE CONTROL FOR THEHEATH HW-202 TRANSCEIVERMy Heath HW-202 transceiver, installedunder the right front seat, was stolen fromthe locked car while it was parked in frontof the house. I had been considering theidea of a more convenient control load tobe located in the dashboard, and placingthe transceiver out of reach. Hence thisproject for trunk-mounting the newmobile rig.

Channel selection is accomplished inthe HW-202 by grounding a diodethrough a resistor associated with a crystaloscillator, in each of the six transmit andreceive channels. The transmit and receivechannels can be switched independentlyon the front panel, but I found thisfeature more of a nuisance than advan­tage while operating mobile. The squelchcontrol is another feature I found dispens­able, once it is set to quiet an idle channel.A volume control is necessary but thisfunction can be done remotely in thespeaker circuit.

The essential items in the dashboard

panel are: A six-position selector switch,speaker relay, fuse holder, sockets forTouch-Tone and microphone plugs, in­dicator light and volume control. Theonloff switch could be included but Ifound a better spot which was reserved fora nonexistent "optional accessory"switch. The four-conductor Touch-Tonesocket and plug, eight-conductor cableand LED pilot light were selected from theLafayette catalog. The speaker relay wasbnught from Radio Shack and themicrophone plug and socket are Heathkitparts. Others are junk-box items.

Except for the l2-volt power cable, forwhich I bought a small roll of No. 12stranded automobile primary wire, thewires carry little current, and resistance isnot significant. I found it necessary to runa separate shielded microphone cable. Theparts are mounted in a 3-1/3 X a-inchpanel which fits in place of the ashtray.

Remote-control connections in thetransceiver require no irreversiblemodification. The unit is assembled andchecked out in accordance with the

ADJUSTABLE TEMPERATURECOMPENSATION FOR VFO,

While trying to stabilize a VFO withtemperature compensating capacitors, Icouldn't seem to find the correct value ofcapacitor. I connected a lOO-pF air­variable capacitor in series with a lO-pFN750 temperature compensatingcapacitor. After a few tries, I found a set­ting of the variable capacitor that yieldedthe desired VFO stability. - Philip J.Reich, W2HUG

A BETTER·LOOKING DIALFOR THE HW·IOIAfter owning my HW-lOl for awhile, Igrew tired of looking at the plain, harshblack-and-white dial: I think it ruins theotherwise excellent appearance of the rig,SUbjectively speaking. I cut a 3-1/2 X1-3/4-inch piece of heavy, green plasticsheet, such as that used on report coversand overhead projectors, and taped it in

Tranamlttlng and Receiving Klnke 49

G3YMC's high·performance 1.8·MHz converter for use with receivers and transceivers coveringamateur bands from 3.5 MHz upward. Q1, 02 see text.

C~SCILLATOR

OUTPUTI 7,3 TO 75MHz

OR~ 3.7 TO 3.5 MHz

T2I~-,

well-filled junk box and came up with thedesign shown (Which by coincidence hassomething in common with the I~-MHz

converter built by PA0GVK and describedin the October TT). The use of a 5.5-MHzcrystal makes it possible to translate theI.8-MHz band to either 7.3-7.5 MHz or3.7-3.5 MHz. G3YMC did not find i-fbreakthrough on 7.3-7.5 MHz any prob­lem, but should it be then of course it ispossible to use 3.7-3.5 MHz, though thisconversion has the disadvantages of hav­ing the main receiver tuning backwardsand also transposing the sidebands.

Tl and T2 for the double-balanced mix­er are wideband ferrite transformers orferrite toroids using bifilar or trifilarwinding techniques. G3YMC suggeststhat the secondaries can be 10 turns bifilarwound or as much in fact as can be woundon; connect the start of one section to theend of the other and use this as the centertap. The primaries or link couplings canbe four or five turns. Details of how allthese can be wound in trifilar form havebeen given previously (for example,ART). The FETs QI, Q2 for the oscillatorsection can be UC734, 2N3819, etc., butnot switching-type devices. The mixerdiodes are preferably Schottky diodessuch as the HP5082-2800 commonlyadvertised for this application, although I

T' , -,

+9V5.5MHz

At~OpF 100pF

A

18pF

0'

-oo«680.

l.'-2.0MH'~

amplifier in the transmit mode, and onboth the first and second i-f amplifier tubegrids when receiving.. This problem wastraced to pin 12 of relay RL2. With therelay removed from its socket, a resistanceof 30 megohms was measured betweenpins 11 and 12 of the relay. When the ac­cumulated dust between the relay contactswas cleaned out, the positive bias problemwas cured. The S meter was zeroed, and Ifound it necessary to replace the 6AU6first and second i-f amplifier tubes. Afterthe alignment was touched up, the 8B-101performed like new. - Tom Monroe.W6GGR

THE GJYMC 1.8-MHz CONVERTER

There are many currently used receiversand transceivers which do not incorporateany facilities for the 1.8-MHz band, andthe question often arises of how to designa simple converter, capable of giving thestandard of good performance needed by1.8-MHz long-distance enthusiasts andyet compact and easy to build in a fewhours.

David W. Sergeant, G3YMC, who isextremely keen on 1.8-MHz DX, recentlyacquired an FT-201 transceiver and socame up against this problem. He spent aweekend digging energetically into his

place between the circular dial and the dialwindow. Another piece of green plasticsheet, 4 X 2 inches in size, was fittedaround the meter case and behind thepanel: It may be necessary to loosen themeter case in order to facilitate slippingthe plastic around it for a light-tight fit.When fastening the plastic behind thedial, be sure the plastic does not interferewith the operation of the dial drive.

These simple changes give a soft greenglow to both the dial and the 8-meter, andgreatly enhance the appearance of the rig.When the HW-101 is turned off, theplastic sheet gives the dial a "blackedout" appearance. - Jim Milburn.WB5BYK

CORRECTING METER·POINTERSTICKING IN THE DRAKE TR-4

Both meters in the TR·4 tend to 'stick atthe far left position when the pointerbecomes wedged in the corner of the dialface. To prevent this, the meters areremoved and a small wire or wooden pegis inserted in a O.030-inch hole drilled inthe meter face. Mark the position for thehole before removing the face. The bot­tom cover of the PA meter and the topplate of the 8 meter are held in place bytwo screws. Locate the peg about 114 inchbehind the dial, in order that the pointerwill hit the peg when the pointer is within1/16 to 1/8 inch of the corner of the dial.If the drilled hole provides a snug fit forthe peg, it won't be necessary to cementthe peg. - Jerry Lieb, WA6GSA

POOR SHIELDING IN AUDIOCABLE[ found that the wrap-around type ofshield used on audio cable, though easy towork with, is a poor choice if used in thepresence of rf fields, such as exist in anamateur station. I encountered the prob­lem of rf feedback in my shack while usingthis cable and no amount of filtering ofthe transmitter would cure it. When themicrophone cable was replaced with thestandard woven-type of shielded cable theproblem disappeared. This suggests thatthis wrap-around type audio cable wouldbe no good for carrying rf. - John Bipes,K6YQX

PERKING UP SLUGGISH HEATHKITSB-IOI TRANSCEIVERS

After six or seven years of use, my S8-101began to show signs of age. The S metercould not be zeroed, and the strongestsignals barely moved the meter pointer. Acheck of the age and ale diodes revealedno fault there, but a slight positive biaswas detected on the grid of the first i-f

50 Chapte,3

Filter section for adapting the Ten-Tee 405amplifier to 160-meter operation.

1,'~~~" 1,':0.0" 1,'~O;"

QL"l

160 METERS WITH THE TEN­TEC 405 AMPLmER

The writer needed an amplifier to go withhis solid-state 160-meter exciter CQSTforNovember, 1974), and it seemed likelythat the Ten-Tee 405 amplifier could bemodified for use on 1.8 MHz. The bandswitch in the 405 is used to select half­wave filters for the band of use. The filtersare the only tuned circuits in the assemblyand are inserted after the broadbandtransformer in the collector circuit of theloo-watt amplifier.

The first experiment called for externaladdition of a half-wave filter network, 50ohms at each port, and with a loaded Q ofI. A filter was made from sections ofMiniductor stock and surplustransmitting-style mica capacitors. Thesame constants as given in the accompa­nying schematic were used. Operation wastried with the band switch set for 80meters. It seemed reasonable that160-meter energy would pass through theSO-meter network since a half-wave filteris a low-pass filter. With the 160-meteroutboard filter installed between theamplifier output and the coax feeder tothe antenna, power from the exciter wasfed to the 405. With approximately 5watts of drive to the amplifier a poweroutput of 50 watts was obtained. Ap­parently the input transformer and com­pensating network of the 405 was lossy at1.8 MHz, thereby accounting for a higherrequired excitation level than for the hfbands. (The manufacturer rates the driv­ing power at I watt for hf-band use.)

Some mismatch between the PA tran­sistors and the outboard filter will resultfrom having the 80-meter network con-

0.01....1'

330k '"". Q01.uF a

INPUT OUTPUT

a ua,eo

•-"

An active filter provides additional selectivityafter the receiver audio clrcutt.U2 - N5741V operational amplifier.

nected to the outboard one for 160meters. Therefore, it is recommended thatpersons interested in making the amplifierusable on 160 meters give up the 80-meterband and rewind the two toroids in theSO-meter filter section. It will be necessaryto install new capacitors in the network.This modification was done by the writer,and performance has been excellent. _WiFB

A SIMPLE AUDIO FILTER

The cw performance of many less­expensive receivers can be improvedsignificantly by the addition of an audiofilter. The circuit combines simplicity andsome gain. The circuit is a bandpass activefilter, using -an integrated operationalamplifier. It has a center frequency of 1kHz, a bandwidth of 100 Hz, and a gainof 10. The filer is powered by two c-volttransistor batteries. Headphones with animpedance of 600 ohms or higher can beused on the output of the audio filter. If itis desired to operate with a loudspeaker,an impedance-transformation stage is re·quired along with some additional powergain.

The N5741V operational amplifier ismade by Signetics and sells for $1. It istheir short dual-in-line version of thepopular 741 operational amplifier. Theentire circuit can be built on a 1 X z-lnchcircuit board and taped to the batteries. Itcan then be mounted in a Minibox ortucked into the receiver. A switch toremove power and bypass the filter is re­quired. - Robert R. Knibb, WA3LlO

'0OHMS

t.a4.2,uH

t.8-2.0 MH~

"4.2,uH'0OHMS

feel that at 1.8 MHz conventional ger­manium diodes, selected for matching,would probably prove quite satisfactory.The whole unit can be mounted in a smallscreened box, such as a tobacco tin, withscreened coaxial connectors for input andoutput; it is important to ensure earthcontinuity since otherwise i-fbreakthrough will be considerable.

With suitable crystal(s) and tuned cir­cuits, of course, the same form of con­verter could be used for almost any re­quired band in the mf or hf range.

Having so successfully solved the prob­lem of receiving I. 8 MHz on histransceiver, G3YMC is now looking intothe question of transmission. - PatHawker, G3VA. Radio Communicationfor December, 1975, RSGB

INSTALLATION AND SELECTIONOF FILTERS FOR THE TS-520

The Kenwood manual suggests removingthe i-f board to install the accessory cwfilter. This job is difficult because of acable harness obstructing the mountingscrews and also the numerous connectionsto the board. The filter is installed easilyby removing the mounting plate for thebias and VOX controls on the side of theTS-520. After removing the three screwsthat hold the plate, there is ample leadlength to allow access to the foil side ofthe i-f board.

A separate spst switch, or the channel­select switch, can be used to choose filtersin the cw position. This is done by switch­ing the brown lead from the ssb terminalto the original ssb terminal or to the cwterminal on the i-f board. The ssb filter re­mains automatically selected in the upperor lower sideband position. - B. J.Owens, WA5QAL

A-M WITH THE ECHO IIOwners of the Echo II, 2-meter ssbtransceiver may transmit a-m by closingthe key and operating in the ssb mode.A-m is received by zero beating the car­rier. - Mark H. Wittmer, WA6FXM

A stcetone level control for the HW·7.

at<2N3393

SIDETONEOSCILLATOR.,.

470SEVERTRACE

•-.,.-

Cit R9

2~... lc4~.0'10.

AF GAIN

HEATH HW-7 SIDETONELEVEL CONTROL

The HW -7 sidetone lacks a method ofreducing the tone level, and it can be ex­cessive to some people. I modified the cir­cuit by replacing R35 with a IO-turnTrirnpot. Two holes were drilled in theboard to accommodate the two leads fromthe potentiometer. The trace between Qlland C46 were severed and connected asshown. The desired sidetone level is easilyachieved now. and operator fatigue isreduced considerably. - David Palmer,W6PHF

Tranamlttlng and Racelvlng Klnka 51

Graphs showing relative power-line noise strength according to specific radio frequency bands.

'0

•A-M BAOADCAST'BAND~ <,

• 8

/~ / -,• -sZ

s 7 <,0 ...---... /z 6

(\ 1\"~1 \s /• r. r'<;•"

,\/ \1 v '-V 1\/'\"• I~ /"'." 4• 'J\ "MH' \f\•

/1 f\ /I..,..

• ~ A. .r:, a" VVV

~• (\"• 2FM BROADCAS( BAN~ V-" h--. AMBIENT NOISE LEVEL,

LOCATION Of. NOIS~URCE

0 1000 2000)( . 3000 4000 5000

DISTANCE ALONG POWER LINE (FEET)

n.c.

"'--vnOOTPUT

02~

p;INPuT 2700

The above technique was effective inlocating the line noise mentioned at thebeginning of this article. However, in thiscase, the culprit proved to be each andevery .insulator on a one-mile length ofpower line, newly constructed using thelatest state-of-the-art techniques in power­line design.

In the past year, at least a dozen powerline leaks have been first located withoutbothering the power company. Of thisnumber, only three required the assistanceof the company's noise experts. The restof the cases were readily fixed by locallinemen, once the source was located. Themethod has also been useful in locatingother sources of noise.

It should be emphasized that on both hfand vhf measurements, widely fluctuatingmeter readings can be expected as onedrives along a suspected power line. Thesevariations may be caused by radiationfrom down leads, ground wires and otherobjects. It may be advisable to make achart showing the various peak readingsfor different frequency ranges."A sampleone is shown which illustrates the impor­tance of the vhf receiver in locating the ex­act position of the offending source.William L. North, W4BX

ADJUSTABLE AUDIO LIMITER

I found the "batteryless" audio limiterdescribed by Lew McCoy. WlICP, (QST,July. 1964) to be very effective. The onedrawback was the I-volt peak-to-peakoutput which proved to be a bit too low todrive my pair of headphones. A modifica­tion to the circuit is shown in the drawing.By adding diode pairs and a rotary switch,the output can be adjusted in I-voltpeak-to-peak steps. Silicon diodes areused because of the O.6-volt drop acrossthem when they are forward biased.

Adjustable audio limiter.D1·D6, Incl. - Silicon diodes, any voltage and

current rating.J1 - Headphone jack.P1 - Headphone plug.

'1 51 - a-poettton, stnqle-po!e, stnate-secttonphenolic rotary switch.

using the receiver tuned to a broadcaststation with voice modulation. Thesevalues also gave the proper amount ofdamping for noise sources also. However,different combinations may be requiredwith another receiver/meter combination.

In the event that more meter sensitivityis required, a small output transformerhaving an impedance ratio in the order of4 ohms to 2000 ohms (not critical) may beinserted between the diode and the plug.The low-impedance winding should beconnected to the plug terminals and thehigh-impedance winding connected be­tween the anode of the diode and thenegative terminal of the electrolyticcapacitor.

While not a problem with the author'sreceiver, the age action with some modelsmay suppress the variations in line noise.Whether or not this would affectmeasurements would have to be determin­ed in a particular application.

Once a noise source becomes bother­some at the author's station, a homemadetransistor receiver covering the range from3.5 to 15 MHz is installed in anautomobile equipped with a temporaryII-foot (3.4 rn) surplus whip antenna at­tached to the car by means of insulatedclamps. The portable a-m/fm receiver,equipped with its meter, is also takenalong in the search. Those who havemobile hf equipment in their cars havehalf the battle already won.

The car is driven around until the areain which the noise is greatest is found.When the noise starts to give a meter in­dication up into the IS-MHz range, onemay expect to be within a few blocks, orperhaps a mile, from the noise source.The objective is to find a localized areawhere the noise is greatest. Once this is ac­complished, the fm receiver is turned on.If the noise cannot be heard, the localizedarea is searched until an indication on themeter is'shown in the fm band.

lN914 3600 +pA

LOCATING SOURCES OF MAN­MADE NOISEAbout six months after moving to my pre­sent location, relatively strong power-linenoise began to appear. First it was inter­mittent, then it gradually became morecontinuous and stronger. Something hadto be done! Cruising the area with an a-mautomobile receiver proved useless inlocating the source of the noise - it wasjust too general.

Recalling Nelson's article in QST forApril and May, 1966, the writer studied itin detail. For anyone having noise prob­lems, a review of Nelson's article is highlyrecommended. Without attempting tocover the ground outlined in the article,let it suffice to emphasize the importanceof the use of some kind of vhf receiverwith a signal-level meter.

Fortunately, the author had a combina­tion portable a-m/fm receiver which hadtwo earphone jacks. The audio-levelmeter shown in the schematic diagram wasplugged into one of them. The first at­tempt, with the audio-level meter merelyinvolved a diode in series with theSOO-microampere meter, thus rectifyingthe audio signal and giving a de reading onthe meter. However, the particular meterused was not sufficiently damped for theapplication and in the presence of fluc­tuating noise, the meter pointer swungviolently back and forth making it im­possible to use it effectively. This difficul­ty was eliminated by the RC combinationshown. It was arrived at by trial and error

Damped audio-level meter lor noise tracing.

52 Chapter 3

Connections to SB-300 receiver.

+6.3V DCREG.

POINTe~ON RFBOARD 4 V4 3 V5

, 4

oscillator tube (V4). Next, disconnect andtape the wire coming from the power sup­ply that is connected to R218, and dolikewise for the wire coming from thepower supply to R22. Connect theregulated + 150-V dc source to these tworesistors. The power supply cable can bepassed through the rear hole that is in linewith the band switch.

If the LMO, BFO and high-frequencyoscillator are used to drive externaldevices such as a transmitter, they shouldbe isolated by means of a buffer stage toprevent frequency changes due to varia­tions in the load. - Frederick H.Schmidt, W4VWS

Voltage and current ratings of the diodesare unimportant. I chose to use threediode pairs, but more can be added ifdesired. - Stephen Pawlowicz

FREQUENCY STABILIZING THEHEATH SB·300The Heath 8B-300 is considered to be avery stable receiver when in good condi­tion. Heath specifies that for a 10-percent,line-voltagechange, the receiver frequencychange will be less than 100 Hz. Afterseveral years of operation my receiver fail­ed to meet this specification'. The maincause of trouble is the filament voltagechange on the linear master oscillator(LMO). The LMO tube is a 6AU6A. Astep change in line voltage produces animmediate change in the LMO frequency,followed by a drift to some new fre­quency. This effect could be reduced, butnot completely eliminated by selecting a"good" 6AU6A. To remove this sourceof instability, a precision-regulated,6.3-volt de supply was employed. Fluctua­tions in line voltage still caused the LMOto shift frequency slightly. A voltage­regulator tube (VR-150) was used tostabilize the oscillator plate voltage. Thesechanges effected a distinct improvement.Then, for a line voltage change of 10 per­cent, no change in LMO frequency couldbe detected. A frequency counter withI-Hz resolution was used for this test.

Unfortunately, the receiver was still notcompletely stabilized. The crystal­controlled heterodyne oscillator was in­vestigated next. It was somewhat surpris­ing to find that the heterodyne oscillatorwas quite sensitive to changes in filamentvoltage as well as plate voltage. Whenthese voltages were regulated, as in theLMO circuit. there was a marked im­provement in receiver stability. The beat­frequency oscillator (BFO) appears to bequite stable without voltage regulation.

The power supply circuit is shown in theillustration. Any circuit capable of fur­nishing regulated voltages of 150 de at 10mA and 6.3 de at 600 mA would besuitable. The value of Rsc (0.82 ohm) waschosen to limit the output current to ap­proximately 700 mAo RI should be ad­justed to produce 6.3-V de at the outputwith no load connected. Current limitingwill occur when the supply is first turnedon due to the low resistance of the coldtube heaters ."

The regulated voltage sources are con­nected easily to the receiver without drill­ing holes or altering the printed circuitboards. Unsolder the two brown wiresconnected to the terminals marked C andD on the rf circuit board. Solder these twowires together and tape their ends to pre­vent unwanted contact with other circuits.Connect the regulated 6.3-V de source tothe terminal labeled C on the rf board.This feeds the regulated filament voltageto the LMO tube (V5)and the heterodyne-

BREAKFROMPOWERSUPPLY OFS8-300 ...... 8REAK

R218

3300 .Jt~228'T~r+-i50V

R22 TO HET.

1000 ' d:-~2e .... OSC.

~0.01

R61000

EXCEPT AS INDICATED, OECIMAL VAWES OF

CAPACITANCE ARE IN MICROFARADS (jlf I ;OTHERS ARE IN PICOfARADS \ pF OR jljlFl·,

RESiSTANCES ARE IN OHMS;k~1000. M·l000 000.

Roo.ss,

IW

BOTTOM VIEWOF U2

1 00 0

0o 0090 0 0 0

,---'\/VV--:::--t--r------<J+6.3VOC

R46800

R'3900

u

2.5V AC

cea

2.5VAC

•

•

PIa.5ASLO-BLO

eRI

325VAC

mA, center tapped; 5 V at 2 A; 6.3 Y at 2 A(Stancor PC·8406 or equtv.).

U1 - Bridge rectifier assembly, 25 volt, 1ampere.

equiv.).Q1 - 2N3055 trenetetor.Q2 - 2N3704 transistor.R2 - 5000-0 linear-taper control.T1 - 117.volt primary; secondary 650·Y at 40

Circuit diagram for the regulated power supply. Unless otherwise noted, all resistors are tta.wau composition. Capacitors are disk ceramic exceptthose with polarity marked, which are electrolytic.C1 - 100·,loIF electrolytic, 450-V de.C2 - 2000·,..F electrolytic, 25·V de.01,02 - Silicon diode, 1000·PAV, 500 mA.F1 - 0.5 A, Slo-Bto type.L1 - Choke, 4.5 H, 50 mA (Stancor C1706 or

Transmitting and Racelvlng Kinks 53

C2

>-r--If---.......----.----\~01

Table 1

Band C1 C2 C3 L1

60·40 Meters 47 pF 47 pF 356 pF 4 ,..H, 14T20 Meters 27 pF 27 pF 100 pF 1 j.lH, 7T15-10 Meters 12 pF 12 pF 50 pF 0.75 ,..H, 5T6 Meters 6 pF 6 pF 50 pF 0.38 ,..H, 2·112T

Coil and capacitor data for the tuneo-tnput circuit shown in the figure. The coil stock is 3/4·inch dia.,32 tpl (B&W 3012).

A tuned circuit for the solid-state preamplifier.Parts values are listed in Table 1.

+12V

4700

EXCEPT AS INDICATED, DECIMALVALUES OF CAPACITANCE ARE

IN MICROFARADS (JIF I; OTHERS

ARE IN PICOFARADS I pF OR J.lJlFl;

RESISTANCES ARE I N OHMS;

k -1000. M-l 000 000 •

4700

J1, J2 - Phono jack.01,02 - Silicon npn rf transistor (Motorola

MPS·91B).

C6 +1o,u~T

1~Vrh

100

1~00

10k

22k

~1'-"'------4_+-I

~

C5

Circuit diagram for the broad-band amplifier. If the amplifier is to be used at 100 MHz, C4, C5, ca.C9 and C10 should be 10,..F in capacitance. C4 Should be omitted if the tuned circuit at upper leftis used.C4, C5, C7, ce, C10 - 0.1 /-IF 100·V (Sprague

Orange Drop or ecurv.j.C6 - 1O-/-IF 15·V tantalum.

GENERAL PURPOSESOLID-STATE PREAMPLIFIERS

Over the past few years there have beenmany articles describing various vhf/uhfamplifiers. There are few types, however,that are good for general-purpose hfamplification. How many amateurs havelistened in vain for signals above 20 metersbecause of a poor receiver front end?How many transceivers have a "dead"sound when the band is out? Here is apreamp which provides usable gain up to100 MHz. It can improve the noise figureof even a good tube-type receiver andshould improve the image rejection of anyreceiver when used with the narrow-bandmodification. The noise figure of the unitdescribed here is 2.5 dB at 30 MHz. This issufficient to provide a IO dB signal-to­noise-plus-noise ratio with 0.07 microvoltof signal at the input.

Inside view of the preamp with, the tuned-Inputcircuit shown at the left. The switch Is not in­cluded in the drawtnq at upper right. It is usedby the author as an on-ott power switch. Theprospective builder might consider including aband switch with an "out" position if theamplifier will be used 'In front of a reasonablygood receiver. Under some operating condl­tlons. it might not be desirable to have thepreamp in the line.

Preamp for HF receivers.

The amplifier consists of a common­emitter stage driving an emitter follower.Generally, emitter followers are notrecommended at high frequencies becausethey tend to be unstable, but in this designthere are no tuned elements following theamplifier and hence the amplifier is quitestable.

As with any high-frequency amplifier,good constructional 'practices should befollowed. Short leads, in-line layout, andcareful bypassing are all necessary. Sincethe unit has a gain of more than 40 dB atfrequencies below 5 MHz, all of thebypass capacitors shown should be used.

If your application calls for wide-bandgain, the device shown is what you need.But if you intend to use the amplifier as areceiver preamp, the circuit shown in theother diagram should be included. It canbe mounted in the same box as thepreamp.

The amplifier has a gain of 23 dB at 6meters and a gain of 30 dB at 10 meters. Itoperates nicely with either a sn-otun or75-ohm receiver-input impedance and willserve as an inexpensive receiver accessory.The total cost, excluding the containerand connectors, is about $10. - DonaldK. Belcher, WA4JVE and Alan Victor,WA4MGX

HW,202 OWNERS, BEWAREI

Do not use an antenna connector with along center pin to plug into the antenna

socket on the rear apron of the HW -202. Ifound out the hard way. The pin was justlong enough to touch the printed-circuit­board foil that carries the 13.8-V dc to thereceiver, causing the foil to open at thatpoint. I [umpered the open circuit andchanged the antenna connector to onewith a short center pin. - Bruce Rattray.VE3FeH/WI

LED INDICATORS FOR THE GLBTRANSMIT/RECEIVE SWITCHES

The OLB model 400B Channelizer hastwo front-panel switches for shifting eachrow of frequency selectors to either thereceive or transmit mode. The operatormust observe the position of the switchesto determine which mode position theyare in. This can be confusing and canresult in operations on the wrong frequen­cy, resulting in unintentional interference.

A simple and effective modification toprovide a positive indication of switchposition can be accomplished by the in­stallation of LED (light-emitting diode)pilot lamps adjacent to each switch, cor­responding to the switch position. Thisentails the careful drilling of four holes inthe front panel of the GLB, the insertionof four LEDs, and the replacement of theoriginal spdt switches with two miniaturedpdt switches to handle the LEDswitching. LEDs of different color can beused if desired, making the indication of

54 Chapter 3

TRANSMITINHIBIT

WHITE WIRETO BCD t INPUTMHz COUNTER

1N9I4

BROWN/WHITEWIRE TO

PTT LINE

Color-coded leads from the board may berouted through the vinyl harness sleevesand result in a neat installation. SI may belocated in several places, depending on theneeds of the operator. The author used aminiature toggle switch, mounted on therear panel next to the dc power receptacle,toward the lower corner. An externalswitch may be connected to a plug com­patible with the ACCESSORY jack. If theI-MHz offset is used frequently, theoperator may choose to mount SI on thefront panel.

Observation of the transmitter outputon a spectrum analyzer confirmed that themodification had no effect on the ex­cellent spectral purity of the FM·I44. Themodification does not require entry intoany shielded enclosure, and no connectionis made to any point where rf is present.

One last reminder: When I-MHz offsetis desired, the original OFFSET switchmust be placed in the SIMPLEX position.Considering the simplicity of themodification, this is a small price to pay.- AI Young, W2TMF

--,..,.r~+t2V±lMHz

ONE MHz OFFSET MODIFICATION

YELLOW WIRE TO"UNLOCK" LAMP

Q'2N3904

FM·144 modifications.

Kl is a tz-volt miniature spdt reedrelay. When transmitting, this relay isenergized simultaneously with the existingT-R relay, whenever SI is closed. Theanode of 019 is separated from the 147terminal on the MHz switch and con­nected to the arm of KI. While receiving,the anode of DI9 is connected to the 147terminal as in the original circuit, butwhen Kl is energized Dl is connected tothe 146 terminal of the MHz switch.

If the operator is receiving in the 146- to147·MHz segment of the band, selectingthe I-MHz offset will switch DI9 to add aBCD U I" to the MHz counter whiletransmitting. When receiving in the 146-to147-MHz segment, the modificationcauses a BCD "L" to be subtracted fromthe MHz counter. The frequency displayof the transceiver will indicate the fre­quency the rig is transmitting and receiv­ing on. Offset direction is determined bythe selected receiving frequency. Theproper offset is automatically chosen, andoperation below 146 MHz or above 148MHz is impossible. Placing SI in theNORMAL or open position restores nor­mal operation.

An additional circuit was added to theFM-I44 which may be of interest toowners of other synthesized rigs as well.Lock-up time of the phase-locked loopmay vary depending on ambienttemperature. A transmit-inhibit circuitwill prevent the rig from transmitting untilthe loop is locked. Voltage dropped acrossthe UNLOCK lamp turns Qlon, whichholds the base voltage of regulator controltransistor Q3 at ground. Turning off Q3,a 2SCI908, cuts off the regulator passtransistor which prevents the transmitterfrom operating. Rl prevents the base­emitter junction of Ql from shorting theUNLOCK lamp. When the loop is locked,the UNLOCK lamp is extinguished, Ql isturned off, and the rig will transmit.Lock-up time is generally very rapid.

Kl andQI may be mounted on a smallperforated board installed between theS meter and the right-side chassis rail.

IAI

_ 0----0 NOIlIllALo-r- IlODEI 0----0 SWITtK

I)POT . SECTION

SWITCH : 'l

NOTE' TWO SWITCHES INST.lLLED.QNE FOil TX 6."0 ONE FOil "XIlOT.. ,UIE WillED IDENTICALLY,

GLB 4008 Channelizer modification. LEDsshow switch positions.

mode selection easily determined. Themodified switch circuitry is shown above.Both replacement circuits are wired iden­tically; however, only one example isshown. The 470-ohm resistor is in serieswith the OLB 12-volt source in the com­mon leg of the switch. Position of theLEDs on the front panel is a matter ofchoice, but they fit nicely within thequarter-circle panel markings shown in B.In addition to the mode-indication valueof this system, the LEOs also provide avisible indication that the unit has powerapplied. - Bill Vandermay, W7ZZ

ADDING I-MHz OFFSET TOTHE KDK FM-l44

Automatic plus or minus I-MHz offsetmay be added to the KDK FM·I44 simplyand economicatly, using the circuit shownin the schematic diagram. No additionalcrystals are required. The only limitationis that the operator must place the rig inthe SIMPLEX mode when the I-MHz off'­set is to be selected. Normal operation ofthe transceiver is not affected by thismodification.

Tranamlttlng and ReceivIng Klnka 55

Chapter 4

Hintsfor the Power Supply

+ "47",f

5"5V VOi'2VI

1N270

(C)

1N270

1N270

47",F VO-;'V,

lN270 ~30~+

2N3904

CR,1 N27

INPUTfROM 47,uF

OSCILLATOR 30V

c>----!jf---<o------'l4----o----{)v

~

'"

INPUTFROM

OSCILLATOR

(A)

put current drain of 0.57 rnA. At an out­put current of I rnA, the voltage droppedto -21.1 volts with an input current of2.45 rnA, and an efficiency of 68 percent.

(8)

~600

+t2V DC

Typical rectifier circuits suitable for use withthe oscillator. The circuit shown in A is avoltage doubler with positive output. The oneIn B will give a negative output equal to thesupply voltage and the circuit in C is a voltagedoubler with a negative output. Resistors are1/2-watt composition.

voltage doubler with positive output. Theoutput voltage will not quite reach twicethat of the supply, and will drop underload. The circuit shown in B is for anegative supply. Output voltage will besomewhat less than the positive supplyvoltage. However, many times an op ampwill ignore such an imbalance.

The circuit shown in C is a negativedoubler which requires some additionalswitching in conjunction to that providedby the oscillator. when the input isswitched to the positive supply, Cl will becharged to the supply voltage with thepolarity shown. The 2N3906 will be turn­ed on by its base-bias resistors permittingC2 to charge to the supply voltage also.The 2N3904 will be slightly reverse biasedby the forward-voltage drop across CRI,and therefore will be turned off. When theinput is switched to ground, Cl makes theemitter of the 2N3904 negative whichturns it on (but reverse biases CRt). The2N3906 has no bias and is off. Therefore,C1 and C2 are connected in series acrossthe output (CR2 also being reverse biased)and a negative voltage doubler is im­plemented. The advantage of these cir­cuits, being .drlven by the oscillatoragainst ground, is that they provide acommon ground from supply to output.The actual output voltage of the negativedoubler will be somewhat less than twicethe positive supply voltage, of course. Itcould be used with a voltage regulatorsuch as a Zener diode to obtain a negativevoltage under load equal to the positivesupply. Indeed, there are dual-trackingregulator ICs available such as the SiliconGeneral 8G350l, the Raytheon RC4194and the Motorola MCl486 which willkeep the positive and negative voltagesidentical.

The circuit values shown were for a verylow current-drain supply for a low-powerop amp. As an example of performance,the circuit in C yielded -23.5 volts noload from a + 12.6-volt supply with an in-

SQUAREWAVEOUTPUT TORECTIFIER

+12V DC,.+;-

POWER SUPPLY FOR NEGATIVEAND POSITIVE VOLTAGESOccasionally a negative voltage may beneeded when only a positive supply isavailable. This may be necessary, for ex­ample, when using op amps. These arevery useful devices, but suffer setbackswithout a dual-polarity supply. Negativeand positive voltages equal to and higherthan the de supply can be easily obtainedwithout a transformer by using an RCoscillator and rectifying to the desiredpolarity. Such an oscillator is shown andoperates at approximately 1200 Hz withadded "totem pole" output transistorsdriven in complementary fashion. Oneoutput transistor is off when the other ison, and vice versa, which alternately con­nects the output load to the positive sup­ply or ground. This gives much better effi­ciency than direct coupling to theoscillator. While a discrete-componentoscillator is shown, it could be built with adigital-logic IC as discussed later.

Three rectifiers are shown in diagramsA, Band C. The one shown in A is a

1001<

2N3904

Schematic diagram of the discrete oscillator.Resistors are 112·watt composltlon.Capacttoreare disk ceramic, Square wave output may beconnected to the input of any rectifier circuitshown at right.

56 Chapter 4

CR'

~

Some of the best bargains in surplus relaysare to be found in the low-voltage deunits. Their use where no battery isavailable, however, often means the con­struction of a separate power supply. Thiswriter has used the circuit shown here tooperate relays from a filament supply. Toprovide the normal operating voltage forthe relay, the ae VOltage should be about2-1/2 times the rated de voltage, since ahalf-wave rectifier is used. CR2 serves tocarry the current generated by the decay- ,ing magnetic field of the relay coil,thereby protecting CRI against high­voltage transients. If a high enough acvoltage is not available, a capacitor inparallel with CR2 will raise the de voltage.This writer used a 50-,..F capacitor inparallel with a relay coil rated at 12 volts,200 rnA, and operated it from a 12-voltfilament circuit. The combinationdelivered only 10 volts, but this was'enough to close the relay reliably. - TheRev. C. R. Clark, K4ZN

RECTIFIER FOR DC RELAYS

A HIGH-PpWER SCR INVERTERDesiring to operate portable from mytrailer, I decided to build a high-power in­verter. The unit described here will workoff either a 24- or 32-volt storage battery.It can also be used with an alternatorcapable of delivering from 55 to 130 A.With a 5S-A alternator, the maximumoutput is 1500 VA (volt-amperes). The130-A alternator will give 3600 VA. Ablower should be used if the output ex­ceeds 1800 VA.. TI is a modified Variac which allowsoperation from either 24/32- or 6O-volt(de) sources. If only 6O-V operation isdesired (some alternators are capable ofproducing 60 V) the 24/32-volt windingcan be omitted. The movable arm on theVariac is removed and the center tap con­nected. The writer used a surplus Variacwhich was capable of handling 20 A. Ithad 205 turns of No. 12 wire for theoriginal winding.

If 24- or 32-V operation is desired, theoriginal 117-V winding of the Variac isused as a secondary and a bifilar primary

A simple method tor operating a de relay froman ac filament circuit. The PIV rectifier ratingshould be 2.8 times the ac supply voltage.

TO A,S

"

+ ,,+ + ,,+A " "FROMA.8

" )~-

1== "+

V,

- yo':' 8VBA +

IFI

A voltage octupler circuit. Inputs A and Bareto be connected to outputs A and B of the ICoscillator above.

transistors, reverse the diodes and elec­trolytic 'capacitors to obtain positivevoltages from a negative supply. The ICoscillator can also be used in a positiveground arrangement. It is also possible torun the oscillator at much higher fre­quencies than those used in the previouscircuits, thus reducing the necessary sizeof filter capacitor. Harmonic output atcommunications frequencies could be aproblem, however.

All rectifier circuits are generallycapable of quite high power levels if high­current rectifiers and switching transistorsare used. The IN270 has low forwardvoltage drop up to currents of approxi­mately 60 rnA, At higher currents, thenew hot carrier rectifiers could beemployed to keep the forward drop lowand the efficiency high. High-currentswitching may best be done by using theoscillator as a wave-form source at lowpower, then switch with power transistorsdriven by it. The Ie oscillator can producebase drive sufficient to switch respectablecurrents if high-gain output transistors areused. The complementary outputs A andB can be used to drive a totem-pole switchsimilar to the one used with the discrete­component oscillator, or complementarytransistors (pnp and npn) could be usedwith a single driving waveform. Most like­ly, the simplest way to achieve high powerwould be with the very high-gain Darl­ington power transistors made byMotorola and others. Thus, there aremany possibilities with regard to thevoltages, polarities, and currents ob­tainable from a single de supply withoutadding a transformer. - Julian M. Pike.WA/ITCU

O.OO1....F

VO':4VIIA

:::~_47....Faov

lN270.,~~n....F

IN270 ;:::; ~ov

lN270

47/JF50V

~I'-+-~""~~--O.+

+ JOVlN270

AO

FROM A,S

'-------08

IC-oscm.tor SubstituteThe circuit above shows a complemen­

tary MOS digital IC can be used as anoscillator in place of the circuit shown forthe discrete oscillator I yielding the sameefficiencies with fewer parts. Either out­put A or B can be used with the circuits ofA, Band C; the arrangement will havecommon ground, and will be essentiallyidentical to the discrete circuit since the IChas complementary MOS outputs. TheRCA CD4001AE and MotorolaMCI4001CL as well as similar chips ofother makers are a good choice here.

The IC circuit has greater capabilitythan the discrete-component circuit sincethe two outputs A and B are exactly out ofphase, or complementary, allowing us toimplement. higher multiplication. Thequadrupler below is found in The RadioAmateur's Handbook and can be used byconnecting to both outputs A and B of D.This arrangement yielded 4O.S volts at 0.5rnA with an efficiency of 62 percent with12-V input. The circuit shown in F is anoctuplet and could, of course, be extend­ed to many more multiplications. Thedisadvantages of these circuits are thatthey do noi have a common ground be­tween supply and output. Also, die poweravailable is small since the IC shouldreally not be called on for more than 3 to 4rnA per gate output. The supply voltagecan vary from 3 or S volts at the low endto 15or 18volts at the high end dependingon the manufacturer.

One can easily exchange pnp or npn

A quadruplet circuit suitable for use with theIC oscillator. The inputs A and B are con­nected to the outputs A and B of the Ieoscillator above. A disadvantage - there is nocommon ground with respect to the initialvoltage source.

ID)

IE)'o--....-----+---()-

Schematic diagram of an IC oscillator. The outputs at A and B give equal amplitude voltages ofopposite phase and may be fed to either the quadrupler or the octupler shown below.

Ripple was 15 mV pk-pk. The outputdropped to the supply voltage at 1.6 rnAdrain, however.

Hint. for the Power Supply 57

700J"\.'6VRELAY

R2.80

1N400t

R'000

2N2222A NON-POLARIZED

"0

relays on 12.:V supplies were reportedsome time ago in IT (February 1973)andARTS. A modified version of one of thesetechniques turned up in Electronics (9December ·1976) but this time primarily asa means of substantially reducing thepower drain of the relays. John R. Nelsonpoints out that useful power saving can beachieved in this way with battery-operatedequipment, taking advantage of the factthat a relay needs only about half of itsnominal voltage during hold-in, providedthat it can be given a boost during pull-ln.By using a transistor to switch in voltagefrom a charged capacitor, the necessaryextra voltage can be provided just when itis needed.

The system shown in the diagram isbased on the non-polarized electrolyticcapacitor which is initially charged to 12 Ythrough Rl: and R2. Closing the switchapplies 12 V to the relay coil and, at thesame time, turns on the transistor, thusdropping the positive side of the capacitorto earth. This effectively forces -12 V onthe other side of the capacitor, puttingsome 24 V across the relay coil which thenpuns in. Once the 'capacitor has dis­charged through R2 and the relay coil,approximately 7 V remains across therelay coil and this is sufficient to keep itenergized.

The circuit as shown is intended for26-Y relays having coil resistances in theregion of 1,000 II; to suit the requirementsof different relays the value of R2 mayhave to be adjusted.

The capacitor should be a 000­

polarized type since there will be a reversevoltage across it whenever the relay isenergized. Should power to the circuit beinterrupted the switch must be opened andclosed to reactuate the relay. A diodeacross the coil protects the transistor fromtransients. -' Radio Communication,February, 1977, published by the RSGB

+12V

Operation of a 26·V relay trorn 12-V supply.

Using the Inverter

To use the inverter, the fuses FI and F4or F2 and F3 are inserted in either the6O-or 24/32- V sockets (but not both) andS3 is switched to the proper position.Always make sure the vibrator is in itssocket - otherwise the fuses may blow ifthe unit is turned on. With 6O-V batteryoperation, it is also advisable to use al-ohrn, 200-W resistor in series with theinverter while starting. It should beshorted out while the inverter is running,however.

The START switch is depressed toenergize the coil of Kl. The contacts areclosed and the inverter is connected to theline. When the STOP switch is depressed,the relay contacts open and the inverter isdisconnected from the line. When theSTOP switch is released, the line is stilldisconnected and remains so until theSTART switch is depressed again. Theoutput voltage of the inverter varied from150 V under no-load conditions to 110 Vwith a 1650-W resistive load. - RussellDunaja, W3BBF

mutating capacitor appear as a reversebias at the cathode of the previously con­ducting SCR.

The comrnutating capacitor (CI) con­sists of 10 120-I'F oil-filled capacitors with400-V (de) rating each. Do not use elec­trolytic capacitors for C1. The SCRs areswitched by means of vibrator G I. VRIlimits the voltage across the vibrator coiland consists of two 6.8-V, 10-W Zenerdiodes.

REDUCING POWER DRAINOF RELAYSTwo ideas for using 24- to 26-V surplus

52sr START DC

STOP ..L INPUT

"'..,.-.-V 0---------.---:"""""0+

'EVREGULATOR

ALT.fiELD

02

"SEETEXT ,----"I----,'"""''?"'

CR,

117V

OQO!lOW,

117VOUTPUT

FROMINVERTER

seOUTPUT 30A

t17V F!lAC

OUTPUT 'OA

Schematic diagram of a voltage regulatorsuitable for use with the inverter and an alter­nator. In cases where this might be oblec­ttonab!e, this circuit would be useful, il the In­verter is used with an alternator or generatoronly.CR4, CAS - 5·A silicon diode, 50 PRY.T2 - 3·A filament transformer, 24·V ct.

winding is added (observe the polarityshown on the drawing). For 24·Y opera­tion, the primary should consist of 38turns (76 total) of No. 8 double-coated(glass) wire. It should also be possible tooperate the inverter on 12 Y (at approxi­mately 720-W output), but the windingswould be halved and heavier wire wouldbe needed. For 32-V operation, the wind­ing would consist of 48 turns (96 total).Since No.8 wire is difficult to work with,4 strands of No. 10 Formvar could beused. Two strands of No. 10 would beparalleled to give the equivalent of onestrand of No.8.

Operation

Operation of the inverter is as follows.Assume one SCR has just been turned onand the other one is in the nonconductingstate. Current will flow in one half of theprimary and the commutating capacitor(CI) will be charged through the otherhalf. When the other SCR is turned on, itshuts off the one that was previously con­ducting. This is because the supply voltageplus the voltage in the charged com-

Schematic diagram of the inverter. The inverter is shown set up for 60-volt operation. For 24/32­volt operation, F1 and F4 are removed from their sockets and F2 and F3 are Inserted at thedotted positions. 53 Is switched to the 32-volt position.C1 - 1'20f.lF (see text for discussion). type 98600 or equivalent).CRl - 2-A silicon diode, 400 PAY. 01,02 - 100·A SCA, BOO PAY (Poly PaksCA2,CA3 - 250·A silicon diode, BOO PAV (Poly no. 92CUl167).

Paks no. 87CU685). 51,52 - Motor start/stop switch.G1 - 6O·Hz vibrator, 12 volt (Cornell-Dubilier T1 - 20·A Variac, 117 V.

58 Chepter 4

---_...._--------

ce0.01

c,

+

C,1000/:11"

+ l!5V

T1 - 117·V pri. 12.6·V ct sec., 1.2 A (RadioShack 273·1505 or equiv.).

VRl - Zener diode, 12 V, 1 W.VR2 - Zener diode, 5.6 V, 1 W.

ly. Within the 500-mA load range, theregulation is approximately 4 percent asmeasured from no load to full load. Notall Zener diodes provide equally goodregulation, so it may be necessary to tryseveral units or to increase the Zener­diode current-limiting resistor to obtainthe indicated value of regulation. Betterregulation could probably have been at­tained by increasing the ac input to thebridge rectifier to 18 volts. This was notdone because it would increase the powerdissipation in the transistors, necessitatingthe use of heat sinks. In its present con­figuration heat sinks are not required. Thetransistors are insulated from the chassisby the use of rubber grommets throughwhich the mounting screws pass. With thepower supply operating under full-loadconditions, the power transistors do notbecome noticeably warm to the touch.This dual-voltage power supply hasproved to be a most valuable addition tothe workbench. - Herbert L. Ley, ex­W3VYN

IMPROVED REGULATOR CIRCUITWhile many amateurs are now usingintegrated-circuit voltage regulators, anexternal current-boosting transistor isusually required to increase the regulatorcurrent capacity. Normal current­boosting schemes, however. require addi­tional active devices to duplicate some ofthe worthwhile regulator safety features(short-circuit protection, safe operating­area protection, and thermal shutdown).Here is a regulator circuit which retainsthese safety features through a current­sharing design. This regulator, intendedfor TTL circuits, has an output of 5 volts

+"1000....F"25V

,.3300

GERA1C,

150k117VAC

EXCEPT AS INDICATED, DECIMAL

VALUES OF CAPACITANCE AREIN MICROFARADS (.Ill") ; OTHERS

ARE IN PICOFARADS\pF OR .II.l'FI;RESISTANCES ARE IN OHMS;

k 01000. M·l 000 000

Schematic diagram of the economy power SUPPly.CR1·CR4, Incl. - Silicon diode, 50 PRY, 3 A.DS1 - Neon indicator lamp.Q1, 02 - Npn power transistor, 40 W (Radio

Shack 276·592 or equlv.).51 - Spst swltch.

ECONOMY POWER SUPPLYIn these days of transistorized equipmentand digital logic, no workbench is com­plete without a power supply capable ofdelivering 12 and 5 volts de withreasonably good regulation. Theschematic diagram of a power supply thatwill answer this need was derived, withsuitable modifications, from power sup­plies that have been featured in the ARRLHandbook. Many of the parts needed toconstruct the power supply can be foundin the average junk box or may be pur­chased from Radio Shack or a similarlystocked parts emporium.

The output current from each supply islimited to approximately 500 rnA. Abovethis level, the output voltage drops sharp-

while adjusting R5 to provide the properoutput level. - Dennis Sommers,WB4TTY

[l(CEPT AS INDICATED, DECIMAL VALUES OF'CAPACITANCE ARE IN lliIlCROFARADS ( .Ill" I ;OTHERS ARE IN PICOFARADS \ pI" OR JI,IIFI:

RESISTANCES ARE IN OHMS;k _I 000, M·lOOO 000.

Inexpensive power supply for battery-operated transceivers.

BASE POWER SUPPLY FOR1-METER TRANSCEIVERSAfter getting my first 2-meter transceiver,it amazed me how many hams besidemyself were running their rigs from bat­teries with chargers. Feeling there must bea need for an inexpensive 12-volt powersupply, I dug through the junk box andfound the parts to build this unit. If allparts for this supply are to be bought new,the cost will come close to $30.

The unit is compact, considering itscapability to handle over 2 A of current,because of the series regulator doing awaywith the need for large filter capacitors.This regulating unit has the capability ofhandling up to 15 A through Q3, so that itcould be used to power a mobile linearamplifier as well as a. transceiver. Thepower supply shown here is capable of the'3 A required to run a Regency HR2A.

The supply is able to go from no load tofull load with only a 0.2-voll drop. Thisworks out to be t.s-percem regulation.The ripple voltage for the unit is notmeasurable at the 200-mA level needed torun the receiver. When the unit is supply­ing 2.2 A, the ripple voltage increases to alevel of 0.06 volt or 0.5 percent.

Output voltage for the unit shown inthe drawing can be varied from 11.5 to12.5 by use of R5 in the ripple-sensing net­work.

By varying the values of R4, R5 and R6the builder .can use the unit over a widerrange of voltages. If the builder would liketo increase the current capability of thesupply, he need only increase the ratingsof TL, CRI-CR4 and Rl. Care should betaken not to make the wattage rating ofRI larger than actually needed, becauseR1 provides short-circuit protection forQ3.

If the builder has difficulty in findingQI (GE RA I), a Zener diode in the rangeof 6.5 to 7.1 volts and a suitable npn tran­sistor may be substituted. Componentplacement is not critical, and the only im­portant requirement is the use of a largeenough heat sink on Q3. Adjustment isaccompished by means of a de voltmeter

Hint. lor the Power Supply 59

at .5 amperes, and a typical load regulationof 1.4 percent.

Rl and R2 provide the necessary cur­rent division (assuming the transistorbase-emitter voltage equals the diodedrop). The voltage drops across Rl andR2 are equal, and the currents through RIand R2 are inversely proportional. to theirresistances. In this circuit, RI has fourtimes the current flow of R2. Forreasonable values of beta, the transistoremitter current will approximately equalits collector current, while the currentthrough R2 will equal the current throughthe regulator. Under overload or short­circuit conditions, the protection circuitryof the regulator not only limits its ownoutput current, but that of the externalpass transistor too.

Thermal overload protection is extend­ed to the external pass transistor when itsheat sink has at least four times thecapacity of the regulator (this is becauseboth devices have almost the same inputand output voltage and share the load cur­rent in a 4:1 ratio). For optimum currentsharing between the regulator and tran­sistor as temperature changes, the diodeshould be located physically near the passtransistor so its heat-sinking arrangementkeeps it at the same temperature.

If the National LM340T regulator isused and mounted on the same heat sinkas the transistor, the regulator should be'electrically isolated from the heat sink asits case (pin 3) is grounded while the case(collector) of the transistor is at theregulator output potential. CI preventsunwanted oscillations, while C2 improvesthe output impedance of the overall cir­cuit. R3 is used to unload the excessivecharge in the base region of the pass tran­sistor when the regulator suddenly goesfrom full load to no load. The single-pointground system allows the regulator senseterminals (pins 2 and 3) to monitor loadvoltage directly rather than at some pointalong a possibly resistive ground-returnpath carrying up to 5 rnA of load current.- William R. Clabo. K9ASLl8

revR< 2N4396INPUT

0.25

J,<ow

ee vOUTPUT, +rh..

Short-circuit protection, safe operating-areaprotection, and thermal shutdown are safetyfeatures of this improved voltage requtetor ctr­cuit.

80 Chep,er 4

FILM-CONTAINER BATTERYHOLDERAn excellent C cell battery holder, whichoffers the advantages of being inexpensiveas well as easily attachable and separable,can be fabricated from 35-mm plastic filmcontainers. Heavy-duty snap fasteners at­tached to both ends of the plastic con­tainer provide the terminals for a C cell,when placed in the battery holder.

Construction is simple; the fastenersconsist of three parts: a ring, socket, andstud. The ring, with any paint removed, iscentered and the prongs of the ring areforced through the plastic container andalso through the plastic cap from the in­side. A socket or stud is then centered onthe protruding prongs of the ring. The en­tire assembly is then set against a hard sur­face and the ring is driven home with ahammer and a short section of l/2-inchdowel rod. The choice of whether to use asocket- or stud-fastener configuration isleft to the individual. Small pieces ofaluminum foil folded several times andplaced in the cap and container, flush withthe end rings, provide excellent batterycontact and also serve as spacers.

Several of the battery holders may beused in combination when needed, andthe required voltage can be obtained bysnapping the appropriate number ofholders together. In addition, the recycledbattery holders are inexpensive. Eight ofthe holders cost a total of fifty-five centsto construct. Allan Hale,WA9IRS/WB8UZG

SIAMESE-TWIN POWER SUPPLY

A power supply for a high-power linearamplifier can contain a lot of metal andgrow into a heavy, unwieldly monster.This became evident after a study of "UseSurplus and Save," October 1967 QST, inwhich WllCP described a supply usingtwo power transformers to obtain thedesired voltages and current. A string ofsix high-capacitance electrolyticcapacitors and associated items add to thisbulk and weight.

An answer to problems of this nature isto build the equipment on two chassis,either of which is easier to move around.The transformers, switching system, andprotective devices would go on onechassis; the rectifiers and filters onanother. Interconnections should be madewith high-voltage cabling and barrierstrips. Quick-disconnect plugs might notbe safe to use at these points. For flexibili­ty, both chassis should be the same size,and if vertical stacking is more practical,heavy aluminum angle stock could beused on the corners. - Julian N. Jablin,W9IWI

A REGULATED POWER SUPPLYFOR FM TRANSCEIVERS

When a regulated power supply capable

of operating a lO-W 220-MHz fmtransceiver from 117 volts ac was needed,all of the parts were rounded up locally inan hour and a half of shopping (includingtravel time). In any metropolitan arealarge enough to support a TV-serviceparts distributor and a Radio Shack store,it should be possible to duplicate thispower supply at the same cost or less. Thepower supply was designed to provide upto 2 amperes continuously at 12 volts,although the output voltage may be ad­justed internally within the range of 9 to13 volts with the circuit constants shownin the diagram.

CIrcuIt Description

Up to point A in the schematic drawing,the circuit is a fairly conventional; step­down transformer, full-wave bridge rec­tifier, and capacitor-input filter. The useof two transformers, rather than one,allows a certain degree of flexibility ofoperation, in that the supply may be usedon either 117 or 235 volts ac with onlyminor differences in wiring. The devoltage at point A is approximately 30. QIis used as a series pass transistor to dropthe voltage at point A of the diagram tothe desired Iz-volt output value, andmaintain that voltage over wide variationsin the output load current. U2 is anintegrated-circuit voltage regulator which,with the aid of a few external' com­ponents, is capable of handling up to 600rnA of output current. Since an outputcurrent of 2 A is desired, however, U2 isused here to properly bias QI, which has amuch higher current rating. The inner cir­cuitry of U2 can be divided into four basicelements: a fixed voltage reference, avariable voltage reference derived fromthe fixed reference, an error amplifier,and an output regulator. An internalZener diode is used as the fixed reference.This reference voltage is applied to one in­put of a differential amplifier (a differen­tial amplifier responds to the. differencebetween two applied voltage levels), whilethe other input is connected to the june-

An adjustable 12·V power supply.

"056-rw-

ae1000

es0,56-;w

6

e

R'6800

VOLTAGEADJUST

uz

@""09 • 000

BOTTOM VIEWS

0': co 0

.6

6.3VAC

n

AL TERNAfECONNECTIONFOR 23:l V AC

IIr e

~ f--------' II ,---'" '"

@'SEE TEXT

** . BE SURE SECONDARYWINDINGS AREPROPERLY PHASED

Circuit diagram for the power supply. Unless otherwise noted, all resistors are 112-wattcomposition. Component designations not listed below arefor circuit-board layout purposes. Capacitors are disk ceramic except those with polarity marked, which are electrolytic.C1 - 1500 j.lFelectrolytic, 50 volts dc (Sprague 02 - Motorola HEP50, 2N706A, or equiv. 3 amperes (Radio Shack 273-1510).

TVA 1318). R3 - 10-kO printed-circuit-mounting pot (Radio T2 - 117-yolt pri., 12.6-yolt at sec. (ct unused),C5 - 1000 j.lFelectrolytic, 50 volts de (Sprague Shack 271-218). 3 amperes (Radio Shack 273·1511).

TVA 1316). R5, R6, R7 - 0.560 t-watt wirewound resistor U1 - Full-wave bridge rectifier assembly, 50DS1 - tz-volt pilot tamp. (Radio Shack 271·072). volts, 10 amperes (Radio Shack 276·1156).Fl - 1.5 A, type 3AG fuse. $1 - Miniature dpst toggle. U2 - Motorola HEP C4069R, MC1469R, orQ1 - Motorola HEP248 or equfv. T1 - t tz-volt prl., e.a-vott ct sec. (ct unused), MCl569R.

tion of R3 and R4 (pin 8 of U2). R3 (inseries with R2) and R4 form an externallyadjustable v(}ltage divider, from the dif­ferential amplifier output (pin 9 of U2) toground. Thus, the output of the differen­tial amplifier will swing to the level thatresults in the voltage at pin 8 of U2 beingidentical to the fixed reference voltage.

A second differential amplifier serves asthe error amplifier. One input (pin 6 ofU2) is tied directly to pin 9, while theother input (pin 5 of U2) is connected tothe power-supply output bus. The error­amplifier output controls the internaloutput-regulator bias of the Ie, which inturn controls the bias applied to Q1.When connected in this manner, the erroramplifier responds to any difference be­tween the power-supply output level andthe (previously adjusted) voltage referencelevel. The output regulator acts on QItocorrect the discrepancy. C3 and C4 areused in the interest of maintainingamplifier stability. R5, R6, R7 and Q2 areincluded in the,circuit to protect the powersupply and regulator in the event of an in­advertent short circuit between the outputterminals or if the current demanded bythe load is too 'heavy for safe operation.The operation of the current-limitingfeature is as follows: When the currentflowing through the parallel combinationof R5, R6 and R7 (equivalent parallelresistance of about 0.18 ohm) is largeenough to produce a o.s-volt drop across Fall pattern and parts layout for the regulated power supply.

Hints lor the Power Supply 61

the resistors, Q2 is biased into conduc­tion. The action of Q2 on the IC internaloutput regulator results in the reductionof the current through QI. The short­circuit output current in this case will belimited to 3.3 amperes (0.6/0.18 = 3.3),which is within the safe regulator/pass­transistor limits. The value of the current­sensing resistance required for short­circuit currents of other than 3.3 amperesis calculated as follows by Ohm's Law:Rsc = 0.6/Isc where Rsc is the current­sensing resistance and Isc is the maximumallowable short-circuit current. If a longrun of cable is used between the powersupply and the load, the voltage drop inthe cable may be large enough to be ofconcern. If this is the case, a separateremote voltage-sensing wire may be runfrom the load to pin 5 of U2, rather thanconnecting pin 5 to the output at thepower supply. The regulator will compen­sate for the voltage drop in the cable. Thiswire may be of a small gauge, as little cur­rent will be drawn through it.

Construction Details

In the author's power supply, most ofthe components were mounted on anetched-circuit board (see the pattern draw­ing), although point-to-point wiring on a"perf" board would have sufficed. As thetransistors inside the IC are capable ofoperation at vhf, it is good practice to useshort leads for interconnecting theregulator components to prevent un­wanted oscillations from occurring. Themanufacturer recommends a low­inductance connection between the caseof the HEP C4069R and ground. No

Inside view of the no-lunkbox regulated powersupply. The use of the 4·inch-square pc board(visible in the right foreground) simplifies theinterconnection of most of the parts. The tu!t­wave bridge rectifier assembly (U1) and theheat sink for Q1 are bolted to the rear Miniboxwall. T1 and T2 occupy the left foreground.

82 Chapter 4

evidence of instability was noted with thiscircuit.

All parts are housed in an 8 X 6 X3-112-inch Minibox (Bud CU-2109-A).Two standoff insulators support the pcboard. while the power transformers, Tland T2, are bolted directly to theMinibox. As Q1 dissipates several wattswhen maximum load current is beingdrawn, a heat sink is required. TheMotorola HEP500, consisting of anMS-lO predrilled heat sink and an MK-15power-transistor mounting kit, is ideal forthis application. In accordance with theinstructions supplied with the HEP500,the MK-15 socket is first installed on theheat sink. The mica washer included withthe MK-15 should be coated on both sideswith a thin layer of silicone thermalcom­pound (Radio Shack 276-1372), with thebottom of Ql and the center area of theheat sink treated similarly. After the QIemitter and base pins are inserted throughthe proper holes in the washer, the tran­sistor is mounted in the socket. The micawasher insulates the case of Q1 (which isconnected internally to the collector) elec­trically from the heat sink and chassis,while the silicone compound increases thethermal conductivity between QI and theheat sink. Care should be taken to preventcontact between the case of QI and anygrounded object, as the full supplyvoltage appears on the transistor case.The current-limiting feature will not pro­tect the device from destruction in eventof an accidental short from Ql to ground,since the current sensing resistors (R5, R6and R7) are connected between QI andthe power-supply output terminals.

The heat-sink assembly is bolted to therear panel of the Minibox with no. 6 hard­ware. The MS-IO is "3 inches high and4- II2 inches wide, so it must be locatedoff center in order to accommodate thefuse holder and the line cord on the rearpanel. A l-inch-diameter hole "waspunched in the rear panel prior to the heatsink installation to allow access to thetransistor socket pins. Short lengths ofhookup wire are used between the pcboard and the transistor socket. U I iscoated with silicone compound and thenbolted to one of the inside walls of theMinibox, which serves as a heat sink forthe diodes. Ventilation of the Minibox isdesirable. Large holes punched or cut inthe sides and bottom of the box andcovered with perforated metal stock canbe used, or ventilation holes can be d-rilledindividually in the metal enclosure. Theregulator Ie is mounted directly on the pcboard, and it does not require a heat sink.

After the pilot lamp, the power switch,and the binding posts are installed on thefront panel, Tl and T2 can be bolted inplace" near the front of the box. Thetransformer primaries can be tied inparallel for operation from 117 volts ac,or in series for 235-volt ac operation. TheTl and T2 secondaries must be connected

in series and in proper phase for the powersupply to operate correctly. If the unload­ed ac output voltage as measured with aYOM is in the neighborhood of 20 volts,the windings are connected properly. If,however, the VOM reads approximately 6volts, the secondaries are out of phase andthe leads from one of the transformersecondaries must be reversed. If theprimary loads are brought out to fourseparate terminal posts, changing from1l7-volt to 235-volt operation will be asimple matter of changing appropriatejumpers. Alternatively, a 117/235 switchmay be installed easily on the rear panel iffrequent line voltage changes are an­ticipated. In either case, attention shouldbe paid to.the matter of proper phasing ofthe windings. The use of "a 3-wire ac cordinstalled in a properly grounded outlet isintelligent practice for this and any line­operated power supply. If a transformerwith a secondary rating of approximately18 volts at 3 amperes is available, it maybe used in place of Tl and T2. It is not ad­visable to use an unmodified 24- or25.2-volt transformer to replace TI andT2. The maximum allowable de inputvoltage to U2 is 35 volts, and the unloadedoutput voltage of a 24-volt transformer,full-wave bridge rectifier, and capacitor­input filter exceeds this value. If such atransformer is on hand, it may be possibleto remove turns from the secondarywinding to bring the voltage down towithin bounds. A Stancor P-8388 open­frame transformer rated at 25.2 volts and2.8 amperes was tried as a "guinea pig"for this procedure. Removal of the outerprotective wrapping revealed that thesecondary was wound over the primary,and that it was possible to remove turnsfrom the secondary without difficulty.The unloaded secondary voltage wasmeasured (the unloaded voltage willusually differ from the listed voltage at therated load) and then 10 turns wereremoved and the secondary voltagemeasured again. The new voltage was 2volts less than the original voltage, givinga figure of 0.2 volts per turn for that par­ticular secondary. It was then possible tocalculate the number of turns to beremoved in order to reduce the unloadedvoltage to 20 volts.

Operation

The supply as described will run con.­tinuously at 12 volts with 2 amperes ofload current. The ripple voltage on theoutput is on the order of 30 mV peak topeak or less. If a higher output current isdesired (8 amperes, for example), the onlylimiting factors in the present componentsare the transformer current rating and thevalue of the short-circuit current-limitingresistors (R5, R6, R7), which can be ad­justed accordingly. If it is desired to havefront-panel adjustment of the, outputvoltage, R3 may be replaced by a conven- "tional pot. - Ed Kalin. WAIJZC

(

Schematic diagram of the circuit suggested for use in charging NICad batteries from de powersource.

.~+

.L-::::~ 821.l-kf~ ~}o.

mw _>00 'W 4 CELL =

.1.4V T

33n.Yl

1I4W =6 CELL -=-

.1.4V =, T

6 CELL

••.5~

A A

c .J. ~l <00· 1_'~2 1W _ 1I2W

I:::::::::4 CELL

CIGAR -LIGHTER -PLUG --

CHARGING THOSE NICADS

NiCad batteries offer an efficient yet com­pact power source which can providegreater design flexibility for portableequipment. An advantage of these cells isthat the output voltage changes onlyslightly over the discharge cycle range ­theoretically 0.15 volt. In an emergencyone can discharge the battery below onevolt, if the equipment will operate at thatde level: The practice is not recom­mended.

A question often asked is '''How manytimes can a NiCad cell be recharged?"There is no definitive answer because ofvariables involved. A guestimation is 500times or more for a cylindrical cell. End oflife occurs when cells no longer provide 80percent of original capacity. NiCads dohave a tendency to self-discharge whennot in use.

A precaution should be stressed inworking with NiCad cells: Never attemptto solder to a NiCad cell or battery thatdoes not have solder tabs. Heat fromsoldering or from a high charging currentmay cause a battery to explode. Usepressure connections for untabbed cells orbatteries. A battery holder is recom­mended. .

The method of charging is one area ofconfusion for many users of NiCad cells.If a charging unit is furnished with a pur­chased piece 'of NiCad-powered equip­ment, use the charger exactly as recom­mended.

Any transformer to be used for a NiCadcharging circuit should provide asecondary voltage of about twice the devoltage rating of the cell or battery to becharged. Never charge NiCads in parallelwithout placing an equalizing resistor inseries with each battery.

When the batteries of a hand-heldtransceiver have run down and a charger isnot readily available, the battery in yourcar can save the day. Using a 6 x 4battery-pack configuration of a popularfm transceiver, you can charge your bat­teries from the cigarette lighter socket ofyour car. When charging in this manner,keep the engine turned off! In addition tovariations in voltage, the spikes and other"garbage" on the 12-volt bus of theautomotive electrical system are abun­dant.

Charging circuits are designed to pro­vide a constant-current charging rate.This means that the resistance of the"outside world" circuit is many timeslarger than the internal resistance of theceIL

Actual design and construction ofchargers can be quite simple. Table Igives ball-park figures to use .for chargerdesign parameters. For a completelydischarged NiCad battery, a typicalrecharge period would be 14 hours. If acell is to be on charge for more than 14hours, switch the charger to a trickle rate.Remember, too, that only NiCads de­signed to take a fast charge should be fast­charged. - Bud Meyer, K2PMA

A modified version of the circuit given, whichallows for recharging one set of batteries whileusing the second set in a mobile (hand'held)rig.

=:::::1"'75 ~v

'0 "5

20"\;

J 4 5 6 7 8 9 to t1 12 \3 14 ~. .HOURS AT C/10 CHARGE Q.

Curves for charge level vs. charge time (rate)for all methods discussed in the text, excepttast-charge types.

SURGE PROTECIIONThe 3000-volt power supply described inthe Handbook (SIst edition), uses a derelay and a dropping resistor which pro­tect the supply from the high inrush ofcurrent at turn-on time. Using the powersupply on 117 volts ac, a simpler protec­tion system, with fewer components, willprovide an equivalent function. Thediagram shows the change in the primarycircuit. When KIA is energized, RI in­troduces a voltage drop in the primary ofTI until the capacitor bank is nearlycharged. When this occurs, the voltagedrop across RI lessens after a small timeinterval and allows K2B to pull in, thus'applying full primary voltage as RI isremoved electrically from the circuit.

This change does away with the needfor a 117-volt de supply to energize thecoil of K2, the large 300-0, SO-wattresistor, and one contact on KI, as it isnot necessary to break both inputs of theprimary. - Bob Varone, WB2GLI

Table 1

-, Typical Values lor R1, R2'

mAEac Ie n =

107.1 22.5 27.1 22.5 •7.1 50 •

1. 22.51. 50· •2B 502B 100 •1. 50 6

I 2B 250

"

5

12

12

R<

. Rd/s Rdls 25Rl WATTS R2 WATTS "2OW K2.

75 1/. N.A. <5A,,.

- tt7VAC H

27 II' N.A. H7VAC COIL PRIMARY

12 1/. 33 1/.150 1/. N.A.6B 1/. 220 1/.

110 1/2 330 11'91 2 270 112'3 11. 120 II''3 5 120 2 Simplified surge-protection circuit for use with

power supply.

Hints for the Power Supply 83

+24V

TOCONTROL

A

e

'"

'"

'"

n.t.

p

OR.

SERIES FIELDWINDING

c

±24V

w

0-20

~~-~-+4' A

lA 24VPILOTLAMP

ARMATUREC

lil CAPACITORS TOTALING20.000,I"F

11 VOLTS THE EASY WAY

Power amplifiers designed for mobileoperation generally. require up to 10amperes of current at l2-volts de. Com­mercial power supplies in this range arequite expensive. A used automobile bat­tery is an alternative. If the battery willnot hold a charge, it is still usable topower an amplifier for OSCAR contacts.

If you try the circuit of the bargain­basement high-current supply shown inthe illustration, the battery will be underconstant slow charge except duringtransmitting periods. The switch in thepositive lead permits the operator to placethe battery in either a charge or operateposition. The level of the electrolyteshould be checked regularly and distilledwater added as needed. Be sure to providegood ventilation for the battery. Thehydrogen gas, which is a by-product ofthe charging process, is flammable. ­W1XZ

+24V CW ROTATION ::24V- 24V CCW ROTATiON

PROP-PITCH MOTOR

This HWA·7 modification reduces hum.

panying diagrams.The control system offered here need

not be used, but the motor will run moreefficiently with de as compared to an acvoltage. The 24-volt secondary can bewound on an old TV power-transformercore, retaining the primary winding. Sincethe duty is intermittent, No. 14 copperwire is adequate for the secondary. Themotor operates over a voltage range from24 to 30. The current consumption in nor­mal use is 6 to 9 amperes, and in very coldweather, 10 to 15 A. The starting currentis in excess of 20 A. - William M.Fugate, W81YD

2702W c

+24

-""-'wt500

0-'

+ o as<20 rnA '"7W R<, '"

3-WIRECABLE

<207W

E-24V

;r.,.,_um'IE3]CALIBRATEDAS SHOWN

Power-supply and diode arrangement at the motor for two-wtre control of a prop-pltcn motor.Relays K1 and K2 are 24·V dc types. The letters P, 0, T, U, V and W refer to the terminals on themotor. Diodes CR1·CR8, lncl. are 100 PRY, 15 A.

The control unit for the prop-pltcf motor. R1 is used to calibrate the meter at full scale and R2 isused to set the meter for zero deflection. R3 is .tocated at the rotator and is used for sensingdirection.

TWO-WIRE CONTROLFOR PROP-PITCH MOTORS

Prop-pitch motor control usually involvesthe use of several wires. The systemdescribed here uses only two wires, whichgreatly simplifies this rotator system.Basically, all of the components arelocated at the shack. Only three wires arerequired for the direction indicator, andtwo for powering the motor. By usingdiode logic, only two wires are necessary.The motor speed is the same in eitherdirection. The direction indicator, powersupply, and the arrangement of the diodesat the motor, are shown in the accom-

r-,~--tof-""-QIL~~RETC.

o-...._~n

('---+-----, IIt17 v

\

12-V TRAN5MITTERf"~~==OR AMPLIFIER

REDUCING HUMFROM HWA-7-1 POWER SUPPLY

Many owners of equipment which uses theHeath HWA-7-1 power supply seem to bebothered by excessive hum. This problemapplies particularly to the HW-7 receiver.A trick used to reduce hum and audiohowl in old-time regenerative receivers isvery effective in curing the problem withthe HW -7. As shown in the illustration,two O.Ol-mF capacitors are connected inseries across the power-supplytransformer secondary. The midpoint ofthe capacitor connection is grounded tothe chassis. - R. J. Beckwith, W1HHK

~. _ 12·V TRICKLE CHARGER

R'1.. 12-V AUTOMOBILE

BATTERY

Bargain-basement high-current supply for 12-Vlinear amplifiers. The battery is charged con­stantly, except during the actual satellite pass.

64 Chapter 4

Chapter 5

Antenna Tidbits

The Harn-M rotator electrical circuit can be modified as shown above for delayed braking. Thedotted lines leading to the 117-V circuit represent original wiring.

LEFTROTATION

~ RIGHT• ROTATION

TOCONTROLCIRCUITS

TO8RAI<E

C2500,l.lF

+ !50V

6

!5000.I\.. RELAY

SOURCE FOR INSULATORSOne item that is almost impossible to find,but is a necessary component for amateurwork, is the common insulator. Feed­through, standoff, and antenna insulatorsjust don't seem to exist anymore. Oneanswer to the problem is to use sheetpolystyrene. Nearly any plastic dealer orhobby shop stocks sheet poly, and the-­material can be cut and drilled to formalmost any type of insulator. Polystyrenewill handle any rf or dc voltage anamateur is likely to encounter and thematerial is extremely low loss. - WllCP

26V

C1200,l.lF

!50V +

4.7

23V

,'--------------~--~--------~rl-,

increases the control voltage such thatidentical readings are obtained duringrotation or at rest. My modification alsocauses the unit to read position wheneverit is plugged in. I have a master switchwhich removes all accessories when thestation is not in use.

To increase the indicator lamp life, Ichanged the lamps to 28-V types. Therelay fits nicely near the left front justabove the screwdriver-adjust calibrationcontrol. The capacitors are fitted easilynear the rear of the meter. - W.J. Short,WB4TBO

UPGRADE YOUR HAM-MWITH DELAYED BRAKING

Since I installed my Ham-M rotator somemonths ago, I have promised myself that Iwas going to install the modificationwhich allows the brake solenoid to remainenergized for a few seconds after endingrotation.

Now that I've had a chance to see thenew Ham-M II control box, and themethod used by CDE to solve the towertwisting problem, I was inspired to getstarted with a modification. In case you'renot familiar with the Model II. it employsan additional brake-release switch requir­ing that you hold the brake-release switcha second or two after releasing the rota­tion switch.

Initially, I started out to use WIFBY'sapproach, but after thinking about thesize of capacitor needed, I decided todesign something that would fit inside thepresent control unit case. My design doesthat without drilling a hole or making anymajor changes to the original wiring.Mostly, leads are unsoldered and tiedtogether and taped.

Circuit Operation

The SOOO-ohm relay is energized by theoperating switch -and held closed afterrelease for approximately 1·3/4 secondsby means of the 500.~F capacitor. Therelay contacts supply primary 120 V to themain transformer, which continues tohold the brake off after rotation power isremoved.

Note the addition of the 200-!'Fcapacitor in parallel with the original50-~F filter. This is required because the500-,..F capacitor across the relay coil in­creases the control voltage, thereby caus­ing approximately a 15° error betweenreadings. The additional 200.~F capacitor

Antanna Tidbit. 85

REMOVABLE HANDLE CONSTRUCTiON

MAKE THE THREE BENDSOF THE ROO IN AVISE.

TWO PIECES WERECUT FROM RODSTOCK

EACH APPROXIMATELY10-7/S"(27,62cm)

1-112"3.81 em

1 ,·,,,'·6.67cm

~

"PANEL-BRACKET II htOUNTING,,----SCREWS - TWOPER BRAcKEt

.--OUTSIDE OF PANEL

~~__--TOWER RUNG

measuring, marking and drilling. The firstmeasurement is from the top of the uppermounting rung on the tower to the top ofthe bottom rung. These mounting rungswere selected to position the panel on the

TWO HANDLES ARE NEEDED WITH EXACTSAME DIMENSIONS.

.....USE TWO NUTS, 114'.20, OF SAME THREADS.....AS RDbs. JAM OR LOCK THEM TOGETHER.THIS MAKES A HANDLE "STOP."

........ THIS SEND MAI<ES THE HOOKOF THE HANDLE. I

~ PANEL HO'" FOR HANOL" SHOULD BE 5" -L'J:::.-- CENTER TO CENTER. TWO PAIRS ARE USED.~

I5-114" OUTSIDE TO OUTSIDE

·'41-- "·'4'.1+ 5" CENTER TO CENTER_~_~__ 12.70cm

THIS SlOE OF PANEL TOWAROS~IN,SIDE OF TOWER.

PANEL WITH MOUNTED "z" BRACKET

STANDARD RODSTOCI( 114".20-36" WAS USED.

LIP OR CHANNEL OF "z" BRACKET-----.SHOWN HOOI<ED ON TOWER RUNG.

Mechanical features of the tower shield. At the top is the installation of the shield on a towerrung. In the middle drawing is the removable handle and at the bottom is the Z bracket.

of these pieces are bolted together to forma Z bracket. The Z brackets are boltedtogether with flat-head (binding-head)brass machine screws.

The panels were laid flat for the

Removable handle construction.

r''''1 r '''-12.54em ~PANEL BRACKET MOUNTING HOLES~ 2.!54cm

/ -ff~ -)if- #'• +- u z"BRACKET BINDING SCREW HOLE~·

~1-l/2'~ 1-l/2~6"

3.81 em3.81cm

1!5.24em

"z" BRACKET COMPONENT PIECES

Installation of the shield on a tower rung.

A TOWER SHIELD

To prevent the "small-fry" from climbingyour tower resulting in possible injuriesand a legal suit, a tower shield willeliminate the appeal of climbing the struc­ture. This tower shield is simple but effec­tive. The low cost and easy constructionmake it well worth the protection andsecurity that most hams need!

The tower shield is simply composed ofpanels that enclose the tower and makeclimbing practically impossible. Thesepanels are five feet in height and are wideenough to fit snugly between the towerlegs and flat against the rungs. A height offive feet is sufficient in most every case.The panels are constructed from 18agauge

galvanized sheet metal obtained and cut toproper dimensions from a local sheet­metal shop. A lighter gauge couldprobably be used. but the extra physicalweight of the heavier gauge is an advan­tage if no additional means of securing thepanels to the tower rungs are utilized. Thethree types of metalsv.used for the com­ponents of the shield, are supposedly rustproof and nonreactive. The panels aregalvanized sheet steel, the bracketsaluminum, and the screws and nuts arebrass. Total cost of all parts was about$20. The tower shield consists of threepanels, one for. each of the three sides,supported by two brackets. Thesebrackets are constructed from six-inchpieces of thin aluminum angle stock. Two

88 Chapter 5

Panel with mounted Z bracket.

ASSEMBLY OF "z" BRACKET

NO HOLES DRILLED IN~LIP PART OF "z" BRACKET

ANOTHER SEALANTFOR ANTENNASThere are many kinds of weatherproofingmaterial available for sealing antenna con­nections and coaxial-cable fittings againstmoisture and corrosion-causing

horizontal in the back yard, considerabledamage was evident. The bolt holes in oneleg were elongated beyond drilling out toalarger size, and, on one. of the 'o'pposiqglegs metal fatigue had cracked thematerial nearly three quarters of the waythrough. Also. we found two frost-splitsin one leg. How could a hollow aluminumtower leg set frost-splits at 30 feet aboveground? Don, WB8NUS,found, theanswer by pushing a length of electricalcord through the leg and finding severalspiders' nests had been formed inside theleg. These had trapped the moisture whichentered 'at the joints above this section anda hard freeze had done the rest.

Upon removing the bolts which held thetwo sections together at the joint wherethe elongation had occurred, the boltswere found to have been etched awayfrom an original diameter of 3/8-inch toapproximately 3/l6-inch at the center. Weremoved all the bolts from the tower andfound this reduction in diameter to bequite common, evidently due to elec­trolysis of the dissimilar metals.

The frost damage and crack wererepaired by hell-arc welding and the twosections where the elongation had takenplace were aligned and welded together.All the other original bolt holes weredrilled out undersize, and new galvanized7/I6~inch bolts were driven in, replacingall the original ones. The coax runs on thetower were checked with the techniqueusing a dummy load at the far end and awattmeter at each end. The rotator andbeams were reconditioned (using rust­resistant paint on the original plated fit­tings) and a hearty crew once againerected my "sky hooks."

If you have had a tower up for severalyears, please don't take it for granted thateverything is still in good shape justbecause it withstood Mother Nature's lastonslaught. Give your tower a goodgeneral inspection with a pair ofbinoculars at least twice a year, preferablyduring a stiff wind. If it is aluminumremove a bolt or two and check fordeterioration. This would also be a goodtime to check the ground connections tomake sure the ground clamps are in goodcondition and tight on the cable which tiesthe tower leg to the ground rod.

Aluminum ground conductors are notpermitted within 18 inches of the earth(according to the National ElectricalCode) and a few wraps of cable around atower leg or a ground rod do not con­stitute a good electrical connection. - H.J. Bell, WA8LAY

ALUMINUM TOWERS - SOMETHINGS TO WATCH FORINine years ago I became the owner of myfirst tower and beam - a self-supportingspire, topped by a new tribander. It was48 feet tall and set in concrete. It wasmade of aluminum (no painting or othermaintenance problems)! Sounds wonder­ful, doesn't it?

Last fall, I noticed some extra flexingatthe middle joint, 24 teet up. Early winterweather in Michigan was not conducive tothoughts of taking down and repairing thetower. Also, it had been up nearly nineyears and a few more months wouldn'tmake it much worse, or so I thoughtl

In late March the condition was muchmore obvious. The tower had taken on a"dog leg" at' the middle joint andwatching it in the brisk March breezesscared me. A tower-lowering party wasorganized and once tb~ system was

tom Z bracket. For panel placement orremoval, the handles are hooked in theseholes in the panels. The hook, on the topof the handle, fits into the top hole ofeach pair of the handle holes. The handleis optional, but for the effort required itcertainly makes removal and replacementmuch safer and easier. - BakerSpringfield. W4HYY and Richard Ely.WA4VHM

"PANEL-BRACKET" MOUNTING____ SCREW HOLES IN THIS

..--- VERTICAL PART.

tower. This distance from rung to' rungwas then marked on the panel. Using thesame size brass screws and nuts, bolt thetop vertical portion of each Z bracket tothe panel. The mounting-screw holes weredrilled about one inch from the end of theZ brackets so that an offset clearance oc­curred between the Z-bracket binding­screw holes and the panel-bracketmounting-screw holes. The panel holeswere drilled to match the Z-bracket holes.

The panels are held on the tower bytheir own weight. They are not easy tograsp because they fit snugly between thetower legs. If the need exists for addedsafety against deliberate removal of thepanels, this can be accomplished by meansof tie wires. A small hole can be drilled inthe panel just above, just below, and inthe center of each Z bracket. Run a pieceof heavy galvanized wire through the tophole, around the Z bracket, and then backthrough the hole just below the Z bracket.Twist together the two ends of the wire.One tie wire should be sufficient for eachpanel, but use two if desired.

The completed panels are rather bulkyand difficult to handle. A feature that isuseful if the panels have to be removedoften for tower climbing or accessibilityisa pair of removable handles. Theremovable handles can be constructedfrom one threaded rod and eight nuts.The two pairs of handle holes were drilledin the panels a few inches below the top Zbracket and several inches above the bot-

Assembly of the Z bracket for the tower shield.

Antenna Tldblta 87

40-METER HALF-WAVE ANTENNA

These matching stubs enable a en-meterdoublet antenna to work on 20 and 15 meters.

THREE-BAND MATCHING SYSTEMFOR A 4O-METER DOUBLETA common method for energizing a half­wave antenna is to feed it at the centerwith parallel-conductor TV lead-in, ortwin-lead as it is usually called, and to usean open stub for matching the 50- to 7Q-lJantenna resistance to the 300-0 impedanceof the line. However, this technique, asdescribed hi the latest edition of TheARRL Antenna Book, generally givesproper matching on only one band.

After a number of trial-and-errorcalculations on a Smith Chart, along withlots of cut-and-try experimenting, Idevised a three-stub matching scheme sothat I could operate my 4O-meter doubleton 40, 20 and 15 meters. The illustrationshows this method and givesthe lengths ofthe stubs and their positions along the

HY-GAIN I8AVTIWB VERTICALANTENNA MODIFICATION

The Hy·Gain model 18AVT/WB is a ver­tical antenna, designed for use on the80-through to-meter amateur bands.Operation on 80 meters is possiblebecause a mobile-type 75-meter loadingcoil and whip are mounted at the top ofthe antenna. Bandwidth on 80 is narrow,and the operating frequency is selected byadjusting the length of the whip. Whenthe whip is cut to the proper length for75-meter phone operation, it is not possi­ble to obtain a proper match on the cwend of the band unless the whip is re­placed with one of the proper length.Rather than purchase a new whipassembly, I fastened a 12-inch long pieceof No. 12 copper wire to the whip withtwo Fahnestock clips. This allows me toslide the wire up and down on the whipuntil the proper position is found, usingan SWR bridge connected at the feedpoint of the antenna. - AI Skornicka,K8WXQ

(Editor's Note; A more permanent method is to usesmall cable clamps to secure the added wire to thewhip.)

A DIELECTRIC "NO·NO"Let's call this a hint, rather than a hintand kink. In fact, I would like to hintstrongly that certain kinds of insulatingmaterial, regardless of how good theylook to the human eye, are definitemembers of the "no-no" family. Vhf anduhf men are especially cognizant of theneed to select suitable insulatingmaterials, as the effect of using an im­proper dielectric substance becomes morepronounced as the operating frequency isincreased.

Among the worst offenders available toamateurs on a widespread basis is nylon.Polyvinylchloride (PVC) is a bad hombrealso. Despite the physicallydurable natureof the materials, they are extremely lossy.In circuits where considerable rf power isused, they will absorb the rf energy, heatup rapidly, then warp or melt. Eventhough the insulating agent may not burnor melt (depending on the power level in­volved), the losses will be high.

The photograph shows the catastrophicresult of using PVC tubing for building aloading coil for a top-loaded verticalantenna. When 300watts of rf power weresupplied to the antenna, there was an im­mediate and constant change in SWR.Eventually the SWR became so great thatthe transmitter would not load into theantenna system.

Examination of the vertical showed the

than the iron wire) to the music wire andthen wrapping it around the hook. - IraLipton, WA20AX

Roof flaShing serves as antenna.

APARTMENT DWELLER'SANTENNAAfter trying several different indoorantenna configurations in my apartmentwith only mediocre results, I thought ofusing the metal flashing around the roofas an antenna. I simply formed a hook outof 1/16-inch model airplane "music wire"and hooked it over the edge of the roof. Aflexible wire was attached to the musicwire and brought into the shack to a con­ventional Lsnetwork coupler. The systemperforms remarkably wellon all bands (80through 10 meters); over 100 countrieshave been worked with it in lessthan eightmonths. In addition, it is quite in­conspicuous. The antenna seems to ex·hibit directional properties favoring thelongest dimension of the building, but iseffective in all directions.

The only difficulty experienced so farhas been corrosion of the music wireleading to poor contact with the metalflashing. This problem has been solved bysoldering a piece of tinned copper wire(which appears to corrode more slowly

COUPLER

feed line. The dimensions shown are forstandard twin-lead, with a velocity factorof 0.82. All of the stubs are open at theends and are made from the same type ofline as the feed line. Note that the twolower stubs are connected at the samepoint on the feed line.

The length of the longest stub is fairlycritical. It should first be cut to 17 feetand then trimmed no more than twoinches at a time, until the SWR isminimum in the center or the desired por­tion of the 20·meter band. The feed linecan then be matched with a 4:I broad­band balun to a 75-lJ coaxial cable fromthe transmitter. With my antenna, thedescribed matching system gives an SWRof less than 2.5 to lover all of the threebands, with minimum values of 1.3 to 1on 40 and 15 meters, and 1.7 to 1 on 20meters. As with any multiband antenna,one must guard against harmonic radia­tion. - Frank Stuart, K7UUC

16'4"(SEE TEXT)

300-0HMTWIN-LEAD

-la

4 TO 1 L-1I=~175-0HMBALUN I <t<&AX

XMTR.

7'5"

s's"

substances. Some of the compounds aremessy to work with and result in an un­sightly mess once they are applied.

During some recenl experiments withvarious sealants, the writer tried a tube ofDupont no. 6111N clear windshieldsealer. A 1-3/4-ounce tube was purchasedfor less than a dollar in the automotivedepartment of a nearby variety store. Thesubstance was applied to a 450-MHzCushcraft 4-pole antenna to provide aprotective coating over the mounting boltsand nuts (to prevent rusting), and overeach of the gamma-rod joints to insureagainst corrosion. Finally, each of thecoaxial connectors on the antenna weredoped with the compound to keepmoisture from entering them.

The result was excellent. After thesealant dried it was completely invisible,yet provided a thin, durable coating overthe protected parts. The life span of the6111 N material should be similar to thatof other compounds designed for outdooruse. - WIFB

88 Chapter 5

Stub-matching arrangement for intermediate run of 75·ohm nnetn a sc-onm system. Dimensionsshown in wevelenqths are electrical lengths for the frequency of operation; the velocity factor ofthe line must be taken into account when calculating the physical length. See text. The portiondrawn to the right of the vertical broken line may be replaced with a 75-ohm load.

IANY LENGTH~T CONNECTORS~ ANY LENGTH

50n I son-I ,BARREL CONNECTORSl\ * rII So-n. I ,I 50-~]

XMTR I t \V ! I t I LOAD

SHORTED ---+ SOJ), I ,oJ), J..-----..: SH0 RTED0.1411'1 ANY LENGTH 0.141>-50-.f). STUB7Sn. I 50-.t"1. STUB

0.1881'1 0.188~

I

INEXPENSIVE CAPACITORSFOR TRAP DIPOLESRecently, I decided to put up a multibandtrap dipole. Finding transmitting-typecapacitors for the traps became aproblem. Roy Purchase, W8RP, sug­gested that I might be able to use a pieceof coaxial cable as a capacitor rather thanthe hard to obtain transmitting capaci­tors.

The proper length of coaxial cableneeded to make the trap resonant at thedesired frequency was determined ex­perimentally. The method used to holdthe trap assembly together can be seen inthe accompanying drawing.

The antenna has been up approximatelytwo months and no problems with thetraps have developed. The RG-Sg;U cableseems able to handle the rf voltagesdeveloped on the antenna. It should benoted that I run 100watts on ssb and cw,

line in an existing or planned 50-ohmsystem.

For fixed-frequency operation, such asat a repeater installation, stub matchingcan be used. The SWR will then be I to Iin the 75-ohm line, and yet the input andoutput impedances will remain 50-ohmsresistive. The stub matching scheme isshown in the illustration. To avoid themaking up of multiple connectors for the7S-ohm portion (hard line can be difficultto work with), all stubbing is done with50-ohm line. Great for running thebargain-priced stuff up a tall tower, eh?

It should bementioned that this is not alossless method of matching. With theSWR theoretically being infinite in thestub sections, there will be inherent losseswhen the matching sections are installed.If the 7S-ohm line is of quite low loss inthe first place, the total losses resultingfrom using it in a SO-ohm system may beless than those of the stub-matched ar­rangement. You can determine the trade­offs yourself, by comparing performancewith the stubs connected versus with themremoved. Of course you'll have to read­just the transmitter tuning and loading forthe different conditions. - KITD

USING 7S-oHM LINEIN A SO-OHM SYSTEMIt is not uncommon these days to findbargain-priced 75-ohm coaxial line. Muchof this coax is the type used in CATV in­stallations, with foamed-polyethelenedielectric, aluminum or "hard-line"jacket, and acceptable loss figures evenfor rather lengthy runs at 220 MHz. Manyamateurs pass up a potential bargainbecause they hesitate to install 75-ohm

standing for five or sixyears, the tubing ofthe three legs was rather firmly "jam­med" together. After some blood, sweatand tears, I devised a disassembly methodwhich worked just fine. The only tools re­quired are three hose clamps of the typewhich tighten like a collet.

This drawing shows how the hoseclamps are attached, one on each leg ofthe tower section. Put each clamp on thenecked-down part of a tower leg, as closeas possible to the full-size part of the legon the adjacent tower section, and tightensecurely. Then, with the tower lying withtwo of its legs on the ground, grab thethird leg near the joint to be taken apartand lift. That joint will pull apart slightly.While holding the tower in the raised posi­tion, loosen the hose clamp on that legand slide it down against the full-size partof the tower leg and retighten it. Roll thetower over so that the leg which you justloosened is now on the ground, and repeatthe process. Continue with the third leg,and so on. I found that I could get from aquarter to a half inch of movement eachtime I did this, and after a few tries oneach leg the sections came apart easily. ­H.H. Hunter, W8TYX

Hose clamp aids disassembly of tower.

top section (loading inductor and 'above)to be leaning at a 30-degree angle withrespect to the lower member of the ver­tical. The inner PVC support tube for thecoil had overheated, causing it to melt theplastic centering disk at the lower end ofthe coil. The photograph shows thewarped inner tubing section - completewith rf burn holes!

The inductor was rewound on two-inchdiameter solid phenolic rod (impregnated­cloth variety), and the problem wasresolved. In an ideal situation (thoughfrail, physically) an air-wound coil, or oneplaced on a ceramic form, would be used.- WICKK

A CLOTHESLINE-SUPPORTEDANTENNASome of the old gang wanted to reactivatea Sunday morning round table on 75meters, but a problem immediatelybecame apparent. A dipole used for thepurpose had long since met its demise dur­ing a New England ice storm and its suc­cessor hadn't fared much better. Whilethe remains of the latter antenna workedon 75, performance was inadequate.

The alternative seemed to be climbingup on an icy roof to install something bet­ter, but this prospect was not met withmuch enthusiasm. However, a clotheslineran from the back porch to a pole in thebackyard, and this seemed like a goodpossibility for supporting a temporaryantenna. Approximately 100 feet ofplastic-insulated hook-up wire were reeledout to the end of the line, and fastenedevery 10 feet or so with clothespins. Thewire was then connected to a homemadematching network and the transceiver.Results were gratifying, and after theround table the wire was rolled up forfuture use. Since the stations contactedwere within 60 miles, the high angle ofradiation from the antenna, because theantenna was so low to the ground, provedto be a definite advantage. - WI YNC

DISASSEMBLYOF TOWER SECTIONS

Recently, I took down my aluminumtower and needed to take apart the towersections. When I removed the bolts, Ifound that I could not just pull the sec­tions apart. After the tower had been

Melted PVC tubinq.

....

Antenna Tldblta 88

and if higher power levels are to be run itmight be necessary to use RG-8/U coaxialcable. Of course the transmitting type ofcapacitors could be used. - Don R.Walters, WA8FCA

REMOVING GROUND RODS

An easy way to remove a ground rod is tograsp the pipe or rod with a pipe wrench.then simultaneously twist and pull. Soak­ing the ground near the rod will also helploosen the ground rod. - Bob Zavrel, Jr.,WA9RAT/7

COAXIAL-CABLE STRAPS

Strips cut from plastic bottles make ex­cellent coaxial-cable and control-cablestrapping. Use either aluminum tacks orbrass screws to resist rusting.

Plastic bottles come in variousthicknesses and colors and usually are notof uniform thickness so select the portionof the bottle best suited for your needs.Antifreeze bottles work very well. Word­ing on the bottle will not be seen since itdoes not show on the reverse side of thebottle. Paper cutters will do a better jobthan scissors or snips. - Katashi Nose,KH6IJ

CUT STRIPS( )

ANTIFREEZE PLASTIC BOTTLE

~~~J!iJ~ WINDOW SCREEN

PLASTICSTRAP

COAX ANDCONTROL CABLE

WALL-...

"'-

SEALED WITH j~BATHTUB SEALER /

FEED LINE

Plastic pipe elbow used as a feedthrough in­sulator.

FEED-LINE FEEDTHROUGHI have found that plastic pipe available athardware and plumbing-supply storesworks well for running leads from yourantenna system through a wall into theshack. It is available in a variety ofdiameters to suit your needs. I found thata 90° elbow on the outside helps preventmoisture problems and the pipe openingcan be sealed with bathtub sealer. - KeithGilbertson, WBIILXM

CENTER INSULATORFOR DIPOLE ANTENNAS

I'm convinced that I've seen this generalidea published elsewhere, and if it hasbeen it is probably worth repeating for thebenefit of people who are new to amateurradio. Nearly all amateurs use a half­wavelength dipole on at least one band,and finding a secure center insulator forcoaxial feed is not always an easy assign­ment - if I may inject a truism!

While browsing recently through a localhardware store I spotted some bins filledwith white plastic Ts and other unions foruse with PVC plumbing pipe. The Tslooked especially interesting, as they camein a variety of sizes (00). I purchased thetwo medium-size units, took them home,then performed minor surgery so that theywould be suitable for my intended pur­pose.

I drilled two holes at each end of thehorizontal part of the T. The two dipolewire elements would be threaded through

the holes and secured there. At the topdead center of the T I drilled a larger hole,through which I threaded the RG-58/Ufeed line. Following the assembly andsoldering of the center section of the

- dipole (see accompanying sketch), I filledthe vertical portion of the T with epoxycement to assure minimum strain of thecoaxial cable where it fanned out abovethe T to join the dipole elements. The ce-.ment was used also to seal the open partof the coax (braid and center conductor),thereby preventing water from enteringthe cable to degrade it.

Inverted-V enthusiasts may wish to in­vert the T and use the stem as the halyardconnection point for the antenna. If thatis done, the entry hole for the coaxialcable will be the first one which was usedas an exit hole in the first example. ­

. WIFB

LIGHTNING ARRESTORSFROM SPARK PLUGSThough many ham stations have effectivelightning protection in the form of direc­tive antennas of all-metal construction.mounted on towers that are well­grounded, there are still uncountedrandom-length-wire and resonant-wireantenna systems in use. Many of thesehave no real protection against lightning,despite the well-publicized need for it.John Askew, W4AMK, who recentlycame back into amateur radio after 2Syears away from it, was lightning con­scious from "way back. ,. But when hestarted looking in radio stores for light­ning arrestors, he found nothing hewanted to trust in this critical role. Par­ticularly, most of them were not suitablefor outside installation, which John deem­ed a must.

Every issue of The Radio Amateur'sHandbook shows spark-gap protectionfor wire antennas and feeders. W4AMKwas about to make up something of thiskind when he had a tune-up job done onhis car and was left with a bag of old spark

OR AS CABLE: STRAPPINGDRILL ~. HOLE

CENTER COND. t BRAID

DRILL NO.6 HOLE DRILL NO.6 HOLE

oUSE AS A

COAXIAL CABLE(S)HOLD DOWN

Inexpensive cable straps can be made fromused plastic bottles.

70 Chapter 5

58/USTATION

A dipole antenna center insulator made from a PVC plumbing T fitting.

•

plugs. Would these work? He calledHeadquarters for suggestions, and thewriter "just happened" to have some oldplugs rolling around in his car after atune-up, too. so some checks were run.

With nothing more than a wirebrushing and cleaning with some greasesolvent, plugs were checked on the Lab'sQ-Meter for capacitance and Q. The Qwas nearly infinite. and the capacitancewas 10 pF. The undersigned uses an end­fed random wire for occasional work onthe bands from 21 through 3.5 MHz. It isungrounded - but is its own protection,being of No. 24 wire eminently"meltable," and strung between twogrounded towers. A spark plug was con­neeted between this wire and the commonground, which includes everything metalin the house and an underground copperpipe to an outside well. No observable ef­feet except a very small retuning forminimum reflected power resulted. Thespark plug stays!

The gap, as the plug comes out of thecar, is probably OK, though purists maywant to file both parts to points, and ad­just their spacing to the lowest that willstand the highest rf power used. Wherebalanced feed lines are used, mount twoplugs on a grounded metal plate at ap­proximately the feed-tine spacing. TheHandbook gives all important safetydetails. - WIHDQ

EASIER INSTALLATION OFCONNECTORS ON COAXIALCABLE

If difficulty is experienced forcing thevinyl jacket of a coaxial cable into a con­nector or reducing sleeve, a shot ofaerosol silicone spray on the jacket willusually allow the cable to be easily fittedinto the connector. - Lee R. wicat,KH6BZF

OPEN·WlRE·SPREADER SOURCE

An excellent source of spreaders for open­wire feed line is fiberglass battens madefor sailboats. The raw fiberglass comes in10 or 12-foot lengths and sells for 70 centsper foot from Hard Sails, Inc., Islip, NY.It may be cut to size and drilled very easi­ly. The finished product is quite strongand an excellent insulator. - BobFischer, WB2EUH

Fiberglass battens for sailboats make excellentfeed·line spreaders.

An antenna feedthrough panel.

ANTENNA FEEDTHROUGH PANEL

It is not always convenient or desirable tobring antenna feeders into the shack byrouting them under a window t to whichan insert strip has been added for thatpurpose. The under-window methodmakes it difficult to seal against weather t

and insects have a way of finding thesmallest of cracks through which to gainentry to the house.

Homeowner-hams who aren't afraid tocut into the siding may fare better byusing the technique described here. Asaber saw is used to cut a square or rec­tangular hole in the wall of the house,after first using a stud locator or similardevice to make sure the hole will be cut ina clear area of the wall. The hole shouldbe approximately I/z-inch, smaller in ver­tical and horizontal diameter than thejack plate that will mount over it. This willprovide ample "shoulder area" for screw­ing the plate to the wall, and will permitadding a gasket of cork or rubber for thepurpose of weatherproofing the area.

After the hole is cut on the inner orouter house wall, find the approximatecenter of the hole by inserting a screw­driver or other long tool into the hole,bringing the tip to rest on the wall surfacein which the mating hole will be cut. Alevel can be placed on the screwdriverblade to assure reasonable accuracy infinding dead center on the opposite wallsurface. Mark that spot with a pencil;then with a long drill bit, bore a holethrough the uncut wall. Use the hole toestablish the center when laying out theborders of the second hole.

The jack plates (two) should have thecoax fittings, steatite feedthroughbushings, ground terminal, and whateverplaced in a symmetrical manner,remembering that one plate will be themirror image of the other. Mount theantenna fittings on both plates, and addcoaxial-cable and wire' extensions to thefittings on one plate. Allow three inchesmore lead length than the wall thickness.

Attach one plate to the wall. Bring theleads through the wall and solder them tothe mating jacks on the remaining plate.Attach the second plate to the wall.

If a feedthrough bushing is used to pro­vide access to an end-fed Wire, make surethe insulation on the wire is capable ofhandling high rf voltages. The writer usesTeflon-insulated No. 16 wire for the pur­pose, but the inner conductor andpolyethylene insulation from a piece ofRG-B/U coax cable can be used as asubstitute.

SWR checks were made to see howmuch reactance was presented by the wallpanel. A 50-ohm dummy load was con­nected to one side of the feedthroughassembly, and an SWR indicator andtransmitter to the other. From 160through 10 meters there was no indicationof SWR. However, the jack panel maycause a "bump" in line impedance in thevhf spectrum. The vhf/uhf builder maywant to mock up a set of plates and fit­tings and check them for SWR before cut­ting merrily away with a saber saw!

The accompanying photograph showsthe author's feedthrough panel (outsidethe house) on which three coax fittings,one single-wire bushing, and one groundterminal have been mounted. GE Silasticcompound was used to seal the edges ofthe plate and wall against weather, dustand insects. - WIFB

ANTENNA FEEDTHROUGHMETHOD

I had a problem when running the end ofa wire antenna into the basement shackwithout replacing a window pane withplastic sheet. I needed a weatherprooffeedthrough, and the photo shows what Icame up with. Materials used were a pieceof II2-inch PVC pipe long enough to gothrough the wall, and a brass rod whichwas 1/8-inch diameter and two incheslonger than the PVC pipe. It was threadedto accept 6-32 hardware. I used two no. 00rubber stoppers, and two each no. 6 brassnuts and washers. Corks may besubstituted for the rubber stoppers. Addi­tional waterproofing is possible if siliconesealant is applied where the stoppers pressinto the pipe. - Art Mueller, WA3BKD

PVC pipe and brass rods are used for thisfeedthrough method.

Antenna Tidbits 71

l17V70

23V

•

CONTROL

.15A""1"4V

30J..lFSOVOC +

.15A14V 16k

CABLEr,

7 I I

I J

J

21 Jvee!

I

3

7

500

+3

ROTATOR

4.7 100mA 1/16A

2.5£\

LIMITRIGHT

BRAKrE...._~ ..

4

.75n=LIMIT LEFT

•4

5 5

e

'\#1'

2 I 2

130pF

"5i5"\i"AC-......,:.H·--"c.....,H--<:>=------------------'8 8

II /L ..J

163

v

Schematic diagram of the CDR control circuit with the W71C/K71C modification.

HAM-M ROTATOR BRAKEMODIFICATIONLast fall I installed a Heights 72-foot free­standing aluminum tower with aTH6DXX Hy-Gain beam antenna. Toswing this beam, I had a CDR rotatorseries no. I that had never been removedfrom the original carton. The immediateproblem was the instant stop feature ofthe CDR with no way to install torsionbars (no guys), as recommended byCornell-Dubilier, on the tower. I readwith interest in QST for May, 1974, thearticle by K8CM 'as well as the conversiondata by CDR to update the series no, I toseries no. 3. My ultimate goal was to turnthe beam and to be able to stop it withoutthe sudden stop. I didn't fancy operatinga separate switch on the control box to de­energize the brake. The CDR control boxhas a switch that, when turned right or leftto the first position, turns on the panellight and energizes the meter circuit togive beam position indication. Whenpushed to the extreme right or left thebrake releases, the beam turns and, im­mediately upon releasing the switch, thebrake is applied while the beam is stillturning.

The enclosed diagram shows the con­version wiring from series no. 1 to seriesno. 3, and also the rewiring of the direc­tion control switch .. The switch, whenplaced in the first position to the right orleft, turns on the panel light, energizes themeter circuit and releases the brake. If thelever is pushed to the extreme right or left,the rotator will turn to the desired posi-

tion. When the lever is returned to thefirst position, the light and meter circuit isstill on and the brake is off. The beamcomes to a gentle stop. After a shortdelay, the lever may be returned to thecenter position, the brake-hold coil is thende-energized and- the brake is applied.

I used this I system last winter, eventhrough some severe wind, and found it tobe completely satisfactory. The wiring issimple and the results are great! A simplerewiring job gives complete control ofrotation with the original switch arrange­ment, with no drilling or altering of thecontrol box case and no need for torsionbars! - George A. Onsum. W7ICIK7IC

A BETTER GAMMA CAPACITORThe gamma rod is fairly easy to make andfasten to the driven element of an anten­na, but the gamma capacitor can presentsome difficult mechanical problems.While this capacitor need not have a veryhigh voltage rating (the gamma-matchfeed point is usually at a high­current/low-voltage point), it must with­stand the outdoor environment.

Common methods for weatherproofinginclude sealed metal, glass or plastic cansfor air-variable capacitors, and the use ofcoaxial capacitors, with the gamma roditself acting as one plate with an air orpolystyrene tubing dielectric. Both ofthese methods require fairly sophisticatedand painstaking design and constructiontechniques.

At my location, a gamma-matched wire

dipole has been in service for 18 months,exposed to the Southern Californiaseashore environment. This antenna usesa fixed-value mica gamma capacitor thatis fully exposed to the weather. Therehave been no observable adverse effectscaused by temperature, moisture, salt orsmog, and the mechanical installation issturdy.

The mica capacitor used in this applica­tion was made by Elmenco, and has ahard-glazed, brown ceramic coating, withthe wire leads brought out at right anglesto the body of the capacitor. The requiredcapacitance value is determined by tem­porarily clipping an air-variable capacitorto the terminals of the antenna and ad­justing this capacitor and shorting barlocation until the desired match is obtain­ed. When a satisfactory match has beenachieved, the variable capacitor can be,removed, and the value determined visual­ly (for example, if a lOO·pF variablecapacitor is used and the plates are about60 percent meshed at the matched condi­tion, 60 pF is a good starting point withthe fixed-value capacitors).

Mica capacitors are stocked in MILvalues and are rated at 1500-V de for lowvalues of capacitance, and lOOO-V dc forintermediate values. At about 15 cents perunit, a dollar will buy an assortment thatwill certainly include the required value(and help replenish the junk box). A briefcut-and-try session should show whichcapacitor brings the desired match. Theselected capacitor, which is light, compactand inherently weatherproof, can then be

72 Chapter 5

\

mounted permanently on solder legs orscrew terminals and coated with siliconegrease or acrylic lacquer to protect leadsand solder joints from corrosion.

The same type of capacitor has beenused in the trap circuits of a two-bandtrap dipole. at 500-watts input. In this ap­plication, high rf voltages were presentacross the traps, so it was necessary toconnect three 1500-V units in series acrossthe, inductor. Adjustment can be ac­complished most easily by using a diposcillator to find the resonant frequencyof the trap (as constructed fromcalculated values) and by compressing orexpanding the inductor to achieve thedesired setting. A heavy coat (or coats) oflacquer is recommended for corrosionprotection for the inductor. - Paul H.Weisz. K6YQ

A neat weatherproof enclosure for an antennatuning network. This box was made withstnqle-slded glass epoxy circuit board.

metal boxes, even if made weatherproof,tend to rust after long exposure to theelements. Aluminum boxes are subject tocorrosion. Furthermore, it is not alwayspossible to locate a ready-made containerof the desired size for a given application.

The photograph shows a 10 x 10 xIO-inch (254 x 254 x 254 mm) housingmade from single-sided glass-epoxy circuitboard: The material was acquired at lowcost from a vendor at a ham-radio fleamarket. One attractive feature in the useof circuit-board material is that a box ofsome specific size can be made readily.The copper surfaces are inside the con­tainer. A high-wattage soldering iron (100W or greater) can be used to affix thewalls in the desired position. The solderwill seal the joints against the weather.

A tuning network for 160 meters isenclosed in the model shown here. Acoating of spar varnish has been paintedon the box to help preserve the glassepoxy. Weatherproof tape has been usedto offer additional protection where thewalls have been joined. A variablecapacitor shaft protrudes from the frontofthe box (knob at right). A rubber grom­met provides a tight fit around thevariable-capacitor shaft to keep dirt andmoisture out of the housing. Theassembly is affixed to one tower leg bymeans of two V bolts and an aluminumplate. Caulking material is used to seal thebolt holes at the mounting point. ­W1FB

CORRECTING ERRATICDIRECTION INDICATORS

The resistance wire in the direction in­dicator potentiometer in CDR rotators isterminated at each end with a rivet. Theconnection between the wire and the rivetoften corrodes, resulting in erratic indica­

. tion, or no indication at all. My solutionfor the problem does not require theoperator to remove the rotator. Afterdetermining which terminals on the con­trol box connect to the ends of the poten­tiometer, I charged up an 80.~F. 450-voltelectrolytic capacitor and discharged it

CUSTOM·MADE WEATHERPROOFENCLOSURESFrequently a need exists for an easy-to­build outdoor box in which to put amatching network for an antenna. Some

Radius in feet = Boom length 2 +2

3-ELEMENT YAGI ANTENNA

If you can't make the physicalmeasurements for any reason, like nothaving the antenna yet, you will want tomake sure it will fit your space before youacquire it. All you need do is study theliterature or advertisements, determinethe boom length that is applicable to theformula and the length of the reflector,and you are in business.

For beams of various length booms, thefollowing formula can be used

If your available space prevents install­ing a "standard" commercial antenna,there are a few tricks you can use. Mount­ing the Yagi vertically is just one; the turn­ing radius resulting will be 1/2 the boomlength. - Robert Weinstein. K4KXR

torque resulting from attempting toelevate a heavy system. - W1XZ

Reflector length 2

2

CALCULATING ANTENNATURNING RADIUS

Crowded living in the world todaysometimes makes it necessary for the'amateur to know if the turning radius ofan antenna will permit rotating it in alimited space. As can be seen in the 'ac­companying sketch, A is the longest (or atleast half) part of the boom extending outfrom the mast or tower, B is one-half ofthe reflector length, and C is the turningradius. In, other terms, C is thehypotenuse of the right triangle formed byA and B. You may remember from highschool math that C equals the square rootof A2 + B2

• Or C2 = A2 + B2 is its usualform.

Boom length and reflector length determineVagi turning radius.

IoI

I0--

-II-0- - --0

I

I I---0--·-0-

__l . __j__~I+I r~~ 0

E" 2r ,r :I L -0

- I

Dimensions for U·100 mounting plate.

USiNG THE ALLIANCE U·l00ROTATOR FOR ELEVATINGSATELLITE ANTENNAS

While it is possible to communicatethrough the OSCAR satellites using a fix­ed antenna elevation of 30 degrees, it isdesirable to have some means of adjustingthe antenna in order that it may bepointed more directly at the satellite. Therotator used should have a direct readoutof angle' of elevation and be of the typethat allows the rotating mast to pass corn­pletely through the body of the rotor. TheAlliance model V·loo is one rotator thatfulfills these requirements. Dimensionsfor a mounting plate are shown in thedrawing. The l/4·inch thick aluminumplate is fastened to the support mast withtwo U-bolts and clamps (Radio Shack no.15-826). One side of the rotor shell has aprotrusion to keep the rotor from slidingdown the mast when mounted normally.This part of the casting is removed withthe aid of a hacksaw, and the rotor ismounted on the plate. The V-loo was notdesigned to withstand severe lateral force,and the loads on either side of the unitshould be balanced. If it is desired toelevate a very heavy antenna, such as alO-meter beam, some sort of thrust bear­ing should be devised to relieve pressureon the rotor bearings. Bear in mind,rotators of this type were designed for oc­casional turning of TV antennas. The in­ternal gears will not tolerate excessive

Antenna Tldblta 73

Iacross the potentiometer. The brief, highcurrent will actually weld the connectionbetween the wire and the rivets, withoutdamagingthe potentiometer. In one case,the connection at one end was completelyopen when measured with an ohmmeter.but after one "shock treatment" normaloperation was restored. - Maryan W.Plaza, W9TMU

USING A HOCKEY PUCKTO INSTALL WIRE ANTENNAS

A hole is drilled in the center of a hockeypuck, and a string is tied through the hole.By tying the end of a wire antenna to thestring and throwing the puck over a treebranch, an antenna may be installedwithout climbing the tree. Theaerodynamic qualities of a hockey puckmake it better suited for the applicationthan the commonly used rock or baseball.- WA4FIB

TRANSMISSION·LlNE LOSSES

The subject of transmission-line losses inthe presence of standing waves has alwaysheld an aura of mystery for someamateurs, even though much informationhas been published on the subject. The at­tenuation chart shown may help dispel allmysteries, for it provides a convenientmeans of determining total losses if theSWR at either the input or the load isknown and if the loss in the line withoutstanding waves is known. (This latterfactor may be obtained from manufac­turers' data or from transmission-linedata such as appears in The RadioAmateur's Handbook, The ARRL Anten­na Book or The Radio Amateur's VHFManual.) Conversely, if the SWR valuesat the input to the line and at the load aremeasured with a reliable instrument, thetotal line loss and the loss of the linewithout standing waves (matched loss)may be determined from the graph.

The horizontal axis of the graph iscalibrated in values representing the SWRat the load, while the vertical axisrepresents total loss in the line in decibels.The curves which are predominantly ver­tical (dotted lines) in the body of thegraph represent the SWR value at the lineinput, and the curves which arepredominantly horizontal in the lowerportion of the graph (solid lines) representthe matched-line loss. Interpolation ofvalues may be made between the curves,and the curves are interrelated so thateach set or family may be considered asanother "axis" of the overall graph.

A couple of examples best illustrate useof the graph. If we had, say 100 feet ofRG-8/U feed line connected between alO-meter transmitter and its load, and ifthe SWR as measured at the load is 3: 1,what is the total line loss and what is the

74 Chapter 5

to1)- II ,

•L> 1/ r Iff9

I ~1/ I0,Vi I :$1hi.,

II s: '7'1+"" I ," I

r ,,'I I I

'"/' , III/s y, J..jf-1\.\1

J,/ I It l~

,s "1 IA '7j, s-:

, V- I /~ if '

41.3, 11.51 IA /

I / 2

, e-!-"'I 2 I I, ,, I , , I

v'1 ',: /s / I, I e

2 I I 4 / YfI, ,

1-11 I O.~, ? /12,

CJ- V,, I /O.2~ , , 0 ,, 11' , , 14

0 , 2 a 4 e e to 12 HI 20

SWR AT LOAO

This graph relates the matched-tine attenua­tion loss in dB to the total line loss and toSWR values at the line Input and load.

SWR at the line input? First we mustdetermine the matched loss of the lengthof coaxial line. Data tables tell us that RO­8/V has a 1.0 decibel of loss per hundredfeet at 30 MHz, a value close enough forour needs. Now we proceed by running afinger along the scale at the bottom of thegraph and locate the value of 3, represent­ing the 3:1 SWR at the load. We followthe vertical "3" line up until we meet itsintersection with the" I" solid-line curvewhich represents I dB of matched-lineloss. At this intersection we may readfrom the calibration scale at the left thatthe total line loss under these SWR condi­tions is 1.5 dB. At this same intersection,by interpolating between the dotted-linecurves, we may also see that the SWR atthe line input is approximately 2.3:1.

As another example, assume that we areusing a length of line with a matched lossof 3 dB and that we measure the SWR atthe line input to be 2: I. What is the totalline loss and the SWR at the load? In thiscase we begin as before, by running afinger along the scale at the bottom of thegraph until we locate the value of 2 forSWR at the load (it'll be the same at theline input if the line is lossless, or has 0 dBof matched loss). This time, however, weproceed by following the "2" dotted lineup and slightly to the right, as this dottedline represents a 2: 1 SWR at the line in­put. We follow this line until we reach itsintersection with the "3" solid curve,representing the matched loss of ourfeeder. From this intersection we mayread (scale at left) that the total line losshere is just a tad more than 5 dB, and(scale at bottom) that the SWR at the load

is 5:1. If we had not known any attenua­tion values in this example, but were ableto measure the SWR at the load as 5:1 andat the line input as 2: 1, we would be ableto determine the matched loss and thetotal loss from the intersection of the "5"SWR-at-load vertical line and the 2 SWR­at-input curve. There's no mystery here, isthere? - KITD

EASY GROUND·RODINSTALLATION

Dig a hole five or six inches deep and sixinches in diameter. Fill the hole withwater. Set the pointed end of the rod inthe center of the hole and start tampingwith the rod as though you were tampinga post. Pull the rod up so the water goesdown in the hole. Insert the rod in thesame hole and push down again. Repeatthis procedure until the rod is down to thedesired depth. - Clarence E. Berry,K9TAT

A plastic block mounted on a right-anglebracket at the tower base serves to support anantenna loading coil.

HY·TOWER LOADING COIL

Shown in the photographs is the methodthat I used to mount a loading coil for myHy-Tower but it is a system that could beused with any tower. I feel it is 'superior tothe method recommended by Hy-Gainbecause there is no mechanical strain onthe coil.

A plastic block is bolted to the base ofthe tower using a right-angle bracket asshown. Holes are drilled in the plastic forcoil-support points, plus the block edges

The coil is mounted over the block. Note theclip lead used for making initial adjustments.

A weatherproof cover is installed.

are rounded 50 that the coil is a press fitover the plastic. The coil is not electricallyconnected at the bottom end - the nutand bolt are for mechanical support. Thewire that runs the length of the tower sec­tion is connected to the upper end of thecoil at the upper support screw. The coiltap is electrically connected at the tower­base feed point. Rain protection is provid­ed by a plastic juice container, invertedover the coil. - Larry Price. W4DQD

ANOTHER CLIFF·DWELLERANTENNAMost transmitters are designed to work in­to 50·ohm loads. Some amateurs, par­ticularly newcomers, don't realize that asimple antenna that provides a low­impedance load in the 50-ohm region is anend-fed wire that is a quarter wavelengthor odd multiple of a quarter wavelengthfor the desired band. When using such anantenna, simply connect one end to theoutput terminal on the rig, and get theother end as high as possible. Be sure touse an earth ground on the transmitter. ­WIICP

ALUMINUM WIRE CONNECTIONSWhen using aluminum wire for elementsand matching stubs on a nO-MHz Yagi, Ineeded a' way to make easily adjustableconnections to the Twin-Lead and to theshorting stub. The solution was to uselarge Fahnestock clips, slipped over theends of the wire before the array wasassembled. A pair of clips were solderedtogether to make the shorting stub. In­cidentally, the insulators shown weremade of plastic pipe fittings, drilled to fitover the 7IS-inch boom, and slotted witha saw to take the stub wires. - DOnn G.Shankland, W8WVS '.

LOW-COST CABLE HANGERSThere is a frequent need for bringingcoaxial cables and assorted control wiresinto the ham shack, Or from one equip­ment rack to another in the same room. A

neat installation will help to keep thenumerous conductors from creating anoctopus of disarray.

This writer recently purchased 12plasticshower-curtain hooks for 79 cents at anearby discount store, hoping to solve aproblem the OM was having. It seems thathe was trying to bring three coaxial cables,a rotator control line, and a shielded pairfor controlling a remote tower-mountedantenna switch into the shack from out­doors. The cables were hanging indisorderly fashion between the tower andthe entrance panel on the rear wall of thehouse. It was suggested that the lines bedressed neatly under the overhang of thehouse, approximately six feet aboveground.

Plastic shower-curtaln hooks provide an tnex­pensive means of supporting cables,

The shower-curtain hooks (see photo)turned out to be ideal for the application.A piece of heavy-duty guy line wasstretched between the lower tower sectionand a support member for the sun porch,anchored in place, and equipped with sixof the shower-curtain hooks. The cableswere then run through the hooks to thepoint where they could be dropped downto the entry panel leading to the shack.

The style of hooks shown here are ofthe snap-together variety, thereby permit.ting them to be opened easily when it isnecessary to add or delete a cable. Onething for sure, it beats holding bundles ofwire together with vinyl-plastic electricaltape. The latter creates a sticky, disgustingmess after. being exposed to the sun inwarm weather. - WICKK

ANOTHER LOOP ANTENNAFOR HUNTERSThe general use of frequency modulation(frn) on the vhf and uhf amateur bandshas complicated the problem of directionfinding (OF). The limiter circuit used infm receivers leaves no easy point in the

receiver from which monitoring of signallevels can be accomplished. The use ofsome other circuit source for indicatingthe OF steer is required.

Most fm receivers include the use of asquelch circuit. An adjustable sensitivitycontrol sets the minimum level at whichthe squelch will "open" and the audiofrom the receiver will be heard. With theantenna described here connected to thereceiver, rotating the antenna will causethe signal to "pop" in and out. To im­prove this effect, some control over theamount of signal the receiver "hears,"and proper adjustment of the squelchthreshold. is needed. The latter is usuallyperformed by the operator and the formeris accomplished by inductively couplingthe feed line from the receiver to theantenna.

The loop is made from 40 inches of3/8-inch OD copper tubing, bent into acircle with the ends about one inch apart.The coupling link is a piece of hard-drawncopper wire, fastened to the center of abulkhead fitting from a small boat. Thesize of the coupling link should be kept assmall as possible since it also might func­tion as a very small loop, rather than acoupling device for the antenna.

To use the loop, it is connected to thereceiver by a length of coaxial cable, withthe coupling link parallel to the loop formaximum coupling of the antenna to thefeed line. After the signal is tuned in, rota­tion of the coupling link will attenuate thesignal until a point is found where a sharpnull will be indicated as the antenna isrotated. PVC plumbing fittings were usedto give the antenna a "finished" ap­pearance; nothing is unusually criticalabout the design. The antenna has beenused to "home" on the transmitter, a25-watt, 2-meter signal from as close as 50feet, and also on the l62.55-MHzWeather Service broadcast station in NewYork, a distance of over 60 miles. - B. C.Algeo. ir.. W3EM

View of the completed loop antenna. The com­pass adds magnetic heading indication to theantenna operation, useful when plotting a"steering" headIng.

Ant.nna TidbIt. 75

Chapter 6

Thoughtsfor CW Operators

KEY JACK FOR ACCU·KEYER

I saved a little space in the construction ofmy Accu-Keyer, built from instructions inQSTfor August. 1973. by using a key jackinstead of a switch for tuning adjustment.It is convenient to just plug my key in: It istess expensive too! - Skip Turner,WB4YXN

THE HEATH TWO·KEY KEYER

When my new HD·141O keyer arrived, Iwas pleased to find that assembling it wasnot difficult. What I did not realize wasthat this was one of those' newfangledsqueeze keyers intended for iambic opera­tion. Although it is true that the built-inpaddles may be used for traditionalnoniambic operation, I found that tryingto adapt my style of sending to the use ofthe paddles was not easy: I did not carefor iambic.

From a discussion with Steve Harney,W9IHH. I learned that the keyer could bemodified for use with a Vibroplex Vibro­Keyer. The simple arrangement is shownin the diagram. I now have a well­engineered keying device with the optionof using a fast external key or the built-inpaddles. - Sam LeBow, WB6FJZ

OASH

EXTERNALr----oVIBROPLEXm KEY

DOT

Modification of the Heath HD·1410 keyer foruse with a Vibroplex Vlbro·Keyer is shownhere. Paddles are tapped at A and B. Groundfor the Vibroplex is obtained from the phonosocket at .the rear of the kever.

78 Chepter 8

ANTI-VOX IMPROVEMENTFOR CW OPERATION

There have been many hints towardspeeding up the pull-in time of VOXrelays while operating transceivers in thecw mode. None of them solve the basicproblem. In some types of equipment theanti-VOX circuits are not disabled duringcw operation and a bucking voltage isbuilt up during reception which mustdissipate through the timing circuits of theVOX control. The result is that part of thefirst dot or dash (or all of it) is nottransmitted.

My own Heath 8840l suffers thisdefect as does the HW·loo. the HW·IOI.the 88-102. I suspect the earlier 88-300and SB-30l as well as other manufac­turers' transceivers do also.

The solution is to kill the anti- VOXamplifiers or the anti-VOX rectifiers (if noamplifier is used) during cw reception on­ly. This is accomplished by opening thescreen or plate circuit to the anti-VOXamplifier, disconnecting the audio to theamplifier, or even disabling the anti-VOXrectifier. The voltage to a transistoramplifier may also be interrupted. Thereare usually extra contacts available onmode switches or relays. Either an open­ing or closing circuit can be adapted.

In the SB-401, contacts on mode switchMIR can be used. First, remove theyellow wire from MIR contact no. II.Also remove the jumper from contact no.12 of M1R to contact no. 9 of MIF.Discard the jumper wire and connect theyellow wire to contact no. 9 of MIF. Thisfrees contacts no. II and no. 12 of MIR.

Next, break the foil on the carriergenerator circuit board between RI42 andC136. This opens the screen circuit ofanti- VOX amplifier V13A. Connect ashort wire from the hot end of C136 toterminal II of switch M1R and another

short wire from RI42 to terminal 12 ofMl R. The screen circuit of V13A will nowbe closed during ssb operation and openduring cw operation. - Kenneth J. Gard­ner, W2BGN

CURE FOR THE WANDERING KEY

Another way to keep a paddle or bugfrom emigrating around the operatingdesk is to use one of those floppy diskssold as bottle or jar sure-grip openers.These openers are approximately 4-1/2 in­ches in diameter. No marks are left on thedesk after use. A disk may also be cutapart and a piece glued to the bottom ofeach foot. - Ray Day, WB6JFD

USING THE HD·I4IOWITH A TRITON IV

After purchasing my new Ten-Tee TritonIV transceiver I found that my HeathHD-141O electronic keyer would not keythe transmitter. Apparently this was theresult of a fairly high key-line voltage. Mysolution was to short out diode D5 andresistor R27. - Richard Gubanich,K3YLI

RF IN THE ACCU·KEYER

Erratic operation of an Accu-Keyer can becaused by rf. To prevent rf from enteringthe unit, an all-metal box should be usedfor the cabinet. A good ground circuit isessential. The TTLs in the Accu-Keyer areeasily affected by rf. I also found with mykeyer that reducing the length of theRG174/U coaxial line from the keyer totransmitter (4 feet to 1 foot) effectivelynullified another source of rf pickup.Jay Kobelin, WA2FIJ

TONEOSCILLATOR

7.!5MVOX DELAY

R9032.2M

RELAYAMPLIFIER

V1ZB6EAe

9

R9032.2M

7.5MVOX DELAY

9

v12B

\EXTRACOMPONENTS

IA)

undesirable. One could be installed on therear apron, but that would be awkward.

The circuit described here makes thisswitch operable via the mode switch onthe front panel and a relay. Relay contactsare connected across the VOX DELAYpotentiometer, as would a pair of switchcontacts. When cw is selected, one of themode switch functions completes the'tone-oscillator cathode circuit. Thesesame contacts are employed in thismodification to complete the relay coilcircuit and energize the relay. Power forthe relay coil comes from the 12·V acheater pilot-lamp line, which is rectifiedby the diode and filtered by the capacitorto provide the necessary de coil voltage.The diode prevents the tone-oscillatorcathode circuit from being completedthrough the 12-V ac line when cw is notbeing used.

7.5MAOD'L POT

IS)

+12VAC

C:316,..to.Ot

PILOTLAMP

BREAKr---~

ALTERNATE Cr'R~C~U~'T~' ",

Vl~A

6EAS

HEATERS

R:3tO1000

WHITE

BROWN

1V:~~'

7 0o3

cw'---_.....J

CW AND THE HW-tOtNo drilling or additional controls are re­quired for this modification of a HeathHW-IOI to permit the use of two differentVOX delay time constants for cw and ssboperation. In cw operation, particularly intraffic nets, fast VOX response isdesirable in order to approach semi break­in operation. In ssb operation, when usingVOX, this same response is unusablebecause it allows the TR relays to drop inand out during pauses in speech. Unfor­tunately, VOX delay is an awkwardparameter to adjust on the side of the rig.

One solution would be to connect aswitch across the VOX DELAY poten­tiometer. shorting it out for cw use andpermitting normal VOX delays for ssb.However. there is no convenient place tomount such a switch without drilling holesin the front panel. This would be

A circuit modification for the HW·101 to allow different VOX-delay time constants for cw and sseoperation. A variation of the circuit is shown at the bottom.Cl - 100 "F, 25 V de.01 - Silicon rectifier, 1A, 400 PIV. 1N4936or K1 - Spdt relay, 12 V dc, 1200 ohms. Radio

equivalent. Shack no. 275.()03.

TO 1.I3,!,IN1 ~'.'f-01 TO 1.17 PIN 6ON MEMORY 7402: ON MEMvAYTO u6.PINe 3 U21A

ON ACcu-I<E'YEA

THE WAtJZC ACCU·STOP

A simple modification to the WB4VVFAccu-Mernory" will allow the keyer pad­dle to perform the same function as theSTOP button, One of the four NORgates that compose U21 (located on thedriver circuit board) is unused in theoriginal circuit. The modification involvesthe following: Connect a jumper wire be­tween pin 2 of U21 and pin 1 of U3 on thememory board; connect a jumper wirebetween pin 3 of U21 and pin 8 of U6 onthe original Accu-Keyer board; connectone lead of a O.OOl-J,(F disk-ceramiccapacitor to pin 1 of U21; and run ajumper from the other lead of thecapacitor to U7, pin 6 on the memoryboard.

When the contents of a memory registerare being read out, it is now necessaryonly to tap the keyer paddle either to thedot or dash side to interrupt the memoryoutput. The output can be continuedfrom the point at which it was interruptedby pushing the RUN button, or alter­natively, a different memory quadrant canbe selected by, pushing the appropriateRESET switch. - Edward B. Kalin,KIRT

Wiring of U21 for the WA1JZC Accu-Stop. Thissection of U21 is unused in its original versionof the Accu-Memory, but is employed foranother purpose if the information above byGarrett is followed. If the builder wishes to in­corporate both changes, an additional 7402 ICmay be added.

'Garren, "The WB4VVF Accu-Keyer," QST.August, 1973.

'Garrett and Contini. "The Accu-Memory," QST,August, 1975.

WA1JZC built this Accu-Memory and keyer In­side a Bud RC-111oo cabinet measuring 3-1/4 x5 x 10 inches (83 x 127 x 254 mm). The sixpush-button switches are for the RUN, STOPand MEMORY QUADRANT SELECT functions.The toggle switches provide for loading thememories, for activating the automaticcharacter-space feature, for transmitter tuningand for switching the readout devices off tolower power consumption. The speed control islocated at the bottom right.

Thoughts lor CW Opsrstors 77

Schematic diagram for an automatic recycling feature lor the Accu-Memcry.

LIGHT DOTS WITH THE TR-4C

Have you been told that your dots are toolight? Perhaps if you have a Drake TR·4C. the transmitter-mixer V4 is being bias­ed too far below cutoff during the spaceperiod. When the key closes about 20milliseconds are required for this bias todecay to where rf output begins.However, when the key opens, rf outputalmost instantly stops. Wave shaping toavoid key clicks prevents this cutoff frombeing completely instantaneous.

The 20-millisecond foreshorteningbecomes evident as chopped or light dotsat moderate keying speeds or faster. Theproblem is especially evident on the firstdot following the initial key closure forsending.

Curing this annoying condition may beachieved by means of this modification:Change RI9 from 300 kllto 1.0 Mil andconnect a 200-kOresistor across C31. Thevoltage divider thus formed cuts the biason V4 to near cutoff but lets rf flowalmost instantly when the key closes.Waveshaping, as mentioned previously,prevents the rf from starting in a true, in­stant manner. The time constant fordischarge of C31 IS shorter following themodification. Keying is crisper but notnear keyclick hardness when .the keycloses. The original keying characteristicis on the soft side. - Ted Chernin,KH6Gl

MAKING A SQUEEZE KEYON A LEAN BUDGET

I recently built the WB4VVF Accu-Keyerbut could not make use of the iambicoperation because the price of a cornmer­dally made squeeze key was beyond thisstudent's budget. My money-saving pro­ject that resulted provided me with adevice with more exact operation and re­quiring less effort.

The circuit functions simply as a dcswitch. The negative voltage on the gatesof Ql and Q2 reverse biases the FETs,which leaves the outputs to Rl l and RI2open. When contact is made across either

CAPACITOR CURES DIT PROBLEM

When I began to use a speed key with mycode-practice oscillator made from a com­monly available module, the oscillatorgave a higher frequency for dit than adah. Placing a 3-IAF capacitor across thesingle dry-cell power source cured theproblem. - Skip Turner. WB4YXN

it may be a long time before I treat mykeyer to a professional-appearing installa­tion in a metal chassis and cabinet, unlesssome kind soul wants to help a lazy andpoor metal craftsman! - Charles Trice,WA4RRB

'0MEMORY

BOARDU6 PIN 4

e

in the diagram are for message quadrantno. 1.

The values for RI, R2 and CI give ap­proximate range of S to 30 seconds,depending on the actual value of CI. Youmight want to experiment with othervalues to suit your needs, but do not useless than 5000 ohms for R2. Otherwise,VIA will lock.

A low to pin 1I of V IB inhibits the startpulse from reaching the memory. The"allow" latch consists of V3A and V3B.SI sets the latch, taking V IB high at pinI I and lighting the LED. This indicatesthat the recycle feature is active. The latchis reset by merely tapping the dit side ofthe keyer paddle. This takes VI B low atpin 11 and turns off the LED.

Setting the latch again does two things.First, the allow circuit is turned on again.Then U2A is triggered to send a pulse tothe memory to send the message again.Therefore, one must press only one but­ton to get back into the "round andround" mode.

OperationTo use the recycle feature, load a

message into area no. I. Press S1 and themessage will be sent as you enable the"allow" circuit. The message will berestarted as often as you desire, deter-:mined by the setting of RI. When you getan answer, just tap a dit and the recyclefeature will be disabled, allowing the con­tact to be made. To start calling again,press 51 and that's it.

By the way, I received a nice certificatefor my participation in the Delaware QSOParty. But with so many events coming up

caR2 0.001 ".,V .,V

6800e ,

'OB

~LED1 "

R'O

''0

ca0001 R.

+OV6800

" "'"74123

R. •\000 ,

HV R'1000

"V

R'1000

,

."

HV

I constructed the little circuit on a smallpiece of pc board and mounted it on ahomemade bracket fastened to the screwholding the socket for the meter pilotlight. An obvious variation would be tomount an extra 7.S MO potentiometer inthe spare hole on the rear apron to pro­vide a second VOX-delay time constant.This would be connected through therelay contacts as shown in the attacheddiagram, and would provide adjustmentfor the response of the VOX in cw.Edwin G. Solov, WA2D1W

TO KEVER BOARDU7PIN6 2

LAZY MAN'S ADDITIONTO THE ACCU-MEMORYDuring a Delaware QSO Party I decidedthat it would be nice to have an automaticrecycle feature to periodically restart myAccu-Memory that complements aWB4VVF Accu-Keyer. After all it tooksuch effort to reach over and push therestart button for the "CQ DEL"message!

The relatively simple circuit is designedto use a 74123 dual-retriggerable,monostable multivibrator. UIA is trig­gered during transmission by logic transi­tions in the output keying circuit of thekeyer board. When the message is com­pleted, VIA starts timing to the presetperiod determined by the setting of RI.When RI is at the minimum setting, R2determines the minimum recycle time. Atthe end of the period, VIA triggers VIBwhich "hiccups" a pulse that shuts off amanufactured AND gate (V3D and V3C)to start the memory. Since only onemessage will be repeated, the connections

78 Chapter 8

A novel squeeze key built within a student's budget.

chosen over etching a design on small sec­tions of pc board. Otherwise, theperspiration from my fingers remainingbetween the edges of the foil after a longnight of DX work was enough to make thepc touch plate stay on. The wires from theplate are brought into the keyer housingwhich is mounted' on rubber feet. Theleads are then attached to the circuit in­puts. Thanks are due W6NKY for hiscomments on the circuit and construction.- J. Gary Sparks. K3ZKH!6

THE ACCD-START

When James Garrett, WB4VVF, in­troduced the Accu-Memory at the DaytonHamvention in 1975, he may have set thestandard for electronic keyers of thefuture. There are always the innovative in­dividuals to dream up an additionaltouch. K1RT proved again the need for avaluable feature when he introduced, hisAccu-Stop circuit.

After hours of experimenting with anNESSS timer IC and the SN74I23monos table device, we designed and pro­duced the Accu-Start circuit. In the finaldesign the Motorola MC960118601proved to be the logical choice for thisunit. It has the ability to be retriggered ordisabled during operation. TheMC9601/8601 monostable multivibratoris designed to produce an accurate outputpulse with a wide range of pulse widthsfrom either edge of an input pulse. Thisone-shot circuit will retrigger when it is inan active timing state and reestablish thetiming cycle from the last input pulsereceived. The MC960I!860I provides theuser with sufficient inputs, thus deletingadditional gating circuitry.

All normal functions of the Accu-Keyer

FRONTVIEW

2

BOTTOMVIEW

(A)

WB4VVF ACCU;-KEYER

Circuit for the Squeeze Key on a Lean Budget. Sensitivity control R should be approximately 10 kO.The touchpoints 1 and 2 are for dots, and 2 and 3 are for dashes.01,02 - Nchannet JFET transistors, 20 V 03,04 - Npn silicon transistors, Motorola

200 mW, 15 rnA, Motorola HEP801. HEP704.

+>V

side or both sides of the touch switch, apositive voltage overcomes the negativebias, turns on the FETs and one or bothof the output transistors, resulting in thegrounding of the outputs and turning onthe keyer. Sensitivity control R adjusts theFET's negative-bias level and can be setfor a given skin resistance to give thetouch switch the proper action,

A small prepunched Bakelite board,used for the circuit construction, wasmounted inside the keyer housing. I useda Minibox which provided ample roomfor the parts. The parts values are notcritical. Substitutions may be made freely.The bypass capacitors, indicated in thediagram, eliminated any possible troublewith rf.

Mechanical construction is not as

tricky as it may appear. I bought some 1/8X 1I8-inch (3 X 3.mm) balsa wood at ahobby shop as well as some O.12·inch, in­stant circuit-board foil. The touch switchis made by cutting eight pieces of the balsa3!4-inch (19.mm) long and then tapingthe instant circuit..board foil along onelong edge, over the ends, and then ontoeach end of the opposite long foil-coverededge for a distance of 114 inch (6 mm).(See the front view illustration.) Then ce­ment the metal covered pieces onto a pieceof angled plastic at a spacing adequate foryour range of touch. Electrical connec­tions are made by soldering lengths ofthin, enameled wire (I used No. 28) to thebottom (foil-covered) edges of thewooden supports as shown in the bottomview. This construction method was

U6 PIN eACCU-STOPCIRCUITAcCU-=-STAAT---· --- - --- - ---­CIRCUIT

iN914

tOOflF00

[:>INOICATES WIRE NUMBERORIGINAL AC.C.U-I(EYERCIRCUIT

The monostable multivlbrator circuit for theAccu-Start is shown here. Numbers shown inthe triangles indicate the wire number in theoriginal Accu-Keyer.

Thoughts lor CW opsrstors 79

Response plot for the active filter. The output voltage a a·dB reference was 0.48 and the inputvoltage was 0.5 V pk-pk. Response plot for a center frequency of 3500 Hz.

J5000 6000tOOO 2000 3000 4000F (Hz)

Ie)

CENTER FREQ.•3::;00 Hz

S.M .• SILVER MICAEXCEPT AS INDICATED, DECIMAL VAWES ~F

CAPACITANCE ARE IN MICROFARADS (jlF I ;OTHERS ARE IN PICOFARADS (pF OR jljlFI:

RESISTANCES ARE IN OHMS;k-1000. ""1000 000.

-401-1--1---1-

pedance speaker or headset. Best results innotching out an offending heterodyne canbe achieved: when the receiver age is turn­ed off. Otherwise, the strongly interferingcarrier would heavily activate the age andreduce the receiver gain, pulling thedesired signal down with it. This filterwould be a useful accessory for an or­dinary ssb transceiver, which normallylacks provision for i-f notching. In mysetup, I am able to take the requiredvoltages for the filter from the VOX ac­cessory socket of the Swan 350. A to-turntuning control makes adjustment swift.The total cost including such a controland the op amps should not exceed $15.- Allen Taflove, WA9JL V

(MC1741G and MC1741P1), substitute pin 7for pin 11 on the drawing, pin 4 for pin 6,pin 3 for pin 5, pin 2 for pin 4 and pin 6 forpin 10, respectively.

PIN 6-t2Vo--..--:-oUt. U2,U3

...LQJl!..Ei+'tooV

r-i-r (Al

1000 2000F (Hz) .

(B)

o

L.----- j....----0

0 -

ICENTER FRED.•

1000 ~z

0

I'lim ~0

0 ~ -

o

PIN 11+\2V~Ul.U2.U3

O.l,uF

,.+;OOV

'"

-4

'0 »;w ,,. ""

,,. ,,.

"'v :::'l'Il' c-~1..'000 r-:

~- :: S,M-'-----"~-

Ui 10W U3 10

"" -> 39~~ Eo2.1+ >"0

R' >..- ;go1000 ". ~ '"'" FREQ

CONTROL900,,.

R2L..; 1000

NOTCHDEPTH

Schematic diagram of the active filter. The preferable tolerance of the 39·kOresistors Is two per­cent. All others can be 10 percent. Tolerance of the silver-mica capacitors should be five percent.R1 - See text.R2 - Otrcult-boaro type.U1, U2, U3 - Op amp, type 741. Pin numbers

are shown for ta-p!n, DIP package (MotorolaMC1741L or MC1741P2). For the B·pin types

was difficult because the test oscillatorused had a harmonic content suppressedby only 50 dB.

Notch depth remains approximatelyconstant over the tuning range, with Qseeming to increase somewhat with centerfrequency. In determining experimentallythe two plots shown, the Q control wasuntouched.

In operation, the input to the filter maybe taken from the speaker or headphonejack of a receiver. Because a 741 op ampwill deliver approximately 12 V pk-pkacross 2000 ohms, a high-impedanceheadset may be connected directly acrossthe output. If required, a suitable bufferstage could be added to drive a lower irn-

A COMPUTER-TYPE ACflVEFILTERThe advent of low-cost operationalamplifiers in the past few years has excitedinterest in their use in RC active filter cir­cuits. Typically. excellent Qs in the audiorange have been achieved without any useof inductors. For band-pass and band­reject filters, resistors and capacitors arechosen to achieve a given center frequencyand Q. However, there are severaldrawbacks to this approach. First,variable-frequency operation is difficult,requiring either ganged potentiometers oracceptance of severely reduced Q. Second­ly, matching of capacitors or resistors maybe required in some designs to realize highQ and good peak response or notchdepth.

There is, however, an alternative. In­stead of using one operational amplifierand an RC input-feedback network con­figuration, it is possible to use three op­amp networks to achieve virtually anysecond-order transfer function. A goodexample of what can be done is a notchfilter using three 741 op amps. Center fre­quency can be varied (using one control)up to approximately 4 kHz, with circuit Qand notch depth remaining practicallyconstant over the range. Componentmatching is not required. Only one setupadjustment is needed: a variable controladjusted for best notch depth.

The Circuit

In the circuit, UI and U2 serve as in­tegrators with a de gain of about 25,000.U3 serves as a summing device. ThelOOO-ohm control, R2, is used as the Qcontrol and is adjusted only once fordeepest notch. RI serves as the frequencycontrol by controlling the "gain" of thedifferential equation, which the system issolving in effect. For easiest tuning, thisshould be a to-turn precision-type poten­tiometer.

The results are impressive for a circuitof such simplicity. Notch depth is at least50 dB. Measurement of absolute depth

with memory and the Accu-Stop aremaintained. S7 disables the Accu-Startcircuit for all normal operation. Enabling57 allows one to provide an automaticstart pulse to the memory after manualentry of data is completed and after thedesired time delay has been satisfied. Thevariable resistor sets the time delay afterthe last paddle closure before the startpulse is initiated. The timing cycle may bereset at any time before timeout occurs.Our use has proved that an appropriatetime is 1 to 1-112 seconds. However, withcomponent values shown, delays as longas five seconds can be reached. But withthat amount of delay the chap at the otherstation may think you fell asleep and starthis call-up. - Gus Gaglio, WB8TJB andJoe Stout. W8HID

80 Chapter 8

,.".

REPEAT

OFF ~-<J---'\,I\iI~--O-.......-~1 /

8

•

and the fall time was too short. C211 (0.02IJF) which determines the waveform risetime was replaced with a O.Ol-,..F diskceramic capacitor. A I.~F, 200-Ycapacitor was installed in parallel withC304: It determines the wave form decaytime. The replacements achieved the pur­pose of shortening the rise time andlengthening the decay time.

These modifications are easily perform­ed. They are well worth the substantial in­crease in the quality of the cw signal. Ssboperation is not affected by these changes.- G. A. Steward, K3Z0L

A MONITOR FOR HEARINGYOURCWTo provide a sidetone monitor for myoidGalaxy V transceiver and to key it at thesame time, I built a unit that is alsocapable of keying a DX-loo. W7MMEhas used the same design for keying a pairof 162Ss in an old converted TC5 beingoperated in the MARS network.

The NE555 is at the heart of my device.It operates well as a sidetone generatorfrom a 9- or 12-volt de supply. The addi­tional circuitry shown in the schematicdiagram is designed for blocked-grid or

4

so 02

1 BLOCKED GRID eos. BUTTOO CONNECTOR

'+;'"J:"

R27"

CI,L0.O\

0'

01

02

'N':.~",. 0;: rt°OI

TOPVIEWNE!S~~

0' ~a •4

A sldetone generator and transistorized keying unit. S1 is shown in position for keying negativeVoltages (btocked-qrtd keying). All resistors are 1/4 watt. Capacitor values are in JlF. $1 is a two­pole, three-position switch.01,02 - Silicon diodes, 1N4005. Q1 - 2N2905 silicon pop transistor.U1 - Signetics NE555. QZ - 2N5157 germanium pop transistor.

o.

"1200

Amateur's Handbook I determined thatthis resistor. had much resistance andshould be lowered to 2000 ohms. It wasreplaced with a 20-W resistor. In addition,a loo-~F, 4S0·Y capacitor was installed inparallel with Ct'tA to provide additionalregulation at the output of the low-voltagepower supply. The chirp was eliminated.

The following changes were made toimprove the keyed waveform to eliminatea mushy sound and a key thump. Indica­tions were that the rise time was too long

o·01rt

IMPROVED CW PERFORMANCEFOR THE SB-401 TRANSMITTERWhile trying to provide my 8B­401l5B-301 combination with a fullbreak-in system, several problems came tolight. The 5B-301 combination is an ex­cellent ssb transmitter but leavessomething to be desired -on cw. The firstproblem tackled was elimination of chirpon the signal. It seems that the chirp is notuncommon in the 8B-400/SB-401 series oftransmitters. Investigation disclosed thatthe problem was poor voltage regulation,with the most critical area being theregulation on the line to the LMO. The in­put voltage to the LMO dropped 10 voltswhen the key was closed. Regulatedvoltage is supplied to the LMO by YRtube Y7 and resistor RIB (4000 ohms).

Using information from The Radio

CONTINUOUS OPERATION FORTHE ACCU·MEMORY

Some amateurs should be interested in amodification of the Accu-Memory (QSTfor August, 1975) that permits repeatmode or continuous operation of thedevice. Such use is applicable, for exam­ple, in sending "TEST DE W6QNB" overand over while the operator is inside thehouse or next door observing the recep­tion on a TV set.

The modification consists of two parts:One is to avoid causing the device to stopafter nine zero bits, and the secondprevents rollover from one messagereadout into the next. Minor surgery andone more Ie are required. Break the con­nection to pin 14 of U7 and pin 11 of UII(refer to Fig. 4 in the original article).Then add the circuit that is illustratedhere.

After the modification is completed,load the message to be repeated in the nor­mal mode. Use the run button to pad thetext as desired. Switch to the repeat modeand hit the message number desired tostart the device. The four-messagecapability is retained in either normal orrepeat modes. - Daniel G. Drath,W6QNB

Circuit modification for continuous- or repeat-mode operation of the Accu-Memcry.

Thought. for CW Operetor. 81

As shown in the second drawing, short­ing the 15 kilohm resistor gives a low­impedance driving source for audio filterssuch as the surplus beam filters. The othermodification connects the sidetone outputfrom the 5B-401 to the headphone jack onthe 5B-301. A spare hole in the back panelof the 5B-301 may be used for installingan additional phone jack which should beconnected with shielded wire to thetransformer tap as indicated in the draw­ing. - Ed Jensen. K9HDP

SEVEN BITS FOR THIS IDEA

Eight bits are required to store an insertfeature in a message and for spacing be­tween words when using the Accu­Memory as originally designed. A bit isequal to the dot element in length. But, tome words fit together more comfortablywith seven-bit spacing than with eight.From my early code training days I learn­ed that the "proper" word spacing isseven bits.

To modify the Accu-Mernory to seven­bit word spacing, I simply connected bothinputs (pins 9 and 10) of NAND gate U3C(7400) to pin 11 of U7. the D or 23 outputof the 7490 decade counter. This outputwill go high when the count reaches 8 inthe 7490 counter, the chip having startedcounting at the start of a word being load­ed. Thus, both inputs of U3C go high at acount of 10002 and the output of the gategoes low, causing the address counters tostop. The eighth bit becomes the first ele­ment of the next character loaded and wenow have a seven-bit word space.

An additional bonus is provided whenone 'wishes to program a pause in themessage. With the counter output at 100(equivalent to 810) , actuation of the runbutton provides a one-shot pulse to thecounter, moving it to 1001 and storing aone-bit space in the memory chip. At1001, however, gate U3C is still forcedlow, the D output of the 7490 is still high,and no further bits are needed to recordthe pause. A second actuation of the runbutton resets the 7490 to ooסס and itcounts back up to 1000 befo'l; being stop­ped. This second consecutive closure takesup seven bits of memory, but should neverbe needed. In the author's circuit each ac­tuation of the button resets the decadecounter to ooסס and each such action

TO"151 F

Fl.2A400 Hz

\OPENTHISCIRCUIT

~nEARPHONE

~JAC'

~SPEAKEA

IDEAS FOR THE SB·JOt

1 have improved the performance of my5B-301 by means of these modifications.The first gives greater selectivity by the ad­dition of another filter. The other changesallow the keying monitor in the 5B-401 tobe connected to the headphone circuit ofthe 5B-301 and the use of audio filterswithout the requirement of transformers.

To obtain greater skirt selectivity, a sec­ond 4OO-Hz crystal filter may be added inseries with the existing filter in the set. Anisolation amplifier is added to properlyterminate the filters and make up for theadded insertion loss. The filter is mountedin the a-m filter holes. A small perforatedboard, about one-inch square, is suitablefor mounting the amplifier. The board issupported easily by means of the leadsconnected to it. The amplifier has a gainof 3 or 4 dB and an input and output im­pedance. of 2000 ohms. Skirt selectivityand ultimate rejection are much improvedby this addition. Although I have not triedit, I presume an ssb filter could be addedin a similar fashion.

IAI

r t,

2.t kHz

r------- ----------.-----,I 33k I: 10k 2200 ;L0.~1!

I II II 0,01 II II I

I :L ..J

~II~

SECONDMIXER

MODESWITCH AM

MS2A

cas

6T' """---+-.+---I

cathode keying. Transistor Ql, chosen forpositive keying, is a 2N5157. It is rated for700 V at 3 A maximum, which is adequatefor use with a pair of 807s or 6146s.

Closing the key circuit causes theNE555 to operate as a free-runningrnultivibrator and turns on Ql forblocked-grid keying when the rotaryswitch, SI, is in position 1. Position 2 isfor tuning and position 3 is for cathodekeying. On my model I labelled these posi­tions G, T and C, respectively.

The unit is assembled in a 5-1/2 xg-l/2 x 2-1I2-inch (140 mm x 216 mmx 64 mm) box. A speaker from a defuncttransistor radio was installed. All inputcircuits were bypassed as shown in thediagram. Good shielding is essential.

The tone frequency is a function of thevalues of RI, R2 and C1, while the volumeis determined by the operating voltage andthe resistor in series with the speaker. Aselected inductor in series with the speakermight do wonders for producing a sine­wave tone. This circuit drew about 35 rnAin the key-down position when operatedfrom a 9-V battery. - Herb Ash, K7ARR

lA' 161

Greater selectivity for the 58-301 is provided by the addition of another filter as shown in thisdiagram. Q1 may be any small-stqne! npn transistor such as a 2N3565. The dotted lines surroundthe added circuitry. This drawing shows a low-Impedance driVing source for using the SB-301 withaudio filters. Darkened lines Indicate the added circuits.

Modification of the Accu-Memory for eeven-bttword spacing. The original circuit is shown atthe left, while the modified version is at theright.

82 Chapter 8

A SOLID-STATE KEYER FORCATHODE-KEYED TRANSMITTERS

When I finally made the decision to buildan all-electronic keyer, the design had tooffer compatible interface with mycathode-keyed transmitter. This meant aswitching -function capable of handlinghigher current than that found in a grid­block keying system. So, off to the partscatalog [ went. Rechecking the surplusads, I found that, sure enough, silicon­controlled rectifiers were readily availableand units capable of handling quite highvoltages and currents were inexpensive.For example, units that would withstand600 volts and carry 6 amperes wereavailable for less than a dollar apiece. Ofcourse, using a silicon-controlled rectifierto key a transmitter required that it beturned off at the end of every character;but this minor problem was solved and thecircuit shown resulted.

Less rf reaches the receiver since there aretwo parallel sections of the 4016A thatopen up. The other two parallel sectionsground the antenna terminal.

My transmitter is the 75 to l20-watt rigshown on page 172 of the Handbook.Since I key the cathode of the 61468 out­put stage as well as a two stage solid-stateamplifier in the VFO, I am also presentinga circuit of the complete keying system.Some old timers like myself, who enjoybreak-in operation, may be interested inthis arrangement. - Wayne H. Sandford,Jr., K3EQ

How It WorksThe character (dot and dash) generator

is essentially the same as the one describedin pre-1974 editions of The ARRL-RadioAmateur's Handbook except for theminor variations required to adapt it tothe TTL ICs available and the needs of theSCRs. Since the Handbook describes theoperation in some detail, the charactergenerator will be described only brieflyhere.

Transistors QI-Q3, along with theirassociated circuitry, comprise a pulsegenerator that generates a negative pulseimmediately when the key is closed, and atregular intervals thereafter until shutdown. The pulses are then applied to twoflip-flops that act as a counter. Q4 is wiredas a two-input NOR gate, and shuts downthe pulse generator at the end of a dot ordash plus space unless the key is still clos­ed. The character output appears at thecollector of QS, and the complementaryoutput at the collector of Q4.

At the beginning of a character, thepositive-going transition at the collectorof Q5 is converted into a positive pulse byCl and applied (through emitter followerQ7) to the gate of SCR Q9, turning it on,and thus keying the transmitter. SCR Q8is off at this time, and C2 is charged to 15

''0

."

\ONE FOR

EACH2N3440

3-2N3440IN PARALLEL TO

/"-""'---C>6146B100 CATHODE

RCVR. ANT.

-6V

+6V

1000

l(EY EMITTERCIRCUITS OF TWO STAGEAMPLIFIER IN SOLlD­STATE VFO (VFO RUNSALL THE TIME)

1000

2700

TO GND

1N914 ,-"-:2-:2).22c-_~_-o~~TN'tJ~~ALRF GAINCONTROL

2N4910

AN OLD TIMER'S SOLID-STATEBREAK-IN AND KEYING SYSTEM

Many years ago I installed a break-insystem on my HRO-5, similar to the oneshown on p, 358 of the 1976 edition ofThe Radio Amateur's Handbook. I havereplaced the relay with a 4016ACOS/MaS switch and a 2N2222 npnsilicon transistor to activate the auxiliaryrf gain control. This improved operation.

51002N2222

1000

-6V

OELAYS TRANSMITTERKEYING TO ELIMINATE

POSSIBLE CHIRP

273300

2N2222

TO l(EY

A solid-state keying system.

3900,

!'i000

resulted in the waste of eight bits ofvaluable memory space.

For those Accu users who employed thesame circuit board design as was madeavailable by the authors, the modificationis extremely simple. Cut the foil which ex­tends between pins 1 and 12of U7 and pin10of U3. At a point beyond the cut, makea solder bridge between this foil and theadjacent foil which connects pin II of U7and pin 9 of U3. - Harold Kalkstein,WA3QQZ

VFO TURNOFF-DELAY

'0'TURN-OFFOELAYADJ

A solid-state break-in receiver control system.

Thoughts lor CW Operatora 83

+,v+15V

+15V

"XMTR

0;:

560 05

>--'4----,

052

'60

EXCEPT AS INDICATED, DECIMAL "AWES OFCAPACITANCE ARE IN MICROFARADS ( jlF I ;OTHERS ARE IN PICOFARADS \ pF OR J,LJ,LFI:

RESISTANCES ARE IN OHMS;k'1000,M-l000 000.

'"

1000

a,

An electronic keyer using silicon-controlled rectifiers. See OST for September, 1977, page 11, for explanation of logic symbols.el, C2 - Far text reference. 01 - 2N560 or equlv. R2, R3, R4 - See text.01·06, incl. - Silicon diodes, 600 PRV, 2 A Q2 - 2N4Q4 or equlv. 51,82 - Spst toggle.

1N3191 or equiv. 03·07, incl. - 2N585 or equlv. T1 - Filament transformer, 6.3 V, l·A second-07 - Zener diode, 5.l-V, 400 mW, 1N751 or 08, Q9 - Silicon-controlled, rectifiers; BOO-V, ary.

equtv. B·A devices used by the author, equ!v. to U1 - Quad 2-input positive NAND gate, typeOSl - Pilot lamp, 6.3 V (no. 47), Motorola HEP R1223, but lower rated devices 7400; 2 sections unused. Connect pin 7 toDS2 - Pilot lamp, 14 V (no. 1815). may be suitable for particular applications. ground and pin 14 to +5 V.F1 - 0.75 A. A1 - Linear taper. U2 - Dual J-K flip-flop, type 7473. ConnectJ1 - Phono or phone jack. pin 11 to ground and pin 4 to + 5 V.

volts through R2, R3 and R4.At the end of a character, a positive

pulse (derived from the positive-goingtransition at the collector of Q4) is appliedto the gate of Q8, turning Q8 on. C2 cannow discharge through the path formedby 05, Q8, R3 and 04. The direction ofcurrent flow is such that the cathode of05 and the anode of Q9 are slightlynegative with respect to ground for thefew microseconds it takes C2 to discharge- which is enough to turn Q9 off.

Q8 is turned off at the beginning of thenext character when Q9 discharges C2 inthe opposite direction. At this time D4 isback biased, and R2 limits the currentsurge through Q9 to a safe value.

DS2 is included to assure sufficient cur­rent flow through Q9 to maintain it in the"on" state when devices that draw onlylow currents are being keyed, e.g., a code­practice oscillator. A resistor of the prop­er value could be substituted for OS2, buta pilot lamp also serves as a TRANSMIT­TER ON indicator.

In the present setup, the keyer handlesabout 150rnA from the transmitter, 5 rnAfrom the monitor oscillator and the 200rnA from OS2. No tests were made todetermine the maximum current-switching

capacity with the component values used,although I suspect it is about twice theamount mentioned above. If morecurrent-handling capacity is required, OS2could be disconnected. However, a bettermethod would be to increase the value ofC2 and decrease that of R3 in proportionto the current to, be switched. If C2 is in­creased beyond about 2 ~F, R4 should bereplaced by a tOO-ohm, 2-watt resistor.Note that C2 gets charged in both direc­tions, so that for larger values ofcapacitance, where an electrolyticcapacitor would be required, a non­polarized electrolytic, or two capacitorsback to back, would be required. I wouldnot recommend that C2 be made largerthan 10 ~F, because then either the timeconstants for charging it would becometoo long, or excessive current surgeswould have to be handled. However, atthat point the current being switchedwould be measured in amperes, and noamateur transmitter should require anygreater amount.

Component SpecificationsAs mentioned in the Handbook, the

diodes marked UIN34"in the paddle cir­cuit must be germanium diodes. Also

mentioned in the Handbook I and just asimportant, Ql must be a silicon transistor.Other than this, almost any parts can beused, keeping in mind the voltage and cur­rent requirements to be met, particularlythe current surges through D3, 04, 05,Q8 and Q9. Note that 04, OS, 06, C2,Q9, and the O.Dl.~F bypass capacitor mustwithstand the key-up open-circuit voltageof the transmitter.

Germanium transistors were used in theauthor's unit because a good supply ofthem was on hand. Silicon transistorsshould work as well. Q4 should have aminimum beta of 60 to assure saturationwhen on. It is also desirable that Q4 nothave good high-frequency response. Agood audio response is adequate, and willprevent spurious pulses being sent to Q6and Q8 during a dash, when both flip­flops change state.

As TTL units have rapid response, it isimportant that all leads into the keyer casebe bypassed, to prevent rf energy in theshack from taking over control of thekeyer. Imagine trying to key the rig on andoff seven million times a second!

A monitor was available elsewhere inthe station, so none was included in thekeyer. One may be connected to the col-

84 Chaplar 8

lector of Q4, with sufficient seriesresistance to limit the current drawn by it.

The SCRs used in the author's unit re­quired some amplification of the pulsesavailable to turn them on. If SCRs withmore sensitive gates are used, Q6 and Q7may be eliminated, and the pulses applieddirectly from the capacitors CI and C3 tothe gates.

The power supply is conventional andstraightforward. The + IS-volt line hasconsiderable ripple, because of the simplefilter used, but this has no effect on theoperation of the circuit.

ConclusionThe keyer has been in use for some time

now, and has been behaving quite satisfac­torily. Even though no heat sinks wereused on the SCRs, the currents theyhandle are so low compared to theircapabilities that no problems have beenencountered or are anticipated.

In addition to the convenience of usingan electronic keyer, .it is comforting toknow that the code being sent is as near"ideal" as the hand of man can manage.- Howard Mark, WA2TNZ

IMPROVED TRANSCEIVERSELECTIVITYAs a proud owner of a commerciallymade, single-sideband transceiver andhaving a keen interest in cw, I sought toimprove the selectivity without replacingthe factory-installed sideband filter. AllenTaflove's active notch filter (QST forMay, 1975) provided the impetus thatresulted in the circuit to be described. Iutilized the notch circuit with variablecenter frequency and negative feedbackfor an additional amplifier stage. The ad­ditional amplifier was a 741 operationalamplifier. Because polarity was reversedthrough the notch filter a non-invertingadder circuit was chosen for the fourth

741. The input signal and feedback signalbuck each other except at the notch fre­quency, providing amplitude reduction ofall but notch-frequency signals. Feedbacklevel (selectivity) is controlled by theSOOO-ohm potentiometer in the feedbackloop. A single dpdt switch can beemployed as shown to switch the notchfilter from the feedback loop to precedethe adder. This allows the device to per­form as a notch filter with additional gain.

Power is supplied by two 9-Vtransistor­radio batteries. As with the notch filteralone, high impedance earphones shouldbe used unless an impedance-matchingstage is provided. In the diagram the boxindicating the active filter does not includethe lO-ohm input resistor that I installedat the input of the overall circuit.

The selectivity appears to be in therange of SO to 100Hz. Approximately $30was spent for construction of the unit. Ithas greatly enhanced the performance ofmy transceiver when I tune in signals on acrowded band. - Art Silvers, WAIUAH

BETTER PERFORMANCEFOR THE MFJ CW FILTERAmateurs who operate from fixed stationsusing the MFJ cw filter will find thefollowing modifications improve the per­formance of the unit. My first recommen­dation is to replace the battery with an acpower supply. The Audiovox Corporationmanufactures a plug-in type that delivers15 volts. An alternative would be to makea power unit such as the one described onpage 365 of any edition of The RadioAmateur's Handbook for 1974 through1975.

For those operators who have high­impedance headphones an audio outputtransformer should be installed in theMFJ for proper matching. I used one soldby Radio Shack (part no. 273-137S) which

330k

+9V

has a 2000-ohm primary and a lO-kOsecondary. The transformer secondaryprovides a good match for the headset.

In order to reduce the effect of noise Iadded the noise limiter/clipper shown onpage 253 of any Handbook for 1973through 1978. A Minibox accommodatedthe components. When properly adjustedblasting is overcome, the initial thump isreduced, and there is an improvement inthe resulting effect of age when used withcw. - Walden Pierson, K9BJA

A HOLD SWITCH FOR THEK. E. ELECTRONICS KEYERWhat I needed for my K. E. ElectronicsMemo-512-R keyer was a hold switch withwhich to tune up my exciter. After perus­ing the box and searching through thediagram in hope of finding a clue to thewhereabouts of the missing switch I decid­ed on this modification.

~GSW<TCH"

~"rJt, K1 ~OUTPUT

Os:A "tune-up" key for the K.E. Electronics Memo512·A keyer.

The junk box contained a small, butadequate, miniature spdt toggle switchwith which to do the job. 1 garnered my3/S-inch hand drill, plus a 1/4-inch bit,and went to work. Several minutes later anice round hole appeared equidistant be­tween the side-tone switch and the outputjack.

After I mounted the switch, all that re­mained was the addition of a couple ofwires in parallel with the keyer outputjack and some attractive rub-on letters.Voila. c'est tout! Work time was 12minutes. - Rick Olsen, N6NR

8200 2 7

"AINPUT 0---...-0-->' 8200

0-_-1-----'-13 + 7416

-o 82002000

Hold switch for Memo keyer.

BROAO

SHARP

,~-L~NOTCH 5\8 ~--~-({;~~CTIVITY~'!!NP~U!IT_-{)~" CONTROL)

Transceiver selectivity ls improved with the use of this filter, adapted from Allen Tallave's activenotch filter (OST for May, 1975).

Thoughts lor CW Operstors 85

FOILSIDE*BREAK FOIL WHERE SHOWN**R2-22kn IN LIEU OF CONTROL FORPITCH***R6-1kn ACROSS 5kn CONTROL ·ro

SIMULATE lk!1 C:JNTROL (8)

At A is shown the schematic diagram of theNE555 sidetone oscillator. At B is shown themodified Radio Shack printed circuit boardused to mount the NE555 rc and its associatedparts. The user of this hint should have theparts on hand and drill the mounting holes forthe placement of those particular parts.

A model of a paddle constructed in the HQ.lab.

light and may be held in one hand whilesending code with two fingers of the otherhand. That's real armchair sending! It isalso human engineered, because it re­quires fewer muscles to operate.

The base is made from soft aluminumabout O.09-inch thick. The panel of thoseold war-surplus tuning units is just right.However, it could be made from wood,Plexiglas, Micarta or any suitable, nonamagnetic material.

Make the shaft from an 8- or lO-pennynail, cut to fit between the bent-up sidesof the base. The paddles should be madefrom O.035-inch steel, each about 7/16 X4 inches in size. Bend one end of each striparound the nail so the two make a goodelectrical connection, but not so tightlythat the paddles move stiffly.

Cut a 1/4 X 1!2-inch piece of Plexiglasto fit snugly in the space between the bent­up sides. Round off the lower edge at theends so it will fit flat against the base.Place one side of it to line up with the edgeof the bent-up parts as illustrated and usea No. 29 drill to make a hole through thePlexiglas and the base. The other two

DOT INSERTION FORTHE ACCU·KEYERThe WB4YYF Accu-Keyer (QST forAugust, 1973) is a fine addition to theham shack. However, the relative ease ofsending code with a dot- and dash­memory keyer is debatable, particularlyamong those of us who are accustomed tooperating dot-memory keyers.

The WB4YYF Accu-Keyer may bemodified, quite simply, to provide dot in­sertion only by disabling the dash inser­tion input to the appropriate NAND gatein the iambic section of the keyer. Thislogic change may be accomplished byremoving pin 5 from U2 (7400) or ,bybending the pin upward so that it cannotenter the IC socket. - David A. Danello,WB40NS

MUTING A DRAKE R-4CWITH AN ACCU·KEYERHere is a circuit I am using for mutingwith my Accu-Keyer. It duplicates thekeying circuit in the Drake R-4C. Invert­ing is provided by connecting the unusedgate on the 7410 as shown. Since the muteline on the receiver has -70 volts, thescarce 2N4888 was replaced with a2N4354. No objectionable key clicks areevident. - Dan Whitman, WB4FHT

that those using this idea have the parts onhand and drill the board to suil Ihoseparts. - Ron Mays, WA3WAE

A KEY YOU CAN'T BUY - YET

You play this key with two fingers on thelevers. It won't slide around, even on aglass tabletop, because the operating forceis toward the base, not parallel to it. It is

(A)

TO R5 CENTER

G:GROUND

TO SPKR. +

J=JUMPER

"5600

"0.1'-U7 r-r-r

PIN 6

A muting circuit for the Drake R·4C when used with an Accu-Kever.

EXISTING CIRCUIT

-ev

ADDITION

~600

MUTINGOUT

IIII

+>V

R10

470

R9

4700

KEYEROUT

Re~600

Q,2N2222

SIDETONE FOR THE ACCU·KEYERPC·BOARD STYLEWhen building the sidetone oscillator formy keyer, the ubiquitous Accu-Keyer, Iused a construction method which may beof interest to builders of most any keyerwhich requires a sidetone. Radio Shackoffers a small (1-112 X 2-inch or 38 X51-mm) experimenter's printed-circuitboard with pads for a lti-pin in-line Iepackage. The Ie pads are drilled and havefeeders to 16 larger pads at the edges ofthe board. I found that all of the sidetonecomponents fit easily on the circuit boardand, since the circuit uses an 8-pin NE555timer Ie (see recent editions of the Hand­book), that the sidetone circuit could bereproduced by cutting the foil at fourplaces and using the eight left-over pads asconnection and mounting points. Theresult is a professional-looking board withno etching required. The schematicdiagram and modified Radio Shack circuitboard are shown. 1 strongly recommend

88 Chepter 8

Q'2N2219

OR2N697

rr;.047470

47Iw

,

Subminiature toggle switch no. 275·324.Mini utility box no. 270·232.Miniature jack and plug asst. no. 274-335.

View of the Accu-Kever component area.

the power supply package gets warm, butnot hot, to the touch.

As can be seen in the photograph, themain circuit board, Brown Brothers keyassembly. and monitor subassembly fitneatly inside a "mini" utility box which isavailable from Radio Shack. The boxmeasures 7-3/4 X 4-3/8 X 2-3/8 inches(197 X 111 X 60 mm) and is rugged, at­tractive and priced reasonably. The grayhammertone finish and rubber feet 'helpgive the completed Accu-Keyer a profes­sional appearance.

The schematic diagram shown was pro­vided with the drilled circuit board obtain­ed from WB4VVF. My monitor-oscillatorwas built on a 1-3/4 X 2-inch (44 X 51inm) scrap of "perf" board, and was thenepoxied to the rear of a two-inch roundspeaker. The speaker was mounted to therear panel by using a scrap of copper win­dow screening as a protective grill. Alsolocated on the rear apron are twominiature phone jacks, one providing aconnection for keyer output and the otherfor de input.

The Accu-Keyer has an automaticcharacter-space feature. After brieflydisabling it during the pre-packaging stageof this project, I decided to use it withoutprovisions to switch it in and out of thecircuit. However, if one is interested in re­taining the in-out feature of automaticcharacter spacing, there is ample room for

TO JUNCTION OF R8 ANDU7 PIN 6 IN KEYER

The WB4VVF circuit board diagram. These are the Radio Shack part numbers used In theassembly.rc 7400 Quad NAND Gate no. 276·1801.Two-Inch, 8-ohm speaker no. 40·245.Perf board assortment no. 276-1391.

PACKAGING THE ACCU-KEYER

This is not meant to be a how-to-do-itarticle, but rather a source of ideas. Thepower supply for the Accu-Keyer is acommercially available ac adaptor, thetype used to power portable taperecorders, radios and calculators. Itmeasures 1-3/4 x 2 x 1-3/8 inches (44X 51 X 35 mm) and furnishes 7.5 V de at130 rnA. After several hours of operation

'00

down so the levers have about 1/16 inchof throw. Then drill and mount the cover.Two plastic tabs cemented to the leversand a piece of felt fastened to the bottomwill finish the key. Hook it up so that theindex finger of whichever hand will beused closes the dot contact, since thatfinger is usually more agile.

As for learning to send with the key myadvice is to make haste slowly. Start atabout seven wpm and practice each letteruntil you can send it perfectly 10 con­secutive times. Then go on to the next let­ter. Only after you become accurate atthis speed should you attempt higherspeeds. - John S. Lewis, W5TS

WEIGHTS FOR YOUR BUG

If your bug weights are too light to makethe dots readable, take some lead sinkers(which can be purchased at most hard­ware stores) and flatten them to about 1/4inch or so. The weights that I used in mycase were of one-ounce size. After theweights are flattened, saw a slit in thesinker and add it to the existing weight onthe bug. - Jeff J. Walters, WN8GNY

[Editor's Note: A copy of this paddle was built in theARRL lab and was the hit of the day. One by one,nimble-fingered employees and visitors tried theirhand at sending with the key. No one seemed to ex­perience difficulty adapting to pushing, instead ofwaggling, the paddles. Bugsenders who wishto use anelectronic keyer without fouling up their bug fistsshould find this little paddle ideal.)

Dimensions of the paddle.

holes in the Plexiglas only are for no. 6self-tapping, hex-head screws, 1/4-inchlong. Remove the hex-head screws fromthe Plexiglas and fill the heads with softsolder. Countersink the hole in the basefor a no. 6 flat-head screw. Put a solderlug on each of the self-tapping screws andreturn them to their holes, with the lugspointing toward the back. Mount thestrip, being sure the screws don't short tothe base. ,

After the pivot-pin holes are drilled, putthe pin through one hole; thread on awasher, both levers and another washer.Separate the levers and determine thelength of the required spacer. Additionalwashers or a piece of 1/4-inch copper tub­ing will do. Drill for a screw in the rearcenter of the base and countersink on thebottom side. Solder a 1-l/2-inch piece offlexible wire or braid for coiled pigtails toeach lever near the end wrapped aroundthe pin. Solder the other ends and a wire(for common to the keyer) to a lug, andfasten the lug to the hole just drilled. Theother two wires to the keyer are connectedto the lugs on the hex-head screws.

The cover may be bent from thin (aboutO.020-inch) aluminum or anything handythat is not magnetic. The magnet (RadioShack no. 64-1875) is glued to the frontedge of the cover in the center, long edgecrosswise. The cover is adjusted up or

Thoughts lor CW Operators 87

NESSS" timer. arid alsO"re~ets 'it as lori~ asanything is being sent. So the NESSSstarts timing just at the end of the lastcode element and holds the regular auto­space feature, on for a longer time throughthe OR gate. The LED helps me know thething is holding and I can double theLED's time on for word spaces. - DavidE. Allen, WB6TAQ

BREAK-IN DELAY FOR THE HT-46Owners of the Hallicrafters HT-46transmitter, treated in II RecentEquipment" some years ago (QST forAugust, 1966), may be interested in thecircuit described here. It is easy to buildand is not expensive. Break-in delay isprovided during cw operation through ad­dition of this unit, and antennachangeover from transmit to receive ismade possible by the plate relay used inthe new circuit. Although we have no in­formation to offer about use of this cir­cuit with similar types of commerciallymade transmitting equipment, chances arethe accessory could be adapted easily foraddition to other kinds of gear.

This assembly is not a VOX box.Hallicrafters did manufacture such an ac­cessory (model HA-16) for ssb operation,and the circuit of that item is contained inthe HT-46 instruction manual for thosewho may want to build one.

All of the operating voltages for thebreak-in delay "gizmo" are borrowedfrom the HT-46; they're taken throughthe VOX accessory socket on the rearapron of the transmitter (J6 on the HT-46diagram). Plate voltage for VI is obtainedfrom pin 6 ( + 260 V), and heater voltageis taken via pin 3 (12.6 V ac). Pin 5 of J6serves as the ground connection after thelead originally connected to it is un­soldered from terminal 9 of KI and con­nected to chassis ground in the HT-46.Pin J of J6 is connected to the keying lineat J2 after being unsoldered from C4 inthe transmitter. The foregoing modifica­tions make J6 unsuitable for use with theHA-16 VOX unit. Those wishing to retainthe VOX-connection facility of J6 mayelect to add a four-terminal connector onthe rear apron of the HT-46 chassis forconnection to the circuit shown here.

One other change was made to theHT-46 by the writer: A jumper was placedacross terminals 5 and 6 of SlA to main­tain cutoff bias on the HT-46 keying lineduring staridby (function switch inSTANDBY mode). Without the changethe outboard break-in delay will actuatewhen the HT-46 is in standby, as VIA will

'. conduct unless the grid is supplied withnegative voltage.

Almost any plate relay will suffice atK2A, provided it is a 'spdt variety. Therelay contacts should have good insulatingmaterial (ample for up to 100 watts of rfpower), and the contacts should be rated

FROM 555OUTPUT.PIN 3

+

;L'P'

RW

,,.

R,

FROM U7 PIN i3/U6 PIN 3

032N2222

KEVER -+5V0",

REGULARQ SPACE

EXTENDEDSPACE

Switch arrangement for regular or extendedspace.

TO PROPER SlOE OF Sl(U6 PINS 9 AND 10.

U5 PIN 12)

individually at IS wpm. This way-students, learn by the sound of each letter instead ofcounting dots and dashes. Movingfrom .5to 13 wpm presents thedifficulty of prop,er spacing of characters if a stop-watch isbeing used. I devised this simple timer cir­cult; it might well be called an Accu-Spacefor the Accu-Keyer. By timing the lengthof the spaces while listening to practice.transmissions, I am able to send tape­perfect code. Timing with a triggeredscope is the best approach.

The pulse from the 2N2222 triggers the

+ov

ra

AUTO.

s~~~~- +5V

"12 UBD

NOW AN ACCU·SPACEI'm teaching beginning and intermediatecode classes for our local club. From thestart I have been sending code characters

a switch on either the front or rear panel.The front panel switch labeled TONE isthe monitor disable switch. If your rig hasa built-in sidetone oscillator, it will not benecessary to use the keyer monitor.

Included on the schematic diagram is alisting of the components with RadioShack part numbers. It is given for thoseinterested in duplicating this packagingscheme. - Hal Morris, W4VUOl3

A copy of QST serves to illustrate the compact­ness of the Accu-Kever and power supply.

A ~ortion of the origin~1 Accu-Keyer ctrcutt is shown here with the addition of an NE555 timer ctr­curt. The 100·kfl potentiometer should have a linear taper. For extended space, the auto spaceshould be ON.

88 Chapter 8

o

~_ .__B_. ~

o 0

oo

(e)

NANDTRUTH TABLE

GROUND

EMITTER FOIL

COLLECTOR

PIN eU7B

!)600J\

PIN 8un

(PULL-UP WILL IMPROVENOISE IMMUNITY)1000

switch. or the straight key. This meansthat the normal state is high or floatingfor TTL. Therefore a NAND can becomean OR with inverted inputs as shown inthe illustration. The table defines any lowinput as producing a high output. All thatwould then need be done is to invert andfeed the original manual key gate input.The two diagrams show the circuit ar­rangernent.before and after modification.

To make the simple changes, these stepswere followed: Remove the wire con­nected to pin 5 of U7 and connect it to pin9 of U7, Attach a wire to pin 10 of U7 fora manuartune switch. Next connect a wireto pin II of U7 and the memory circuit.Prepare a 2N3904 (or similar npn plasticswitching transistor) as shown in B. Solderthe emitter to the ground foil and the col­lector to pin 5 of U7. This connection canbe made at the manual key pad. A5600~ohm, 1I4~W resistor is then con­nected from the base lead to pin 8 of U7.This completes the modification, It leavesthe operator with the choice of normaloperation, or by grounding either thememory lead, the manual key, or the tuneswitch, the output is turned on. - Ed­ward Tanton, WA4BAA

HEARING AID FOR THETEN·TEC KR5 KEYERA Radio Shack code-oscillator module forunder $2 provided me with the basic unitfor a sidctone monitor for my Ten-TeeKR5 keyer. The small module fits easilyinto the KR5 cabinet. and may be placed

(0)

JUMPER

:3 -+12.6V

5 GROUND

1 -7BV(KEY)

6 +260V

TO MEMORYOR HANO KEY/TUNE

§=TO TRAN'MOR<SI

TOMANUAL

TO KEYTUNE

SWITCH

D-~,

BECOMES:

V-E

(A) (8)

oa6.8V--.w

TO C)--;::::=~MEMORY

AFTER:

BEFORE:

Accu-Memory circuit modifications for normal operation or activation of the memory output bygrounding the memory key, using the manual key, or operating the .tune switch. A NAND tr.uthtable is shown for reference. Lead connections for the 2N3904 are Illustrated at D. The resistorleads are shorter than indicated (for clarity). The leads should be routed directly across the IC.

builder's choice. Phone connectors suitable.K2 - Plate relay. See text. (Advance GHE·2C­

10,000 used by writer.)P1 - Plug furnished with HT·46.R1 - Linear-taper, 2.5-megohm control, car­

bon type.

ed. Moreover, my front panel was alreadylaid out. The solution came from theNAND truth table.

The output from thc 7420 will go lowwhen true via the keyer logic, the tune

6 V1B

RELAY DRIVER

D1 "-33~ ~O,5, 1M

D1,

O.Ot

~

DC AMPLIFIER

2

V"12AT7 t

2.2M

X·OOt

iOOO

EKCEPT AS INDICATED, DECIMAL

VALUES OF CAPACITANCE AREIN MICROFARADS lj.lFl; OTHERS

ARE IN PICOFAAAOS(pFOR Jlj.lF);

RESISTANCES ARE IN OHMS;

~ 01000. 101.1 000000

COMPLETE FLEXIBILITYFOR THE ACCU·MEMORYI have found a small change in theWB4VVF Accu-Memory that is probablyin great demand from those who prefer acompletely flexible keyer with no com­promises. The change is accomplishedwith the third section of the triple, three­input, NAND 7410 used on the mainkeyer board and two additional parts.

To interface the keycr and the memory,one must utilize the manual key gate. Itcan no longer act as the manual inputsince by so doing a TTL output gatewould be brought forcefully and fatally toground. Solutions involving output con­nections are not satisfactory since morethan one type of output may,very well beemployed. In my version I have"both grid­blocked and cathode output's selectedfrom the front panel. Switching the out­put and the various straight key and tunefunctions at the same time was too involv-

at 2 amperes or more. The builder can usea 5000- or IO,OOO-ohm relay, or any valuein between those ohmic amounts.

R1 is the delay control. With the com­ponent values specified, the delay range ison par with most commercial break-indelay circuits. Shorter delays can be had.by making Cl lower in value, or vice ver­sa. If receiver muting is of interest, use adpdt relay at K2A. The second set of relaycontacts can be used for that application.- WIFB

Schematic diagram of the break-in delay assembly. The circuit can be built in a Minibox, andshould be shielded to prevent rl energy from causing adverse effects. Flxed-value capacitors aredisk ceramic. Decimal-value capacitors are in /-IF. Fixed-value resistors are 1f2·watt compositiontypes.C1 - High·quallty 0.5 I'F. 100 volt or greater.

Mylar, polystyrene, or glass capacitor recorn­mended.

D1, D2 - Low-voltage silicon diode; 1N914 orpower-supply type rectifier diode suitable.

03 - 6.a·volt Zener diode.J1·J3, incl. - Ohassts-mount coaxial fitting of

Thoughts lor CW Operetors 89

An inexpensive Radio Shack code oscillator can be converted to a sidetone monitor for the Ten­Tee KR5 keyer by using this circuit.

NEWLEAD

KiB 0

C CATT~ODE.. CIRCUIT

K'A"-----<O

BREAKILEAD

R9''9DC

C,O

~0.02

you, loosen L, and adjust it so that thereis a little. spring pressure on the side thatneeds help. Retighten L.

If cathode keying is desired, move theblack lead from hole C to the next foil (theother side of R9). This is the only wiringchange.

Connect the keying relay betweenKEYED LINE and BATTERYNEGATIVE on the external terminalboard. I used a Magnecraft 132MPCX4mercury-wetted reed relay with alOOO-ohm coil. (See the Allied Radio In­dustrial catalog.) I mounted this directlyon the terminal board by means of twoshort pieces of No. 14 wire running fromthe relay coil to the terminals. The relaycontacts then key a SO-watt buffer (in thecathode) on the rig.

The electrical change and relay can beomitted if you have only grid-block keyedrigs within the voltage limits of the keyer

'CC,~250,lJF

4

R9

RADIO SHACK MODUL.E NO. 20-m~.5

A

22C4

~2~O,llF

rFPINJACK,

B0--.....----11---......,

takes a little more force to snap onemicroswitch than the other. If this bothers

-+ REEO RELAY

DB

cr--------o--+--~

O.MPS6~14

2200

near the keyer relay. The simple wiring in­volves connecting terminal A on themodule to the + side of the relay coil. B isconnected to the pin plug that is added. Cis connected to the minus side of the relaycoil.

A phono jack was installed under theKRS TRANS pin plug. A miniaturepushbutton was mounted under the 6-12V pin plug. This spst pushbutton switchwas connected across the TRANS pinplug.

While I chose to keep the speaker out­side the KRS box, a small speaker couldbe placed inside the box. Since I alreadyhad an old transistor radio with a speakermounted in the cover, 1 arranged to haveit plug into the KR5 sidetone pin plug.During the first month of operation, per­formance was faultless. - Velio S.Bussicone, W9IlL

Fast, easy sending with provision for cathode keying for the Heath HD·10 keyer is made possiblewith this circuit shown at A. Mechanical changes for the HD·10 paddle illustrated at B.

IAI

SWITCHBRACKET

DETAIL

SHOULDERSPACER

lSI

D~~~~+4~b NEIi

ACVRAUDIO

oDOT DASH

KEYEDLINE

oHANDO

KEY

KEY LEVERASSEMBLY

SWITCHBRACKET

KEYLEVER

HEATH HD·I0 KEYERMODIFICATION

I have been using a modified HeathHD-lO keyer for several years now andhave a simple modification which permitseasy, fast sending, and also provides forcathode keying. Here are the details,which should help other HD-IO owners.

First see page 16 of, the assemblymanual. Then remove the leaf springs andthe shoulder spacer. Center the key levelin the center of the slot by adjustment ofbracket L. Loosen the screws that hold Lto the plate, adjust the bracket so that thelevel falls in the center of the slot andtighten the screws.

Next, adjust brackets Nand P so thatthe operating buttons of the microswitch­es are against the key lever and partlydepressed. A short movement of the levertoward one side should snap themicroswitch on that side closed. andreleasing the lever should allow it toreopen, which pushes the lever back tocenter. A little "fiddling" will get this ad­justment just right.

When this is done, you may find that it

90 Chapter 6

output transistor. The relay, of course.permits keying anything within the limitsof the relay contacts. - Albert B. Booth,W4SSM

AUTO·RECALffiRATIONFOR CW DECODER

I have built two cw-to-alphanurnericdecoders from the original article byThomas Riley, WA1BYM (QST for Oct­ober, November and December, 1975).They drive Burroughs self-scan displaysand the following Auto-Cal circuit. Underlive and test conditions both units are ableto resynchronize using the Auto-Cal fromsix to in excess of 100 wpm from a singleclock.

The loss of system lock or change inreceived speed can cause various out-of­sync conditions: up/down counter toosmall or large resulting in all Ts or Es, orcharacter-spacing loss resulting in C =TETE. The decoding of all Ts or Es, orany combination of both, will incrementthe binary counter, U35, until a count ofeight. This will cause an automatic Recalthrough U7D. Any dotldash pattern thatis decoded and shifted into the dotldashregisters will reset the counter throughU36B. - Thomas.W. Hart, WB50HM

Ul-t4U2-t4

LH-l~

U2-i!>

e

AUTO-CAL U21-9...- ----'

An Auto-Recalibration circuit that will synchro­nize the Riley cw-to-atpbanumer!c converter.

AN OLD CW FAVORITEThe sideswiper is the forerunner of themodern paddle used with electronickeyers. As is the paddle. the sldeswiper isessentially a spdt switch with a return-to­neutral feature that assures you that yourcarrier doesn't remain on the air betweendots and dashes. With it, a practicedoperator can sideswipe along at a goodclip, well above the speed anyone withouta rubber wrist can achieve with a straightkey. In use, one swings the arm of the keyback and forth between the contacts, withelements of Morse character being formedalternately at right and left (left and rightdoes just as well). It's a dot if your dwelltime on the contact is shorter than yourdash dwell time - although sometimes

dots tend to come out longer than dashes.Sideswiping compared to straight keyingis something like flag waving as comparedto using a well hand pump, a wagglingversus a pumping motion.

One of the important characteristics ofthis basic instrument is that its action isfaster than that of a straight key. On theother hand, perhaps a most importantfeature (which sets aglow the warm feelingmany of us have for the sideswiper) is thatit gives real character to one's fist. Suchcharacter isn't achievable with modernkeyers by any but the most dogged - andit's impossible with a keyboard. The ac­cent was a much more reliable identifier ofthe operator than was his chirp or hisl20-cycle note (in sideswiper days 12Q.Hzhum was virtually unknown). The accentwas almost better than a fingerprint. Itnever was clear why the FCC didn'trecord a little bit of each operator'ssideswiper fist for its gumshoe operations(maybe they did!) since his accentcouldn't be faked as can a call sign.

With a sideswiper there's an opportuni­ty for each cw operator to do his ownthing that is much more in harmony withmodern ideas of individuality than is thehomogenization of fists resulting from theuse of such modern electronic aids askeyers and keyboards. It is suggested thateach cw operator review his own fist ob­jectives and consider the sideswiper, par­ticularly the modernized version that isdescribed below, for code characterbuilding.

Construction Details

The classical homebrew sideswiper isbuilt from fundamental items found inany ham's workshop 35 years ago: aporcelain-base dpst knife switch (just tryto find one now!), a hacksaw blade, a 6-32X 1/4-inch machine screw and nut, andabout two feet of friction tape. The switchis disassembled, the two blades are used toform a pair of rear supports for thesideswiper arm, and the terminals arereformed to make the opposing contactsspaced about 3/32-inch apart. The exactdimensions are unimportant. A hacksawblade is then selected (those with anumber of teeth missing are preferredover new blades, but the number of teethper inch is unimportant since they areground off anyway), cut to length, andmounted as shown. Finally, the classicalkey is completed by winding the frictiontape over the end of the blade to producea soft, comfortable "knob" (much betterthan the cold feel of a plastic knob). Ex­perienced users will mount the key on awooden baseplate that is large enough toprevent the key from scooting around inuse and that is finished to match the decorof the shack.

Basic Design ImprovementAfter lengthy experimentation during

the building program, required by an in-

ability to find in the junk box any non­dried-out friction tape of the type re­quired for the classical design, it wasdetermined that the currently availableplastic electrician's tape is an entirelysatisfactory substitute - and in fact pro­vides the basic modernization. One'sfingers no longer stick to the knob whenthe key is first made. Instead, the smoothplastic tape encourages the use of thesideswiper immediately on completionand does not require dirty fingers toeliminate the stickiness, as was necessarywith tape of the earlier specifications. Ex­perienced sideswipers will recognize thisbasic improvement in the homebrew keyas a valuable contribution to the evolutionof the instrument. - John Myers, W9LA

ANOTHER ANTI-SLIDE IDEATo keep a keyer or bug in place, I glue twopieces of fine-grade sandpaper back toback. The keying unit was placed on thepaper and remained in the same positionthroughout long slugfests of cw opera­tion. The sandpaper won't scratch thetable either! - Chris G. Skuza, WA2ISO

BUG TO KEYER PADDLE,AND BACK TO BUGHere is an idea for modifying your bug foruse as an electronic keyer paddle. Thismodification will allow you to change thebug hack and forth between bug and pad­dle quickly without much effort.

Remove the weights from the vibratorarm. Glue a small fiber block from behindthe dot contact to the vibrator arm. Thisprevents the dot contact spring fromoperating. Underneath the base-plate,remove the bus bar connecting the dashand dot terminals. Adjust the key arm sothat as the dot contact is made thevibrator arm touches the damperassembly. Wiring is straightforward.Reverse the above procedure to restore theunit to its original configuration.Robert Anderson, WB9FTA

KEYING A TRANSMITTERWITH A TAPE RECORDERThis simple envelope detector and wave­shaping circuit uses a low-cost quad­NAND gate module to enable "instantreplay" of recorded cw transmissions.Diodes DI and D2 protect the gate fromexcessive input voltage swings. (TypelN270 diodes were used, although anysmall-signal switching or general-purposediode should be suitable.) R3, C2 and D3provide envelope detection of theamplified and clipped audio input. R6provides positive feedback to suppressoutput oscillations which can occur whenTTL gates are subjected to slow rise- and

Thoughts lor CW Operntora 91

EPOXY2 BLOCliS OF NONCON­DUCTIVE MATERIAL.DRILL AND TAP FOR'-8 SCREWS,

41*4 OF ACTUAL SIZE

ALL BARS iCRS

POLISHED.

2 PADDLES ­ANY SUITABLEPLASTIC MAT'L.

capacity would be desirable. It seemed tome that most of the logic in the Accu­Memory was devoted to timing andoperating the RAM. Because of the natureof the tri-state RAM, installing two addi­tional RAMs in the memory circuit didnot seem foreboding. The main problemwas physical - how to accomplish thisfeat without disassembling the unit andwithout cutting leads on the existingRAM. Another consideration was to re­tain the rf immunity of the keyer memory.

My plan was to attach a piggy-back,16-pin socket to the existing RAM, sinceall leads of the pair would be connected incommon except for pin 13, the chipselector of Cl;;, according to the ICmanual. A 7432 quad-NOR gate waschosen for selecting the pair of RAMs.The total memory, after modification wasample for most situations.

Fortunately, my Accu-Memory wasconstructed with sockets which eliminatedthe need to unsolder connections on theunderside of the board. Installation of theadditional RAMs was done according tothe following sequence: Remove the ex·isting RAM from its socket. Bend pin 13at right angles to the other pins. Place itback in the socket. Bend pin 13of the newIe-pin Ie socket at right angles also. Placethat over the existing RAM, lining up thebent pins. Solder the new IC socket to theexisting RAM, waiting 20 seconds be­tween finishing one pin and working onthe next. Pin 13 is not soldered. Care mustalso be exercised to avoid soldering the ex­isting RAM into the original socket.

At this point, the additional RAM andthe piggy-back socket are removed fromthe existing socket. Insert a piece of wirefirmly into pin hole 13 of the existingsocket. Solder a length of wire to pin 13of

DOWEL PINEPOXY OR"LOCTITE"IN PLACE.

DOWEL PIN.GOOD SLIDEFiT HERE.

TO TRANSMITTERGRID-BLOCKKEY INPUT

SET GAPS BY HOLDING AND TURNINGSCREW WITH NEEDLE NOSE PLIERSAND TIGHTENING NUT.

e

BASE:METAL ORHARD WOOD.

C3;;r;O.001

2- ....8 ROUND·HEAD SCREWSTO HOLD THE PAODLES ON.7 DRILL THROUGH FOR ROLL PIN,

9~::::;:r~~~~~::::=:::::=,:::-- ROLL PIN

R6

2N,::i400

2700

+C24710V

R5

330

R3750

11 10 9

2-"8 SET-SCREWS

;lf~ES--'" ...............SECURED -,BY NUTS -,

AND RDUND- _~'~tg~=}~;~~~~~~HEAD SCREW. -,

LIGHT SPRING:CUT COILS UNTIL SUITAeLECOMPRESSION IS OBTAINED.

DRILL AND SET'WITH EPOXY GLUEOR "LOCTITE"IN PLACE.

SN7400N

D3

especially if a steel base is used). The mainparts are made of 3/8-inch, cold-rolled­steel rod, cut and filed to fit as called foron the drawing. - Jim Baker, VE3CJB

EXPANDING THE ACCU·MEMORY

After operating my Accu-Memory for awhile, I realized that an enlarged memory

Mechanical drawing of the VE3CJB keyer paddle.

'"

0\

R42200

!~~0rO--~'------,

TAPERECORDERPRE-AMPOUTPUT

TAPERECORDERHIGH-LEVEL

g~J~~6 ()------+

A simple envelope detector and wave-shaping circuit for instant replay of recorded cw transmts­slons.

fall-time signals. Rl is used to lower the"floating" input threshold to the gate andincrease circuit sensitivity.

For low-impedance recorder outputs orhigh-level audio outputs, the low side ofRI should be disconnected from groundand used as the audio input point; thevalue of R2 should be increased ifamplifier hum or background noise is stillsufficient to trigger the circuit falsely. Ofcourse, an audio-filtered and impedance­matched input to the tape recorder greatlyassists in generating a perfect noise-freeoutput replica of the original input signal.- Andrew H. Kilpatrick, K4YKZ

VE3CJB KEVER PADDLE

The Canadian amateur who purchasesparts manufactured outside Canadanaturally has to pay import taxes; whenfaced with the cost of purchasing a keyerpaddle plus the tax, I balked! One solu­tion to this problem seemed to be to comeup with a scheme to build a keyer paddle.I finally made one that looks and feels asgood as the commercially manufacturedunits. I got to thinking that maybe thereare other hams who, for one reason oranother, would be interested in my designlayout.

The paddle's construction is such that itdoes not require the use of any uncom­mon household workshop tool. The onlypower tool required is a hand drill(naturally a drill press would be preferred,

92 Chapter 6

100.-JVV'v-o +'V

KEYER WEIGHTING

Charlie, an old friend who just receivedhis Novice license, asked me a question:"How fast can you copy?" As I started toreply, I realized that there was no simplepat answer. There was no unqualifiednumber I could give him. It required a lit­tle discussion that went something likethis:

My cw receiving speed is almost whollydependent on the sender's quality or ar­ticulation, his rhythm, spacing, and keyerweighting. I can read a super operatorsuch as Flo, W7QYA, at 50 words perminute and there are some hams I strainto copy at 10 words per minute. And someof the hard-to-copy hams are not begin­ners,' either, but old timers who have ex­acerbated their bad habits. And the trou­ble is that it takes a lot of courage to tell afriend that he has a lousy fist - sort oflike telling him he needs a deodorant.

A few years ago, I was involved in somerather elaborate measurements of speechintelligibility conducted by CruftLaboratory of Harvard University. The"articulation percentage" was the percentof words understood with differentamounts of noise and with various fre­quency responses. From these tests camean understanding of just what was re­quired for accurate, articulate speechunder various conditions.

The same general observations apply tocw. The pitch. for one thing, should becentered around I kHz where the ear is themost sensitive, especially at low levels ofsound. It acts as a band-pass filter ofsorts.

An all-important factor in producingeasy-to-read cw is the "weighting" of thekeyer or the setting of a bug. This is theratio of the dit and dab length to the spacebetween them. The classical ratio is 1:3, inwhich the dit is 1/3 the length of a dahand equal to a space. However, in prac­tice, it is a bit choppy in the range of 15-20wpm. where most of us work. Increasingthe character length about 15 percent

STORAGE1

STORAGE 2

es in the keyer. Every second pulse fromthe timer resets the memory. Fifteenseconds (or whatever interval is desired)later, the memory is stopped, and after 15secondsis restarted for as many cycles asdesired. The unused position on the rotaryswitch allows the operator to disconnectthe timing circuit from the keyer, for syn­chronization with WWV.

This circuit works very well and takesmuch of the hassle out of meteor-scatterwork. It may also be of interest to EME(moon bounce) workers, with appropriatechanges in the time constants. - MichaelR. Owen, WBSDOJ

RF IN AN ELECTRONIC KEYER

When I operate my Hallicrafters FPM-300Mark-II transceiver in the 4O-meter bandand above, rf apparently enters my HeathHD-1410 keyer . The trouble waseliminated by connecting a O.OI-J,(F, I kV,bypass capacitor from one of the l17-V acsupply leads to ground as shown in thediagram. - A. D. McMahone, WB9FCK

•10

14323

6 " tOV

8 .. PIN '3(TOP lC) U2

7

PIN13CBOTTOM Ie) Ul

PIN t3{BOTTOM leI U2

PIN i3 --e---,(TOP Ie) U2 .....

PIN 13SOCKET U1

An enlarged memory is achieved for the Accu·Memory by incorporating this circuit.

the old RAM and another length to pin 13of the piggy-back socket. Reinsert the oldRAM in the original socket. The newRAM should be inserted in the piggy-backsocket in the same direction as the originalRAM. Installation procedure is the samefor both new RAMs.

The 7432 was wired without the use ofprinted circuits by using the dead-bugmethod. Simply bend all leads of the IC90 degrees so that they are pointing awayfrom the device. Necessary jumpers wereadded. The Ie was secured with acrylicto-second glue to the top of U6.

Except for the short jumpers, shieldedwire was used throughout the project toavoid rf pickup. After completion thekeyer retained immunity to rf. I was ableto mount the miniature dpdt switch, in­dicated in the drawing, on the front panel.

This modification provided one keyerwith two independent memories. Eachwill function the same as the originalmemory. Moreover, the four RAMs pro­vide 4096 bits of storage. - Jake Gold,WB2AFS

METEOR·SCATTER TIMINGMODmCATION FOR THEACCU·KEYER MEMORY

My primary interest is operation in the2-meter band. Therefore, I spend muchtime calling CQ, so the Accu-Memory isquite helpful. Meteor-scatter contacts aremuch simpler: The memory takes care ofthe repetitious transmitting of my ex­change. I developed the modificationshown in the schematic diagram toeliminate the need to synchronize pressingthe appropriate memory switch with thesweep second hand of a clock. VI, anNE555 timer, provides timing pulses at in­tervals determined by the setting of Rl.VI "clocks" V2, a flip-flop, the Q outputof which stops the memory of the keyer.The output of U I is applied through thefive-position switch to the RESET switch-

BYPASS CAPACITORINSERTED

i.olJJF;:J:;1000V

Reduction of troublesome rf in the HO·1410 may be obtained by connecting a 0.01 ,liF, 1-k"capacitor from the 117·V line to ground as shown In thIs diagram, An alternative wou~d be to con­nect two O.Ol-,liF capacitors in series across the line. grounding the common connection betweenthe two capacitors.

Thoughts lor CW Operetors 93

-25V

TO CENTERPIN OF J4

TO PIN 4OF PB--I407

6V

. J-t----_<SOk

§'07~l-+---]TO CRYSTALS

1 v"

and slice through the foil leading to pin S.Drill a small hole at the top of the pin Sfoil.

4) Remove R7, and jumper pin 5 to theemitter of Q3 with a small insulated wire.

S) Mount a SO-kll potentiometer on topof the chassis. 1 taped this in to preventdamage and to preserve trade-in value.One side of the potentiometer goes to pin4 of PB-l407 and the other to the centerpin of J4; which is the key input.

6) Underneath the chassis, wire a tran­sistor as shown in the diagram. I used a2N2222A with long leads.

7) Adjust the SQ-kll potentiometer toremove the backwave. The Yaesu FL-IOIwill now operate beautiful QSK, as therewas never any hash and now nobackwave. - Max Cornell, WA'SIG

Backwave on the Yaesu FL·101 eliminated withthis circuit.

the ham at the receiving end. If your keyerhas a preset factory adjustment, by chang­ing a resistor or installing a variable con­trol, you can tailor it to your individualpreference.

With the increased interest in highercode speed these days, perhaps we need anew Q signal to request advice on op­timum setting. Or to suggest a change. Ifit was in general use, it would be a help inproducing more legible cw at any speed aswell as less strain and tension. - AlbertKahn, K4FW

THE YAESU FL-IOIThe Yaesu FL-WI, when using full break­in with the T-R switch in the ARRLHandbook, operates beautifully exceptfor an annoying backwave that will maskweak signals. The finals and the driver aregrid-block keyed. To correct thebackwave problem, I decided to key anadditional stage. The heterodyneoscillator was selected because of the con­struction of the unit and convenience.

I) Remove PB-I407 from its socket.2) On the socket, disconnect the

ground lead from pin S.3) On PB-I407 use a sharp-edged knife

CLEANING CAPACITANCE­ACTIVATED KEYER PADDLESCapacitance-activated keyer paddles, suchas the Data Engineering ElectronicFeather Touch, become erratic in opera­tion when dirt and oxide build up on themetal grid. The dirt may be removed witha soft cloth moistened with denaturedalcohol. - Wayne E. Whitman, W9HFR

gives about the same readability but is alot more pleasant to read for it issmoother and a little musical.

For speeds above 2S wpm, weightingbecomes extremely important. Shorteningthe characters with respect to space in­creases the articulation and the greater thespeed, the shorter the bit lengths shouldbe to make it easy for the ham at the otherend. The greatest problem for an operatorof a DX station is to read the call signs ofstations calling in a pile-up, especiallyunder "wide open" band conditions.Sometimes a call is discernible only for asecond or so. To be read, it must be clean.If the signal is fairly weak, (in a pile-up ofloud signals, all often appear weak) theright combination of moderate speed andshort weighting will often bring a reply tothe station that is several S units below theothers who are pounding away withslurred signals.

An easy way of visually determiningproper weighting is to connect an ohm­meter across the keyed output. When thedit side is actuated, the meter will readhalf scale for a 1:3 ratio. This is, ofcourse, because a dit is equal to a space.This is the basing point.

Some electronic keyers have variableweighting; others have factory presetweighting. Most can be modified to pro­vide the ideal weighting for your par­ticular style of operating. If your normaloperation is in the 15-20 wpm range. youwill find that an increase of about 15 per­cent will give you the best balance of ar­ticulation and smoothness. You willsound great, be easy to copy. If, however,you are QSOing some pretty fast com­pany, reduce the characters by the sameamount and you will be doing a favor for

94 Chapter 8

Chapter 7

Portableand Mobile Quickies

A battery-saver device can reduce the consumption of walkie-talkie and hand-held equipment dur­ing standby by a factor of 10 by using an astable multivibrator to switch the receiver off exceptfor brief "sampling" periods every few seconds. When the presence of a signal is detected by thereceiver squelch or muting circuits the receiver remains "on".

original cycle of events reoccurs. Q5 actsnot only as a switch but, in conjunctionwith 03, as a voltage regulator.

The authors state that it is important touse high-gain transistors throughout sincelow-gain types, e.g., BC237, BC307 (HEP729, HEP 715) do not switch effectivelyand can give rise to unpleasant noisesfrom the receiver as it switches. ItIs sug­gested that tantalum capacitors should beused for CI, C2 and C3; theyare smallerand have lower leakage. Since the sam­pling time and duty cycle is affected byboth capacitor values and transistor gains,some experimentation may be needed,especially with C3, to get the desiredresults. The original unit was built on apiece of paxolin less than one inch squarewith O.l-W resistors, and was able to fitinto quite a compact walkie-talkie.

The current drawn in this particularunit with the mute closed is normally 40mA, but with the battery saver in opera­tion the average current drops to 4 rnA,

+li!V

'so 0'

"HEPSOOO2

22020

0.

D. HEPSOOO2 02lN4148 ~6~ 330~ C2 lN4148

SQUELCH 2.'SWITCHEDSUPPLY TO(+WITH SIGNAL) RECEIVERc, D.

<0' 0A~2

<2V

"." .0' 410~

about 25 seconds before the sampling cy­cle begins. The following notes on circuitoperations and necessary precautions arebased directly on the Break-In article.

When the receiver is switched on, Cl isinitially discharged but then charges slow­ly through the 330-klJ resistor and thebase-emitter junction of Ql, holding Qlon which in turn forces Q2 off. EventuallyCl becomes fully charged, so that basecurrent ceases to flow in QI, turning thistransistor off and causing Q2 to switchon, which in turn works through thesystem until Q5 is turned on, so providingpower for the receiver. If during the sam­ple listening period there is a signal pre­sent, the squelch circuit in the equipmentprovides an input voltage to 01. Thiscauses current to flow through Olandthe 5600-ohm resistor, so that base cur­rent flows in Ql, turning Q2 off andholding the receiver on. When the signaldisappears, however, CI again chargesthrough the 330-klJ resistor and the

BATTERY CONSUMPTION SAVING

When using hand-held and other battery­operated equipment over extendedperiods of time it is clearly desirable tokeep consumption to the minimum possi­ble that allows the system to functionwithout significant loss of efficiency. Onetechnique that for some years has beenfairly widely used in professionalequipments is the use of a low duty cycleduring standby operation of the receiver,automatically switching the equipment tonormal receive conditions when a signalappears. In other words, this means thatthe muted receiver "listens" for perhaps10 percent of the total time, taking a brieflook at the frequency every few seconds.If the squelch or muting circuit then in­dicates that there is a signal coming in, theinterrupt condition is disabled and thereceiver stays on until perhaps 10 secondsafter the signal has gone, when the sam­pling process is restarted.

A number of suitable "battery saver"circuits that accomplish this sampling pro­cess have been described: for example,one by Dr. D. A. Tong, G8ENN, wasgiven in Wireless World for March, 1972,pp. 124-5; another by Intech Inc. in Elec­tronic Design; and the latest by JohnRumsey, ZL2TNK, and Peter Williams,ZL2ARW, in Break-In for August, 1975.This one is basically similar to the G8ENNdesign but uses rather less components.The New Zealand design was intended foruse with a specific group-project walkie­talkie but there is no reason why it shouldnot be used, possibly with minormodifications, for other equipments.

All these systems depend on an astablemultivibrator to provide the basic I: 10duty cycle and use this to control a tran­sistor power switch which interrupts thepower to the active devices in the receiver.

In operation the receiver is held oneither initially or after transmission for

Portebl. end Mobile Qulckl.e 95

th-us providing a' very worthwhile exten­sion of battery life, particularly where theequipment is required to operate for ex­tended periods on standby.

On the subject of battery economy, it isinteresting to note that the range of Vartabatteries, made in Germany, now includesa miniature sealed NiCad 9-V battery,type TR7/8. It is the same size as the well­known PP3 transistor battery, withsimilar connections, but can be rechargedsome hundreds of times (provided care istaken). The capacity is 90 mAH; unfor­tunately details of the price are lacking:obviously NiCad units are expensive com­pared with primary cells but for anyoneusing a lot of batteries it should work outcheaper in the long run. - Radio Com­munication, December, 1975, RSOB

SHOCK MOUNTING FORMOBILE RIGSA large percentage of mobile-equipmentfailures may be caused by vibrationdamage while in motion. Before installingmy new mobile rig, I placed a rubbergrommet over each mounting bolt, to actas a shock absorber. The grommets are in­stalled so that they are compressed be­tween the mounting bracket and thedashboard of the vehicle. - Howard A.Johnson, WA8QBJ

INTERFERENCE·FREE CARREGULATORElectronic solid-state voltage regulators asa part of "car electrics" are attractive fora number of reasons - not least becausethey have no mechanical contacts to pro­duce sparks that can be a difficult-to­eliminate source of interference to mobileoperation.

John King, G4CFJ, when using a 1.8MHz mobile rig in a car with a fiberglass

(glass reinforced-plastics) body, found itimpossible to suppress the voltageregulator with any of the usual tech­niques. So in the end he adopted the solid­state regulator arrangement shown in theillustration.

In this system the battery volts are com­pared with the reference volts across a 6-8V Zener diode. When the battery voltageis low, the 741 operational amplifier ICprovides an output of about + 12 V, turn­ing on Cl and C2. This causes generatorfield current to flow and the generatoroutput to charge the battery. As soon asthe battery volts rise beyond that of theZener reference, the 741 output drops toabout +2 V and the field current is turn­ed off. The battery is prevented fromdischarging through the generator bydiode Dl which should have a currentrating of at least 20 A.

G4CFJ mentions that when he installedthe new regulator he left the original onein place and simply placed cardboard be­tween its contacts to stop it from working.The wires to A, F and D connections weresoldered to those already on the oldregulator. It should be noted that the cir­cuit as shown is suitable only for negative­earth systems, but by changing npn to pnptypes and suitably connecting the diodes,it should be possible to adapt the systemfor positive-earth vehicles.

If the generator output is too low (orhigh) it can be adjusted by changing thevalue of Rl (1.5 ohms nominal); Rtshould be set to give 13.5 to 14 V from thebattery. - Radio Communication,March, 1976, RSGB

MOUNTING MOBILE EQUIPMENTA convenient place to mount mobileequipment is below the instrument panel.The mount is constructed from aluminumangle stock and a piano hinge, both ofwhich should be available from the do-it-

AUTO INSTRUMENTPANEL

STOCK

MOBILEEQUIPMENT

RUBBER--CUSHION

TRANSMISSION HUMP

W5TBC's mobile mount.

yourself counter at most hardware stores.This scheme makes a rigid mount, yetequipment may be removed easily by pull­ing out the pin in the piano hinge. ­Robert T. Paige, W5TBC

LOCKING ACTIONFOR MOBILE MICS

A simple modification to my mobile michas made long-winded QSOs a bit easier.By carefully filing a notch in the push-to­talk button, a locking action can be addedto almost any mobile mic. The sketchshows the placement of the notch. Careshould be taken to keep filings from faIl­ing into the mic case. With my mic, itwasn't necessary to remove any more than1/16 inch from the control button. Besure to check frequently for locking ac­tion. - Gene Kusluski, WA8YIT

1~6 :;-__+--.....:4" "G

+--=- 1ZV

A

0'HEP253R

o

100

"'-'6W

F

0'HEP232

473W0'

HEP714

,1100

'60

1Z0k

6e

LM741

470470

470 0'e.ev

4O"6""iiiW

033.9V

4OO'iilW330

Solid-state voltage regulator used by G4CFJ to overcome the problem of regulator interference to1.8 MHz mobile operation. Unmarked resistor to base of Q2 is 20 ohms.

Notch in PIT button removes need to press theswitch continually during 050.

96 Chapt.r 7

The complete' system 'showing bike, wooden frame, generator, YOM and so forth. Lest anyonetrespass, that is K2FJLT's basset hound, Josephine, keeping watch.

This shows the method of suspendlng,and'bracing the rear of the bike.

MAN + BIKE = POWER

Is it possible and practical to devise anelectric generating system using man­power and a bicycle mechanism to deliverenough energy - 100watts or more - sothat it would be a meaningful source ofcommunications power in a time of need?After conducting a few simple ex­periments,the answer to the question wasmanifestly - yes. The jury-rigged,garden-variety mechanical system de­scribed here hopefully will serve to en­courage more sophisticated' experimenta­tion and design that would inevitablyresult in a more efficient application ofthe principle.

The system is basic and simple. The rearwheel of a five-speed bicycle is used tofriction drive a small-treaded lawn mowerwheel which was force-threaded directlyonto the shaft of an old 12-V deautomobile generator. from the junk box,of course. Power was taken directly offthe generator to run an amateur hf

This shows the contact point between the bikewheel and generator wheeL The long threadedbolt is the vertical axle that allows the gen­erator to rotate horizontally toward the bikewheel, because of the pressure from thespring. The probes are from the YOM.

transceiver - an FT-IOIB. Voltageregulation was accomplished by connect­ing a YOM across the generator andpedaling so as to maintain a voltagereading of 13.5 volts or so.

The generator was-mounted so that thewheel on its shaft would be in line andmake direct contact with the bicyclewheel. The amount of contact pressurewas found to be important if not critical,and this pressure was varied by spring­loading the generator to the bike wheeland adjusting the tension in the springwith a turnbuckle. Another advantagederived from the spring was that it allow­ed compensation for the circumferentialirregularities of the wheels. The orienta­tion of the generator to the wheel wassuch as to ensure that the direction of thebicyclewheel rotation would tend to pushthe generator away from the contactpoint. A function of the spring was to ap­ply an opposing force and thereby main­tain the needed contact and pressure. Forthis to be possible the generator had to bemounted on a pivot which allowed it torotate a few degrees horizontally towardthe wheel when the spring was attached.

With the 27-inch (686 mm) bicyclewheel driving a 5-3/4-inch (146 mm)generator wheel, and with the derailleurtype gear system set at the fastest speed,this ad-lib system aIlowed for thegenerator to be rotated about 1125 rpmwhen delivering full' output under man­power conditions. A refinement was toadd 32 ~F of capacitance across the, out­put terminals of the generator to reducethe armature-caused hash to an insignifi­cant level.

The mounting of the bicycle was ac­complished by building a frame of two­by-fours. A I-inch pipe was U-bolted to

the top bar of the bicycle frame allowing. about 12inches to extend out over the rear

wheel. The rear of the bicycle was thensuspended from the frame and stabilizedat the wheel hub, using improvisedbrackets on each side. The front wheelwas removed to facilitate portability andto improve vertical stability when a solidlog or block was placed under it. A longaluminum bar was used to provide addi­tional stability from the rear to the top ofthe wooden frame.

Some design considerations suggestingthemselves are: use of a direct drivesystem from pedals to generator shaft; thedetermination of optimum rates of pedal­ing incorporating proper ratios ofassociated sprockets or gears; use of low­friction bearings and high-quality gears;mechanically linking the individual's armsto the system to assist the legs (When legmusclesbegan to tire we simply pushed onour knees with our hands); exploitation ofthe flywheel principle; careful choice of a

OUTPUT12-14V

DC

+F

GENERATORCHASSIS

"F" is the field terminal of the generator. Forthis application the field terminal is connecteddirectly to the frame. "F" is also the B + ter­minal. The remaining terminal is B-. Thegenerator used was a Delee-Berny, 12·V dc,model 1100304.

Portable and Moblla Qulcklea 97

Two triangular hinges are bent as shown in A,and mounted under the dash. B shows theposition of the brackets with the Swan 350 inplace, and C shows the brackets with the Poly­Comm e-meter rig installed.

determined by minimum reflected powerindication on the SWR bridge. Alter­natively, the correct tap may be found byexperimentation, and the wires soldered inplace. An enclosure is not necessary,though desirable. - Alan Applegate.WB6BHE

CONTEST LOGGING WHILEMOBILE

During mobile contest operation, 'nothingis more difficult than logging stations. Atone or two contacts a minute, it canbecome tiring to search for the logbookand grope for a pencil. However. there isa solution to the problem: the MobileDesk.

The Mobile Desk snaps onto the frontof the steering wheel and eliminates theneed for finding a place to write on. It wasbuilt from a 10 X 12-inch (254 X

305-mm) piece of I/g-inch thickMasonite. The board is held to the wheelby two Sears type 34 K 6123 cable clamps,and an ordinary spring clip is used tosecure the logbook to the board. For add­ed convenience a hole was drilled in theboard, and a beaded chain like those usedon key chains was passed through it. Apencil was then taped to the free end ofthe chain. To prevent marring the steeringwheel, masking tape should be wrappedaround that part of the wheel over whichthe clamps are to be snapped. - RonDagavarian, WA2FLO

OPERATING 12·VOLT EQUIPMENTFROM THE CAR BATTERYSome manufactured amateur radio equip­ment is designed for operation at 12-voltsde, maximum. At operating voltageshigher than 12 volts, damage can occur tosome of the components, especially thetransistors and I'Cs, and circuit perfor­mance can be degraded significantly.

Since most fully-charged automobilebatteries provide something in excessof 12volts - usually 13 volts or more - somemeans should be employed to lower thepotential to 12 volts, thus protecting theequipment from possible damage. A casein point is the Motorola P33BAM fmtransceiver. The driver tubes will exhibitvery short life if the filaments are operatedat more than 12volts for a period oftime.

Tests with a commercially built, solid­state cw transceiver showed that severechirp resulted when the unit was operated(YFO-activated) at any voltage higherthan 12 volts. A simple way to lower theoperating voltage is to take advantage ofthe forward voltage drops of one or moresilicon diodes. Usually the voltage drop isbetween 0.4 to 0.7 volt per diode. Themore diodes used, the greater the voltagedrop across the series string. The diodecurrent rating is chosen according to thetotal current drain of the equipment; thediodes should be rated at twice the currenttaken by the equipment, or greater, toprovide a margin of safety for the diodes.Diodes with a 50-PRY rating are fine forthis application.

The diodes offer an added benefit ­protection against circuit damage shouldthe supply leads mistakenly becomereversed! - WIFB

SERIES-CONNECTEDDIODESI <2-VOLT \j:ll .I~ (~ D+

EOUIPMENT . 13.5-VOLT. . ~_SOURCE

EquIpment that is designed to be operated at amaximum of 12-volts dc can be safely operatedfrom a tully charged car battery (13 volts ormore), If a suitable number of diodes Is con­nected as shown. See text for diode specifica­tions.

(e)(8)

DASH DASH

Z;"3;:] \@'DOOR HINGEl , DOOR I

HINGES

(A)

"~O,G~"-.:-:

OE'

TRANSCEIVER MOUNTINGBRACKETSMy problem has been to find suitablemounting facilities for two transceiversthat I use for mobile operation. I own aSwan 350 and I have a Poly-Comm6-meter transceiver on loan from c.d. Iwanted some type of mounting bracketsthat would hold either rig, in spite of thefact that there is a difference of 2-112inches in the widths of the transceivers. Inaddition, I wanted to answer my wife'scomplaint that the Swan mountingbracket kept gouging her knee when no rigwas in the car.

~ After a couple of experiments withplumber's pipe strap, I thought about try­ing hinges. Sure enough, by mounting apair of a-inch long, triangular doorhinges, I solved my problems. I didn'teven have to drill extra holes in the hinges,as there were four holes to choose fromfor installing the rigs. To accommodatethe Poly-Comm, the smaller of the twotransceivers, I simply bent the hangingportion of the hinges slightly near the bot­tom. When not in use, the hinges can befolded up and held against the dash withmagnets or strips of tape. - JamesHoffer. WA80VC

A method for matching an hf mobile antenna.

generator for the system so as to obtainthe highest possible efficiency; choice ofan efficient voltage-regulator circuit; in­clusion' of a battery-storage system..

Perhaps the most interesting of theitems mentioned is that of the flywheel,which, through energy-storage properties,can offer several advantages to a man­powered system. For example. a flywheelwould tend to act as a mechanical voltageregulator. This results from the fact thatin a one-man pedal system there are twopower strokes per pedaled cycle whichproduce voltage irregularities in pace witheach pedal stroke. Once rotating, aflywheel would tend to apply a relativelyconstant force to the rotating mechanicalsystem, resulting in a more regular rota­tion of the generator shaft, thereforediminishing the voltage irregularities.

Lest anyone be misled, it is a dramaticexperience to "ride" the bike and pedalup to about 13 volts without a load, andthen to suddenly feel the drain of 90 to120 watts being taken from the systemwhen the switches are thrown, filamentsheated, and key pressed. It is a good bitlike suddenly having to pedal at a fastpace up a steep hilL - Edward Yadzinskt,W2DNZ

MATCHING TO HFMOBILE ANTENNASMany hf mobile antennas will not presenta good match for the 50-ohm output im­pedance of a transceiver. Feed-point im­pedances range from 12 to 35 ohms and,while SWR is often high, losses are smallbecause of the short length of coaxialcable between the rig and antenna. Whenusing a transceiver with broadband tunedcircuits, the high SWR may result in er­ratic operation, because of the mismatchthat exists between the rig and the anten­na. The author designed an rfautotransformer to allow better matchingwhen operating a l-kW mobile rig. Tl hasseven bifilar turns of No. 12 enameled orTeflon-insulated wire, on an AmidonT200-2 core. The winding (see drawing) istapped at 2, 3, 4 and 5 turns from thecold. or ground. end. A single windingwill suffice for power levels under 500watts. SI may be used to select the tapwhich provides the best impedance match,

98 Chepter 7

-------------------

Circuit diagram of the fow-cost encoder. All resistors are 1/4 watt.KB1 - Keyboard (Poly Paks no. 92CU3149). Yl - 1.000 MHz (Mariann Labs no. MLl8P,Q1,02 - 2N3643 or equtv. Sherold Crystal no. HC-6).U1 - Motorola MC14410P.

KEYBOARD.

SWITCH DETAIL ENCODERCOLUMN rooo MHz

VI

~~W r-IDf-r 15Mv

Ka' '0 9

,..2 OSCIN OSCOUT ts -ooo, e "' YO0

4>- • ",• e a '000 0'U, LOW

-} , BAND )-H:1' "17 B "' MC14410P

10009' H'G H "

~:~ +".;; -} e ". BAND

~ ~

~0

C3 C2 cr y"

T ra ra .. B

LSI =9V

,C:: r?' CR3

1N4001 rh

CODE FOR COMMUTERS?

Many amateurs have found that it is onething to struggle through the Morse test toobtain the coveted Class A (Extra Class)permit; something rather different to feelreally at home with cw operation. Itmakes all the difference if you persevereuntil 12 wpm seems a little like flag­waving. There is a common belief that ashort spell of cw operation on the bandswill quickly convert a 12 wpm capabilityinto 20 wpm; this is only partly true - somuch amateur "traffic" follows well­defined patterns that it is by no means theideal way of bringing up your speed.

This brings a note received from DickRollerna, PA0SE, putting forward somethoughts on a novel way of finding time

because the flat front of the radio wasneeded to mount the keyboard. Also, withthe speaker mounted by itself, only twoleads are required from the encoder boardto the case back. (The encoder board ismounted on the keyboard side and there isless chance of breaking leads when chang­ing batteries.) I used RTV bathtub caulkto mount the circuit board and speaker inthe radio case. This method has been usedsuccessfully on other projects.

AlIgnment ond Operation

Because all major wiring is done insidethe chip, and a crystal is used as thef'requency-determ ining element, notweaking is necessary. If no tones areheard when a key is depressed, check allthe connections.

The encoder has worked successfullywith all thelocal machines on the first try.With any reasonable signal into therepeater, it is a simple matter to hold theencoder to the mic and set up the auto­patch. - Chet Gorski, KIMYQ

The view shows the Inside of the encoder. TheIe and fransistors are mounted on.e piece ofVectorboard at one end of the case.

is possible to generate all the requiredtones for the typical patch.

OreultDetIlls. ,TItehearior theencoderis,the Icarid

wJille I use a 12'switchkeyboard, four­row ~'ndthree~olumnjnputs,'the chip will'accept a four-by-four switchboard. TheMCI4410P is designed toaccept digitalinputsin Ii two-of...ight codeformat andto digitally synthesize the high- and low­band sine waves specified by tile telephonetone-dialing systems. The chip doesn'thave adequate output to drive a speakerso two transistors, QI,'llIld,< Q2,', are con­nected i~ aco~J>o~ndserie5'rnodefo:drive

lII\ ~-ohm speaker. Operating from a9',volt battery, total-current drain is3' rnAidling, and slightly, over 100 rnA whendrjving the speaker to full audio capabili­ty,

Construction Details

If it is not already obvious from thephotographs, the encoder was constructedin a transistor radio case. There are plentyof "burnt-out" radios around and theymake good housings for projects such asthis. [ was able to use the speaker. Also,the case was chosen because it met my"shirt-pocket" size requirement. Garageand tag sales are good sources of tran­sistor radios.

All the components were assembled onVectorboard, and all the wiring for the ICis to a socket, rather than directly to thechip. Although the IC has internal protec­tion against high-static voltages or electricfields, it is advisable that the chip not beremoved from the conductive foam "ship­per" until it is ready for use.

The speaker in the radio was moved tothe back of the case (some holes weremade in the back for audio to escape)

The completed encoder is shown here. TheTouch-Tone pad is just the right size to fit onthe average small transistor radio case.

AN ACOUSTICALLY COUPLEDENCODER

A Touch-Tone encoder can be built usingacoustic coupling to the transceiver, thusavoiding direct modification of thetransceiver itself. The Motorola IC,MCI4410P, makes the project feasible. Itis a unique Ie that contains all gating,dividing, decoding and driving circuitry inone package. Also included in the packageare all the components necessary for acrystal, L-C or external oscillator input.Incidentally, by using the MCI4410P, it

Portable end Mobile Quickie. 98

Detailed drawings shOWing how the receiver head is coupled to the transceiver dial.

FLANGE AND HUB

3/8" SCREWS

TRANSCEIVER....-DIAL

TRANSCEIVER+--PANEL

•

o ' ,

12 FT. CABLE TO CONTROL ON DASH..

ly simple, but frequency control is moredifficult. This article shows one methodof how the latter can be done with a SwanCygnet 260.

Two surplus-type, CRV-232S3,receiver-tuning controls are needed, alongwith 12 feet (4.6 m) of flexible controlcable, type MC2lS. These can be obtainedfrom Fair Radio Sales in Lima, OH.Other components necessaryare a flexiblecoupling to fit a 1/4-inch shaft and hard­ware to mount one of the receiver headson the transceiver.

The dial assembly from one of thereceiver heads is removed and the head ismounted on front of the transceiver asshown in the photograph. The authordrilled a hole in the front panel of the 260and fastened a flange directly to thetransceiver dial, as shown. This wasnecessary since the dial drive on thistransceiver was of the friction type andsome slippage occurred. Only minormodifications may be necessary withtransceivers that use other types of drives.

The flexible cable is then run up to thedash where the other receiver head ismounted. Before the setup is installed, thecalibration on the dashboard head shouldbe changed so that it matches up with theone on the transceiver. A new one wasmade by the author and consisted of aplastic base with a shoulder and a dustcover. Sandwiched in between is anopaque dial with the new calibrationmarks. These can be of the builder'schoice and decal-type numbers were usedin the unit shown. - George Tamer,W4BAD

AUX.TUNING KNOB

AIRCRAFT RECEIVERCONTROL (MODIFIED)

/

45 T01 RATIO

. FLEX.

COUPLING

+CRY

23253

from a piece of 24-gaugegalvanized steel.Next I beveled the large center hole in thebody with a half-round file, and counter­sunk the three mounting holes so that no.10-32 flathead machine screwswould dropin slightly below the body surface. Aftermounting the plate, I put a couple of coatsof spot putty (available in automotivestores) over the indentations, sanded andpainted the area, and proceeded with thetrade. - Gene Halvorson, WA9UA U

MOBILE HINT:A PENCIL WHEN YOU NEED ITEver hunted for a pencil while mobiling?Keep one on the top surface of thedashboard. A piece of magnet from anold speaker will stick to any convenientlocation on the dash. And an ordinarywooden pencil with about three wide­spaced turns of baling wire or equivalent(not copper) around the shaft willcling tothe magnet. For long trips a piece ofscratch paper can be placed beneath themagnet, which will hold the paper firmlyenough for quick operation notes. ­Harold A. Thomas, WSHJM

REMOTE CONTROL FOR AMOBILE TRANSCEIVERWhy clutter up the front seat of your carwith mobile gear? It can be installed easilyback in the trunk compartment, out of theway, and still be controlled from thedashboard. Running the speaker, volumecontrol, and mic leads up front is relative-

for regular practice sessions, originallysuggested in his Reflecties column in Elec­tron. He writes:

"Many commuters spend considerabletime each day in their cars. PA0WV hassuggested that this largely lost time couldbe put to good use by listening to tapedMorse as an exercisein copying cw. Somesuitable practice material is recorded on acassette recorder and replayed in the car.

HI have put this idea into practice andfind it most useful. The almost daily prac­tice soon results in good progress. Myown favorite material is the 4O-minutenews bulletin transmitted daily by PCHfor Dutch ships. If there is any question ofcopyright, as arises with the PCHmaterial, it is better to ask permission touse transmissions in this way. - RadioCommunication, March, 1976, RSGB

DUAL·FUNCfION COAXTo permit use of my mobile antenna whenrunning the mobile rig on the workbench,I installed a length of RG-8/U from thecellar to the garage with a wall-mountedSO-239 on each end. Also, I use a shortRG-8/U patch cable from the car antennato the SO-239 fitting in the garage. As anextra benefit, I find this coax handy forpiping 12-volts de from the bench powersupply to the car battery for an occasionalovernight charge. - Raymond DeMers,W2KVP

RETURNING A CAR USED FORMOBILE OPERATION TO ITSORIGINAL CONDmONRecently I was about to tradeautomobiles, when the car appraiserstated he would have to deduct $10 forfilling in the holes on the rear deck wheremy antenna was mounted and painting therefilled area. Having on hand part of acan of touch-up paint as well as a good­sized junk box, I went to work. First Iremoved the antenna and used the base asa pattern for a backup plate, which I cut

MOBILE LOG DEVICEI have found one,solution to the problemof keeping a log when operating mobile.The unit is a pilot's flight-plan log holderthat has a curved bottom that fits snuglyon the operator's leg. A leg strap is pro­vided to make sure the log stays putl Aclip at the top and bottom of the deviceholds the log sheets in place. The gadgetholds two pencils and even has a built-inpencil sharpener. A night light poweredby two small batteries is also included. Myunit was manufactured by Jeppesen &Co., and probably can be purchased ataircraft supply houses or the local airport.

Alan R. Haywood, K6AUE

100 Ch8pt8r 7

'"

ce1101$14

0'21012222

".~

lOOk

'. ,U3

,a

,..•

aae

'0'

.,""

. "lOOuF

'""'"

~

4101914

027eO~

COM.

"4100•

"'12.6VAC BRIDG£RECTI­

FIER

,.'--o---r "B

B

,"

TO 117\1 ACGENERATOR

[KCEPT AS INDICATED, DECIMALVALUES OF CAPACITANCE ARE1M MICllOfARADS (~F 1; OTHERS

ME IN PICOFAR...OS l pI' OR Jl,llFl;RESISTANCES ARE IN OHMS;

k ",000.101'1 000000

Circuit for protecting equipment from overvoltage.

OVERVOLTAGECUTOUTFOR FIELD DAY GENERATORS

When powering equipment from smallgasoline generators, the line-voltageregulation usually leaves something to bedesired. Since our club was not wellenough endowed to afford a magneticregulator, some other means of protectingthe equipment from overvoltage wasneeded. The circuit I developed is shownin the schematic diagram.

The 117-V ac output from the generatoris applied to a 12.6 V filamenttransformer. VI and U2 rectify andregulate one input to UJ, which is used asa comparator. DJ and Cl act as a peakline-voltage monitor. When the voltageapplied to the noninverting input of U3exceeds the 5 volts applied to the invertinginput, the output of U3 goes positive,turning on QI, which applies power to thecoil of KI, a small12-V de relay. The nor­mally closed contact of Kl opens, remov­ing power from the coil of K2, a 115-V acrelay. The contacts of K2 must be capableof passing the current demands of theequipment in use.VRl, a 5-volt Zenerdiode, is required because the output ofU3 is slightly above the negative supplyterminal (pin 4) when saturated. If aZener diode is not used, .Qt cannot beturned off. R1 provides the necessaryhysteresis to prevent the relays from chat­tering when the input line voltage is closeto the threshold.

To adjust the circuit, connect a variable

ac source to points A and B. With 125volts applied to the circuit, adjust R2 untilK2 drops out. When the applied acvoltage is reduced, K2 will again pull in.The pin numbers for U3 shown in thediagram are for the TO-5 package. D2shorts out the reverse-polarity voltagewhich results when power is removedfrom Kl. FI should be able to pass thenormal load imposed by the equipmentused. Power requirement of, the over­voltage protection circuit is insignificant.- P. Hansen. W8TWA

A "FIXED-LOCATION"POWER SUPPLY FORMOBILE EQUIPMENT

Mobile equipment permanently mountedin a car can usually be operated "fixedlocation" for extended periods of timeonly at the expense of either anoverheated engine or a run-down battery.And, of course, gallons of gasoline can beconsumed while the car motor is beingused to generate primary power for themobile supply. If operation takes placeduring a hot afternoon, you're also in forsome personal discomfort caused by theextra heat radiated from the motor. Igni­tion noise generated by your own car isstill another annoyance that results from"leave-your-motor-running" operation.

Most of these problems may beminimized or completely eliminated by us-

ing a field-type battery charger as sug­gested by W7FVI. Our version of this sup­ply is used to charge the car battery, butthe same unit may be used to keep life inany storage battery being used in the field.

The charger consists of a small gasolineengine, an old auto generator and avoltage regulator. These are mounted on aplywood base equipped with handles.Output from the generator is coupled tothe car battery through a long length ofheavy duty two-wire cable. Naturally, thelength of the cable will be determined byhow much you want to separate thecharger and the battery. If you want lotsof separation so that racket from thecharger can be kept in the background asmuch as possible, just remember that thecable may have to carry 30 amperes ormore if the generator-battery system isdesigned for 6 volts. Figure on a wire sizethat will handle 15 or 20 amperes if thecharger is a 12-volt affair. - Jack Miller,W9WTY

VHF MOBILE

Recently we mentioned an Americanreview of professional vhf mobile radiodevelopments during the past few years(TT, October). This month it is possible tocome a little nearer home and draw atten­tion to a very detailed survey "Mobile vhfand uhf radio systems in the UK," by D.A. S. Drybrough, G8HEV, lEE Reviews.

Portabla and Moblla Qulcklaa 101

Tlble 1Propag.tlon Losse. From Llrge Obstructions

HIIV-d)ADDITIONAL"L~~~ 12 ~ ~ ~ ~ 1m

80 MHz 3x5 5x5 7x5 10 12x5 17125 MHz 4 6x5 9 11 x5 14 19170 MHz 4x'5 7x5 10 13 16 20x5460 MHz 6x5 11 x f 14 16x5 20 24x5H is height above line-of-sight path (in meters); d is distance to obstruction from nearest terminal(km).

sine wave. The subaudible tone should beintroduced' into the transmitter just afterthe deviation control. Since most audio iscut off in the low-frequency ranges, it isnecessary to inject the tone after anyaudio processing. Two output filters areshown. It will be necessary to select thefilter that performs best with a particularrig. For other subaudible tones, usecrystals that are 16,384 times the desiredfrequency. - Edward Gellender,WB2EA V and Manny Marcel, WB2BON

R.

R. .0'~VV'v--lf--o·~k:.5rX

'"22>

USING A CENTER-LOADEDLOW-BAND WHIP ON 50 MHZ.When I had my 3.9-MHz loading coil inmy Master Mount mobile antenna, I ac­cidentally turned my multiband, j-watt rigto SO MHz. On hearing a station, I gavehim a call, and much to my surprise, hecame back and gave me a fair report.Since then I have had several dozenSO-MHz contacts using this combination,some of them with stations that were morethan 30 miles distant.

After my initial vhf QSO with the low­band antenna, I tried each of the availablecoils in making a test with one station. Wediscovered that the 7-MHz coil gave asmall but noticeable improvementwhereas the 14-MHz coil or a jumperacross a loading coil gave a seriousdecrease in signal strength.

Somewhat later I put an SWR bridge atthe input of the 50-ohm coaxial cablewhich feeds the antenna, Themeasurements were consistent with theseobservations: The SWR was the least (2:I)with the 7-MHz coil and only slightlyhigher with the 3.9-MHz coil. Perhaps theSWR could be lowered by trimming a coilexactly. but the' inconvenience seemshardly worthwhile since losses in a shortline are insignificant when the SWR isdown to 2:1.

While at 50 MHz the electrical length ofthe whip is less than a half wavelength, itcan be surmised that the presence of the7-MHz coil accidentally loads it to make it

-1'rJ7 l' l'

.0'r-'V\f\r~-"v'V\""1r'v.'v-"""-'VV\""">-'VV'v--I(-o~~:i.

1000

rl:OOPF ALTERNATE

lN4001

~ +,,~v~

10P:J:

+12V O--*.....,~...,OR 9V

BATTERY

in circular polarization (or perhaps diver­sity techniques). - Radio Communica­tion, December, /975, RSGB

MOBILE NOISE SUPPRESSIONCoaxial capacitors for ignition spark coilprimary filtering must be installed withthe shortest leads possible. I found thatthe capacitors with threaded terminalshave the same thread as the screws pro­jecting from the spark coil. The capacitorsmay be threaded directly onto the coil ter­mina�s resulting in no leads at all! Ofcourse, the capacitor's metal case mustbegrounded to the coil case. This can bedone with copper straps soldered to thecapacitor and coil cases. - James W.Stuckey, W5ZJO

SUB·AUDIBLE TONE GENERATORThe following circuit is an unusualmethod for generating a subaudible tone,commonly, known as P IL, Channel­Guard, CTCSS, etc. The circuit is unusualin that a 2235-kHz crystal is used with acounter chip to produce a 136.5 Hz (EIAno. 4) tone. The signal from the oscillatorgoes through 14 divide-by-two flip-flopsto produce the low-frequency square­wave output on pin 3 of the Ie. Thesquare wave is then put through severalstages of low-pass filtering to develop a

Method for generating a continuous, subaudibJe tone.

Vol. 122, no. lOR, October, 1975 (aspecial issue of Proc. lEE). It traces thedevelopment, current practice and possi­ble future trends over the whole field ofprivate and public-service!mobile opera­tion. For example, a detailed table lists allthe frequencies used, including channelwidths and the paired channels for varioustypes of services, typical ranges with fmand a-m systems (showing significant ad­vantages to fm despite its vulnerability toflutter losses). For the future still nar­rower bands are forecast (aided by phase­locking techniques) together with a con­tinued search for improving reception inthe presence of interference and fading.

Among all the data is an interestingtable of the signal losses that can be ex~

pected from large obstructions in thepropagation path, showing how thesevary at different frequencies.

In VHF Communications, Vol. 7! no.3, 1975, T. Bittan, DJ0BQ/G3JVQ, re­ports some of his findings on aerialsused for mobile telecommunications. Hemay set a few dovecots fluttering withsome interesting conclusions on the ad­vantages of horizontal polarization, andintends to follow this up with designs infuture issues for circularly polarized om­nidirectional mobile aerials. Conventionalvertically polarized mobile aerials, he sug­gests, can result in signal fluctuations ofmore than 70 dB due to multipathpropagation effects while a vehicle is inmotion. At high speeds he also found thatthe 1I4-wavelength whip gives significant­ly better performance than theSIS-wavelength whip, mainly due to anadditional bending caused by the extralength. He believes that for mobile ap­plications, the field strength of a horizon­tally polarized signal is usually far moreconstant than with a vertically polarizedone, due to less attenuation of the directwave (vertically polarized 'signals are par­ticularly subject to attenuation by trees),and because fewer multiple reflections arepresent. Further, radiation characteristicsdo not vary as much as with verticalwhips, so long as the horizontally polariz­ed aerials are at least 112 wavelengthabove the car roof. If- it were not forrepeaters, apparently, he would haveeveryone using halos; but as things' are,the best of both worlds seems to be found

102 Chapter 7

------------

TO AUTOSYSTEM

CAR 8ATTERY

, III).,D'

TO MOBILEEQUIPMENT

_ EXTRArJ, BATTERY

IGNITION NOISE ANDSUPER·NOISY VEHICLES

For a long time it has been recognized thatignition interference from some vehicles isvery much more vicious than from others,though little attempt has been made in thepast to measure the differences, and thereremains a considerable amount of work tobe done in determining just why these dif­ferences arise. Some idea of the cornplexi­ty of the individual noise characteristics ofdifferent vehicles is indicated in a paper byR. A. Shepherd of Stanford Research In­stitute, entitled "Measurement ofAmplitude Probability Distributions andPower of Automobile Ignition Noise atHf", IEEE Trans. on VehicularTechnology, Vol. VT23, no. 3, August,1974. The paper is based on a largenumber of measurements made alongsidea busy freeway (motorway) and showsthat most of the ignition noise between 24and 30 MHz is contributed by a smallnumber of vehicles radiating strong in­terference. It was found that there is agreat difference in the noise characteristicsof individual cars, particularly differentmodels.

It was found that an engine is a complexnoise source and does not radiate a pulseof the same amplitude for each successivefiring of the spark plugs; the pulses canvary by up to 30 dB in amplitude, andeven successive pulses from the samecylinder vary appreciably. On somevehicles there are two rf pulses associatedwith each spark-plug firing. the secondfollowing the first after an interval ofabout I ms, it being usually about 10 dBlower. It is still not clear whether this dou-

Diodes are used to isolate the extra batteryand mobile equipment from the automobile'selectrical system, although both batteries arecharged by the car generator.D1, 02 - 70-amp, 50 PIV silicon diodes.

the voltage regulator or to the other bat­tery. The forward voltage drop across thediodes is somewhere around 0.7 volt, so itmay be necessary to advance the voltageregulator for an additional 1 volt. Mostdiodes will operate at temperatures up toISO· C, so they can be mounted right upin the engine compartment. Of course,they must be isolated from ground andmounted on an insulated heat sink. I useda 1/4 x 4 x 4-inch aluminum sink foreach diode. - Robert V. Grater,K6SUB/4

SPEECHAMP

The circuit as shown is a matchingdevice which will allow a high-impedancemicrophone to be used with the originalspeech circuit in the transmitter withoutany changes in the equipment. It uses twotransistors and doesn't need a power sup­ply. The operating voltage is obtainedfrom the voltage developed at the cathodeof the speech-amplifier tubes. It probablycould be built small enough to be installedin the microphone case or under its base.By throwing switch SI the microphonefeeds straight through so that it can beused with equipment designed for high­impedance input.

Transistor Q1 is used in a common­collector circuit to step down the im­pedance of the microphone to match theemitter-follower transistor Q2, whichfeeds the signal into the low-impedancejack of the speech amplifier. The outputvoltage from the unit is comparable tothat of a carbon microphone but is freefrom the characteristic hiss sound andnasal quality. - E. S. Millman, W3WNE

IIII,,,,

~

DIODE-SWITCHINGMOBILE BATIERIES

This battery system is useful in mobilework when it is desired to keep the car'selectrical system isolated from the mobileequipment. In this plan, an extra batteryis installed to power the mobile equip­ment. Although the car's charging systemkeeps the accessory battery up to par, themobile equipment draws only from thespare battery, leaving the car battery toperform its regular duties. All of this isdone without any mechanical switching.The system shown in the drawing requirestwo silicon diodes, Dl, D2, and the extra6- or lz-volt battery. The two diodes areconnected so that the car generator willsupply both batteries with charging CUr­rent (through the voltage regulator), butneither battery can feed current back to

100.

IOO~

appear to have a length of about 3/4wavelength. If one is willing to accept avertically polarized mobile antenna whenmost stations are horizontally polarized,he is unlikely to find one that is more ef­fective than this one. - Yardley Beers,WeEXS

CAR·BATIERY REMINDERS

Always keep battery terminals clean andtight since corrosion reduces the chargingcurrent supplied to the battery by thecharging system.

Periodically check system voltage with avoltmeter to make sure the generator isdeveloping sufficient voltage. Look forexcessive voltage drops caused by loose-orhigh-resistance cables.

Check specific gravity with a hydrom­eter once a month and recharge the bat­tery if necessary. Add distilled water tothe battery as required.

Check regulator setting after regulatorhas come up to operating temperature.Too high a setting of the voltage regulatoris damaging to the radio, light bulbs, andignition contacts. Too low a setting willallow the battery to become discharged.- R. Griffin, WIVON

Microphone impedance steo-oown adapter. Jack J1 is the microphone jack on the transmitterspeech amplifier. All resistors are 1/2 watt.Pl - Plug to mate with J1. 51 _ Dpdt switch.01,02 - 2Nl07 transistors.

mGH·Z TO LOW·ZMICROPHONE ADAPTER

Many commercial and home-built mobiletransmitters are designed for low­impedance. carbon-microphone input.The input speech circuit is usually agrounded-grid arrangement as shown tothe right in the diagram. However, it issometimes desirable to use a high­impedance microphone with the equip­ment, since a crystal or dynamicmicrophone has better fidelity andfreedom from the hiss and "blasting"sound familiar to the carbon type.

Portable end MobIle Quleklea 103

Avoid repeater time-out with this circuit.

ELIMINATION OF STATICIN FAN·DRIVE BELTSReceiver static is sometimes a problem forme when my forced-air furnace operates.I traced the trouble to the fan belt. I hadheard that a belt dressing was availablethat would cure static, but I wanted toeliminate the noise as quickly as possible.Using a rag saturated with alcohol, [cleaned the belt thoroughly and the staticcompletely disappeared. .- James S.Collier. W2QBB

close the switch contact. Mercury switchescould be substituted on the hood andtrunk lids if desired.

When 81 is closed, anyone of the door,trunk or hood switches can trigger therelay, Kl. One set of the relay contactsgrounds the horn relay, causing the carhorn to sound. At the same time, theother set of relay contacts providesanother path to ground for the relay coilwhich keeps the alarm system going in theevent the car door, etc., is closed. Thesystem can only be made inoperative byopening switch 81 with the key. - G. M.Miller. K5REVand Tom E. White, Jr.,K5AUN

MOBILE SAFETY

Ian Mant, GSAVJ has drawn attention tothe danger of beryllia (beryllium oxide)contained in some silicon planar tran­sistors. At "Communications 76," M.Arrowsmith added to this warning bywriting: "Beryllia has a unique combina­tion in that it is a good insulator but also afirst-class conductor of heat. It is a hard,clean material which is normally perfectlysafe to handle. However, beryllia dust ishighly toxic and can prove fatal. Dust orchippings can be formed by accident oreven deliberately by someone not aware ofthe danger. So where is one to find ber­ryllia? How can it be recognized? An ex­perienced engineer is likely to know thatberyllia can be found in rf power tran­sistors. On the other hand, exposedberyllia in the form of, say, washers is in­distinguishable from ceramic. It istherefore important that all items contain­ing this material be clearly identified in anequipment manual. ,.

This seems a clear indication thatberyllia may be found not only in sometransistors but also, for example, in theform of washers used in the mounting ofpower transistors on a chassis or to heatsinks. It is well worth remembering thiswarning when dismantling or modifyingsolid-state equipment stemming from theprofessional market.

A check-list of safety factors for mobileradio designers also appears in this paper,as follows:

I) Fixings on dashboard-mountedequprnent should not be likely to breakaway under impact.

S:9NACm

~390AND/OR ANO/OR II

LEO

'D·2 ,

3 •4 ,

NE555TOP VIEW

TO HoT S,CA~I~~!~~R~

,p.J""

Alarm system for protection against theft ofmobile equipment.K1 - 6· or tz-vott relay dpst.51 - Key switch, spst.52·S6 ,.... Normally open button switches.

MOBILE BURGLAR ALARM

This circuit is an inexpensive, simple, yeteffective alarm for protection againsttheft of mobile equipment. When switch51 is closed to the "ready" position, thealarm is armed and opening any of the cardoors, hood or trunk will actuate the carhorn, which will give an audible alert. Thehorn will continue to blow, even if thedoor, trunk or hood is closed.

Switch SI is a "key" switch that can belocated at any convenient spot on the out­side of the car. Switches 82-86 - andthere can be as many of these switches asneeded - are the normally open buttontype used as auto courtesy light switches.These can probably be obtained from alocal car junk yard or purchased newfrom an automobile distributor. Theswitches are installed on each of the cardoors and on the hood and trunk lids insuch a way that opening any of these will

®. DELAY TO 3 MINUTES

®.2 Hl APPROX. FLASH RATE

~"1PTT SWITCHON MIC

10'

'"

TlME-OUT WARNING+;2V TO e.ev DC

PROTECTING MOBILE RELAYSOld voltage regulator boxes make ex­cellent relay enclosures for mobile ap­plications. The boxes are weather-tight,easy to mount, and usually have a hole ortwo in the bottom for bringing leads in orout of the box. Discarded voltageregulators can probably be obtained atlocal garages. - Rathbun B. Griffin.WI VON

ble pulse results from the abrupt cessationof current flow across the spark-plug gapor from the closure of the breaker points.

Generally, the more cylinders there arein a vehicle, the more ignition noise is pro­duced; again, the average noise power in­creases monotonically with engine speed.

During the investigations a vehicle wasdeliberately made as noisy as possible (forinstance by using copper ignition wire),yet it was found not to be the noisiestvehicle on the road. The super-noisy carshave average powers of 40 dB or moreabove "quiet" cars, and some parallel in­vestigations in Spain showed noisyvehicles exceeding the median vehicle by35 dB. - Radio Communication, March,1975. RSGB

TIME·OUT WARNINGIf you are one of those hams accused ofbeing a clod (or worse) because youalways time-out the repeater, this devicewill help make you one of the good guys- not a bad guy. It can be made from afew parts that provides either a visual oraudible warning and can be preset to anydesired time interval. Referring to the cir­cuit diagram, when pin, I of the firstNE555 is grounded, the timer starts timingto a preset limit. If the preset limit isreached, pin 3 provides a ground outputto the second NE555 which pulses at a2-Hz rate.

A kit is available from Sharp Co.,23715 Mercantile Road, Commerce Park,Cleveland, OH 44122. - Fred Sharp.W8ASF

104 Chapter 7

2) No sharp edges.3) Recessed controls behind an impact­

absorbing panel.4) Fire-resistant grades of glass-fiber

boards for printed circuits.5) No exposed beryllia.6) No components operated beyond

their ratings.7) Adequate installation instructions

with special advice to users with electronicfuel-injection systems or anti-skid devices.

In respect of item 7, M. Arrowsmithnotes that there have been instances whererf from a mobile transmitter has resultedin the malfunctioning of electronic fuel­injection and anti-skid braking systems ontrucks plus other less serious occurrences.In such cases, he points out. it is difficultto categorize either the transmitter or theelectronic systems as intrinsically unsafe.though together they may form a poten­tially lethal combination. - Radio Com­munication, July, 1976, RSGB

NICHROME IGNITION WIREREDUCES INTERFERENCE

Some automotive-parts distributors carrya resistance type of ignition wire whichuses nichrome instead of carbon as theresistive conductor element. This wire ap­pears to be more resistant to aging andmore effective in reducing ignition-noiseinterference. - Murray Lampert.VE3FXA

HOMEMADE MAP HOLDERFOR PORTABLE AND MOBILE USE

A useful aid to mobile and portableoperation, especially handy during public­service events, is a magnetic map holder.A piece of galvanized steel sheet may becemented to a sheet of masonite andpainted, if desired. Small fasteners withattached magnets, similar to those used onclipboards, will hold the map, as well asany message blanks and slips of notepaper. - Spencer L. McCarty, W2GTI

KEEPING COOL ON FIELD DAYKeeping coolon Field Day while pound­ing brass or keeping up a steady pacebefore the microphone can betroublesome: This is important when thetemperature is high and the sun shinesrelentlessly on the operating position.Placing one's feet or hands in a bucket ofcold water can be very refreshing. Thismethod serves as a heat sink for thehuman body. - James W. Milburn,WB5BYK

A S/B·WAVELENGTH ANTENNAFOR BASE, PORTABLEAND MOBILE USEI have made versions of this antenna formy car, for permanent installation athome, and another mounted on a camera

The SIS·wavelength antenna mounted on acamera tripod.

tripod for use when operating from a por­table location. As shown in the photos,the base is a convenient length of al·l/4-inch (32-mm) diameter aluminumtubing, with PVC pipe fittings press fittedino the pipe and acting as insulators. Thematching coil is 1-1/4 turns of 5/16·inch(8 mm) copper tubing, 5 inches (127 mrn)in diameter. The ratiating element is atelescoping automobile whip, whoselength is adjusted to approximately 39inches (0.99 m); and a sliding tap on thecoil is used to obtain a minimum SWR.Adjustment is fairly critical, but once the

Matching coil for the 5lB-wavelength antenna.

proper length of the whip and correctposition of the tap are found, they may bemarked by scratching the appropriatemetal surface. - Ralph Netzley, W9WZO

MOBILE OPERATING AID

Having the mobile rig microphone handywhile driving has become a bit of aproblem because many present-day carshave vinyl-covered dashboards. Bolted ormagnetic hangers are no longer reliable ordesirable. A happy solution comes fromthe boating 'scene.

Velcro Corporation, Marine ProductsDepartment, manufactures a fasteningsystem that becomes very useful forholding everything from microphones andpencils to entire radios. This system suitsthe inventive nature of radio hams welland it is expected that uses will be foundfor portable antennas and beams, travelcases, routing wires, holding Iogbooksandtelegraph keys, and so forth.

The Velcro fasteners are made ofthousands of tiny hooks on one piece ofbacked material and tiny matching loopson the second piece. The hooks interlockwith the loops when pressed together andrelease rapidly when peeled apart. Thisnon-metallic device can be cut to shapewith scissors and sewn, stapled orcemented in place. It doesn't jam, rust orcorrode, and will hold even when wet. It ispractically foolproof.

I have applied one piece (the loops aresofter) to the microphone of my DrakeTR-22 with the other piece attached to myautomobile dashboard. Actually. thehooks were placed in both of two cars sothe rig can be used with the same conven­ience in either car. I also applied thehook part to the TR-22 carrying case sothe mic would not dangle to the ground orget squeezed accidentally in a pocket.

A visit to most marine stores shouldturn up a large, floor-mounted displaywhere a variety of sizes are available. Forthose who are not close to a marina, theproduct is manufactured by Velcro Corp.,Marine Products Dept., 681 Fifth Ave.,New York, NY 10022. My wife reportsthat the sewable variety of Velcro can befound in department-store notioncounters. - Dwight B. Hill, K2KWk

USING AN AUTOMOBILEBC ANTENNA FORTWO·METER OPERATION

When an additional transmitting antennais prohibited or undesirable on anautomobile, this simple circuit will permita 2-meter mobile stationto transmit andreceive through the be antenna. Both theamateur equipment and the broadcastreceiver may be used' simultaneously .withno adverse effect on either.

Impedance between the be antenna andthe 2-meter unit is matched by means of

Portable and Mobil. Quickie. 105

CAR FLOOR

ALIGN FOR LOCK

2-1/2" ~ 114"EYEBOLTS

MOBILE

EQU~

Sl8.wavelength whip. Two coat hangers,a piece of wood and some tape were allthat was needed to boost the IO-wattsignal enough for .'solid copy" at thereceiving end. The diagram shows theconstruction features of the reflectorwhich could easily be made into a direc­tor. Maximum gain was obtained with aspacing of IS to 20 inches (380.508 mm)between the radiating element and thereflector. - W. H. Collins, W6RWH

+---0",

02

"'o--"...-lIY'n----<i>---oJ2

A matching network for using an automobilebe antenna with z-meter equipment.J1 - RCA phone connector or equivalent.J2·J3 - Motorola automobile antenna

connector.C1 - 30 pF, ceramic or air variable.L1 - Two turns of No. 14 wire, 112-inch dia­

meter. May be required for matching.L2 - Amidon toroid T50 wound with No. 18

wire.01,02 - Silicon diode, 1N94 or equivalent.

Ll and Cl. The be receiver front end isprotected from transmitted signals byRFC L2 and diodes 01 and 02.

No deterioration of the be signal isnoticed when the 2-meter set (in my casean Icom IC-22A) is connected to theantenna system. No interference or desen­sitization of the be receiver is noticedwhen transmitting in the high-power posi­tion.

The network was built in a Miniboxwith Jl at one end and J2 at the other.Maximum separation of Ll and L2 wasprovided. CI and L1 are to be adjustedfor minimum SWR with all connectionsmade and the cover placed on theMinibox. No attempts to measure theSWR should be made without the cover inplace or with the be set disconnected. ­Virgil S. Hinson, W5URP

COAT HANGER USEDTO BOOST SIGNAL

In order to activate a distant z-meterrepeater while operating from a campsite,I hastily fabricated a reflector for my

DIRECTOR 3B"-~->l1

OR REFLECTOR 42"

LONQt-""I.---TAPE

WOOD POST

, I

A director/reflector for a two-meter verticalantenna may be quickly made from two coathangers.

MOBILE BURGLAR ALARM

To protect my mobile equipment fromtheft, I mounted a normally closed, push­button switch behind the equipment.When the equipment is installed theswitch is open and is connected in parallelwith the car horn button, so that if theequipment is removed the spring returnpush-button will complete the horn circuitand discourage the thief from any furthertampering! - Lynn Kuluva, K6IMI

" ~ ~"<, ..... ....... "-

J ~ ]-, $?vE CO~CTOR $to

<I:3 0XTAL KEY

A child's lunch box used as a transmittercabinet.

EQUIPMENT CABINET

The next time you need a small cabinet fora portable or mobile rig, try a child'slunch box. To protect the componentsthat protrude from the front of the con­tainer, handles can be installed as shown.In order to service the unit, it is onlynecessary to unsnap the fasteners on topof the box. - Mike Bailey, WB4DCW

FISHING FOR A PLACE TOSTORE YOUR MOBILE ANTENNA?Here is an idea for those hams who wishthey had a place to store their mobileantennas when parked in a lot, or someother area that is not safe for any type ofradio equipment (theft). If the antenna inuse cannot be stored in the trunk of thecar because of the size of the antenna,simply install fishing-pole racks on the in­side of the car just above the level of thedoor tops, when not in use, the antennacan be dismounted and installed in theracks, out of sight. - Henry G. Eve/and,WB2SXDI2

A means of padlocking mobile equipment.

THEFf·PROOFINGMOBILE EQUIPMENT

The sketch I provided shows how I theft­proofed my Cheyenne and Comanchemobile equipment. Two 2-1/2 X 1/4-incheyebolts are used - one attached to thefloor of the car, the other to the bottom ofthe equipment. Any kind of equipmentsupport may be used. The eyebolts arealigned so that when the equipment is in­stalled, a padlock or combination lockcan be inserted through the eyebolts andlocked. - Francis Neubauer, K30KF

DESK-N-PORT:THE MOBILER'S DESKOne disadvantage of working mobile isnot having as much space in a car as isoften needed. I wanted to be able to keepmy log, equipment manuals and otherpapers in a compact unit which wouldprovide a small writing desk as well. I useda thick three-ring, loose-leaf binder, andpunched all documents I wanted to carryto fit. Important papers such as a bandallocation chart and OXCC CountriesList, were plastic-laminated beforepunching. A large spring clip keeps the logfirmly attached to the notebook cover. Tocarry pencils and QSL cards, a plastic,zippered pouch was found to be useful. ­Henry G. Campbell, Jr., WA4DLN

CAR-RADIO DUMMY ANTENNA

When bench-testing a car radio, a suitabledummy antenna to simulate the fender orcowl-mounted antenna can be constructedfrom a couple of 39-pF mica capacitorsand a small aluminum box. The circuit forthe dummy antenna as shown is placed inseries with the signal generator and thereceiver. Motorola-type connectors are

Jl r--------, J2

'NPu4+-f~ t1t'"~ 39 I

L __I-__ J

Dummy antenna to simulate a car antenna.J1, J2 - Automobile antenna connectors

(Motorola 1741),

108 Chapter 7

mounted on the aluminum box. A varia­tion on the circuit uses adjustable trimmercapacitors which can be adjusted after theunit is assembled, in which case small ac­cess holes must be placed over the trimmeradjustment screws. - Sol Davis,W3WPN

PREPARING YOUR CARFOR WINTERAmateurs who have mobile equipmentshould prepare their cars for coldweather. Check the generator for properoperation. Remove the battery cablesfrom the battery terminals. Clean' thecables and terminals whileusing a solutionof baking soda and warm water. Avoidgetting the solution in the cells. Rinse thebattery carefully with clear water aftercleaning. The terminals and connectorsshould be shined with sandpaper. If thecells appear to be low on electrolyte bringthem to the proper level with distilledwater. After reconnecting the battery, ap­ply Vaseline or axle grease to the connec­tors and terminals to slow down corro­sion.

Next check the antenna system forpossible faults. A thin coating ofLubriplate or Vaseline on the threads willmake removal easy and will preventmoisture from affecting the contact be­tween the antenna segments. The coatingdoes not interfere with conductivity.

When cooler weather arrives, a changein crystal frequency can be expected.When the transmitter is inside the car,allowing the heating system to bring thepassenger area to normal roomtemperature will in turn keep the crystalsoperating close to the desired frequency.For crystal-controlled transmitters kept in

a trunk it is possible to use a set of crystalswhich under normally cold conditions willfunction on the desired frequencies. ­Bruce McCreath, VE3EAR, from theBluewater Radio Club Bulletin

NYLON CORD

An arrangement for preventing antenna sway.

PREVENTING MOBILE·ANTENNASWAY

It wasn't very long after going mobile thatI had to solve the problem of antennadetuning because of antenna sway while inmotion. As many before me have done, apiece of nylon cord tied to the luggagerack eliminated the backward leaning ofmy Webster Bandspanner. But sidewaysmotion caused operating problems.

The IS-cent golf club separator, widelyacclaimed for its coil-form shape in theDelta Loop antenna, was again pressed in­to service. It is easily fashioned into astandoff insulator. The ends are notched

to fit both the antenna and luggage rack,and it is held in place by wide, flexibletape. If the tape breaks and the standoff islost, it can be replaced cheaply and easily.- Baxter Williams, W5KYB

WINTERIZING VHF MOBILEANTENNASWinter is once again around the corner,and for those who travel by car, thatmeans driving through snow, sleet andsanded and chemically treated streets andhighways. Many hams now have vhf-fmtransceivers in their cars, and of coursethe antennas to go with them. This hintshould help save you from possible ag­gravation later on.

Start by removing the mount from thecar; completely disassemble the mount.Remove the coax and rinse the mountwith hot water for about 10 minutes.After drying the mount thoroughly (useforced hot air such as that from a "hotcomb"), check the antenna with an ohm­meter; infinity should be indicatedwithout the coax connected. Reconnectthe coax to the base of the antenna. Themost common cause of antenna problemsin the winter is salt deposits forming insidethe base of the antenna; therefore, someform of sealer should be used to preventmoisture and other foreign material fromgetting into the base of the antenna. Ichose silicon sealer for use in my antenna.

For cleaning the antenna connectors orremoving corrosion from the outside ofthe mount, a common household cleanerof the powder variety can be used. Atoothbrush makes a good applicator andthat, coupled with some elbow grease, willclean up the connector in quick time. ­Bill Horger, WB8SFZ

Portable end Mobile Quickie. 107

Chapter 8

VH F Band-aidsand Tricks

A simple modification of the Heath GR-110VHF Scanning Monitor to make channel selec­tion easier.

HEATH GR-ll0 SWITCmNGSIMPLIFIEDAfter] completed the construction of theHeath GR-110 VHF Scanning Monitor, Ifound the action of the channel selectorswitch inconvenient. To manually selectchannels the operator must place theMANUAL!AUTO switch in the manualposition and then push the SELECTswitch. If a channel is active, the selectswitch is inoperative until the station stopstransmitting or until the channel is lockedout. Needless to say this is a lot of buttonpushing just to advance to another chan­nel.

The procedure was simplified by con­necting a jumper between pins 2 and 3 ofS3, the select switch. Also pin I of S3 wasconnected to pin 14 of IC101. As a resultthe receiver will break the lock with anychannel regardless of the position of themanual auto mode switch and whether ornot a station is transmitting on a channel.I find this improvement worthwhile on

PREAMPLIFIER BURNOUTSoon after arriving in WI-land I startedexperiencing random burnout in mypreamplifiers, each constructed with tran­sistors and JFETs. Initially, I blamed it onelectrical storms. The problem, however,increased dramatically in the winter, atime when electrical storms are usually ata minimum. By then I was even losing mysecond-stage preamps and multipliers inmy LO chain, occasionally.

How could this be? All normal methodsfor burnout protection failed to improvethe problem, including diode protectionand input filters. The plot thickened whenI left one of the preamps terminated in aSO-ohm load. It still blew out! .

Next, a high-impedance battery­operated, digital voltmeter was borrowedand connected to the B + on thepreamplifiers. Everything seemed fine un­till keyed my kW transmitter on 80-metercw (where I spend most operating time inthe winter). When I used my east/west­dipole, the de voltage in the preamplifierwent wild. By using the west sloper thetrouble disappeared.

Suffice to say, the problem was two­fold. There was rf pickup in the power­supply lines to the preamps and rectiflca-

A protection circuit for prevention of pre­amplifier burnouts.C1 - 0.1 JlF Mylar or ceramic disk capacitor.D1 - 1N914 or equiv.FT1 - 0.OO1-JlF feedthrough capacitor.

amateur frequencies where the receivermay lock on one channel for some time.When I become curious about the activityon other frequencies, I simply push theselect button once to advance the channelin the manual mode or start the scanner inautomatic. - Richard Drew, K9PJB

PROVIDING A TUNABLEVHF-FM RECEIVERHere is a trick for providing a tunable vhf­fm receiver. The main station receiverhere for the low bands is a HallicraftersSX-IOIA along with crystal-controlledconverters for 6-, 2~ and 1-1/4-metercoverage. This receiver has a double­conversion, i-f strip using a 1650 kHz firsti-f.

Also at hand is a Hammarlund FM-SOAvhf-fm transceiver, that has a l6S0-kHzsecond i-f. To use the SX-IOIA as atunable front end for the FM-SOA fm i-fstrip, make these simple changes. First,remove V5, the SX-IOIA second mixertube (6BA6), insert the center conductorof a short piece of coaxial cable (low­capacitance type works best) into pin 1(grid) of the now-empty 6BA6 socketbase.

Connect the other end of the cable tothe grid circuit of the Hammarlund first16S0-kHz i-f amplifier, pin 1of the 6BH6.Removing the receive crystal or mixer tubewill disable the front end of the Ham­marlund transceiver.

This lash-up permits me to listen to29.6-MHz fm and tune in 6-, 2- and1-1/4-meter fm with the convertersv Sen­sitivity is adequate for casual listening.With a little experimentation, comparablehybrid arrangements for other sets may befeasible. - John F. Sehring, WB2EQG

ca

"

AUTO.

M....NU....L/....UTOSWITCH

SELECT SWITCH

e,,.

YEL.

9:",, ' ..--" GRN.

108 Chapter 8

tion in the "idiot" diode. 1 Eliminating theidiot diode or shortening the power­supply leads was unsatisfactory.However, placing a O.l-J.lF Mylar or diskceramic capacitor ahead of the idiotdiode, as shown in the illustration,prevents rf from reaching the diode.

While this cure may not solve all burn­out problems of a similar nature, it shouldgive longer life to those expensivesemiconductors where hf operation isprevalent. - Joe Reisert, WIJR

'Reisert, "Ultra Low-Noise UHF Preamplifier," HamRadio, March, 1975.

MORE AUDIO POWERFOR MOBILE FM TRANSMI1TERSAn article in a back issue of QSTmention­ed that a lack of sufficient audio poweraffected many mobile fm transmitters. Togive my set more talk power I added anaudio amplifier constructed in modifiedform from the' circuit shown on p. 17 ofQST for July, 1976. The diagram 1 haveincluded here shows the changes. In theprocess of making the addition to mytransmitter I also built a squelch systemsimilar to the Johnson Fleetcom systemand tied it to my VHF Engineering typereceiver.

Because 2N2222 transistors are readilyavailable I used them for the amplifier,but .substituted a matched pair Of RadioShack audio output transistors. for thoseshown in the QST circuit. They workedwell without making any circuit changes.Now my transmitter can really stand upand talk! - Walter Boller, W0EAHI9

ABOUT THE FM AND REPEATERCHARGER

I have built a NiCad charger from theschematic shown on page 89 of PM andRepeaters for the Radio Amateur. I use itto charge all my nickel-cadmium batteries,but there is one problem. The schematicdiagram shows that the output 'is notisolated from the 117-V ac line. Whencharging hand-held equipment with an ex­ternal antenna connected, the chargermay be grounded through the antennasystem, quickly destroying the lOO-ohmresistor along with the diodes. Someamateurs may not be aware of this condi­tion.

A useful modification I have incor­porated in my charger is the installation ofa 117-Vneon bulb across the output as aload indicator. The bulb will glow whenthe charger is on and no load is connectedacross the output. When charging hand­held devices, the indicator light will go outshowing that a good connection has beenmade at the terminals. - Joe Felardo,WB6EGW

HEP 53001 - ANINEXPENSIVE REPLACEMENT

An economical replacement solid-statedevice for use in the output stage of theWilson 14025M and the Drake TR-22 isthe HEP S300lmanufactured byMotorola. This silicon npn.rf power tran­sistor is rated at 5-W output and maxi­mum voltage is set at 6S for 1 A of cur­rent. Many electronics parts stores carrythe 53001, which sells for considerably

less than the price of the equivalent tran­sistors provided by Wilson and Drake. Ihave found that the 53001s perform justas well as the original equipment. - DaveKarpiej, KITHP

REPEATER WALL MOUNTINGThe arrangement shown in thephotograph has been handy for servicingor removing the equipment for myrepeater, WR0AGP.

The transmitter and receiver aremounted in the same fashion by means ofGE "Strip for Walt Mounting. It I usedfour barrel bolts. one at each corner of theframe. Each unit may be swung to theright or left by lifting t"" of the bolts, andmay be removed just as easily from thewall. - Paul Grauer, W0FlR

Four barrel bolts were used to mount thisrepeater equipment. The bolts allow the unit tobe swung in either of two directions for easyservicing without dismounting.

tt2Vo-....---....-------..----,

2200

LIN,POT.

'O.

0.01

+rr,50.u F

10.2N2222 ...- ....--1

2200

0.'

8200

2N2222....-H--.....--+--+-r-oo«

t12. V

1N67A

TO

,~~, o.ot

,01-+-~.-,0-.....-i X' XO~O~O-rL...-o.-o,.....-,o-.....-H

+'2V 1-

AUDIOAMPLIFIER

2.200

'00EXCEPT AS INDICATED, DECIMAL VAWES OF

CAPACITANCE ARE IN MiCROFARADS \ jlF 1 ;OTHERS ARE IN PICOFARADS I pF OR JOJOF}~

RESISTANCES ARE IN OHMS;k.IOOO. 101=1000 000.

1N67A

8200 IN67A

T 6 .856\( rf-J

6,S.uF

.}-+-_----4-...--'V\~..,.hr_'_+ f-------------------l

2N2222

An audio amplifier for Improving the operation of mobile trn transmitters,

VHF Band-aids and Trtcks 109

SlholPLEX

RPT

RECEIVING NOAA WEATHERREPORTS ON 2·METER FM RIGS

Most 2-meter fm transceivers are suffi­ciently broadbanded to allow reception ofNOAA weather reports on either 162.40.162.475 or 162.55 MHz by installing theproper receiver oscillator crystal. If theoperator travels, it might be useful to havecrystals for each frequency installed in therig, allowing one to receive- currentweather information while in transit. ­Bob Migliorino. K2 YFE

DUAL OFFSET FOR THE HW-1011

With a 147.75/15 repeater going on the airin New Castle, IN, several area amateurswere faced with the problem of installing+6OO-kHz offset crystals in our HW-2021sets without losing either simplex or-6OO-kHz repeater capability. In addi­tion, I disliked the idea of drilling holes in

the case to install an extra switch. This isthe solution I came up with.

Prepare and install a new switch ac­cording to the illustrations. The extracrystal can be put in any convenient loca­tion, but leads should be kept short. Mycrystal has been placed between the chan­nel switch and the case.

With the original configuration theselector switch offered the choice of oneor two crystals. The dual switch (see draw­ing) provides selection of either plus orminus 600 kHz when the repeat mode isused.

This modification, performed on twoHW-2021s in New Castle, has beensatisfactory. For this reason, I trust theidea will be beneficial to other owners ofthe HW-2021 as well as to operators ofother sets where an extra switch is neededbut space is limited. - Paul L. Schmidt,WB9BAP

ORIGINAL SWITCH

~

FRONT

OFHW

20Z1

+!--+RPT DOWNRPT

TOesc

SIMPLEX RPT UP

_L

[:=J 10.7 10.1 c::J c::J u.s MHzrL MHz MHZrL .r XTAL

XTAL XTAL

SIMPLEX

TABS 00--+ TO OSC

~.""10.7 MHz

XTAL

=J c::J 10.1 MHz

1 1 XTAL

Modification of switches, and circuit changes for providing dual frequency offset for the Heath HW·2021. Steps to be followed: (1) Split two iden­tical switches as shown. Switches must be same size as original. Lift tabs and remove bottom, wipers and case. File switch to one-half originalwidth. (2) Reassemble the two hatt-swttches into one unit. Reinstall combined switch in case, replacing wipers and bottom and bending tabs down.(3) Remove original switch and carefully install new switch and crystal. The new switch functions are shown at the upper right. The orIginal andmodified circuits are illustrated at the lower right.

110. Chapter 8

-----_.._----- _ ....

An economical portable a~tenna for 144, 220and 420 MHz.

RA.OI"L PLUGS INTO

.... BANANA

@==;c=====,==,===?,'JACK-..- GFtOUNO RADIAL (4 FOR EACH BANO)

Resistance (Ohms)

41.439.337.135.031.830.0

Current (A)

.150

.140

.130

.120

.110

.100

to ground circuit of Q2. If the high­impedance choke, RFCS, is replaced by aseries-resonant circuit broadly tuned tothe crystal fundamental frequency, andshunted by a low value of resistance toprovide a de return for the base, frequen­cies below the desired fourth harmonic arediscriminated against. The revised circuitis shown. Suitable values of L, C and Rare about U I'H, 49 pF and 470 ohms,respectively. It bears emphasizing that theharmonics referred to are not thosegenerated in the Class C doubler andamplifier.

Incidentally, since a no. 47 pilot lampwas suggested as a tune-up load, thecharacteristics of this lamp may be of in­terest because it may be used similarlywith any QRP project. They are tabulatedfor a typical no. 47 lamp.

The lamp will actually show color indaylight at SO mAo Note that at ap­proximately the rated current value thelight level changes much faster than theresistance does, so that by using either aparallel or series carbon resistor with thelamp we can make a visual tuning in­dicator of nearly constant resistance forload purposes. Forexample, if we wish toapproximate the resistance of a quarter­wave whip, a 200-ohm resistor in parallelwith the lamp will result in a load whichwill vary from 31.2 to 34.4 ohms while thelamp brilliance varies from 40 percent to100 percent. These characteristics aretypical of tungsten-filament lamps, Thesame procedure can be employed withlamps of different ratings for other low­power uses by proportioning the brillianceand currents and then takingmeasurements of voltage and current todetermine the lamp resistance. - J. H.Ellison, W6AOI ,

Voltsge (V)

6.25.54.824.23.53.0

Tabl.1Percent ofRsted Light

100604020104.5

The varactor diode, DI, rectifies the rfvoltage present on the crystals anddevelops a dc voltage across R4. Thisvoltage often exceeds the bias voltageestablished by divider R3 and R4, causingthe operating point of the diode to shift toan area where the capacitance change pervolt of audio is considerably less than canbe obtained with the bias voltageestablished by the divider. Since thedeveloped-voltage magnitude depends onthe activity of the particular crystal in use,it can also change the effect of the seriescapacitor. The rectified voltage developedacross R3 can be reduced to an insignifi­cant value by feeding the bias voltagefrom R3 and R4 through RFC 1 to thediode. This change is shown in the draw­ing and assures that the operating bias forthe varactor diode is that value set by thedivider.

The third item concerns the base biasesof the transistors in the Ie package Vi.The RCA integrated-circuit manualshould be referred to for the schematic forthe CA3018. Probably because ofmanufacturing tolerances, I found itnecessary to increase base biases to get op­timum transistor operation and properaudio, even though resistor values firstused-were within less than 5 percent ofthose specified. This point should beborne in mind only in the event of un­satisfactory deviation or audio quality.

The final item concerns unwantedsignal output. Because of the smallnumber of tuned circuits employed, andbecause of the high gain of the transistorsused, there is considerable feedthrough inthe final-stage output of the oscillatorfundamental frequency and second andthird harmonics. These can be reducedconsiderably by a slight change in the base

BANANA

JACI<.S (-4)

t1/-4 WAVE ANTENNA

~===7===;!)t MILLEN PLUG

-If 37001

PORTABLE ANTENNAFOR 144, 220 AND 420 MHz

Budget-minded vhf operators needing aportable antenna for operation on 144,220 and 420 MHz will find this homemadeversion worth the effort. The handful ofcomponents may be mounted convenient­lyon a Minibox. The antenna and radialsare made from No. 12 solid copper wire.Banana jacks 'are used for connecting theradials. The antenna wire should besoldered to the center conductor of theMillen plug. Prune the wire for an SWRof 1:1. - Jim Webb, WA6TQA

PlP SQUEAK MODIFICATIONSThe Pip-Squeak 2-meter fm transmitter,described in QST for September, 1972,may be improved by a few simplemodifications. Reference should be madeto the schematic diagram and the pc­board layout in the original article.

The first item concerns the oscillatorcircuit where each crystal has a series trim­mer capacitor. With the use of high­accuracy crystals as recommended, asingle trimmer may be sufficient if thecrystals are connected together at thelower end, This also makes crystals inter­changeable in the sockets.

The second item is of more significance.

,

~ ,ViC1 /~ "

1~ " ~rh ;L"

The author found that better varactor-diode per­formance can be obtained by placing RFC1between the diode and the bias network. Referto the original article for component deelqna­tton.

02

R470

A series-resonant circuit is connected to thebase of 02 to aid in suppressing unwanted har­monics.

CONSTRUCTION HINTSFOR VHF CONVERTERS

Quite a few vhf enthusiasts still like tobuild their own converters, Doing ityourself currently comes close to necessi­ty. with the unfortunate tendency of thelarger manufacturers to abandon the con­verter field - at a time when mixed-bandsatellite activity brings the need for con­verters back into focus.

The difficulty of obtaining suitablecomponents, and doubts about one'sability to make satisfactory circuit boardstend to scare off would-be builders ofsimple equipment. Requiring only elerncn-

VHF Band·alds and Tricks 111

The WA3HMK converter is built on circuitboard, mounted on a small aluminum chassis.Af circuits are at the bottom, in this view.

tary tools, the 2-meter converter shownhere, worked out as a joint project byK3HEC and WA3HMK, is simple tobuild, yet its performance is adequate forweak-signal work. You may find some ofits ideas useful even if you don't duplicateit entirely.

Mecbanlcal and Circuit DetaU.Circuit board is used for the base plate

and principal partition, but it is one-sidedstock, used as sheet metal, with no etchingrequired. It is2-1/2 X 4-1/2 inches (64 X114 mm), mounted on a f-Inch high boxof the same dimensions. Push-in Teflonstandoffs are used as tie-points, as are

Interior of the z-meter converter, with com­ponents in the same position as In the layoutdrawing.

several feedthrough bypass capacitors. In­expensive Centralab S29-series tubularcapacitors for tuning the rf circuits aremounted in an unusual but simple way, toavoid the common problem of looseninglock nuts. Small holes are drilled adjacentto opposite sides of the mounting nut. AZ-shaped stiff wire or thin piece of copperor brass is then soldered to the outer sur­face of the nut and to the metal film onthe underside of the base plate. This locksthe trimmer firmly in place and provides agood ground connection.

The layout drawing can be used toduplicate the original if the builder keepsin mind any differences resulting from

r-r-.--- 4.- :-.---~Io ~P& I

XTA1 18 17 0 1"A~'r-,!,':-,.N.Y~II~ ~~ 1"

~Ol i - -M!i;0~~ ]

J3 + S'PC1

C21 110~ ... In I 2~N _@_ -@-@--(iHl>-0--<1>-o I I I OJ 11 I 13 0

HOLES1-7, TEFLON STANDOFFi8~13,.001 FT

I 3~~" "1

F~~¥'~~I]LEAD TO C4

Layout details for the main plate and partitionfor the z-meter converter. Both are single-sidedcircuit board. Hole dimensions and positions,where given, ere approximate and may varywith components used, but general layoutshould be followed.

component substitutions. The long parti­tion is also circuit board. The small one inwhich the first rf amplifier transistor iscentered is sheet brass or copper, butcould also be board material, if desired. Itis 7/S-inch square, with a hole in .thecenter just large enough to pass the bodyof the E·300 transistor. The gate lead issoldered to the shield. The source anddrain leads run directly to CI and C2,respectively. All the other transistors aresupported by their leads, which are about1/2-inch long.

___ --~.r co".. -- --Jj

RFAMP.

'4"t.lH. 10

III

~---~----~

10010.

RfAMP.3NHl9

~ 3N181)

100k

1.5pH

MIXER40&1!l (3N14H

>00

ElOTTOI<! VIEWS

3M~9 40613 2N918

"A" 'AoDyS EVCASE

''0

,'"

osc.

2200

cao

Schematic diagram a~d parts informati?n for the WA3HMK converter. Decimal values of capacitance are in J.lF, others in pF. Resistors are 112 wattor less. 500·pF capacitors are button-mica feedthraugh types (surplus). The 0.001 IJ.F capacitors are small ceramic types (Centralab MFT.1000).C1·C4, Incl. - 10·pF tubular ceramic trimmer or for best noise figure. L4 _ 2.7 to 4.2 J.lH, slug-tuned coil (Miller

(Centralab 829·10). .. L2 - 4·3/4 turns, like L1. 4307).L1 :- 6 turns No. 16, 318-rnch dla., spaced wire L3 - 4 turns No. 22, 1I4-inch dla., 5116 inch R1 _ Adjust for 5 rnA drain curent, or lowest

dla. Tap at 2·112 turns from bypassed end, (6 x 7 mm) long. nois~ figure. Final value in original unit,

112 Chepter 8

220 ohms.Y1 - 116·MHz overtone crystal (International

Crystal Mfg. Co.).

The first rf stage is a grounded-gateamplifier using a low-noise JFET. Thesecond rf amplifier and the mixer areMOSFETs. The oscillator contains a low­cost bipolar transistor. Almost any vhfoscillator type should work. The injectionportion of the converter is of interest inthat a 116-MHz crystal is used,eliminating the need for multiplier stagesand their attendant problems of unwantedfrequencies that can generate spuriousresponses. This is especially desirable in asimple layout such as this. Injection canalso be supplied from an external source,merely by removing the crystal, Yl, andfeeding 116-MHz energy into the phonojack at the lower left. This provisionmakes the converter suitable for use intransverter service, an application now inthe process of being tried by WA3HMK.

The circuit diagram is drawn in a man­ner that will illustrate use of feedthroughcapacitors as tiepoints and bypasses. Allthe O.OOl-~F capacitors are small ceramicsof the IT type. The 500-pF capacitors arebutton-micas. Both types are often foundas surplus. Each capacitor is shown in thecompartment or partition in which it ismounted. All parts shown below thebroken line are on the oscillator side ofthe partition. All above are in the rf por­tion.

The converter was checked in theARRL lab and used in communication atWIHDQ. Sensitivity and gain were ade­quate for weak-signal work. Spurious

-------, "1.:'"1,

-------~

.oot

rc

H'·""'OUTPUT

. ",~

'''1

PARTITION

""" +

responses, often a problem in simple con­verters of the oscillator-multiplier type,were conspicuous by their absence. Thevalue of RI should be adjusted for a CUr·rent drain of about S mA, or for optimumnoise figure. The original is 220 ohms, buthigher values may be needed. CI and theposition of the tap on Ll should also beoptimized for noise figure. Converter gaincan be controlled by varying resistorvalues in the second stage. - WIHDQ

REMOVING GLITCHESFROM THE HA-201 AMPLIFIER

Soon after we acquired our Drake TR­22C, we discovered the joys anddrawbacks of QRP operation in the2-meter band. To upgrade the power weadded a Heath HA-201 amplifier only tofind unanticipated difficulties. There werelarge excursions in amplifier stability anda loss of receiver sensitivity. Moreover,there appeared to be less than the ratedoutput even though the amplifier wasoperating with 13.8 V de. The difficultywas one of improper interface be­tween the TR-22 and the HA-201, center­ing mainly around the switching circuit.

Compatibility between the two unitswas achieved by the use of a carrier­operated relay (COR). After installationof the COR, the HA-201 performed nor­mally with 10 to 12 watts of output acrossthe 146-148 MHz band. Thereafter, therewas no sign of instability.

Construction of tbe COR

Remove diodes DI-D6 (iN4149s), in­clusive. Extract C5 (8-60 pF trimmer) andthe quarter-wavelength lines for Tl andR2 (RGI74/U). Two of the IN4149s areto be used on the COR board. The rest goto the junk box along with C5. Theshielded cable, however, is retained. Thecomponents just mentioned are from theelectronic switching circuit.

The relay circuit is built on a RadioShack perfboard (no. 276-1395) with theuse of Radio Shack flea clips (no.270-1392). Dimensions for the VectorBoard are 2 x 1-1/2 inches (5.08 x 3.81em). A solid-wire jumper is used on theamplifier board in place of D2 and D5.Mount the COR board in the area for­merly occupied by Tl and n. Mountingboles should be drilled just to the right ofhole J and hole E on the circuit board,utilizing no. 6-32 hardware. Be sure thereare no live traces that are shorted to theground bus. If necessary, the traces maybe trimmed with an X-acto knife.

The shielded cables, originally used forTl and T2, are now used for the input andoutput lines and are respectively con­nected to the input and output connectorsof the COR circuit. A connection is alsomade from the COR board to points A, B,Land M on the HA-20l board. Tieall theshields together at a single point (at one ofthe flea clips near KI or the COR). Con-

nect the COR B + lead to the fused side ofthe 12-V line on the HA-201 and theCOR. Then return the lead to the groundtrace on the HA-201. If desired, a smallspst switch may be added in series with theamplifier B + lead for use as a HlILOswitch. This will provide flexibility notfound otherwise.

When the installation is completed con­nect the HA-201 amplifier to the TR-22C,or any exciter capable of providing 1-3watts of driving power. Apply 13.8 V deto the amplifier and a SO-ohm load to theoutput of the HA-201 through a watt­meter. The relay closure should be heardwhen the exciter microphone button ispressed with an indication appearing onthe wattmeter. Adjust CI-C4 for maxi­mum output. The amplifier will run lO-to12-watts output across the entire 146-148MHz band with no instability.

Tune-up should be on 146.94 simplex ifpossible. Use o( "94" alleviates the prob­lem of lost output at band edges. Ratherthan use a YOM as a tuning aid, it is bet­ter to employ a wattmeter for all vhfwork. -DaveKarpiej, KITHPandMarkStarin, WAITZK (from the InsuranceCity Repeater Club Newsletter)

THE RIGHT CHANNELSFOR THE HW-202

Some radio amateurs who own the HeathHW -202 find on occasion that their setmay be transmitting on one channel whilereceiving on another. Those operatorswho line up the crystals so thatTRANSMIT is directly above RECEIVEin the push-button configuration can rec­tify the problem readily.

From a sheet of 1/4-inch Plexiglas, cutfour pieces 9/16 inch X 3/8 inch. Cementeach piece between a transmit button anda corresponding receive button so that thetransmit and receive buttons may beoperated simultaneously in correspondingpairs. This system avoids the problem ofleaving anyone button in the wrong posi­tion.

The plastic inserts should be filed suffi­ciently to prevent them from being solarge that the switch arms could bedistorted. Before cementing them intoplace, the Plexiglas pieces should slideeasily between the upper and lower pushbuttons. After securing the pieces withDuco household cement or the equivalent,wait a few hours before operating theequipment to allow the cement to hardenproperly. This project is worth the effort!- John Baldwin, WIKUO

MINIMIZING ADJACENT-CHANNELQRMI would like to share with others this pro­cedure that has worked well with my IcomIC-230 to minimize adjacent-channel in­terference from repeaters operating with

VHF Band-aids and Tricks 113

Sotto-state relay. The LEO is a surplus type, but a Radio Shack replacement should not be dlt­ficult to obtain.

-etev 330

+12V

2Nn06

UHF·TV AMPLIFIER LOWON NOISEI have been unhappy with noise figuresfor many uhf preamplifiers. Satellitetransmissions on the 70-centimeter bandas well as other signals seemed to becovered by the noise inherent in manycommercial uhf-amateur preamplifiers.All seemed to increase noise along withthe signal strength. I was pleased to even­tually find that the Winegard uhf-TVpreamplifier AC-499O, on the other hand,performed excellently for signals in the 70em range. It brought the signals up instrength without noticeable increase innoise. On several occasions no trace ofsignals was evident until the AC-4990 wasswitched into the antenna system;

Additionally, the 4990 may be used forthe 9OO-MHz region should any radioamateur bands be allocated there. Thispreamplifier functions well in the publicservice band, 450-512 MHz, shared withTV in some areas. A power supply is pro­vided with the AC-4990, making itconvenient for antenna mounting orlocating near a 70-cm receiver. - RonaldMarx, WA2CTZ

A LOW·NOISE PREAMPLIFIERFOR 432·MHZThis amplifier was developed as part of alow-cost, 400-MHz radiotelescope.Although it does not represent theultimate in low-noise operation, its per­formance is much better than many com-

1000

,,.

+ 12 V TO XMTR 0-----''<...../

HEP 246 OR HIGH

ClIMENT PNPDEPENDINGONLOAD,

33002N3904

EXCEPT~ INDICATED, DECIMAL VALUESOF CAPACITANCE AREINMICROFARADS

lJ,iF); OTHERS AREINPICOFARADS (pF OR

JJ}lFl; RESISTANCES AREINOHMS;

k"1000, M,,1000000.

,­COROUTPUT(DC)

ternational Crystal Co., 10 N. Lee,Oklahoma City, OK 73102. The module ismounted in a small Minibox, and a1000·pF ceramic feedthrough capacitor isused to bypass the 6-volt supply to theoscillator. The oscillator output is con­nected to a phono connector, and small­diameter coaxial cable joins the output ofthe module to the grid of the tube former­ly used as the oscillator. If the 1oo-kOgridresistor was connected across the crystalsocket, it should now be connected direct­ly from the grid pin of the tube to ground.Since the module requires a 6-volt supply,two lOOO-ohm resistors are connected as avoltage divider across the I2-volt supply inthe transverter. - Dr. Ralph E. Taggart.WB8DQT

SOLID·STATE RELAYFOR REPEATERS

The device shown was designed byW0INK to interface with solid-state vhfreceiver and' transmitter strips. Our2-meter repeater is now completely solidstate and has a current drain of only 400rnA when in operation. The LED, whenlit, indicates the transmitter is in opera­tion. The delay of the "tail" can be ad­justed by changing the value of Ct. For anormal squelch tail, a value of 20 fJF isused. The relay is driven by the COR cir­cuit. Several CORs that could be usedwith this relay are described in FM andRepeaters for the Radio Amateur.Mike Wisch. WB0LGC/WRMEN

IS-kHz separation. With the use of aCFS-4SSG filter, a weak repeater can becopied even though a much strongerrepeater is belting the airwaves just 15kHz away. Remedies for two situationsare described.

Case 1: The interference is equal onboth sides of the signals from the interfer­ing repeater. Installation of a CFS-455F(or G) filter, performed in the same man­ner as recommended by Icom for the CFS­455E filter, will do the trick. The 0 filteris sharp and if the received signal is offfrequency or over-deviating there may besome distortion. The G filter is best foruse in areas with strong repeaters.

Case 2: The interference is greater onone side of the frequency used by the in­terfering repeater. This condition is caus­ed in a receiver that does not have the i-fcenter on 10.700 MHz.: For example, thei-f center frequency may be 10.703 or10.697 MHz, 3 kHz off center.

These are the steps to take for the sec­ond case. Install a CFS-455F (or 0)filter. Adjust anyone of the LO crystaltrimmers to center any remaining in­terference. If the interfering repeater is on146.715 MHz, adjust the LO trimmer sothat the interference is equal on 146.70and 146.73 MHz. A strong signal will berequired if the G filter is used.

Next, with the aid of a counter, adjustthe three mixer trimmers to put thetransmit oscillator back on frequency. Forexample, adjust the set for 146.70 MHzfor on-channel operation, 146.10 MHzfor - 600 kHz and 147.300 MHz for+6(l()'kHz.In my case it was necessary toadd a 160-pF capacitor in parallel with themixer trimmers for proper adjustment.

Once the mixer frequency is adjusted,the remaining La trimmers may be set ontransmit. The discriminator coil, LS(LS-15) must be recentered. With a signalknown to be on frequency, set LS-IS fromzero with a zero-center meter. Thatcompletes the modification. I might addthat the filters, mentioned above, may beobtained (at the time of this writing) fromMurata, 2 Westchester Plaza, Elmsford,NY 10523. - Richard Weinstein, W3HSF

IMPROVED LOCAL·OSCILLATORPERFORMANCE IN THE K9UIF2·METER TRANSVERTER

The K9UIF transverter, which appears inThe Radio Amateur's VHF Manual is oneof the most popular and effective designsin existence. One consistent difficulty hasbeen the instability of the local oscillator.The oscillator may drift during warm-up,and its frequency will shift when theoscillator is tuned. The high drive levelsrequired also may result in instability, as aresult of the subsequent high crystal cur­rent. An OX oscillator module and EXcrystal provide an excellent substitute forthe oscillator. They are available from In-

114 Chapter 8

"[Editor's Note: A representative of KMC Semi­conductor was consulted about the noise figureobtained by the author. His opinion was that itis not impossible to have a 1.5-dB noise figure ifusing a selected 2N5652; most are capable ofproviding 2 dB. For consistent results a K6007 isrecommended. which can produce a 1.6-dB flgure.]

drilled in the board for all mounted com­ponents; where ground connections areneeded, the leads are simply soldered tothe board. This type of constructionresults in the shortest possible lead lengthfor all components, and is very simple todo. The amplifier may be fastened to theopen side of an aluminum chassis to forma compact, well-shielded unit.

The inductors should be installed sotheir leads are as short as possible, butkeep the coil at least 1/4-inch from thecopper surface or from other com­ponents. The transistor should be install­ed last and soldered carefully. Do notbend its leads close to the body, or theymay break.

AdjustmentThe amplifier is adjusted for maximum

gain using a signal generator or a receivedsignal. The collector current should bechecked and set to the value which givesbest noise figure; this will be very close to3 rnA. The collector current can be variedby changing the values of the baseresistors, RI and R2, or by varying thesupply voltage by no more than ± 2 volts.

It may be necessary to trim the indue­tors in order to achieve a smooth pass­band response. For best results, the inputinductor should be connected fromground to the center pin of the input con­nector, and CI should be connected to thesame point by a short wire. The band­width is also affected by the value of C2;increasing this value by a few pF willbroaden the frequency response.

If oscillation should occur, be sure thetransistor leads, especially the emitterlead, are well soldered and as short aspossible. Oscillation is usually caused bypoor construction practices, bad grounds,or poor layout.

To improve the gain, at the. cost ofnoise figure, the base resistors Rl and R2should be changed, to increase the collec­tor current to a maximum of about 10rnA. R2 may be replaced by an rf chokewith a small potentiometer connected inseries, to make the bias point variable .

There is no reason why this circuit can­not be used at 220 or 144 MHz, with evenbetter performance. All that would beneeded is to change the input and outputtuned circuits and increase the value of C2slightly. - Steven A. Maas, K3WJQ

YRl \2.;

9V+

not obvious from the schematic. Neitherneutralization nor shielding is needed. inspite of the high frequency and high gain,because of the low input impedance of thetransistor. The amplifier should be uncon­ditionally stable, even when mistuned.Also, because the 50-ohm transmissionline is in parallel with the input tuned cir­cuit, wide-band response is obtained. Inenvironments where interference is aproblem, the input connection and tran­sistor base may be tapped lower on LI.narrowing the bandwidth.

Power is supplied by a 9-volt source.preferably a small transistor radio battery.Current drain is only 3 rnA. A 12-voltZener diode is connected across the powerconnection to protect the transistoragainst excessive voltage and impropersupply polarity. The maximum Vee of the2N5652 is only 20, and the device is notvery forgiving.

To protect against lightning damage (ifthe unit is mounted at the antenna, as itshould be) some means should beemployed to ground the antenna. The oldtrick of connecting two diodes across theinput will not protect the delicate basejunction of the 2N5652, and will ap­preciably increase the amplifier noisefigure.

ConstructionThe amplifier is built on a 2 X 4-inch

(51 X 102 mm) piece of copper-cladprinted circuit board, using miniatureceramic insulated terminals. Holes are

C4

r C' .001

~.001

RFC1 432: MHz., 4.4,u.H...432: MHz

J2

10 OUTPUT

s:ti.L2

.2 C,22' •• l;~~",0

Circuit DescriptionThe circuit is a basic common-emitter

amplifier, with tuned input and outputcircuits. It has some attractions that are

EXCEpT AS INDICATED, DECIMAL VALUES OF

CAPACITANCE ARE IN MICROFARADS I JlF I ;OTHERS ARE IN PICOFARADS (pF OR jljIFI:RESISTANCES ARE IN OHMS;k.1 000, M~IOOO 000.

The circuit board for the 432·MHz preamplifier.

J1INPUT

mercially made units, and the cost andsimplicity are hard to beat. The circuituses a 2NS6S2 transistor, although a2N5651, 2N5650 or K6007 can be used forbetter noise performance. The author'sunit has 12-dB gain and a noise figure ofless than 2 dB; 1.5 dB has been obtainedwith a selected transistor.· The total costcan be less than $20.

If greater gain is desired, the amplifiercan be modified by changing theoperating point of the transistor. Accord­ing to the manufacturer of the 2N56S2, aS- to 8-dB increase is possible, and greatersignal handling ability and linearity isachieved as a bonus. The cost of this gain

. improvement is an increased noise figure.

Schematic diagram of the 432-MHz preamplifier. The 2N5652 or K6007 transistor may be obtainedfrom KMC Semiconductors, Parker Ad., Long Valley, NJ 07853, or from their distributors. Cl andC7 are 2- to lB-pF glass piston trimmers (JFD VC-4G or equlv.). L1 and L2 are 1 turn, 3lB-inch dia.,no. 16 tinned copper; L2 Is center tapped.

A WIDE-BAND PREAMPLIFIER

The wide-band preamplifier I built for usewith my frequency counter has a simple

VHF Band·alds and Tricks 115

OFF

'7470

R2

ECG1,3A1HEP~3

330

CR'ECG1091HEP134

7

O'VOC

;:;:'0'

C~, ECGIQ9I

Rt HEPt34

0.002 47

INPUT >-~r-f=1--<~---,----,.-j

+4~V DC

This wide-band preamplifier provides additional gain for effective frequency-counter operation.

PROTECTIONFOR 432·MHz CONVERTERS

K3POP has provided this transistor pro-

ware store parts are used for mounting.See the self explanatory mechanical draw­ing. - E. R. Angle, WA6GUY

.Ul.1llll1ii~sCRIBEIlERE

center-punch each side of the boom wherescribe lines intersect. DrilJ the holes byworking up in drill sizes to, the desiredhole diameter in order to obtain a smoothround hole. Drill each hole separately. Donot drill completely through the boom.MisaJignment will otherwise result.

Mechanically rigid vhf antennas can befabricated from aluminum rods. Hard-

.032 SlOEBRASS PLATE S

.032 BRASS SOLDER

A precision element, hole-altgnment, marking jig. The device allows uniform scribe markings in alldirections. To use, clamp the antenna boom to avoid rotation. Place the jig on the boom. Makethe required marks. Drilling should be done from each side - not through from one side.

design but works well. Tests indicate again of 20 dB at 50 MHz. The unit, con­structed of commonly available parts, isassembled in a metal box. Input leadsmust be shielded. RI, the input loadingresistor. may-vary with the type of probebeing used. Where a probe is not used, alength of RO-59/U may be connected tothe amplifier input, and RI should beplaced across the input end of the RO­59/U. The value of the resistor should be270 ohms. The need for R2 is determinedby trial and error and will depend uponthe input of the counter. I found 100ohms works well for frequencies up to 45MHz.

A bias potentiometer is used for gaincontrol. To adjust the amplifier, set thepotentiometer for maximum gain butbelow a point where oscillation maybegin. It is suggested that if the unit isused close to equipment that coulddevelop a signal level of I volt or more,diodes D I and D2 should be incorporatedin the circuit. - Ira J. Arnold

This drawing shows a method of constructing a beam antenna by using aluminum rods.

<,THREAO#S-40

.12S CIA. AL.U. ELEMENT

---..1 BOOM l­OlA.

THREA01l4_28.DRH..L&TAP#5_40 ~

ELEMENT \ ALUMINUM ROD 11• 1/4" CIA. l

-==-I'111'1/.--r§ § I§ siB i# :~T40 114" --+1 I~I, i

BOO'" ......-""""O1A.

FOR THE VHF ANTENNA

Positioning holes in boom material forvhf beam antennas poses a specialproblem. The drawing I have providedshows a jig that was built to accuratelyscribe marks on the boom. Constructed of0.032-inch brass sheet, the jig can be madewith hand tools. The two side plates aremade together (for accuracy) and arebolted to the small aluminum hand level.-The horizontal bottom plates are solderedin place. A small, long spring can be at­tached to the jig to go under the boom tohelp keep the jig in place if desired.

First the boom is secured to preventrotation. Element positions are thendetermined along the boom. Place the jigon the boom, marking vertical andhorizontal scribe marks. Accurately

118 Chaptar 8

'----#liWIRE

An Interference filter and protection device for 432·MHz convener transistors.

REPLACING THE ANTENNA JACKON THE HW·2021

Owners of the HW -2021 hand-heldtransceiver made by Heath may havediscovered that the soft metal used in theexternal antenna jack does not, stand upwell. When mine became troublesome Ifound that a miniature closed-circuitphone jack (no. 274-253) sold by RadioShack fits perfectly in place of the originaljack. This replacement features a strongreturn spring which seems to eliminate theproblem involved. I might mention thatRadio Shack packages these jacks three toa container. The extras could be used asspares for future replacements or sharedwith other HW-2021 owners. - BillTubbs, WA6FFI

rear window. The antenna was pruned forminimum SWR and the pruned end wastaped to the glass.

While the antenna system is a com­promise, my mobile transmitter producesfull quieting through the local repeater.Performance is good well out to thefringes of the repeater range. My fellowRATS (Richmond Amateur Telecom­munications Society) deserve mention forbearing with me during tests on the RATS28/88 repeater, WR4ACW. - ArthurBaltz, K4ARE

'Ne+- C~NNr.CTOR

antenna was several inches forward fromthe center of the rear window. Only alI4-inch drill was used for the hole in theplastic-cloth shelf trim. A female auto­radio socket was installed with the soldertab protruding through the trim as shownin the drawing. For the antenna a 20-inchlength of No. 32 enameled wire was used,one end being soldered to the connectortab and the other temporarily taped to the

.'~f------ ----------4~

II Q (~2 Q It ''' -<I I ~~.,. r-'''~~ :5" ->1.

T"~

tection device which should be of interestto just about everyone. It consists of alow-Q, half-wave filter with diodeslocated at the peak voltage point. Thefilter has an insertion loss of only 0.062dB at 432 MHz and provides the bonus ofadequate selectivity to clear interferenceat most locations. With 400 watts beingpassed into the filter, less than 80 mw wasmeasured at the output. The diodeschosen are 1N914s but the choice is notcritical. - Allen Katz, K2UYH

THE 2S-CENT MOBILE ANTENNA

The rip-off, the car wash and transferringequipment to a new car present commonproblems for amateurs who operatemobile equipment. An external antennaon an automobile is an advertisement ofthe presence of mobile equipment.Without the antenna or mount, a radiothief might well ignore the car.

General Motors had embedded thebroadcast radio antenna in the windshieldof my 1976 Buick. This triggered a seriesof thoughts as solutions leading to the in­stallation of a 2-meter. quarter-wave whipjust inside the rear window. A steel pan.welded to the body, is located under thetrim and insulation of the rear windowshelf. The location seemed logical for aninside antenna.

A II2-inch hole and two lI8-inch, se1f­tapping screw holes were drilled from theinside of the trunk. Location for the

TRANSPARENT TAPE

REAR WINOOW--_J

FIBER CLOTH TRIM

CONNECTOR

REAR SHELF

A thin wire that is nearly Invisible may De suspended from the rear window of a car to the reardeck as an antenna for a-meter mobile operation.

VHF Band-aids and Tricks 117

Chapter 9

Notionsfor Various Modes

EXCEPT AS INDICATED, DECiMAL VAWES OF

CAPACITANCE ARE IN MICROFARADS \ .IIF) ;OTHERS ARE IN PICOFARADS ( pF OR .IIjlF)',

RESiSTANCES ARE IN OHMS;k·10QO, lo'I.tOOO 000,

Circuit diagram of the SSTV tuning aid. Both controls are of linear taper. All fixed resistors maybe 1f4 watt. All capacitors except Cl may be disk ceramic.C1 - Q,2IJ.F Mylar or polystyrene. In the unit L1 - Surplus BB-mH toroidal inductor.

photographed this value was obtained by U1 - Dual operational amplifier, type 5558,connecting two O,1'IJ.F capacitors In parallel. 8·pin, dual in-line package,

CRl - LED, Radio Shack 276-041 or equlv.

6

SWITCH

'0'THRESHOLD

0,01lN270

cr0'<

+t 2 vo-I\J\IV--'

c.t \N210

DETECTOR

at pin 1 of the IC. A signal below thelimiting threshold should appear as a sinewave. As the level of the signal is in­creased, the top and bottom of the sinewave will be clipped symmetrically if thebalance is correct,

The threshold adjustment for UIB actslike an intensity control for the LED. Itssetting is not crucial, and in operation italmost becomes one of personalpreference. With no signal at the input theLED will glow continuously at one ex­treme setting of this control. Back the set­ting off until the LED becomes ex­tinguished. Now connect the SSTV signalfrom a camera, a tape recorder or from areceived signal that you know is properlytuned. The flashing or flickering of the

\200-HzFILTER

nominal. In this case selection of another4700-ohm resistor or paralleling oneresistor with another of much higher value(27 to 47 kO) is in order. Next measure thevoltage at pin I of VI. Slowly adjust thebalance control in either direction andnote that just a small adjustment causesthe voltage to swing from 1 V to 11 V,(This range will be greater for supplypotentials higher than 12 V.) Carefullyperform a fine adjustment of the controlby setting it for a voltmeter reading at pin1 of 6 volts (or one-half the supplyvoltage).

If you have an oscilloscope, you cancheck the balance adjustment by injectinga very low-level audio signal at the inputof the tuning aid. Monitor the waveform

RECEPTION OF SSTV SIGNALSTUNED CORRECfLYWITH THIS DEVICETuning in ssb signals for voice receptionpresents no problem normally. But ad­justing a receiver for SSTV is somethingelse because a person would have diffi­culty trying to determine the correct pitchof the SSTV tones being heard from aloudspeaker. This compact tuning aidsolves the problem.

Construction and AdJnstments

The circuit may be constructed insidethe enclosure of an existing monitor. or itmay be housed separately in a small metalbox like that shown in the photographs.Component layout is far from beingcritical.

An unmodified 88-mH toroid should beused for Ll , and Cl may be a stock-valuecapacitor or appropriate combination.Some builders may wish to precision tunethe filter to 1200 Hz with the aid of a fre­quency counter. This is best done after theremainder of the circuit is completed, sothe filter is tuned under operational condi­tions. Before doing this. however. itwould be wise to check the receivingmonitor, as its own sync circuitry mayoperate most effectively at a frequencyseveral hertz removed from 1200. Preci­sion tuning is not essential for satisfactoryuse of the instrument.

The limiter balance should be adjustedfirst. Ground the audio input connectionand, using a voltmeter, perform a coarseadjustment of the balance control by set­ting the voltage at pin 2 of VI to exactlyequal that at pin 3. If this condition can­not be reached within the range of thecontrol, it is because one or more of the4700-ohm voltage-divider resistors are

-sornewhat removed in value from

118 Chap'a, 9

An inside view of the tuning aid. The circuit asconstructed here is housed inside a 2 x 4 x1·S/8-lnch Mlnibox, The LED is supported by itsleads and protrudes through a grommeted holein the front of the enclosure, Phono type jacksare fastened to a bracket for audio and tz-voltInputs, with clearance hates for these jacksdrilled In the back cover.

LED will be readily apparent. As the con­trol is backed off farther from the settingobtained earlier, the intensity of theflashes will diminish. You can find a set­ting for which the LED will glow onlyduring the 30-ms vertical sync pulse, onceevery eight seconds. The setting should beadvanced slightly from this position, sothat a flash is observed for every syncpulse. Find the setting you prefer most bytuning around some SSTV signal frequen­cies on the air.

With a little experience, you'll find thatit takes but a few seconds to tune SSTVsignals "on the nose" with this handy tun­ing aid. - KITD

TEMPERATURE COMPENSATIONFOR THE QST AFSK GENERATORSeveral of us who built the RTTYgenerator described by WB2RHM onpage 36 of the September, 1969, issue ofQSThave experienced problems with con­siderable frequency changes resultingfrom thermal effects. Possibly some hamsplaced their generators on or near otherequipment which radiated heat. hi mycase, the room temperature may vary asmuch as 25°C.

While the mark frequency held within a

J< ? CR'

0;: ~ T'

""/.TO

~,(

few Hertz of the correct value, the spacefrequency drifted widely with changes oftemperature. By simply placing a fingeron DI, the IN914 frequency-shift diode, Ifound that the diode was sensitive totemperature and that the space frequencywould begin to drift rapidly. While ex­perimenting I also discovered that by plac­ing two parallel 25,(X)()..ohm thermistors(obtainable at parts jobbers) in parallelwith RlS (the S20-ohm resistor) the ther­mal effect could be reduced so that thespace frequency remained within 6 Hz ofthe nominal value of 1170 Hz. Mygenerator is designed to operate at1000-1170 Hz.

Because the thermistors affect the RCtime constant of the oscillator, thegenerator frequencies should berecalibrated. Some experimenting may beneeded to find the correct thermistorvalue for the required frequency andtemperature compensation. Thermistorsmay be used singly, in series, or inparallel. - Fred Mumma, W3KEK,K3TXG

UPDATE YOUROSCARLOCATORIf you're one of the 20,000 amateurs whohave found OSCAR quickly and easilywith your own OSCARLOCATOR, youmay have noticed that something wasmissing. You guessed it - beam headingsfor directional antennas.

Here's an easy way to adapt yourOSCARLOCATOR to give approximateazimuth and elevation information at aglance.

Using a permanent, nonwater-base,

o

------------------

felt-tipped marker (available at all sta­tionery stores), trace the illustrated designon your Q'THz'Rangeflnder (the small cir­cle that shows the satellite's range) or aseparate sheet of mylar, available at artsupply stores. The elliptical shape willyield more accurate results for NorthAmerican latitudes on the polar projec­tion map.

Place the center of the overlay on yourQTH. The straight line, now labeled "0"(zero), should be aligned so that the ar­rows point north. This indicates 0 degreesazimuth.

The lines radiating from the center giveazimuth bearings at 30-degree intervals,while the concentric circles give elevationbearings of 0, 30 and 60 degrees. With therelatively wide beamwidth of typicalOSCAR antennas (about 60 degrees for alO·dB gain antenna), estimates betweenthe marks should be adequate; you shouldhave to reposition your antennas onlyevery two minutes or so.

Using your updated and improvedOSCARLOCATOR is simple. The "OrbitFinder" overlay still gives the number ofminutes after equator crossing (EQX) thatthe satellite will be within range.

If, for example, the path of a given or­bit crosses the 30-degree elevation oval atan azimuth of ISO degrees on the modifiedoverlay, then at that instant the satellitewill be 30 degrees above your horizon anddirectly south of your QTH. With the newoverlay, you can jot down the az-el data attwo-minute intervals we1l in advance of anupcoming pass. This will let you devoteevery precious minute between ADS(when you first hear it) to LOS (when youlose it) to operating. - Jon Alquist,WAIIWYX

Two thermistors provide temperature compen­sation for the WB2RHM RTTY generator.

Using this QTHfRangeflnder will provide accurate ADS, LOS and beam headings for all OSCARpasses in the Northern Hemisphere. To determine OX possibilities, center the original (circular)Rangefinder on the area you are interested in working (London, for example). If OSCAR will bewithin range, the orbital track will fall In the area where the two Rangefinders overlap,

Notions lor Various Modss 119

(S)

_.C

l2':005 '" Q1 B

0,1 E. HEP724

TO TONESELECTOR SWITCH

IIIIII'~FKfFKFKFfK

\001 TO PTI LINE

12V ON RCVEC2 35"F GND ON XMIT15V _____

470

1~'

U1NES66'4 5

10 K

SWITCHCOMMON

GROUND +9V /

It10K

OUTPUT TOAUDIO LINE

I}M

OS

IT = 3 X RI X CI

A STABLE TONE GENERATORFOR REPEATER ACCESSThis circuit was brought forth in an effortto sidestep some of the problems of tone­burst generators, such as instability I

temperature effects, difficulty of adjust­ment, or hard-to-find components. Costwas also a consideration; the unit can beduplicated with all new parts (excludingthe pc board) for about $10. Stability issuch that drift is less than one hertz afteran hour of operation. Potentiometersallow ease of adjustment to the desiredfrequencies of operation.

Oreull Descrlptloo

The design is centered around aSignetics NE566V phase locked loop IC.'The tone frequencies are determined byCI and RI plus R2 through R7. Thecapacitance remains constant and theresistance is changed to set the varioustones. The formula

is used to calculate the frequency ofoscillation.

The total resistance needed is approxi­mately 28 kll for 1800 Hz and 20 kll for2400 Hz. Since the overall resistance, be­tween the extremes, is only 8 kG, poten­tiometers of IO·kO value were used to ad­just the frequency and a 50-kll unit wasused to set the range. Shunting CI withQI causes the tone to cease. The values ofC2 and R8 determine the burst duration.

In operation Q I has + 12 V applied tothe base and is in full conduction, shunt­ing Cl. When the PTT lioe is grounded,QI will cut off and allow the PLL tooscillate. C2 will begin charging throughR8 and again force Q I into conduction,shunting CI, and stopping the oscillation.The 0.05-~F capacitor and the I-Milresistor provide isolation 'and a high im­pedance to the audio line.

Construction

Since the NE566V is a voltage­controlled oscillator, it is very sensitive tovoltage changes and a Zener-diederegulated supply is a necessity. TheHEP724 (Q l) must be removed from thecircuit in order to adjust the tones;therefore, a socket should be used for thistransistor.

The circuit is constructed on a pc boardmeasuring 1-114 X 2-7/8 ioches (32 X 73mm). A single-pole, 6-position switch isused to select the desired tone. Don'tforget to provide an ON-OFF switch.Some people get upset if you are usingtone-burst and the repeater doesn't re-

, Quire it. .

Parts-placement guide for the generator. View Is from the component side; shaded areas are cop­per toll. A method of obtaining regulated power for the generator from a tz-vott source is shownat B.

II- I9V DC

+<>-;:+, n R7

III

,0' J

h R6II,

W. I \\)OR5

III

'jOk J

h R' SI? TONE'0' SELECT

[JR3

'0'

h R'

1500~ 00'51 NOTMOUNTED

R2- R7 lNCL. ON BOARDR' TONE AOJUSTMENT50.

RANGE

" 0.05 1M

o~6 8 , ~TONE OUTPUT

~ U,:5 FUNCTION 1GENERATOR

NE556V

'0' 7 J~ Yn.c. n,c. EXCEPT AS INOICATED, OECIMAL

rh VALUES OF CAPACITANCE ARER8 IN MICROFARAOS {j.IF); OTHERS<0. Q1 ARE IN PICOFARADSIpF OR JlpFl;

TO PTT~24 RESISTANCES ARE IN OHMS;

470 C2 fV)12V KEY UP,~ co • .,00.0. Mol 000 000

GROUND \f.a.. To.005KEY OOWN 35IJF15V rh

I Phase-Locked Loops Applications, SigneticsCorporation. 811 East Arques Ave., Sunnyvale,CA 94086.

Schematic diagram of the tone-burst generator.a - Motorola HEP724 or equlv.R1 - 50-kG miniature pc-mount control, Radio

271-219or equiv.R2-R7, Incl. - la-kG rnlnlature pc-mount

control, Radio Shack 271-218or equtv.Ul - Function generator (PLL) IC, Signetics

NE566V.

120 Chaptar 9

-------~--

A "no-smoke" antenna switching arrangement for the Any station.

A 60-Hz oscillator, an amplifier and a 12.6·V center-tapped filament transformer provide 117·V aefor teleprinter motor.

•

CENTERTAPPED

FILAMENT

TRANSFO~AC

E:,

FACSIMILE TRANSCEIVER FORWEATHER-SATELLITE PICTURES

Considerable interest in adapting the plen­tiful Western Union Telefax unit forsatellite pictures has seemed evident.W4NK's antenna and desk-facsimile pic­ture in the October. 1973, QST(p. 69) hasalso stirred considerable interest. SinceEssa 8 has deteriorated to a "flying phan­tom" of its original state and with bothNOAA I and 2 pumping out excellent pic­tures in both infrared and visual modes, ameans of converting the Telefax for thereception of the 48-line scan of these andfuture satellites is in order. Using weathersatellite bulletins from WIAW, the writerwas able to catch pictures from NOAA 2on the day after launch with equipmentsimilar to that described.

The reception of the satellite signal, ap­prox. 137.S MHz, is the first step. Here

While the thought of such de-regulatedmotors has merit, I have made aqualitative investigation of the use of aspecial ac supply for machines with syn­chronousmotors. The circuit for the sup­ply is not complex, but certain points hadto be considered when the unit was beingbuilt, namely the battery supply voltage.the frequency, and the current/voltageratings of the transformer.

Fundamentally, the power supply con­sists of a 6O-Hz oscillator driving anamplifier and a phase splitter. The bestoutput device would be a push-pull audioamplifier used in conjunction with acenter-tapped filament transformer.When one considers the 12.6 voltsavailable from an automobile storage bat­tery, plus rms and peak voltages inherentin the situation, a 12.6-volt rms center­tapped filament transformer being drivenby a push-pull audio stage is the bestmeans of obtaining 117-V ac (rms) from12.6-V de produced by the battery. Thesestipulations required the device to be solidstate.

The 6O-Hz oscillator can be calibratedwith an oscilloscope and a WWV receiver.Using Lissajous figures, one can comparethe 60 Hz with the 6OO-Hz signal. If theunit is operating properly, the two fre­quencies will produce a 10:I scope trace..This supply could be very useful inemergency vehicles. - Rodney B. Moos,KIJCAZ

FOR MOBILE RTrY

A number of years ago mobile RTTY wasa topic for discussion here in Minneapolis,MN. Frequently these discussions turnedto de-regulated motors for the teleprinter.

receivers and transmitters and it is not un­common to hear of a receiver beingdamaged by rf when a mixup occurs.

The circuit I have shown will preventsuch accidents and also eliminate the in­convenience of having to change cablesmanually. Any receiver or transceiver canbe used in conjunction with a maintransmitter. Also, any antenna or dummyload can be used with any rig or receiver,while the SWR bridge, as well as anoscilloscope, may remain in the line, readyfor use.

No receiver can be damaged by themisapplication of rf, but misapplicationof an antenna could cause damage to atransmitter if not spotted quickly byobserving the SWR indicator.

Features of the switching arrangementare shown in the illustration. Coaxial­switch no. 1 selects the receiver ortransceiver to be used. It also provides abench-testing jack where a transmitter orreceiver may be tested. Switch no. 2selects the antenna to be used or a dummyload if desired. Any equipment connectedto switch no. 1 is disconnected from theantenna line by the action of the antennarelay controlled by the main transmitter.The ssb transceiver is available for usewhen not transmitting RTTY as is receiverno. 1 (for receiving RTTY on the hambands only) and the general coveragereceiver, no. 2. The latter may be used forNavy MARS phone or RTTY reception.- Melvin Leibowitz. W3KET

TRANSCEIVER ANTENNA RELAYCONTROLLED BY ANT.

RECEIVER MAIN TRANSMITTER .,*' ( ANT..,

RECEIVER COAX COMMON., SWITCH., MONl TOR ANT.SCOPE .,

BENCHTESTJACK ANT.

SPARE ••

ANTENNA SWITCHING FOR RTIYMy main interest is RTTY. For this modeI have a separate transmitter. When Iplanned my present installation I wantedto avoid damage to my other equipmentthrough a moment of forgetfulness thatwould allow a mixing of coaxial cableswhen bringing another receiver on theline. Many ham stations have multiple

TV BACKDROPWith more amateurs using SSTV and fastscan (regular) television, the need for awhite backdrop becomes important forthe production of high-contrast pictures.The installation of a white roll-type win­dow shade hanging from the ceiling,mounted a few feet behind the subject,provides a suitable background for thispurpose. - Robert W. Gervenack,W7FEN

Adjustment

Remove Ql from the circuit. This willallow the oscillator to run continuously.Connect a counter to the junction of theO.OS-IJF capacitor and the I-MO resistor.

Set R2 through R7 to minimumresistance, then adjust Rl for 2500 Hz.Set the selector switch to position I andadjust the corresponding control for thedesired frequency. Repeat this with therest of the potentiometers.

After setting all of the controls replaceQI and check the burst duration. Using avalue of 3S ~F for Cl will give a burstduration of 0.4 second. If a differentduration is desired change the value ofCl. Do not change the value of R8.

Comments

During the testing of this circuit oneunexpected advantage of using a rangecontrol (R1) came to light. If you shouldchange power sources and a different sup­ply voltage results, the tones will need tobe reset. Remove Q1 and select a tonewith the switch. Adjust the frequency ofthat tone using Rl. You will find that theother tones will be correct and need nofurther adjustment. - Glenn Dickenson,WB5BAF

Notions for Various Modas 121

The modified carriage-return mechanism fornonoverline operation.

CARRIAGE RETURN FUNCTION NECHANISN

(LEFT REAR VIEW)

CARRIAGERETURNLEVER

15Z893125001

3640

CARRIAGE RETURN

SLIDE ARM

\

BACK SPACE

SLlOE:RM/

153Z6/

CARRIAGE:

RETURNBAil

caused by the print hammer striking thecharacter which follows the line feed ­which also causes carriage return ­before the carriage has completely return­ed. There are three possible remedies forthis problem:

1) Only copy stations which use a non­printing character code after the line-feedcode.

2) Do not use nonoverline when copy­ing offending stations.

3) Use a machine that can complete thecarriage return before the next character isstruck.

This article explains a simple modifica­tion which allows the carriage return onreceipt of the carriage return code to beoptionally selected in addition to thenonoverline function without removingthe typing unit from the cabinet.

The modification consists of using apart of the on-line backspace-functionmechanism to perform the carriage-returnfunction. In order to do this a carriage­return-function bar along with theassociated function lever, function pawl,function-pawl clip, spring plate, andsprings must be installed in slot 9.of thestunt box. The rest of the modificationconsists of adding a back-space slide armalong with its retaining plate and a back­space bail. Many Mark 1I1 machinesalready have the back-space bail installed,so you only need to add the back-spaceslide arm and retaining plate. The back­space bail is installed on the same shaft asthe carriage-return bail as shown in thedrawing. A carriage-return slide arm maybe used in place of the back-space slidearm if one is available and if either thetwo-slot extension on the rear of the armis removed or slot 8 of the stunt box is not

W7UGV shows, designed to smooth 2400Hz (4800 Hz after demodulation), to ap­prox. 0.0033 ~F for the 9600 (19200) Hz.The time required for printing a ten­minute picture has also been reduced toabout three minutes. - Lindsay R.Winkler, W7A VE

Spacers may be made from the body of a ball­point pen.

PC-BOARD SPACERSFROM BALL-POINT PENS

The bodies of empty ball-point pens makegood pc-board mounting spacers, as in­dicated by the illustration. They may becut to any desired size. I used Bic ball­point pens because they have straightwalls. - Jose M. Armengol, WA2BNM

SELECfABLE NONOVERLINEFOR THE TELETYPE MODEL 28Nonoverline is a valuable function formost amateur radio teletype applications.However, the trend toward higher baudrates, coupled with poor operating habitsof some amateur and commercial stations,makes correct copying of these stationsimpossible with the nonoverline function.The authors have yet to find a Model 28typing unit that will complete the carriagereturn function in the "less than onecharacter length" required when a print­ing character follows the line-feedcharacter at 100 wpm. Thus, whennonoverline is being used annoying black"blobs" appear roughly one third of theway across the page. These blobs are

SPACER

'Anderson, "Amateur Reception of WeatherSatellite Picture Transmissions," QST,November, 1965.

IMcKnight, "Evolution of an Amateur Weather­Satellite Picture Station," QST, April, 1968, andFeedback, QST, July, 1968, p. 67.

IAn alternative arrangement is to use a circuit withprovisions for trimming the crystal frequency, suchas described in "A TTL Crystal Oscillator,"QST, February, 1974.

"King, "Conversion of Telefax Transceivers to Ama­teur Service," QST, May, 1972, and Feedback,qST, Nov. 1972, p. 33.

'Splllane, "ESSA II," Technical Correspondence,QST, December, 1966.

the articles by K2RNF,' W4MKM,' and2-meter information in The RadioAmateur's VHF Manual are the startingpoint. Hand-held dipoles operated in theshack or the backyard with a little ex­perience will often outperform some ofthe complex antennas now in use, so keepit simple, at least at first. A good con­verter is a must, and remember, thereceiver must be fm and have a 2Q-kHzbandwidth or more.

The second hurdle in the project is theconstruction of a standard-frequencygenerator putting out exactly 16 Hz. Thisis best done by dividing down from a1.6-MHz crystal oscillator with fivedecade counters. The oscillator must beexactly on frequency or skewing of thepicture will result. Use of compressiontype crystals which can be adjusted byeither loading with a pencil or solder, orby grinding with kitchen cleanser such asAjax. is desirable. J The need for the16-Hz frequency will become evidentshortly.

Driving the drum at the correct speed isthe third problem. The drum of the deskFAX, when driven by 6O-Hz line voltage,turns at 180 rpm, which is near four timesthe satellite's 48 lines per inch. An exactmultiple of four would be 192 rpm. Inorder to speed up the drum from 180 to192 rpm we just feed in a higher frequencyof ac, To find the correct frequency weuse simple ratio and proportion of 60/180= x/192. Solving for X we get 64 Hz, orfour times 16. Restating all this, if werecord 16 Hz on the left channel of ourstereo tape recorder and the picture infor­mation on the right simultaneously at

••. 1-7/8 ips, and then play back at 7-1/2 ips,·,.we will multiply both the outputs by four.·::I;.The 64-Hz output should be fed into the

':'voice coil of a reversed outputtransformer. The 5000-ohm winding istuned to resonance to help shape the48-Hz output to a sine wave. This outputis fed into the input of a 15-watt audioamplifier to feed 130 volts under load intothe drum motor. This will turn the motorat 192 rpm in synchronism with the videoat 192 lines per minute which is being fedinto the stylus through the Telefaxamplifiers. The only changes necessary onthe Telefax are those of King" to make itfunctional for amateur facsimile, and theaddition of a dpdt switch to transfer themotor, including its capacitor, from theac mains to the new line from the 64-Hzamplifier.

Since the pictures which are now pro­duced are negatives, some means of inver­sion is necessary. The writer used a dc in­verter already at hand and would recom­mend for simplicity's sake the system usedby W7UGV,' which lets one use theoriginal stylus amplifier of the Telefax.The frequency of the subcarrier has beenmultiplied from 2400 to 9600 Hz in thetape recorder and one must reduce thevalue of the 0.08-~F filter capacitor that

122 Chapter 8

'"TO TRANSMITTERMIC. INPUT

9U2C

10 7400

~~oo

<000

3300

moo

woo

DescriptionBracket, Retaining plate for back­space slide arm.SCrew.Used wlth 153254,Lock washer. Used with 151657.Clip. Function-pawl clip.Function lever.Function pawl.Plate, spring.Spring.Wick.Spring.Spring,Function bar (carriage return).Back-space slide arm. A modifiedcarriage-return slide arm may beUSed.Back-space ball.SCrew. Used to couple back-spacebail and carriage-return bail.Lock washer. Used with 152893.Washer. Used with 152893.

Table1

Parts for Model 28 NonoverllneOperation

Tele­type

Corp.PartNo.

153254

153255152693

364015011

1516572191

15212715264215265315266015724072522905174703

152667153262

SCHMITT TRIGGER741~

aa 2A 2Y'" 9 9

,

14 13 12Vee 20 2C

(B)

''Vused. There is a screw in each end of thecarriage-return bail shaft which may beremoved allowing the shaft to be pulledaway from the machine so that the back­space bail assembly can be placed on theshaft. This operation requires sometwisting and turning, but it can be done.Once the parts have been installed, thecarriage-return adjustment should bechecked. Note that the screw in thecarriage-return bail extends through a slotin the back-space bail to couple the two.They are not screwed together rigidly.

With the modification completed, thefunction pawl in slot 9 can be disabledwith the pawl clip and the nonoverline willoperate in the normal fashion. The clipcan also be set so that slot 9 is active andthe machine will carriage return on receiptof the carriage-return code with thefollowing line-feed character interval pro­viding the time needed for completion ofthe carriage-return function.

We have found this feature to be ex­tremely useful when copying. lOO-wpmpress stations, some amateur stations, andcertain types of teletype art where over­lining is used on purpose. The requiredparts necessary for nonoverline operationare listed in Table I. - Lenox Carruth,Jr., WA50VG and Dick McDonald,K5WOR

An electronic, positive FAX converter. Part A is the basic schematic diagram. There are no con­nections to pins not shown in the scnematlc diagram. Part B is the component layout for theprinted circuit board, shown from the component side.

AN ELECTRONIC FAX CONVERTERAmateurs who have the model 6500facsimile machine may be interested inthe positive FAX converter that I havedesigned and built. The circuit shown herealso has provision for sending electronicsync bars.

In my installation all components aremounted on a pc board. the lO-kllpotentiometer in the output circuit is a

multiturn type. It should be set for the in­put level to the transmitter. R2 on the fac­simile machine must be adjusted carefullyfor proper operation of the converter. Theoutput frequency ranges between 1500and 1600 Hz. I found that best results

were obtained with the pc board mounted.within the machine. All resistors are 1/2watt. They are mounted vertically. The pctype of capacitors used are obtainablefrom Radio Shack stores. They work well.- Robert A. John, WB6FVL

Notions lor Various Modas 123

7- or 9-pin miniature tube socket to obtaintwo individual pin sockets. Solder strand­ed wires to the pins, using the holes just asyou would if the socket were intact. Pusha piece of No. 18 wire into one of the pinsand after soldering, nip it off, leavingabout 3/16 inch. Two short pieces ofspaghetti, about 5/8 inch long, slippedover each pin. Will insulate the bare metal.This small pin and socket will allow foreasy connection and disconnection whenrequired for modifications. - W. ConleySmith, K6DYX

Small disconnect junctions made from parts ofold tube sockets.

~FAX

PUSHBUTTON

R·1168

MONITORSPEAKER

+ 2S0Vo-.....----'

LAMP DRIVER

'0'CONTRAST

*''0i.a

88mH

lOOOnII

LOW PASS FILTER0.022

+---,--."...-.ji---?--.,..----,

* SEE TEXT

LO·Z.~

FROM)RECORDERRIGHTTRACKOUTPUT

The effects of hum and noise are reduced In the Deskfax with this filter.

A representative circuit for SeR relay control for auto-startrmotor-cetey sections of Rnydemodulators.

This circuit shows how a high-voltage, passtransistor may be used to turn gas-dlschargedisplay lights on and off.

DISPLAY

DISPLAY

PASSTRANSISTOR

••'""i72W

BREAK,

.,47'1/2W

HIGHVOLTAGE

RECTIFIER

AFTER:

BEFORE'

FOR READOUTOF DIGITAL INSTRUMENTS

The readout of such digital instruments asclocks, panel meters, multimeters andothers using Nixie lamps or seven­segment, gas-discharge displays, may beturned on and off by means of this simplecircuit. High-voltage transistors such asMJE345, ECG! 54 or MPS A42 may beused. One should note that the display willbe on when S1 is in the off position andvice versa.

Some commercial digital instrumentsemploying the early type seven-segment,gas-discharge displays, such as SP75I andSP752, may show anomalies which showup as display flicker. This effect may beeliminated by means of the simple

the final step: Replacing the relay with anSCR or, if an ac motor is being con­trolled, with a TRIAC. (SCRs conductonly on half cycles.) Caution: Whenreplacing relays with solid-state devices,always avoid circuits which present poten­tial hazards, such as an ac primary chassisground.

Here is a representative circuit for SCRrelay control which has been used with ex­cellent results in RTTY auto-start/motor­delay sections of homemade RTTYdemodulators at WB8DKX and W8KDC.Pick-up/drop-out times can be varied bythe combination' RIICl, and also varyconsiderably with the SCR type (in thiscircuit the times are 1 second and 3seconds respectively). It is virtually im­mune to cw, voice, etc., and keys only ona RTTY mark tone (2125 Hz). DI and D2are silicon diodes, 50 PIV or greater, ifneeded, for the ac relay - the contacts ofwhich should be capable of handling theload being switched, plus a safety factor,of course. - Dick Weeden, W8KDC

TUBE SOCKET YIELDS MINIATUREDISCONNECT JUNCTIONSNeed a few disconnect junctions for wir­ing between pc boards or from circuitboard and panel controls? Use a pair ofside-cutters to shatter a moulded phenolic

7-;--<0 it7 VA~+~ TO TELEPRINTERMOTOR

A NOISE AND HUM FILTERFOR THE DESKFAXIn the process of modifying my DeskfaxAPT equipment for use withphotographic paper, 1 found that thisfilter circuit and audio amplifier improvedthe operation by reducing the effects ofnoise and hum. A Radio Shack I-wattaudio amplifier compensated for insertionlosses through the filter. An equivalentamplifier could have been made fromtubes and components contained in theFAX unit. This circuit may be of help toothers. - Lindsay R. Winkler, W7A VE

SCR RELAY CONTROLFOR RTTY, VOX, AND COR

Ad' One would expect to find more extensive·;,~use of SCRs in present day relay-control

circuits, given the desirability of economy,reliability. simplicity, and state of the art.

'. Often an SCR can replace up to severaltransistorized or tube stages in RTTY,VOX, COR, and other relay-control cir­cuits.

The threshold triggering effect of theSCR can be used to advantage here, trig­gering being automatically suppressed onlow-level noise and similar interference.Because of its turn-off characteristics, acis easier to control with an SCR than is de,

Some experimenters may wish to take

124 Chapter 9

\l

Display flicker, occurring on some commercialdigital instruments, may be corrected bymeans of this modification.

modification shown in the schematicdrawing. This modification was effectiveon a series of Weston no. 1230 units andshould provide good results for otherdevices. - Jose M. Armengol, WA2BNM

AFTER

MAKING CIRCUIT BOARDSWITH AN END-MILL CUTTER

A method I use for making copper-clad,circuit boards may be of use to otheramateurs. Instead of using etched printed­circuit boards, I use a drill press with anend-mill cutter to remove unwanted cop­per. With this process, [ have successfullymade several boards described in TheRadio Amateur's Handbook.

To adjust the tool for proper depth ofcut, the end mill is placed in the drill pressand set for a depth that is just below thebottom of the copper. Drill-press speedshould be approximately 3000 rpm. Thediameter of the cutter I use is 1/16 inch.After adjustment is made, the circuitboard can be moved very carefully in anydirection. - Joseph Schnipper, K3RFL

ReferencaDance. Electronic Counting Circuits, 1967.General Electric Transistor Manual. 1964.Malmstadt, Enke and Couch, Digital and Analogue

Data Conversions, 1973.

of the converter by changing the value ofthe input resistor. For example, aI-megohm resistor yields a basic 100voltrange. Ohmmeters and milliammeters canbe adapted. One should be aware of thepossibility of over-range readings whenthere are a limited number of displaydecades in the frequency meter. A polarityindicator could be added just as well.

For stability of calibration, the positivesupply should be regulated to a percentageequal to the accuracy of the least signifi­cant digit. Cost of the converter was lessthan $20. - D. K. Trueman, VE4A Y

-,ADO 100pF, 1000V OISC

BEFORE

HIGH VOLTAGE RECTIFIER

(

(aREAl< lOOk

\,,:

This diagram shows a voltage-ta-frequency analog/dIgital converter.U1 - 741 operational amplifier. 28877, or equlv.Q1 - Silicon npn transistor, Hitachi 2SC281, Q3 - P·N, bar-type, silicon untluncttcn transls-

cr equtv. tar, Texas Instruments 2N1671·B or equlv.Q2 - Germanium pop transistor, Hitachi C - 7-45 pF ceramic trimmer capacitor.

+9V REG.

0'

f-oOUTPUT

8600

4700

"

-9V C

,"' '00 0.002

"00.

1N400\

+.o-J\fI.I\r....----i100k

ANOTHER ANALOGIDIGITALCONVERTERIn developing a system to expedite fieldreadings for geophysical surveys, [employed an analog-digital converter.The converter is a voltage-to-frequencytype, for which the output is stored on acassette recorder. The recorder is playedback to the input of a digital frequencymeter to recover the information. Theconverter input is 0-1 volt, and the outputfrequency is 0-10 kHz.

The converter, when connected directlyto the frequency meter, becomes a digitalvoltmeter. With the availability of digitalfrequency meters, the converter becomesa useful accessory for the ham shack.

The circuit is conventional. My re­quirements were dictated by the frequencyresponse of the aforementioned recorder.It should be possible to change the range

Notion. lor Varlou. Mod.. 125

Chapter 10

Data for PC Boardsand Solid State

Counto100200300400500600

rlbl.1

Voltageo123456

A SIMPLE ANALOG/DIGITALCONVERTERThere are times when an analog/digitalconversion is desirable. I designed this cir­cuit for that purpose, so that it may beused with any counter having a one­second time base. I use a Heath IM-l 102.

Section I of the schematic diagramshows the basic integrating circuit con­sisting of an operational amplifier and aunijunction transistor along with a fewcomponents which form a linear voltage­to-frequency converter. The only problemis that the input voltage has to be refer­enced to the ± 12-Vline. Also, the outputpulse (negative) is of very short duration,creating a possible problem for somecounters.

Section 2 shows an input amplifier thatinverts the input, thereby referencing theinput voltage to ground. Section 3 in­cludes a second operational amplifierwhich changes the output pulse to asquare wave, clearing the way for use withany counter.

An option is shown in Section 4 wherean NES55 timer is added operating withintervals of one second on and one secondoff. With this time base, it is possible toconnect the output of the converter direct­ly to a type 7490 counter and have a directreadout. Three 7290s and decoders,however. would be needed.

The upper limit of the basic converter is

NPN OR PNP WITH A YOMA simple outline is offered below to deter­mine the base configuration and type (npnor pnp) of a transistor. The only testequipment required is a YOM.

The first step is to set the YOM in theproper mode. Place the meter in the R X100 position. The black meter lead is con­nected to the COM. meter terminal, andthe red lead is connected to the YOA meterterminal (on some VOMs it is just 0).·

The next step is to find the lead on thetransistor 'that shows about the sameresistance to each of the other two ter­minals. This is the base. Note the color ofthe meter lead. If red, the device is npn, ifblack, it is pnp. At this point, the baselead is known and the type is known.

Now set the meter to the high-ohmsscale (R x lOOk). Place the meter leadsacross the other two leads on the tran­sistor. Reverse the meter leads to locatethe lowest meter reading. Note the polari­ty of the meter leads. If the device is npn,then the black lead is on the collector andif it is a pnp type, then the red lead is onthe collector.

The last terminal on the transistor, bythe process of elimination, is the emitter.In a power transistor the case is generallythe collector. It should be noted thatalthough these tests are quite helpful inlocating the different elements and typesof transistors and will work 95 percent ofthe time, not all transistors can be iden­tified in this manner. - G.D. McKechnie.W4lKB

"[Editor's Note; Not all ohmmeters have the samepolarity (red +, black -) when in the ohms posi­tion. In some instances, black may be the positiveterminal. Confirmation of the test lead polaritymay be found by placing the milliammeter acrossthe leads while in the R X 1000 position.Proper meter movement will determine the ohm­meter polarity.]

,001

NE~~~

6

r - - .O-j <--.'---'-',\ \~, 001,

i;-S1,IL _ -L-.--+---+---+--+----1

A scud-state, timed-alarm circuit.SW1 - Remote, hidden trigger switch, N.O.SW2 - Remote, hidden arming switch (close

to energIze or arm the system).S - Mallory Sonalert SC616N. Rated 80·95 dB

at 2900 Hz, 6·16 volts, 4-16 mAoNote: Builder may choose switch type for SW1.When closed by action of an intruder, a neqa­tlve pulse is delivered to pin 2 of the NE555turning it on to drive the Sonalert through pin3.

lOO~

0.47

THE UBIQUITOUS NE555 TIMER

Recently I wanted a timed-alarm circuitbut did not want to bother researchingpast issues of electronic magazines to lookfor one. The solution was the NE555timer and a simple negative-pulse arrange­ment. This Ie combined with a simplelow-cost circuit provided an alarm thatcould be set for a given period of time,then automatically turned off. With thecomponents shown in the diagram the ONtime is about three minutes. Increasing Ror C lengthens the ON time and vice ver­sa. One must remember, when buildingthis circuit that electrolytic capacitors varywidely from their marked ratings. Thiscan result in timing variations from one

• timing circuit to another.The device is particularly useful in con­

nection with an intruder- or theft-alarmsignal to limit the time the alarm operates,to conserve battery power and to limit an­noyance to neighbors should the alarm beactivated. - Charles L. Shaw. K8ET

126 Chepl.r 10

.H4TO

+C9

;L~ ROO2"4.7101

R9 CT CB4ro. 0.01

0.1

Like the original tube' version. the ageline must be of very high impedance. Thiswould be the case with an FET i-f system.If this circuit is to be used with anintegrated-circuit or bipolar i-f amplifiersystem, a low-impedance driver would benecessary. - Dick Stevens. WIQWJ

A HIGH-CURRENT, LOW.VOLTAGEREGULATOR FOR TTL CIRCUITSWhile many amateurs are now using­integrated-circuit voltage regulators, anexternal current-boosting (a series­dropping element) pass transistor is usual­Iy required to increase the regulator cur­rent capacity. Normal current-controlledregulator schemes. however, require addi­tional active devices to duplicate some ofthe worthwhile safety features of theregulators - l.e., short-circuit protection,safe-operating-area protection and ther­mal shutdown.

Here is a regulator circuit which retainsthese safety features through a current­sharing design. This regulator, intendedfor TTL circuits. has an output of 5 voltsat 5 amperes, and typical load regulationof 1.4 percent.

RI and R2 provide the necessary cur­rent division (assuming the transistorbase-emitter voltage equals the diodedrop). The voltage drops across RI andR2 are equal, and the currents through R"Iand R2 are inversely proportional to theirresistances. In this circuit, Rl has fourtimes the current flow of R2.

For reasonable beta values, the tran­sistor emitter current will approximatelyequal its collector current, while the cur-

'ITOk...'0'

SECTION 3 '

U1.J'>--;--+-==--CiOuTPUT

AGCo--<~-----~-lIf--;-~

SWITCH 03

EXCEPT AS INOICATED, DECIMAL VALUES OF

CAPACITANCE ARE IN MICROFARADS (pF \ ;OTHERS ARE IN PICOFARAOS ( pF OR jljlFl;

RESISTANCES ARE IN OHMS;k.l000. 101-1000 000.

AMPLIFIERAMPLIFIER 02

0' 2N339tAcMPF1Q2C3

co 0 B C,

IN~~To--1G 0.'0.'

0.' s 0' oa.T".,

'M R2+C2 47Qk

'.' .B4700 15iT .4 3300 00'

3300 RT 2000

that across R9/C', Q3 conducts andclamps the age bus to ground. D2 is thecharging diode for the 0.01 ~F agecapacitor. Age threshold is determined bythe value of RT. The value should be be­tween 100 kO and 470 kO depending onthe age threshold desired.

Schematic diagram of the hang-age system. Beetetcre are 1f2-watt composition.C2, C4 - 5 j.lFelectrolytic, 15 volts. 03 - 2N5716 FET.e9 - 50 IolF electrolytic, 25 volts. AT - See text.01-03, Incl. - Silicon diode, 1N914. T1 - Audio transformer, 10,OOO-ohm primaryQ1 - MPF102FET 10 2,OOO-ohm secondary (Radio ShackQ2 - 2N3391A transistor. 273-1376 or equtv.j.

2N2169

"00

"".

SECTION 1

• •400k

• • •INPUT 100~ • •

• •'00

eeoc

II .o-~----,....-----~----i---o~12VIII

(ftlo:: 'N""'~61 2000

;Lesse 5: ~E. ~-'V'vv--III -o--....-~'N\~-----..J

III I

'. I +12'1 OR TO NE"S(lF USEO)_____ J._ - - --- - ----- - T - -- -,----- ---- ---

SECTION 2 SECTION 'I

approximately 6 volts. A resistive type ofdivider can be used at the input to increasethe limit to any value needed. Also it ispossible to add a rectifier at theinput tomeasure ac voltages. Ohmmeter rangesmay be included.

Construction notes: The output maynot follow the input below the l-volt levelbecause of operational-amplifier offset.Preferably, check the operationalamplifier and UJ separately to observe therange and linearity. The SOOO-ohm. poten­tiometer in the collector circuit of QImust be adjusted for the transistor used.There is interaction between the twopotentiometers. - Robert D. Corbett,WICH

-------- ' ...J _

Circuit for a simple AiO converter.

'Goodman, "Better A.V.C. for SSB and CodeReception," QSTfor Jan., 19S7, p. 16.

SOLID-STATE HANG AGCI converted Goodman's hang-age circuit!from a tube to a solid-state system. Itworks as a hang-age system should - very

-fast attack time with no age "pop." QIand Q2 function as audio amplifiers. 01 isthe age diode, with C7 and R9 serving asthe charging network. Q2 output isstepped up through the 2-to 100kO audiotransformer. D2 charges RIO/C8 to ahigher voltage than that across R9/C7.which keeps the FET (Q3) cut off. A2NS716 was used because of its low pinch­off voltage. When the voltage acrossRIO/CS decays to a lower voltage than

PC Boenta end Solid Stete 127

IA)

EXTRA TURNS

COIL TERMINAL

r:I

rr~p,~~~~~nrSHORT ING CON-NECTIONS {FORMAIN COIL ANDEXTRA TURNS}

result of spacing, plating thickness, andthe physical relationship of the compo­nent placement and the location of the cir­cuit ground plane. The fixed printed coilmust be trimmed in order to obtain thedesired inductance value.

One solution of this problem is shownin the diagram. A spiral-like coil is printedwith several extra turns which increase therealizable coil inductance; shorting con­nections are also included to reduce the in­ductance. The shorting connections notonly short the extra turns, but also shortout several turns of the main body. Coiltuning is accomplished with relative easeby removing the shorts until the desiredinductance is.obtained.

Approximate printed coil lengths andfabrication parameters are obtained bycalculation from circuit models or ex­perimentally determined design curves.After the approximate coil dimensions areobtained, the printed-coil layout is con­structed with the several extra turns andshorting bars .. Shorting connections arethen removed from the coil until the exactvalue of inductance is obtained. This pro­cedure calibrates the layout and subse­quent photoetching process.

Once the exact coil geometry is ob­tained, the designer has several options. Ifthere are a limited number of activedevices in the circuit, the existing printedcircuit art work may be modified byremoving the appropriate shorting con­nections. On the other hand, if the circuitcontains a large number of active devices,individual coils may be trimmed to ac­count for differences in active deviceparameters. The former approach wasused in a phased-array receiver. Nineteencoils of values from 0.05 to 0.1 mH wereused in a variety of circuits such as delaylines, hybrids, and amplifiers. For thelarger coils a tolerance of plus or minustwo percent was obtained, and a toleranceof plus or minus one percent was obtainedfor the smaller coils. The cost per coil wasvery competitive with commerciallyavailable fixed or tuned devices. In addi­tion, the other advantages of the printedwiring approach were obtained at minimalcost.- NASA Tech Brief 69-10665

A spiral printed-circuit coil.

FERRITEBEADS

FERRITEBEADS

'",~---__-e----{''I-''''< 116;CF~~~~;~T

TRANSFORMER

~---_-e----{''I-''''< II ~~CF~~f~;~TTRANSFORMER

Use of hlgh·wattage Zener diodes may beavoided by these circuits.

~O-90WATT NPNAUDIO TRANSISTOR

~O-90WATT PNPAUDIO TRANSISTOR

(B'

stock Zener diodes of the 50-watt variety.The accompanying diagram shows how aI-watt Zener diode, an inexpensive 50- to9O-watt audio transistor along with a half­watt resistor, can be connected to performthe same function. Circuit A uses a siliconor germanium pnp transistor. The voltagerating of the Zener diode should beapproximately 0.3 volt less than thedesired bias voltage for a germanium tran­sistor and approximately 0.7 volt less for asilicon unit. The circuit at B uses an npntransistor. Again either a germanium orsilicon transistor may be used, and theZener-diode voltage rating is the same asthat for circuit A. The transistor shouldbe bolted to the chassis, using the chassisas a heat sink. In circuit A the transistor

can be bolted directly to the chassis, butthe circuit at B will require a mica in­sulating washer because the collector(case) is above ground. Ferrite beads areplaced on the transformer center-tap leadto discourage parasitic oscillations ­adapted from a circuit in the article "TheAmplified Zener," which appeared in theSeptember, 1970! issue of ElectronicsWorld, copyright 1970 by Zlff-DavisPublishing Company. (All rights re­served.)

(Editor's Note: Many thanks to J. F. Dunten,K5DQT, for calling this circuit to our attention.]

DESIGN OF PRlNTEDoClRCUlTCOILS

The fabrication process of printed circuitcomponents results in essentially fixed­device parameters. Considerable variationin the inductance value of coils occurs as a

+ R' 2N4399

O.2~

1""6W

'0tov

'" R,

A regulator for TIL circuits.

AN ALTERNATIVE TO HIGH­WATTAGE ZENER DIODES

High-wattage Zener diodes! the type usedto develop bias in some linear amplifiers,are often hard to find. While they are notterribly expensive, not many distributors

BOTTOM VIEWOF LM 340T-05

$INGI.E POINT GROUNO

rent through R2 will equal the currentthrough the regulator. Under overload orshort-circuit conditions, the protectioncircuitry of the regulator not only limits itsown output current, but that of the exter­nal pass transistor. too.

Thermal overload protection is extend­ed to the external pass transistor when itsheat sink has at least four times thecapacity of the regulator (this is becauseboth devices have almost the same inputand output voltage and share the load CUf­

rent in a 4: I ratio).For optimum. current sharing between

the regulator and the transistor as a func­tion of temperature changes, the diodeshould be located physically near the passtransistor. so its heat-sinking arrangementkeeps it at the same temperature.

If the National LM340T regulator isused and mounted on the same heat sinkas the transistor, the regulator should beelectrically isolated from the heat sink, asits case <pin 3) is at ground potential whilethe case (collector) of the transistor is atthe regulator output potential.

Cl prevents unwanted oscillations,while C2 improves the output impedanceof the overall circuit. R3 is used to"unload" the excessive charge in the baseregion of the pass transistor when theregulator suddenly goes from full load tono load. The single-point ground system,allows the regulator sense terminals (pins2 and 3) to monitor load voltage directly,rather than at some point along a possiblyresistive ground-return path which may becarrying up to 5 A of load current.William R. Calbo, K9ASL/8

,

128 Chaptar 10

+VCC

An FET and transistor combination used toprovide the equivalent of a voltage-controlledZener diode,

VOLTAGE-CONTROLLED ZENERThe use of two complementary bipolartransistors to form what is in effect an ad­justable Zener is fairly well known. Avariation of this approach is noted inPracticalElectronics (January, 1976) sug­gested by I. D. Evans. He uses a junctionFET (2N3819) and bipolar npn transistor(BCI69/2N27l2) to form the equivalentof a voltage-controlled Zener. This isbased on the so-called "amplified Zener"arrangement but replaces the Zener diodewith a resistor (Rl) and the usual resistivebranch of the network with an FET whoseresistance (R2) varies in accordance withan applied control voltage: see thediagram. The FET resistance controls thevoltage at which the transistor turns "on"and can, if required, be readily controlledremotely. - Radio Communication,March, 1976, RSGB

HEP 246 OR HIGHCURRENT PNPOEPENDING ONLOAD

+ 12V TO XMTR V--"<.- ./

MARKING ETCHED-CIRCUITBOARDS

Etched-circuit boards can be neatlymarked with component designations andpolarities by using waxy rub-on transferletters. Alphabets of various sizes can bebought at art supply stores. The waxy let­ters act as a resist, leaving the marking inthe copper after the board is etched. Ialways include W9IWI in a corner of theboard to show who made it. - JulianJablin, W9JWI

+ 12V

LOW-COST ETCH-RESISTANT PENSAND A NEW SLANT ON ETCHANTBATHSLess-expensive etch-resistant pensubstitutes are Sanford's Sharpie perma­nent ink marker for narrow lines, andSanford's Impact with a wider tip.

For etching printed-circuit boards, I usea one-gallon mayonnaise jar. Place thehoard to be etched face down on the In­side of the jar, with the jar resting on itsside in the sink. Pour in enough etchantsolution to wet the surface of the board,and put the cover on the jar. A plastic grillreduces the chance of breakage and the ir­ritating noise of the glass rolling in thesink as the etchant is agitated. The etchingprocess may be hastened by placing the jarin hot water, keeping the water levelbelow the mouth of the jar. By holdingthe jar up to the light, it is possible todetermine when etching is completed; andwhen it is, the solution may be poureddown the drain or back into the jar. Theboard may be rinsed while still in the jar.With this method, it is never necessary tohandle the etchant directly, reducinggreatly the chance of spills and stains.- John H. Bordelon, K4JIU

EXCEPT AS INDICATEO, DECIMAL VALUES OF

CAPACITANCE ARE IN MICROFARADS \).IF l ;OTHERS ARE IN PICOFARADS (pF OR J.IJlF):

RESISTANCES ARE IN OHMS;kK 1000, MolOOO 000.

FROMCOROUTPUT(DC)

12k E

47k

Solid-state relay, The LED is a surplus type, but a Radio Shack replacement should not be dif­ficult to obtain.

one of the socket pins. Do not let the tiptouch the foil beyond the point of solder­ing. Bend this end away from the ICsocket. Prepare each of the necessarysolder points on the board for eachsocket. A "Z" pattern will make holdingthe wire against the board easier whensoldering: That is, bend the wire onedirection on one side of the board and inthe opposite direction on the other side.

Now, bend outward each socket pinwhich must make electrical contact onboth sides of the board. These piris shouldcorrespond to the wires just soldered. Bevery careful with them since they may beeasily broken. Solder each socket pin tothe proper place. Soldering wires on bothsides of the board may be necessary formechanical support. This should be doneif the majority of socket pins make elec­trical contact only on the Ie side of theboard. Tinning both the socket pins andthe foil on the top of the board can be .helpful. That's all there is to it. - TonyStalnaker, WA4LPJ

2N3904

SOLID-STATE RELAYFOR REPEATERS

The device shown in the diagram wasdesigned by W0INK to interface withsolid-state vhf receiver and transmitterstrips. Our 2-meter repeater is now com­pletely solid state and has a current drainof only 400 rnA when in operation. TheLED, when lit. indicates the transmitter isin operation. The delay of the "tail" canbe adjusted by changing the value of Cl.For a normal squelch tail, a value of 20 ~Fis used. The relay is driven by the CORcircuit. Several CORs that could be usedwith this relay are described in FM andRepeaters for the Radio Amateur.Mike Wisch, WB6LGC/WRMEN

VOUTPUT

1000R'lOOk

2N2712

s

o2N3B19 ~-+-r

VCOf'TROL G

WORKING WITH IC COMPONENtSWhen working on a project using ICs anddouble-sided pc boards, one may find itnecessary to solder IC pins on both sidesof the board. Although the IC may besoldered directly to the board, a morepractical approach 'is to install a socket.Use of the IC socket facilitates componentreplacement and may save an Ie fromdamage caused by excessive heat whilesoldering.

Mounting the socket on a pc board maybe difficult because of the short pins onthe socket. An easy solution is to use asingle conductor of stranded hookup wireto make pin extensions for the socket.

Place the end of a strand through thehole in the board for each IC pin whichmust have soldered connections on bothsides of the board. Bend one end of thewire against the board on the side op­posite the Ie. Do not let the end passbeyond the edge of the foil to be soldered.Solder this end.

Next, turn the board over. Cut the endof the strand to a length equal to that of

PC Boarda and Solid Slate 129

An arrangement for a simple BCD converter and readout.

(Al (C1

[0 100jOOOI ::[O::j

circuit draws 4 rnA. The frequency rangeis selectable from 15 Hz to 150 kHz,although a I.S- to IS-Hz range can be In­eluded with the addition of two 5.1'!' non­polarized capacitors and an extra switchposition. Distortion is approximately onepercent. The output level under a lightload (10 kG) is 4 to 5 volts. This can be in­creased by using higher battery voltages,up to a maximum of + and - 18 volts,with a corresponding adjustment of Rf.

Pin connections shown are for the TO-5 ,case. If another package configuration isused, the pin connections may be dif­ferent. Rf (220 ohms) is trimmed for anoutput level about five percent below clip­ping. This should be done for thetemperature at which the oscillator willnormally operate, as the lamp is sensitiveto ambient temperature. Note that theoutput of this oscillator is direct coupled.If you are connecting this unit into circuitswhere de voltage is present, use a couplingcapacitor. As with any solid-state equip­ment, be cautious around plate circuits oftube-type equipment, as the voltage spikecaused by charging a coupling capacitormay destroy the IC. - Tom Schultz

a,(L1GHT-OOTS)

(81

::[o::j= Ii I

r- "mm -----1

__ MASK (THIN SHEET METlll)

(014----- PC - BQdRfJ

, B c 0

0 0 0 0 0. , o 0 0

, 0 , 0 0

, , , 0 0

, 0 0 , 0

e , 0 , 0

0 0 , I c, , , I ,B 0 0 0 I

s I 0 0 ,

QQ'"

SCREEN ----.

o

A SIMPLE BCD CONVERTERAND READOUTThe arrangement shown will take a binaryinput and convert it directly to a decimalreadout using four clamps (or LEDs).This eliminates the need for decoder/drivers. Nixie tubes or neon lamps andprovides the ultimate in a low-costreadout.

Each decade digit consists of fourlamps in back of a mask as shown in thedrawing. The lamps correspond to thebinary positions for 1, 2, 4 and 8. Onehole is drilled in the mask for the "I"position, two holes for the "2" position,and four holes for the "4" position. Asmall hole over a larger one is drilled torepresent the "8. II

In reading the display, one could merelycount up the lighted dots (except for 8 and9). But with a little practice, the digits canbe read on sight. The figures for I, 2, 3, 4and 6 resemble the numbers themselves(with a little imagination). Only 5 and 9are new but can be learned with little dif­ficulty. - Peter Hansen, DK4YD

ETCHING METAL PANELSDecal labels on radio equipment oftenwear and peel off quickly, particularly ontest equipment subjected to constant use.Etched labels, on the other hand, providepermanent identification of control knobsand dials.

To etch a steel panel, pour hot paraffinover the area to be labeled. When cooled,letter the label into the paraffin with asharp pointed instrument, scraping themetal clean to form the letters ornumerals. Neat lettering can be insured byusing a lettering guide from a stationery

store. Remove any wax shavings with afine brush and place a drop ofhydrochloric or nitric acid on each letterwith a medicine dropper. Several applica­tions of acid may be necessary to obtainthe desired depth. When etching has beencompleted, wash the panel with cold waterand peel off the remaining wax. Theetched characters can be filled with paintor nail polish.

The necessary acids can be obtained insmall quantities at most drugstores, butare highly corrosive and should not bebrought in contact with the skin. Con­tainers should also be properly labeledand have tight plastic or rubber caps.Joe A. Rolf, KSJOK

SEMICONDUCTOR CIRCUITREPAIR HINTWhen a diode or transistor "blows,"knowing why is a help in order toeliminate the cause and to prevent furtheroccurrences. If the failure was caused bytoo high a current, the semiconductorwould be open because of the overheatingand melting of the pn junction. If avoltage spike or high voltage was thecause, the device will be shorted inasmuchas holes will be punctured in the pn junc­tion. This hint has proven helpful andreliable for me in troubleshooting tran­sistor and diode circuitry. - Rick Liftig,WAIISD

AUDIO OSCILLATORA wide-range audio oscillator that willprovide a moderate output level can bebuilt from a single 741 operationalamplifier (see diagram). Power is suppliedby two 9-volt batteries, from which the

"'" -""-sar '"+~

6

4~

'" 11::iOO-9V

~ ee'0'________ oJ

FREa.

SIB so.4

~L?J'-";;: .;O.O!!

;J:O.OO!!

;;:o.OOI::i

m~470

ElCCEPT AS INDICATED. DECIMAL VAWES OFCAPACITANCE ARE IN MICROFARADS (jlF I ;OTHERS ARE IN PICOFARADS I pF OR jljlFI;RESISTANCES ARE 1'-1 OHMS;k 0 rooo, 11I01000000.

SWITCH 1POS. FREQ.

t 1!!-1~OHz

2 1~O - l!lOOHz3 1!lOOHz-1!l.Hz4 15- l!lO~Hz

A simple audio oscillator that provides a se­lectable frequency range. A2 and R3 controlthe frequency and At varies the output level.

130 Chapter 10

--_.__._--------

pulses. Then the logic probe could be usedby those who have no high-speedoscilloscopes to trouble-shoot clock cir­cuits. pulse generators, and the like. ­Ray Dagenais, VE3ARJ2N2222

6, +

680

2N60~~

+o----.----+-----~__-,( ,>----<>-_-<)+1~-2~V DC 13V DCUNREG. _~ ~_REG.

Simple high·frequency indicator by PA0FMYusing an LED as indicator.

+5V

twS'J~

RESEil

A HIGH.FREQUENCY INDICATORWITH LEDThe use of a light-emitting diode as a low­cost indicator is noted in a short item byF. Maters, PA0FMY, in Electron forMay, 1975. This appears to be a usefulgimmick to have around. - Radio Com­munication, August, 1975, RSGB

Suggested circuit for adding pulse-testingfeature to the Rogers logic probe. See text forparts description.

1000

7

'"PULSE- C1TEST 0---1 1-+-----'-,----.,

INPUT l~pF

1000

[Edilor's Note: There are several ways in which apulse-testing feature can be added to the Rogers logicprobe. The circuit of the drawing is suggested as a sim­ple approach. The circuit may be constructed as aseparate module, and is used in conjunction with thelogic probe without requiring any modifications to theoriginal device. UI is a quad 2-input positive NORgate, type 7402, half of its sections being unused. 51 isa momentary-push normally open switch. CI may bedisk ceramic, and its value it not critical

With no connection or with a steady-state de level(either a logic high or a logic low) at the pulse-test in­put, depressing and releasing 5' willcause the "0" in­dicator of the logic probe to light and remain lit. Assoon as a positive going logic pulse of 3.5 V or more isapplied at the pulse-test input, the "!" indicator ofthe logic probe will light and remain lit. After connec­tions are made 10 the circuit under test, 51 may bedepressed and released repeatedly, and a train ofpulses will be indicated by the "1" indicator becominglit each time after the reset switch is released. With arelativelysmall value for CI, as shown, the circuit willnot respond to any wave forms except fast-rise-timepulses and rf.j

PULSE·DETECTOR CIRCUIT FORTHE VEST·POCKET LOGIC PROBEI have built the vest-pocket logic probedescribed in QST. I I used LEOs as in·dicators, instead of the incandescentlamps, with a 220-ohm resistor in serieswith each LED. It is a wonderful test in­strument to check logic circuits, and han­dy to use. What I would like to know is ifit could be modified so that it will indicate

BEWARE OF PROTECTIVE DIODESA word of caution regarding the use ofprotective diodes across the antenna inputterminals of solid-state receivers is inorder. If separate antennas are used fortransmitting and receiving, severe TVI canbe created by the diodes rectifying thetransmitted signals and reradiating themon many frequencies in the rf spectrum. Idiscovered this while experimenting withmy solid-state receiver. I was attemptingto see if the diodes really protected thefront-end rf transistor stage by leaving thereceiver connected to its own antennawhile transmitting with a 350-watt rignearby. I was impolitely informed by theXYL that I was raising havoc with thetelevision set. As soon as the receiver wasdisconnected from its antenna, the prob­lem disappeared. If the same antenna isused for transmitting and receiving such aproblem should not exist. - GlenBenskin, K6UH

'Rogers, "The Vest-Pocket logic Probe," QST,August, 1972, p. 46.

LONGER LIFE FOR CIRCUIT·BOARD ETCHANTStoring ferric-chloride etchant (the typeused for etching printed-circuit boards) ina refrigerator will prolong the usefulnessof the solution. Chilling the etchantcauses precipitation of free copper to thebottom of the container as "mud." Theclearer liquid can be poured into anothervessel and the "mud" then washed out ofthe original container with clean water. ­W. H. Fishback, WIJE

7

EASY PRINTED-CIRCUIT LAYOUTAfter reading the article on printed cir­cuits in January, 1970, QST, some pro­cedures that I use came to mind. On lay­ing out the board, I use Clear-Print graphpaper, ten squares to the inch, since mostsolid-state components use 0.1 inch ormultiples thereof, for lead spacing. Thelines on the graph paper are handyreferences for drawing interconnections.Crossovers are placed so they cross at thegap formed by a component.

After laying out the circuit, the graphpaper is trimmed to size and affixed to theboard with a transparent tape. A No. 60drill is then used. to cut mounting holesthrough the paper layout. The layout cannow be used as a schematic (or wiring)diagram when painting the etch-resistmaterial on the board. I use nail polish forthis. The brush tip should be cut at anangle to allow the lines to be made finer.- Ross W. Stevens, W6FRE

STANDARD COMPONENTS PRO·VIDE EFFECTIVE REGULATIONThe standard voltage regulator circuitwhich uses a pass transistor referenced toa Zener diode often fails to provide suffi­cient regulation under widely varying CUf­

rent demands. Perhaps this is true becausea higher current demand translates into alower-ohmage emitter load for the passtransistor, . hence, a lower input im­pedance appears at the base with a rise inbase-to-emitter voltage, resulting in a con­sequent drop in output voltage from thesupply.

The diagram illustrates a circuit usingstandard components. This provides farbetter voltage regulation. The 741 opera­tional amplifier compares the outputvoltage of the supply to the 13-volt Zenerreference, -and with nearly an open loopgain, adjusts the pass via the 2N2222 emit­ter follower for essentially 0 differentialvoltage. I use this circuit to power myKenwood TR-7400A and experienceregulation of better than 0.1 volt from noload to 8 amperes! - C. R. Macciuer,W8MQW

This circuit provides voltage regulation of better than 0.1 volt from no-load to 8 amperes.

PC Boards and Solid Stste 131

0.01~F

PIN 23 o--r(-----<J+12<6V

~220k

-t2.6V

R,

Shown is a light-flasher board and the patternfor the etched circuit board to build it on.

DIG THIS DIGITAL CLOCK HINTI constructed several digital clocks whichcontain the MM5314 chip described byKelley in QSTfor November, 1974and asdescribed in the 1974edition of The RadioAmateur's Handbook. I experiencedsome difficulty with stability with both theac and mobile models. My solution to theproblem may interest other amateurs.

With the ac model, I bypassed pins 13,14 and 15 with O.OI-IJF capacitors. I alsoplaced a O.OI-IJF capacitor across the filtercapacitor. In the mobile unit I installedO.OI-IJF capacitors as described above andchanged the multiplex circuit as shown inthe diagram. After these changes weremade both clocks appeared quite stable.- Robert S. Putman, K7ACP

02

Rl R2 R:!

"

third, there is a much greater latitudeavailable in the placement of parts.

Anyone who has access to a Dremeltype drill can make his own boardswithout resorting to chemical etching.After laying out the desired pattern onpaper and transferring the design to thecopper foil, it is a simple matter to cutthrough the foil with a fine rotary saw, ora small emery-saw wheel.

Shown is a typical circuit and the boardthat I would etch, drill, place componentson, and have in operation in about 30minutes time. Although this is a simpledesign, I have made more complex circuitsin about the same time and they have re­mained in operation a long while withoutfoil failure. - F. T. McAlltster,W8HKT/4

Stabilizing circuit for digital clock.

LRUBBERGROMMETS

102.102 mm

VERTICAL PC HOLDER

(CABLE CLAMP)

HORIlON1Al. PC HOLOER( CABLE CLAMP l

t

way to achieve this higher voltage is to add.silicon diodes in series with the Zenerdiode. Each diode will add approximately0.5 to 0.7 volts to the regulated voltageamount (see diagram). It is considerablycheaper to stock a couple of Zener diodesand a handful of silicon diodes than tostock a Zener diode for every voltage thatmight be required in the course' of anexperiment. - Robert A. Sullivan,W6YVA/4

ETCHED-CIRCUIT BOARDSWITH NO FUSS

In the course of making a considerablenumber of circuit boards during the pastfew years, I have arrived at a style, whichthough not suited for many commercialrequirements, is sufficient for mostamateur needs. Instead of etching anelaborate pattern of lines, circles, dotsand curves, I have designed all of myboards in a mosaic, or floor-tile pattern. Ifind three distinct advantages to thismethod of layout. First, there is less cop­per foil to be etched away; second, thereare no fine lines of foil to pop off theboard when extra heat is applied; and

A THIRD HANDHere is a hint that could be a great helpfor kit builders and homemade equipmentbuilders. When soldering or working withpc boards often one has need for morethan two hands. This device can serve asthat "third hand. "

Obtain a small block of wood, 4 x 4inches. Fasten rubber grommets to thebottom of the block to prevent scratchingthe worktable. Screw cable clamps to theblock for holding pc boards, wire or com­ponents while working on a project. Extraclamps may be added to hold additionalpc boards. - Rick Cole, WD4CTA

This simple wood block with clamps makes auseful tool for holding circuit boards.

When mounting the motor above the tray, thelevel of agitation can be adjusted by movingthe chain on the rotating arm.

ALUMINUM PLATE WIHI

r wo RUBBER BUMPERS

ZENER + DIODEFrequently, while experimenting, the needarises for a Zener diode of a slightlyhigher voltage than is on hand. An easy

An alternative for higher-voltage Zener diodes.

LOW'SPEEO MOTOR

/ AND GEAR BO~

PRINTED-CIRCUIT AGITATOR

Aft~r reading about etched-circuit board's,a different method of agitating the traycame to mind. I took a fairly heavy pieceof aluminum, and on the underside of oneend, mounted two rubber bumpers. Thesebumpers, or feet, allow it to rock withoutmoving around on the workbench. Asmall chain, as shown in the sketch wasadded to the other end of the piece ofaluminum and was attached to a rotatingarm mounted on the output shaft on themotor/gear assembly. The amount of traymotion is adjusted by properly placing thechain on the moving arm. The assemblycan be moved, cleaned or stored by justremoving the chain. - Harold D. Mohr,K8ZHZ

132 Chapter 10

A

Ac buzz elimination, SB-102: 47Accu-Keyer:

Dot insertion: 86Packaging: 87Rf shielding: 76Sidetone: 86With Drake R-4C: 86

Accu-Memory:Addition: 78Continuous operation: 81Expansion: 92Flexibility: 89M.s. timing: 93Word spacing: 82

Accu-Space: 88Accu-Start: 79Accu-Stop mods: 77Ac lines, grounding: 8Acoustically coupled encoder: 99Adapter connectors: 20Afsk generator temperature compensa-

tion: 119AGC, solid-state hang: 127Aids for the Station and Shop: 7Alliance V-l00 for satellite antenna: 73Alligator clips, installing: 19Aluminum:

Bonding: 18Etching: 16

Aluminum tape for shielding: 17Aluminum towers: 67Aluminum wire connections: 75A-m, Echo II: 51AMSAT-OSCAR 7, Mode B, transmit­

ter: 12Analog/digital converter: 125Antennas:

Apartment dweller's: 68Car-radio dummy: 106Cliff-dweller: 75Clothesline-supported: 69Coat-hanger: 106Connector, HW-202: 54DF: 75Feedthrough methods: 71Hockey puck installation: 74Matching to hf mobile: 98Mobile BC for 2 meters: 105Portable vhf: 111Sealant: 67Switching for RTTY: 121Tidbits: 65Turning radius: 73Vhf hints: 1165/8-wavelength: 105

25-cent mobile: 11750-MHz mobile: 102

Audio-cable shielding: 50Audio filter I simple: 51Audio limiter, adjustable: 52Audio power for mobile fm transmit-

ters: 109Audio protection, HW-202: 46Audio oscillator: 130Auto-recalibration for cw decoder: 91

B

Backlash, Heath VFOs: 47Base power supply for 2-mcter

transceivers: S9Batteries:

Consumption saving: 9SCurrent measurement: 28Diode-switching mobile: 103NiCad, revitalizing: 16Recycled: 14

Battery-charge indicator for 1402SM: 45Battery holder, film container: 60Battery-replacement circuit notes: 25BCD converter and readout: 130BC receiver as makeshift test gear: 34Belts, replacement: 39Bonding aluminum: 18Break-in and keying, old-timer's solid-

state: 83Bug to keyer paddle and back: 91Bug weights: 87Burglar alarm, mobile: 104, 106

C

Cable hangers: 75Cable harnesses: 11Calibrating a de VTVM or FET YOM:

27Calibrating frequency meters: 26Calibration, harmonic generator for: 30Capacitance-activated paddles, cleaning:

18Capacitance, reading with YOM: 33Capacitor:

Gamma match: 72Improving rotor connection: 11Trap dipoles: 69

Car:Battery care: 103Battery, operating 12-V gear: 98Care: 107Restoring after mobile operation: 100

Carbon microphone replacement: 9Cathode-keyed transmitters, solid-state

--------------

keyer: 83CATV TVl: 10CDR rotator indicator: 73Ceramic tube cleaner: 11Chokes, ferrite material: 15Circuit boards:

Holders: 15, 19Marking etched: 129With cutter: 125

Cleaning capacitance-activated paddles:18

Clegg FM-27 I-watt position: 41Coaxial cable:

Dual-function: 100Straps: 70Wiring to wafer switch: 16

Coder practice for commuters: 99Coil:

Ferrite material: ISTightening slug-tuned: 15Toroidal forms: 18

Color coding diagrams: 10Connector:

Adapters: 20Adapter, type F to BNC: 17Coaxial cable installation: 71Weatherproofing: 11

Continuity tester: 24Control belt, replacement: 39Converter:

Analogidigital: 125G3YMC 1.8 MHz: 50Hints for vhf: 111Protection for 432-MHz: 116

CPO dit cure: 78Cw:

Filter switch for TS-520: 44Monitor: 81Monitor, Swan 270: 46Operation, HW-101: 77Operation, SB~40I: 81Operators, thoughts for: 76

D

De-voltage measurements: 26Deskfax filter: 124DF antenna: 75Dial drive, slipping: 18Dial:

HW-101: 49Slippage, Heath VFOs: 47

Dielectric "no-no": 68Digital:

Clock hint: 132Clocks, more on: 14Readouts: 124

Index 133

Diodes:Beware of protective: 131Protective: 7Testing: 26

Dipoles:Center insulator: 70Trap capacitor: 69

DIP pins, alignment of: 18DIP-socket idea: 16Disconnect junctions from tube

sockets: 124Drake:

Receivers using SB-650 display: 38R-4B VFO: 48R-4C with Accu-Keyer: 86R·4C, WWV reception: 40TR-4 meter sticking: 50TR-4 outboard receiver: 40TR-4C soft dits: 78TR-22 power transistor: 109

Drill bit selection: 18

E

Echo II a-m: 51Economical FET voltmeter: 21Economy power supply: 59Electronic bias switching: 45Enclosures, weatherproof: 73Equipment:

Cabinet: 106Erratic performance: 40Feet source: 19Table: 8

Etchant baths and etch-resistant pens:129

Etchant, longer life: 131Etching metal panels: 130Etching with no fuss: 132

F

Facsimile transceiver for satellitepictures: 121

Fan-belt static elimination: 104FAX converter: 123Feed-line feedthrough: 70Ferrite material for chokes and coils: 15FET:

Protection in tester: 18Voltmeter, economical: 21YOM, calibrating: 27

Field Day:Generator, overvoltage cutout: 101Keeping cool: 105

Field-strength meter, simple: 30Filter: .

Active cw: 85Computer-type active: 80Simple audio: 51TS-520: 51

Fm transceivers, regulated supply: 60Frequency meters, calibrating: 26Frequency stabilization, SB·300: 53Frequency standard for 2-meter fm: 38Frequency standard, vhf secondary: 13

G

Gamma match capacitor: 72Genave GTX-2oo intermodulation: 42Generator, man- and bike-powered: 97

134 Index

GLB 400B T-R indicators: 54GMT "Hour Hand": 8Grounding:

Ac lines: 8Strap: 17

Ground-rod installation: 74Ground rod removal: 70G3YMC 1.8 MHz converter: 50

H

Hallicrafters:HT-46 break-in delay: 88SR-4OOA power drop: 37

Ham-M:brake: 72delayed braking: 65

Harmonic generator for calibration: 30Heath:

GR-11O switching: 108HA-201 glitches: 113HD-IO mods: 90HD-141O rf bypass: 93HD·141O with Triton IV: 76HD-141O with Vibro-Keyer: 76HG-IO output: 47HW -7 hum reduction: 42HW-7 sidetone: 51HW-7 RIT: 41HW-16 on 20 meters: 44HW·101 cwoperation: 77HW·101 dial: 49HW-101 key clicks: 40,43HW-101 VOX response on cwo 42HW -202 antenna connector: 54HW-202 audio protection: 46HW·202 channels: 113HW-202 remote control: 49HW-202 tone-pad connection: 45HW-2021 antenna jack: 117HW-2021 dual offset: 110HW·2021 offset: 36IM·103 rf elimination: 47SB-101 and separate receiver: 46SB-101 OSCAR reception: 46SB-101 S-meter and i-f: 50SB-102 ac buzz: 47SB·102 hum: 47SB-2oo duty cycle increase: 37SB-2oo/transceiver recovery: 37SB-3oo frequency stabilization: 53SB-30l cwoperation: 82SB·303 TVI: 36SB·401 anti- VOX on cwo 76SB·401 cw operation: 81SB-401 relay response: 48SB-650 on Drake receivers: 38Transceiver S-meter change: 37VFO dial slippage: 47

Heathkit:HM-102 modification: IIHWA-7-1 hum reduction: 64IM-I04 modification: 30

Henry 2K-4 overcurrent relay: 46High-frequency indicator with LED: 131Holding equipment in place: 7,9, 11,

12, 76, 91Hum, SB·102: 47Hy-Gain Hy-Tower loading coil: 74Hy-Gain 18AVT/WB 75/80 adjustment:

68

I

Ie components, working with: 129I-f test probe: 24Ignition:

Interference reduction: 105Noise: 103

Inductors, homemade vhf toroidal: \9Insulator source: 65Inverter, high-power SCR: 57

K

KDK FM-I44 I MHz offset: 55K. E. Electronics keyer hold switch: 85Kenwood:

TR·7400A Touch-Tone: 38TS·520 cw filter: 44TS-520 filters: 51

Key:Sideswiper: 91W5TS, the: 86

Keyer:Solid-state for cathode circuit: 83Weighing: 93

Keyer paddle:VE3CJB: 92Cleaning capacitance-activated: 94

KW Electronics KW-lOOO relay con­nector: 39

L

Latching relay source: 8Lenses on SSTV cameras: 12Lightning arrestor from spark plugs: 70Limiter, adjustable audio: 52Line-voltage indicator: 38Log, mobile: 100Logic probe, pulse detector for: 131

M

Map holder: 105Measurement, anterina radius: 73Measuring power output: 27Meteor-scatter timing for Accu-Memory:

93Meter cases, cocoa boxes: 25Meter sticking, TR-4: 50MFJ cw filter modifications: 85Mic adapter, high-Z-to-Iow-Z: 103Mics, locking action: 96Mini-Miser's 4O-meter leakage: 47Mobile antennas:

50-MHz: 102Matching to hf: 98Storing: 106Sway: 107

Mobile:Be antenna for 2 meters: 105Burglar alarm: 104, 106Holding equipment in place: 105Mounting equipment: 96Noise suppression: 102Protecting relays: 104Quickies: 95Remote control: ]00Rigs, shock mounting: 96RTTY: 121Safety: 104

Theft-proofing equipment: 106Vhf thoughts: 101Winterizing gear: 107

Mobiler's desk: 106Modulator for IO-watt transmitter: 39Monitor, cw: 81Mounting brackets, transceiver: 98Muffin·fan noise reduction: 40

N

Nail polish uses: 13NiCads:

Charging: 63Restoring cells and holders: 17Revitalizing: 16

NOAA weather on 2-meter rigs: 4gNoise:

Ignition: 103Locating man-made: 52Suppression, mobile: 102

Novice-band dial: 38

oOffset, KDK-I44: 55OSCAR reception, SB-IOI: 46OsciHator:

Audio: 130Unusual crystal-controlled: 9

Overcurrent relay, 2K-4: 46Overvoltage cutout, generator: 101

p

Pc-boards:Data: 126Spacers: 122Work aid: 132

Panel:labels: 20trim: 20

Pencil when you need it: 100Pipe sizes. and strengths, steel: 17Pip Squeak mods: IIIPlating, solder: 16Polar to rectangular converter: 12Portable and mobile quickies: 95Power output. measuring: 27Power source, high-current 12-V: 64Power supply:

Fixed for mobile gear: 101Hints for the: 56

Preamplifier:Burnout: 108General-purpose: 54Low-noise 432-MHz: 114Uhf-TV low-noise: 114Wide-band: 115

Printed-circuit:Agitator: 132Coil design: 128Layout, easy: 131

Probe, rf: 35Prop-pitch motors, two-wire control: 64

Q

QRP SWR/power meter: 22QRP transmitters protected by metering:

43

R

Regulated power supply for fm trans-ceivers: 60

Regulatorcircuit. improved: 59Regulator, interference-free car: 96Relay response, SB-40I: 48Relay, solid-state for repeaters: 129Relays:

Adjustment of polar: 10Protecting mobile: 104Rectifier for dc type: 57Reducing power drain: 58

Remote control:HW-202: 49Mobile rig: roo

Removing solder: 16Repeater-access tone generator: 120Repeater:

Solid-state relay: 114, 129Time-out warning: 104Wall mounting: 109

Rf:Elimination, IM-103: 47In keyer: 93Probe: 35Shielding, Accu-Keyer: 76

RTTY:Antenna switching: 121Mobile: 121

sSafety, mobile: 104Satellite antenna elevation: 73SCR inverter, high-power: 57SCR relay controi for RTTY, VOX and

COR: 124Sealant, antenna: 67Sealants: 14, 15Semiconductor circuit repair: 130Shielding:

Aluminum tape: 17Audio cable: 50

Siamese-twin power supply: 60Sideswiper key: 91Sidetone:

Accu-Keyer: 86HW-7: 51

Soldering-iron:Cord: 16Tips: 14, IS

Solder:Plating: 16Removing: 16

Solid-state data: 126Spaghetti tubing source: 18Spreader source: 71Spurious signals, a cause: 45Squeeze key on a lean budget: 78SSTV:

Camera lenses: 12Tuning device: 118

Static, elimination of fan-belt: 104Station layout ideas: 7, 13Steel pipe sizes and strengths: 17Sub-audible tone generator: 102Surge protection': 63Swan 270 cw monitor: 46Switching, electronic bias: 45SWR/power meter for QRP: 22

T

Tape recorder, keying a transmitter: 91Taped messages, circuit for: 13Teletype Model 28 nonoverline: 122Temperature compensation, VFOs: 49Templates for quick tuning: 43Ten-Tee:

KR5 sidetone: 89405 on 160 meters: 51

Test aids: 30Test gear:

BC receiver as: 34Ideas: 21

Test points, providing: 18Theft-proof mobile equipment: 106Tightening slug-tuned coils: ISTimer, NE555: 126Tone encoder, acoustically coupled: 99Tone generator for repeater access: 120Tone generator, sub-audible: 102Tone-pad connection, HW-202: 45Toroidal coil forms: 18Towers:

Aluminum: 67Disassembly: 69Shield: 66

Transceiver mounting brackets: 98Transceiver stand: 8Transistor checker: 26Transistor tester:

Five-cent: 24Universal: 28

Transistor type with VOM: 126Transmission line:

Losses: 74Matching: 69

Transmitter:AMSAT-OSCAR 7, Mode B: 12Keying with tape recorder: 91

Transverter, improvement in K9UIF: 47Tri-band match for 40-meter doublet: 68T-R indicators, GLB 4ooB: 54T-R switch, foot-operated: 39TTL voltage regulator: 127Tube extraction: 17Tuning templates: 43TV backdrop: 10, 121TV1, CATV: 10TVI source: 7

(J

Unusual crystal-controlled oscillator: 9

v

VFOs, temperature compensation: 49Vhf:

Antenna, hints: 116Band-aids and tricks: 108Mobile, thoughts on: 101Secondary frequency standard: 13Toroidal inductors, homemade: 19

Vhf-fm receiver, tunable: 108Vise for small parts: 14Voltage protection from car battery: 98Voltage regulation from standard com-

ponents: 131VOM, reading capacitance: 33VTVM, calibrating: 27

Index 135

W

Wafer switch, wiring coax: 16Weather:

2·meter fm rigs, on: 1102-meter rigs, NOAA: 47

Weatherproofing connectors: IIWheatstone bridge: 32Wilson:

136 Index

1402SM battery-charge indicator: 451402SM changes: 361402SM power transistor: 109

Winterizing mobile gear: 107Wire:

Aluminum connections: 75Source: 14

wire-wrapping tool: 18Wiring, an easy "third hand": 14WIAW locator for handicapped: II

y

Yaesu FL-IOI full break-in: 94

z

Zener diode alternative: 128Zener, voltage-controlled: 129Zener + diode: 132