worldradiohistory.com · Test solid state devices in, or out of, circuit Fast location of shorted, open and leaky components Test diodes, transistors, LEDs, electrolytics, FETs, MOS

MAY 1982 70p

Australia AS 2 40,0,Belgium BFR 77.tCanadaCanada CS 3.25Denmark DKR.$805Germany DM. 6.50Greeraj DRA. 160.00Holland DFL 8 00Italy L 3100Norway NKR. 24.00Singapore MS 5 5. 0Spain PTS 240.00Switzerland FR. 6.50U.S A. S 3.75

Test solid state devices in, or out of, circuit

Fast location of shorted, open and leakycomponents

Test diodes, transistors, LEDs, electrolytics, FETs,MOS and CMOS etc. PLUS ...

FARNELL OSCILLOSCOPE 6 C12

INTINSITY FOCUS

looriur Off PO X5

'v Farnell

PONENTSoscilloscope!

Full function, dual trace, 12MHz oscilloscope

Fine sweep and gain controls

Differential measurement mode-essential foreffective servicing of disc drives and taperecorders

Kopf

VOLT /01V

.5

50

RIODER COMP° A1

Mide LAvelTEST

Cn2 2

V

Probtis

rskExt

TrIppor

VOLT /0IV

10

SO

10 5

AC DC 12 CH2

A really versatile 'scope for the test, service or development engin

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,70pF

Details from: FARNELL INSTRUMENTS LIMITED WETHERBY LS22 4DH TEL. (0937) 61961 -OR (05827) 66123 (SOUTHERN OFFICE)WW --001 FOR FURTHER DETAILS

Vlgital fitter unomicroprocessor

Front cover shows antennae of theSwiss PTT at Niederhorn televisiontransmitting station. Photo:Hamer -Smith Collection

NEXT MONTHMicro -controlled radio -code clock -usesthe MSF standard -frequency time -codetransmission to provide automaticallycorrected date and time information.The design uses a 6502 microprocessor -decoder and a reliable receiver design.

Heretics guide to modern physics is acontroversial investigation intoelectromagnetic theory, photons,duality, quantization, matter waves,indetermancy and haziness.

Psychology of crisis control, therequirement for new types ofequipment for data marshalling andmethods of training personnel areexamined bye consultant engaged inthe planning of control complexes.

A high power mosfet amplifier isdescribed in a series beginning with anexplanation of design problems,followed by a new modularpreamplifier design.

Underground radio, a review ofprogress in the use of radiating cablesin mines.

Current issue price 70p, back issues (ifavailable) £1, at Retail and Trade Coun-ter, Units 1 & 2, Bankside IndustrialCentre, Hopton Street, London SE1.Available on microfilm; please contacteditor.By post, current issue £1.6p, back issues(if available) £1.50, order and paymentsto EEP General Sales Dept., QuadrantHouse, The Quadrant, Sutton, SurreySM2 5AS.Editorial & Advertising offices: Quadrant House, The Quadrant, Sutton, Sur-rey SM2 5AS.Telephones: Editorial 01-661 3500. Ad-vertising 01-661 3130.

Telegrams/Telex: 892084 BISPRS G.Subscription rates: 1 year £12 UK and£15 outside UK.Student rates: 1 year £8 UK and £10outside UK.Distribution: Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS. Tele-phone 01-661 3500.Subscriptions: Oakfield House, Perry -mount Road, Haywards Heath, SussexRH16 3DH. Telephone 0444 59188.Please notify a change of address.USA: $39 surtace mail, $96.30 airmail.US subscriptions from IPC B.P. Sub-scriptions Office, 205 E.42nd Street, NY10017USA mailing agents: Expediters of thePrinted Word Ltd, 527 Madison Avenue,Suite 1217, New York, NY 10022. 2nd -class postage paid at New York.

IPC Business Press Ltd, 1982 ISSN0043 6062

wirelessworld

MAY 1982 Vol 88 No 1556

ELECTRONICS

TELEVISION

RADIO

AUDIO

20 ARMS AND THE MAN

30 ORCHESTRAL SOUND, HALLS AND TIMBREby Denis Vaughan

34 LANGMUIR THIN-FILM THROUGH FOR MOLECULARELECTRONICS

35 NETWORKING SMALL COMPUTERSby Philip G. Barker

40 TELEDON VIDEOTEX IN UK

41 DIGITAL TELEVISION STANDARDSby A. Howard Jones

42 COMMUNICATION COMMENTARY

44 MICRO -CONTROLLED LIGHTING SYSTEMby John D. H. White and Nigel M. Allinson

47 16 -CHANNEL DATA ACQUISITIONby Pat Hickey

50 CIRCUIT IDEAS

52 DIGITAL FILTER DESIGNby B. M. G. Cheetham and P. Hughes

57 LETTERS TO THE EDITOR

61 DIGITAL OPTICAL RECEIVERSby Ian Garrett

54 NEWS OF THE MONTH

67 EPROM PROGRAMMERby IL S. Lynes

70 DISC DRIVE POSITIONERSby J. R. Watkinson

76 DESIGNING WITH MICROPROCESSORSby D. Zissos and Jane Pleus

78 CEPSTRUM ANALYSISby R. B. Randall and Jens Hee

81 NEW PRODUCTS

120 Index to advertisers

WIRELESS WORLD MAY 19821

THE HEADSETTHAT'S WAYAHEAD OF

ITS TIME.

THE DANAVOX HMT 808.The Danavox HMT 808 is the most advanced headset of its kind that you can buy today.Employing Danavox expertise and quality throughout, it offers many unique features at a

remarkably low price.

Lightweight. Weighs only 35 gramsComfortable and hygienic. Does not go inthe ear so it can be comfortably positionedin seconds Versatile. Can be worn underthe chin or over the head using single ear ofbinaurallyMultiple version microphone.Available with either magneticmicrophone or electret with noisecancelling feature and pre -amplifier formatching into telephone systems

Technically advanced. Pre -amp employslatest thick film technologyEasyservicing and repairs. Quick changing ofearphones, cords, earpieces and switches Realistically pricedDanavox qualityengineering and guarantee.

For full details contactJohn Carter at Danavox.

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ectromc ro ersSecond User Test Equipment.

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ANALOGUE VOLTMETERSBruel and KJaer2409 'TRUE RMS Average and Peak 2Hz -200KHz £250.00Hewlett Packard3400A True RMS ImV-300V I 0Hz- 10MHz

£600.003406A ImV-3V FSD 10KHz-1 2GHz £850.00Marconi.TF2600A ImV-100V FSD 10Hz- 10MHz

£245.00TF2603 RF Millivoltmeter 300W Sensitivity50KHz-1 5GHz £525.00TF2604 Electronic Voltmeter AC20Hz-1.5GHz 300mV- I KV DC 10mV- I KV.0 20 -500MS2 £350.00Rohde 8 Schwarz.URV RF-DC Millivoltmeter DC 501AV-1050V RF10KHz-2GHz £950.00

ANALYSERSHewlett Packard141 T/8552B/8555A 10MHz-18GHz £9750.00332A Distort ion Meter 5Hz-600KHz £495.00333A Distortion Meter with Auto our. £675.008407A/84I2A Network Analyser £1950.008555A Plug in 10MHz- I 8GHz £5000.00Sound Technology1 700A measures distortion down to 0 002%.AC voltage 300V -300V. S/N Ratio I 00dBDynamic range. power into 80 0.001%distortion Oscillator . £950.00MarconiTF2370 Spectrum Analyser 30Hz-110MHz0 I dB and 5Hz resolution £6500.00TK2374 Zero loss probe for TF2370 £375.00TektronixR491 Spectrum Analyser I OMHz-4OGHzAS NEW £3500.00

BRIDGESBoonton.63H Inductance Bridge. 0-110mH. Bridgefrequency 5-500kHz £1250.00MarconiTFI245A + TF1246 '0' meter £1100.00TM4520 Set of Inductors £350.00

Rohde 8 Schwarz.LRT 18N6100} Inductance Meter 1pH-1000H2 2-285KHz £395.00Wayne Kerr

8642 LCR 0 1% £750.00

FREQUENCY COUNTERSFluke19I2A 7 digit 520MHz £425.001920A with Option 13 9 Digit 1GHz £750.00I925A Multifunction, EMI Proof 9 DigitI 25MHz £625.00I 953A Counter Timer Opt 14. 15.0-1 2`-iGH:with pi escalers IEEE interface

£975.00Hewlett Packard5340A 8 Digit 10Hz 1 8GHz £3750.00

Marconi.2432A 8 digit 10Hz-560MHz Battery/Mains

£650.00

DVM's AND DMM'sFluke8022A 31/2 digit hand held £65.00Solartron.7055 Microprocessor DMM Scale Length20,000 AC/DC volts. resistance I uVresolution £495.00

OSCILLOSCOPESMarconi.TF2213/1 + TK2214 X -Y Display andmemory £550.00rPhilippsP'1 25MHz Dual Trace Portable £475.00Tektronix.453A Dual Trace DC 60MHz Portable SweepDelay £750.00465 Dual Trace Portable Oscilloscope DC -I 00MHz 5mV-5V/div. Full delayed sweep.

£1395.00465 with DM40 £1450.00475 Dual Trace 200MHz Portable £2000.007603 100MHz Mainframe with 7A I 8N and7853N ' £3000.007704A 200MHz Mainframe c/w 7A22 Diff.Amplifier, 7A26 Dual Channel. 7880 Timeba seand 71385 Delaying Timebase £4610.00SI Sampling Head. As New £450.007D 14 Digital Counter plug-in 525MHz

£850.00Texscan.DUI 20 12" Display £425.00

RECORDERSWatenabe.MC641 6 Channel 250mm Chart Recorder

£1495.00Yokagawa3047 2 Channel 2 cm/HR - 60cm/MIN

£435.00

SIGNAL SOURCESHewlett Packard.4204A Decade LF Osciilator. 10Hz-1MHz.I mV - 10V into 6000 £695.0060613AM Signal Generator. 50KHz-65MHz.AM 0-95% . . ............. £850.00608F I 0-455MHz AM/PCM Modulation 0.IpV-IV output £600.006168 I.8-4.2GHz int or ext PCM/FM0.1uV-0.224V £1000.0061613 UHF Signal Generator. I 8 to 4 2GHz Intpulse Mod £1000.006518 Test Oscillator, 10Hz- 10MHz.0.1mV-3.16V £415.003200810-500MHz Signal Source . £475.003320A Frequency Synthesizer. 0.01Hz- I 3MHz.

£995.00Marconi.TF144H/4 AM Signal Generator 10KHz72MHz 2pV-2V £750.00TF2002B AM/FM 10KHz-88MHz £1 200.00TF2170B Synchronizer for TF200213 £450.00TF9958/2 AM/FM 200KHz-200MHz £695.00

TF2005R 2 Tone Signal Source 20Hz-20KHz0-1 I I dB in 0.1d13 steps £295.00TF2008 AM/FM 10KHz-5 10MHz built insweeper Output 0.2wV,200mV £3500.00TF2016 + TF2I73 Synchroniser AM/FM10KHz-1 02MHz £2000.00TF2950/8 Mobile Radio Test Set £1950.00TF2I69 Pulse Modulator for use with TF201 5or TF2016 . £200.006070 Signal Source 400-1200MHz £695.00

Philips.PM57 15 Pulse Generator 1Hz-50MHz E675.00PM6456 Stereo Generator. £250.00Racal9081 Synthesized AM/FM Phase and Pulsemodulation 5-520MHz £2200.00RadiometerSMG I Stereo Generator £375.00

TRANSMISSIONMEASURING EQUIPMENTSiemens.D2040 Selective Level Analyser and Voltmeter10H z-60KHz £1200.00D2072 + W2072 Level Meter and Oscillator50KHz-100MHz. £2200.00W2006 + D2006 Carrier Level Test Set. 10KHz-17MHz -100 to + 10dB . £1650.00W2007 + D2007 Carrier Level Test Set6KHz-I8 6MHz -120 to + 20313 £1800.00Wandel and Golterman.PF-I Digital Error Rate Measuring SetConsisting of PFM- I Digital Error Rate Meterand PFG-1 Pettern Generator..£2490.00SPM-6 and PS -6 Level Measuring Set.6KHz-113 6MHz, -1 1038 to + 2038 Mains /battery operation £2150.00

PCM-1 PCM Test Set. PDA 64 PCM SignallingAnalyser. PSM-4 Level Measuring Set Scanner.PDG-I Digital Signal Generator, PDA-1 PCMDigital Signal Analyser P.O.A.

MISCELLANEOUSC2r5 AFar Power meter 20Hz 30KHz IONW50W input imp 1 2 10000 £250.00Fluke3010A Logictester Self Contained PortableFull Spec on Request £8500.00Hewlett Packard.355E 12d8 Programmable Attenuator unused

£90.008403A Modulator Fitted With 8732B PINMODULATOR £1500.0084I2A Phase Magnitude CRT display fornetwork analyser £1500.008482H Power Sensor 100KHz 4 2GHz ASNEW £250.008745A S Parameter Test Set Felted with11604A Universal Arms 0 I-2GHz 12750.0059308A HP -18 Timing Generator £300.00Marconi.TF2162 M F Attenuator 0-1 11c113 £135.00TF21635 UHF Attenuator 0 1420B 500impedance DC- I GHz £250.00TF233 I AF Distortion Meter20Hz-20KHz £395.00TF2500 AF Power Meter 7 ranges 1001, wattsto 25 watts £275.00TM8339 AC/DC mixer for use with TF2702

£250.00Philips -

PM5519 Colour TV Pattern Generator ASNEW £650.00PM9380 Camera and Accessories (as new)

£200.00Rohde and Schwarz.MSC Stereo Coder 30Hz-I5KHzTektronix41 A PAL Test Signal Generator £1 750.0048 IC PAL TV Waveform Monitor £2375.0091 Constant Amplitude Sig. Gen 350KHz-00fV1Hz 5mV-5 5V £250.0006 Square Wave Generator I nS risetime0Hz-IMHz without accessories £175.00

284 Pulse Generator 70pS risetime £1250.002901 Time -Mark Generator £195.00Telonic.1006A Sweep Gen 450-850MHz

£500.00

£750.00

Please note: Prices shown do not include VAT or carriage.

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13A/6SW Sloping£26, £1.50 P&P + VAT

PEL 1£44.50, £1.50 P&P + VAT

PEL 3£65, £2.25 P&P + VAT

TR9 £38.75, £2.50 P&P + VAT

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13A/4SW£22.40, £1.50 P&P + VAT

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T13A/5£21.75

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DELIVERY EX -STOCK

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Stocks of standard itemsexceed a quarter of a million.Individual units to the tightestspecification made to order.

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4 WIRELESS WORLD MAY 1982

ADCOLA,SOLDERING TOOL

with

Electronic TemperatureControl Circuit

contained withinthe handle

DESIGNFEATURES

NO MOVINGPARTS

NO MAGNETICEFFECT

NO MAINSSPIKING

MINIMALMAINTENANCE

FULL RANGE

/TheAdcola 444 operates from 24VAC.

control circuit is based on a specially designed

range normally factory set at 360°C is fully

integrated circuit and uses a thermocouple

variable between 220°C -420°C. The

50 VA. 50/60Hz. supply. Temperature

temperature sensor.

OF PUSH INSOLDERING TIPS

FAIL SAFECIRCUITRY

Full specifications and prices from

fRegel Trod& Mork

ADCOLA PRODUCTS LIMITEDADCOLA HOUSE, GAUDEN ROAD, LONDON SW4 6LH.

Telephone: 01-622 0291/4 Telex 21851 ADCOLA G



We supplyFLUKEfor Industry

* NOW WITH A 2 YEAR WARRANTY

* Fluke 80221331/2 Digit hand held LCD. DMM. AC/DC volts.DC/AC current, resistance, diode test. 0.25% basicDC accuracy. Overload protection. Vinyl carryinge85wcase C90 £8.00

* Fluke 80218.Same spec as 80228 with additional audio tone forcontinuity. Vinyl case C90 £8.00 £95.00

*Fluke 80201331/2 digit 0.1% basic DC accuracy. DC/AC volts.DC/AC current, resistance, diode test andconductance. Continuity beeper. Vinyl case C90£8.00

*Fluke 80241331/2 digit. 0.1% basic DC accuracy. DC/AC volts,DC/AC current, resistance. Diode test,conductance, logic + continuity detect +temperature. Peak hold on voltage and currentfunctions, continuity beeper. Vinyl case C90E8.00 £155.00

FLUKE 8050A41/2 Digit LCD DMM with true RMS on AC voltsand current DC volts 200mV- I KV. I OmVresolution AC volts. 200mV-70V. 10mVresolution. DC/AC current 2000-2A. 0.010resolution resistance 200f2-20Mf2. 0.010resolution. Also reads dB direct referenced to 16stored impedances. Conductance ranges 2mS and200n5. £255 mains model £285 mains battery.

FLUKE 8012A31/2 Digit LCD DMM with true RMS on AC voltsand current. DC volts 200mV- I KV, 100mVresolution. AC volts 200mV-750V. I 00mVresolution. DC/AC current 200mA-2A, 0. :NAresolution. Resistance 200D -20M0. 0.10resolution Low resistance 21-2 and 2052. Imf2resolution Conductance ranges 2mS-200-200nS£229.00 mains model £259.00 mains battery.

FLUKE 8010A31/2 Digit LCD DMM Same spec as 80I2A plus aI DAmp AC/DC current range, but not lowresistance range. £175.00 mains model £203.00mains battery.

ACCESSORIESA8 I -230 Battery eliminator £14.00C90 Carry case for hand held £10.00801-600 Amp clamp £68.0080J-10 Current shunt 10A £22.0080K-40 N.V. probe 40kV £56.0080K-6 H.V. probe 6kV £40.0080T- 150 Temperature probe £72.0080T -H Touch hold probe £36.0083RF R.F. probe I 00MHz £40.0085RF R.F. probe 500MHz. £69.00Y8102 Thermocouple probe £41.00

Y8103 Bead thermocouple £18.00Y8104 K type thermocouple termination £8.00

Y8I33 Deluxe rest leads E13.00

0001SEr:77116t

The above prices do not Include carriageor VAT 115 %J.

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BLUE L.E.D'sThis revolutionary NewBlue LED, the ESL 50B2, fromAnglia Components is amiracle of scientific tenacitypreviously thought to belight years away.Its applications in scienceand industry are unlimited.

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OUTLINESPECIFICATION

Package: Tii case

EmissionWavelength: 490 n Metres

LightOutput: 2.0 m.c.d. at 12 mA

ForwardVoltage: 7.5 volts



HM 307OSCILLOSCOPESingle trace. DC to I OMHz. Risetime35nS. 5mV/cm to 20V/cm. Timebase0.5µS -0.2S. Built in component tester.LPS technique provides stable andreliable triggering up to 30MHz £138.00

HM412-5Dual Trace. DC to 20MHz 8 x 10cmdisplay with internal graticule. Rise timeI 7.5nS. Variable input 2mV-20V/cm.Add and invert modes. Timebase0.5i4S-0.2S with sweep delay I 00nS- ISx 5 expansion. X -Y operation Z

modulation. Trigger CHI CH2. CHI /2.Line or EXT £350.00

HM 203 PORTABLEOSCILLOSCOPEDual Trace. DC to 20MHz. 8 x 10cmdisplay. Risetime I 7.5nS. Sensitivity5mV/cm-20V/cm. Timebase 0.5pS-0.2S.x 5 magnifier. X -Y operation. Auto or

variable trigger. Channel I , Channel 2,line and external. Coupling AC, or TVlow pass filter. Weighs only 6Kg. Size(m.m.} H. 145, W. 285, D. 380 £220.00

HM705Dual Trace DC-70MHz 8 x 10cm displaywith internal graticule. Risetime 5nS.Variable input 2mV-20V. Add and invertmodes. 95nS Signal Delay Line.Timebase SOnS- IS/cm with SWeep delay100nS-IS x 10 expansion. XY

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* SWR; Better than 1.5:1on channel.

MULTI FREQUENCYTRAP DIPOLES 2-30MHz

THE SMC TRAPPED DIPOLE ANTENNAhas been developed to satisfy the needs of commerical and military users. It is capable ofoperation between 2 and 30 MHz on as many as four spot frequencies - each capable ofaccommodating many channels. Excellent matching and efficiency with a single coaxialfeed is offered by the use of SMC H10 traps and the incorporation of a ferrite balun in afull halt wave design. NB: Power absorbing terminating resistors are not employed. Theantenna may be deployed using one or two support masts, installation (incorporating SMClight duty portable masts) can be easily effected by two people in half an hour.

Antennas

SMC/TDA/2 2 fret:1E125, SMC/TDA/3 3 freq £170, SME/TOA/4 POA.

Complete Installation2 freq antenna, 2 10m support masts, kit bags, erection equipment £434.Exact specifications are to customers' requirements.(Above include 30m UR67, balun etc).

SMC Masts and Towers;cost effective.Support structures, 250 models available.

* Tubular aluminium alloy masts 20-60ft.* Tubular steel masts 3-4.5" Dia. 20-100ft.* Self-supporting, telescopic, fold -over towers 20-60ft.* Self-supporting and guyed towers 20-16011.

SOUTH MIDLANDS COMMUNICATIONS LTD.

OSBORNE ROAD, TOTTON Telex: 477351 SMCOMM GSOUTHAMPTON SO4 4DN Cr., Tel: Totton (0703) 867333


ONLY £48.50 Post free, nc VAT Lbla1;..4 PfaXilD

CERFJ,SUE1Send cheque or official order for promptdelivery. Telephone orders will be

HOLDS UP TO SIX EPROMS despatched C.O.D. at no extra charge.SAFETY INTERLOCKED TRAY Also available in London from:FAST ERASE TIME Technomatic Ltd.QUALITY STEEL CASE Transam

MONEY -BACK GUARANTEE and in Aberdeen from:Granite Chip.

NORTHERN ELECTRONICS .11=11.1111.1110051 Arundel Street, Mossley, Lancashire Tel: Mossley (04575)4114


RADIATION DETECTORSBE PREPARED VIEW THRU LENS

Ideal for the experimenter THIS DOSIMETER WILL AUTOMATICALLY

DETECT GAMMA AND X-RAYSII UNIT IS SIZE OF FOUNTAIN PEN & CLIPS

ONTO TOP POCKET PRECISION INSTRUMENT MANUFACTURERS CURRENT PRICE OF A

SIMILAR MODEL OVER f25 EACH 0-5R

British dpsign & marlutactiueTested and fully guaranteed. Ex -stock delivery.

As supplied to Fire Services/Civil Defence

HEAmys

FREE Alg7,7,t4c17,'

f6.95COMPLETEWITH DATA

Official Orders welcome

01-723 1008/9CALLERS: 404 EDGWARE ROAD, LONDON W2 lED

Mail Orders/Export Enquiries to: 11-12 Paddington Green, London W2


FAST ERECTING

CLARKMASTS

Here is the expertiseyou can depend on

Clark P.T. mast,vehicle -mounted in

Range -Rover. The P.T.series of masts is

widely accepted byinternationalbroadcasting

authorities. It is forfield strength

measurement workthat they have been in

particular demand.Extended heights

4.1m. to 21m.

Years in thisspecialistfield

When you choose a mastfrom the comprehensiveClark range you areassured of a high standardof Engineering andoperational reliability.

Why compromise?

Extended heights 4metres -30 metres, capableof lifting headload 1 kg. -200 kgs. Sectional ortelescopic air operated forfield or vehicle mountin.Write of phone us forletails today.

CLARK MASTS LTD.Binstead,Isle of Wight,P033 3PA, England.Telephone: Ryde (0983) 63691, Telex 86686.



ec row ro ersDEC SALE

a selection from ourhuge stocks

SYSTEMS11/34A CPU 128KB MOS, 2 x RLO1 disks, H960cab, LA36 Console RSX1 1 M Licence . £8,750.0011/44 CPU 256KB MOS, dual TU58, 2 x RLO2disks, H9642 cabs, LA120 Console RSX1 1 MLicence £17,450.0011/70 CPU 512KB MOS, RWM05 disk, LA120Console £57,000.00

PROCESSORSPDP8A 101/2" 32KW MOS [NEW] £1,750.00PDP11/04 101/2" 32KB MOS [NEW] £3,625.00PDP11/34A 128KB MOS £5,000.00PDP1 1 /34A 256KB MOS £6,250.00PDP11/35 32KW Core £2,350.00PDP11/40 96KW Core, KT110 £4,650.00PDP11/44 256KB MOS £11,500.00PDP11/44 256KB TU58, Cab £12,750.00PDP11/45 32KW Core, Cab £5,950.00PDP11/45 96KW Core Cab £7,450.00PDP11/70 512KB MOS £30,000.00

DISK DRIVESRK06 14 meg [NEW] £2,500.00RK611 RK06 & ctl £4,250.00RLO1 5 meg £995.00RL11 RLO1 & ctl £1,745.00RLO2 10 meg £1,450.00RL211 RLO2 & ctl £2,200.00RWM05 RM05 & ctl [NEW £26,500.00RXBE Dual Floppy & ctl [NEV ] £995.00RX1 1 BD Dual Floppy & ctl [NEW] £995.00RXV1 1 BD Dual Floppy & ctl [NEW] £995.00

VDU & PRINTEROFFERS

HAZELTINE 142000 VDU27 x 74 Display, 64 ASCII, RS232,full half duplex and full editing XYcursor addressing and batch mode,green phosphor CRT, detachablekeyboard.SPECIAL QUANTITY DISCOUNTOFFER1-2 £299.00 5-9 £255.003-4 £275.00 10+ £250.00

AJ832 DAISY WHEELPRINTER / PLOTTER

Scoop purchase of Anderson -Jacobson AJ832 Daisy WheelPrinters complete with full keyboardintegral stand and RS232 interfaceUtilising thefamous QUMEPrinter Mechanism1-4 £995.005-9 £950.0010+ E895.00

LINE PRINT RSDEC LP11-VD 300 1pm Drum Printerupper/lower case, including controlmodule £2,750.00DEC LP04 900 1pm upper/lower casedrum printer BRAND NEW SURPLUS,including control module £5,750.00DATA PRODUCTS 8600 band printerincluding control module £3,750.00

DEC LA35/LA36 andLA180 MATRIX

PRINTERSLA36 30cps keyboard printer withintegral stand, 132 column tractor -feed, upper/lower case ASCIILA36 with 20mA interface £450.00LA36 with RS232 interface . £495.00LA35 - Receive only version ofLA36 - AMAZING VALUE:LA35 with 20mA interface

£250.00LA35 with RS232 interface £275.00LA180 high-speed output printerwith 180 cps printing, 132 columntractor -feed, upper lower caseASCII. Integral stand [NEW]LA1 80 printer standard parallel(Centronics type] interface .,£495.00LA180-ED with optional RS232 or20mA interface £870.00

AJ212 ACOUSTIC COUPLERSSpecial Purchase of Anderson -JacobsonAcoustic Couplers suitable for use withRS232 or 20mA devices, full or halfduplex, at speeds up to 300 baud.Attractive wooden case £125.00VT50 AND VT52 OECSCOPE VDUSVT50 OECscope, 12 x 80 upper caseASCII, 9 switch -selectable baud rates75-9600 baud, 20m4 or RS232interface £250.00VT52 OECscope, 24 x 80 upper/lowercase ASCII, 9 switch -selectable baudrates 75-9600 baud, 20mA or RS232Interface £525.00All items reconditioned unless otherwisestatedADD 15% VAT TO ALL PRICES 9Carriage and Packing extra

Electronic Brokers Ltd., 61/65 Kings Cross Road,LLondon WC1X 9LN. Tel:01-2783461. Telex 298694

=mi = 1 =mi = i =1 7. i =El = I =mil::. iml r.ilr.l=ml=Electronic Brokers I =14 7, I i - I =11

ww- 023 FOR FURTHER DETAILS SIM

Sinclair ZX81 Personal Combthe heart of a systemthat grows with you.1980 saw a genuine breakthrough -the Sinclair ZX80, world's first com-plete personal computer for under£100. Not surprisingly, over 50,000were sold.

In March 1981, the Sinclair leadincreased dramatically. For just£69.95 the Sinclair ZX81 offers evenmore advanced facilities at an evenlower price. Initially, even we weresurprised by the demand - over50,000 in the first 3 months!

Today, the Sinclair ZX81 is theheart of a computer system. You canadd 16 -times more memory with theZX RAM pack. The ZX Printer offersan unbeatable combination ofperformance and price. And the ZXSoftware library is growing every day

Lower price: higher capabilityWith the ZX81, it's still very simple toteach yourself computing, but theZX81 packs even greater workingcapability than the ZX80.

It uses the same micro -processor,but incorporates a new, more power-ful 8K BASIC ROM - the 'trainedintelligence' of the computer. Thischip works in decimals, handles logsand trig, allows you to plot graphs,and builds up animated displays.

And the ZX81 incorporates otheroperation refinements - the facilityto load and save named programson cassette, for example, and todrive the new ZX Printer

BASIC manualEvery ZX81 comes with a comprehensive, specially- writtenmanual -a complete course in BASIC programming. fromfirst principles to complex programs.

Kit:£49'-SHigher specification, lower price -how's it done?Quite simply, by design. The ZX80reduced the chips in a workingcomputer from 40 or so, to 21. TheZX81 reduces the 21 to 4!

The secret lies in a totally newmaster chip. Designed by Sinclairand custom-built in Britain, thisunique chip replaces 18 chips fromthe ZX80!

New, improved specification Z80A micro -processor - newfaster version of the famous Z80chip, widely recognised as the bestever made. Unique 'one -touch' key wordentry: the ZX81 eliminates a greatdeal of tiresome typing. Key words(RUN, LIST, PRINT, etc.) have theirown single -key entry. Unique syntax -check and reportcodes identify programming errorsimmediately. Full range of mathematical andscientific functions accurate to eightdecimal places. Graph -drawing and animated -display facilities. Multi -dimensional string andnumerical arrays. Up to 26 FOR/NEXT loops. Randomise function - useful forgames as well as serious applications. Cassette LOAD and SAVE withnamed programs. 1K -byte RAM expandable to 16Kbytes with Sinclair RAM pack. Able to drive the new Sinclairprinter. Advanced 4 -chip design: micro-processor, ROM, RAM, plus masterchip - unique, custom-built chipreplacing 18 ZX80 chips.

Built:169.95Kit or built - it's up to you!You'll be surprised how easy theZX81 kit is to build: just four chips toassemble (plus, of course the otherdiscrete components) -a few hours'work with a fine -tipped soldering iron.And you may already have a suitablemains adaptor - 600 mA at 9 V DCnominal unregulated (supplied withbuilt version).

Kit and built versions come com-plete with all leads to connect toyour TV (colour or black and white)and cassette recorder.


iter-

16K- byte RAMpack for massiveadd-on memory.Designed as a complete module tofit your Sinclair ZX80 or ZX81, theRAM pack simply plugs into theexisting expansion port at the rearof the computer to multiply yourdata/program storage by 16!

Use it for long and complexprograms or as a personal database.Yet it costs as little as half the priceof competitive additional memory.

With the RAM pack, you canalso run some of the more sophisti-cated ZX Software - the Business &Household management systemsfor example.

ZX816 Kings Parade, Cambridge, Cambs., CB2 1SN.Tel: (0276) 66104 & 21282.

LFREEPOST - no stamp needed. Offer applies to UK only.


:. --

PC:pa I

3'o "'77vr --..-,t 7-o ....."-'1,/.4 ra NEXTJ

s-. - -PRINT

Available now-the ZX Printerfor only 149.25Designed exclusively for use withthe ZX81 (and ZX80 with 8K BASICROM), the printer offers full alpha -numerics and highly sophisticatedgraphics.

A special feature is COPY, whichprints out exactly what is on thewhole TV screen without the needfor further intructions.

At last you can have a hard copyof your program listings -particularly

useful when writing or editingprograms.

And of course you can print outyour results for permanent recordsor sending to a friend.

Printing speed is 50 charactersper second, with 32 characters perline and 9 lines per vertical inch.

The ZX Printer connects to the rearof your computer - using a stackableconnector so you can plug in a RAMpack as well. A roll of paper (65 ftlong x 4 in wide) is supplied, alongwith full instructions.

How to order your ZX81BY PHONE - Access, Barclaycard orTrustcard holders can call01-200 0200 for personal attention24 hours a day, every day.BY FREEPOST - use the no -stamp -needed coupon below. You can pay

by cheque, postal order, Access,Barclaycard or Trustcard.EITHER WAY - please allow up to28 days for delivery. And there's a14 -day money -back option. We wantyou to be satisfied beyond doubt -and we have no doubt that you will be.

rTo: Sinclair Research Ltd, FREEPOST , Camberley, Surrey, GU15 3BR. Order-1Qty Item Code Item price

£Total

£Sinclair ZX81 Personal Computer kit(s). Price includesZX81 BASIC manual, excludes mains adaptor. 12 49.95Ready -assembled SinclairZX81 Personal Computer(s).Price includes ZX81 BASIC manual and mains adaptor. 11 89.95

Mains Adaptor(s) (600 mA at 9 V DC nominal unregulated). 1.0 8.95

16K -BYTE RAM pack. 18 49.95

Sinclair.ZX Printer. 27 49.95

8K BASIC ROM to fit ZX80 17 19.95

Post and Packing. 2.95

0 Please tick if you require a VAT receipt TOTAL £

*I enclose a cheque/postal order payable to Sinclair Research Ltd, for £*Please charge to my Access/Barclaycard/Trustcard account no.

'Please delete/complete as applicable L1111111111111111Please print.

Name: Mr/Mrs/Miss 1 1111111111111_111111Address 1 11111111111111111111111h1111111_L111111_111111111111

WRW 051

WIRELESS WORLD MAY 1982 11

a

4

IEEE PROGRAMMABLES from TIME(TWA

9814 IEEE PROGRAMMABLE VOLTAGE STANDARDA higher performance voltage standard with 4 ranges from 0.1 volt to 10 volt output. Accuracy is 0.01% and the

(i) . resolution of setting is 1 in 200,000. Output resistance is less than 0.01 ohms, and output current adjustable20mA-200mA. Temperature coeff is less than 20ppm/°C and long term stability better than 50ppm per year. Fullmanual control is available via front panel controls. Available for benchtop use or 19" rack mounting.

9816 IEEE PROGRAMMABLE VOICEA high quality speech synthesizer which has a 280 word vocabulary. By suitable programming via the IEEE busit is possible to output single words, phrases and sentences. The vocabulary has been chosen to be applicableto many ATE applications.

4

amiss aim0 RE

Xi 1116661Sill

9815 IEEE PROGRAMMABLE SCREWDRIVERThe unit has been designed to overcome the problems of adjusting large numbers of multi -turn trimmers inATE systems. The screwdriver is fully programmable via the IEEE bus with 3 speeds of rotation and 2 selectabletorque values available. The unit is supplied complete with a flexible drive shaft and drill chuck into whichvarious adjusting tools can be located.

9810 IEEE/PROGRAMMABLE POWER SUPPLY0-33V in 0.1V steps. Local or remote (IEEE) operation. Fully programmable on the IEEE bus with 3 settablecurrent limits 1mA, 10mA and 1.1A. A dual version of the 9810 is also available. The unit is 3 Euro units high andstandard 19" rack mounting width.

9812 IEEE PROGRAMMABLE SWITCH24 double pole changeover switches are available with full IEEE control. Each switch is rated at 1 Amp, 30V dc or100V ac. Thermal emfs have been minimised to less than 1pV per switch. All outputs are on the rear panel alongwith the IEEE address selector switch and bus connector. Manual control of the switches is also provided via aset of front panel switches which also incorporate LED indicators.

9811 IEEE PROGRAMMABLE RESISTANCE0-1 Megohm in 1 Ohm steps, fully programmable via the IEEE bus. Accuracy is 0.1% over most of the resistancerange. Resistors are rated at 1 watt each. An attractive feature is the option to switch to local operation when theoutput resistance can be set up manually via front panel switches.

TIME ELECTRONICS LTD, Botany Industrial Est., Tonbridge, Kent, England TN9 1 RS. Tel: 107321 355993. Telex: 95481


%MX% Ity3110. XLR CONNECTORSE2.04

Line Male A3M £1.36 Chassis Male D3M E1.19

4 5, 6 and 7 fin versions and large selection audio adaptors available

NEUTRIK XLR CONNECTORSLatchless Chassis NC3-FZ £0.67 Latchless Chassis Male NC3 MZ £0.59Line Female NC3-FCC £1.34 Line Male NC3-MC El 15Female Chassis NC3-FP E1.65 Chassis Male NC3-MP £0.87

4,5 -pin, PCB and black versions and large selection of audio adaptors available

Line Female A3F £1,59 Chassis Female D3F

XLR LNE MAIN SERIESXLR LNE 11C £3.87 XLR LNE 12CXLR LNE 32 £2.89 XLR LNE 31

E3.76£4.14

BELCLERE AUDIO TRANSFORMERSEN6422 Ratici 1 .r4- 2. Freq. 40Hz-35KHz. PRI 150/6000. sec. 600/2.4K0 £3.64EN6423 Ratio 1 1:6.45 + 6.45. Frea. 40HZ-25KHz. PRI 150/6000. sec. 6.25K/25K0 £3.64SKT-723 MuMetal Screening can, 39dB reduction 50Hz ext. field E1.15Trade enquiries welcome; quantity discounts available. All prices subject to V.A.T. Call, write or

phone. Min. order £10. Please add £1 postage. Access, Amex, Barclaycard.

KELSEY ACOUSTICS LTD.28 POWIS TERRACE LONDON W11 1JH

1111011.CLAVCAPO

01-7271046/0780

ww - 015 FOR FURTHER DETAILS

ELECTRON GUNSTV TUBE COMPONENTSIf you are Rebuilding or Manufacturing TV Tubes - We are theleading suppliers of Electron Guns and TV Tube Components to theTV Tube Industry. We specialise in all aspects of Electron MountTechnology.Our product range includes more than 250 gun types for Colour, InLine, Mono and Display Tubes along with Mount Parts, Bases, Get-ters, Sealoffs, and all other associated items for TV Tube Production.A Full Technical Back-up and Advisory Service is available to allcustomers Worldwide.Please request our current catalogues and Data Information.

GRIFTRONIC- EMISSION LTDTelephone: (0789) 76452/764100. Telex: 312354 Grifem G

2 SWAN STREETALCESTERWARWICKSHIREB49 50PENGLAND


Box CleverWith 1,100 instrument cases inI over 750 sizes, and some 250,000

case parts currently in stock, wecertainly enable you to box clever.

A practical solution to every0 electronic packaging requirement,without the problem of high tooling

costs, that's our aim at West Hyde. By being able to supply an'off the shelf' enclosure for just about any electronic or

electrical instrument, we can certainly make sure when itcomes to enclosing your particular product, we can

help you to box clever! For more informationsend for our catalogue, price £1.00 inc. P&P.

EST HYDEWest Hyde Developments Ltd., Unit 9,

Park Street Industrial Estate, Aylesbury, Bucks. HP20 1E1..Telephone: Aylesbury (0296) 20441. Telex: 83570 W HYDE G.



Memotech's New Memory System for the MC81

It growsas youprogress

Memopak ]6K Memory Extension£39.95 inclVAT

It is a fact that the ZX81 has revolutionised home computing.and coupled with the new Memopak 16K it gives you amassive 16K of Directly Addressable RAM. which is neitherswitched nor paged. With the addition of the Memopak 16Kyour ZX81is enlarged memory capacity will enable it toexecute longer and more sophisticated programs. and tohold an extended database.The 16K and 64K Memopaks come in attractive. custom -designed and engineered cases which fit snugly on to theback of the ZX81. giving f irm. wobble -free connections.See below for ordering information

Coming Soon...Memotech iii.Res GraphicsCentronics Interface and Software DriversMemotech Digitising Tablet RS232 Interface

MEMOPAK RAMHI-RES GRAPHICS

CENTRONICS

All these products are designed to fit 'piggy -back fashionon to each other. and use the Sinclair power supply.WATCH THIS SPACE for further details. We regret we are as yetunable to accept orders or enquiries concerning these products-- but we II let you know as soon as they become available

How to order your Memopak.By Post: Fill in the coupon below and enclose your

cheque P O. Access or Barclaycard number.By Phone: Access Barclaycard holders please ring

Oxford (0865) 722102 (24 -hour answering service).

I

I

Please make cheques payable to Memotech LimitedPlease debit my Access/Barclaycard* account number

' Pease delete whichever does not appfi

SIGNATURE

I NAME

I

DATE

Memopak 64K Memory Extension429.00 incl VATThe 64K Memopak is a pack which extends the memory ofthe ZX81 by a further 56K. and together with the ZX81 gives afull 64K. which is neither switched nor paged. and is directlyaddressable. The unit is user transparent and accepts basiccommands such as 10 DIM A(9000).

BREAKDOWN OF MEMORY AREAS0-8K . Sinclair ROM8- 16K . This section of memory switches in or out in 4Kblocks to leave space for memory mapping. holds itscontents during cassette loads. allows communicationbetween programmes. and can be used to run assemblylanguage routines.16-32K .. This area can be used for basic programmes andassembly language routines.32-64K 32K of RAM memory for basic variables and largearrays.With the Memopak 64K extension the ZX81 is transformed into apowerful computer. suitable for business. leisure and a)

educational use. at a fraction of the cost of comparablesystems

Unique 3 monthtrade-in offer!When your programming needs have outgrown the capacityprovided by 16K RAM. and you find it necessary to furtherextend your ZX81's capacity. we will take back your 16KMemopak and allow a discount of 15.00 against yourpurchase of our 64K model.''We reserve the right to reject for discounting purposes units ahave been either opened or damaged in any way

Please send me:Quantity Price Total

16K RAM. Assembled £39.95

64K RAM, Assembled £79:00

Postage £2.00

ADDRESSTotal Enclosed

wwl II We want to be sure you are satisfied with your Memopak - so we offer a 14 -day money back Guarantee on all our products. I

Memotech Limited, 3 Collins Street, Oxford OX4 1XL, England Telephone: Oxford (0865) 722102/3/4/5 I

WIRELESS WORLD MAY 1982 WW 094 FOR FURTHER DETAILS 13

Air conditioning

is not enough!£117* CAN BE!

Electricity mains cause all sorts of problems, whichGalatrek solve.

You need Galatrek Voltstab protection for voltagesensitive circuits. Galatrek offers the most economicalprotection against mains variation, high voltage transients,momentary breaks and even supply failure.

We have a comprehensive range of Constant VoltageTransformers (CVT) from 250VA for efficient, trouble free useof microprocessors, computers, scientific production andprocess equipment and instruments.

For TOTAL SAFETY AND EFFICIENCY the GalatrekVoltstab" Uninterruptible Power Supply (UPS) unit offers theultimate in protection. The output voltage is stabilised,transient attenuated and sinusoidal. Even in a power failureor when the input varies fromzero to 30% above normaland the frequency starts todrift, the Galatrek UPSensures normal power supply.

*f 117 (ex. VAT) ex works.

Mr R Koffler, Galatrek InternationalScotland Street, Llanrwst,nr Colwyn Bay, Gwynedd LL26 OAL,North Wales, Great Britain.Tel No: 0492-64031 1/64 1 298Telex: 617114 KB Galahu

0 INTERNATIONAL

I

I

I

ALATREK

Name

Address

Voltstab is theRegistered Trademark

of Galatrek International

Please send me full detailsof CVT units 0Please send mefulldetailsof UPS unitsPlease send mea requirement check sheetPleasedo an on -site investigation

O

Country Tel


RADICICODECLOCKS

are powerful and comprehensive instruments which receive, decodeand analyse time -coded standard frequency transmissions to provideaccurate, secure and completely automatic time/calendar or synchro-nisation systems.

Applications Automatic master clock and slave controller. Synchronisation of separate equipment and events. Programmable energy management system. Computer clock/calendar with battery backup. Data logging and time recording. Process and equipment control. Broadcasting, Astronomy, Navigation. Satellite tracking.

If you have a time or synchronisation problem,write or phone for further details of our portableand new microcomputer -controlled RadiocodeClocks.

Circuit Services, 6 Elmbridge DriveRuislip, Middlesex. Ruislip 76962


OLYMPIC TRANSFORMERS LTD224 Hornsey Road, Holloway, London N7. 01-607 2914

L.T. TRANSFORMERS PRIMARIES 220-240VFULLY SHROUDED TERMINAL BLOCK CONNECTIONS

SR. Tip Amp Prlse Crr. Sec. Tri Pap Prki Crr.12-241 12r 44 246 2A £1.50 £1.20 0-24-3141-481100 2 E7.00 £120

12-241 121 101 241 54 £7.50 £1.40 0-24-304148100 4 F12.80 01.130

12-241 12112A 241 BA £13.00 £2.00 0-24-30-40-41000 0 010.130 F2.40

12-241 121 200 241 10A 02.00 £2.20 0-24-304048400 10 £27.80 £3.00

12-241 1211 30A 241 I5A £18.10 £2.40 0-20-28-34-40-500 2 £0.70 £1.20

0-12420-24-300 2 £5.40 E1.20 020-2024-40-500 4 £10.00 £1.80

0 12 1120 24 301 3 £8.25 £1.50 0-202824-40-509 8 £14.00 £2.40

0-12-10 20-24-300 5 £11.20 f1.70 0-20-28-34-40-500 10 £23.50 £2.80

012 II 20 24 300 10 C10.00 £1.80 02428-34-40500 12 £20.00 £3.50

STEP DOWN TRANSFORMERS FORAMERICAN EQUIPMENT

0-240-110V For use with 50 cycles Non -Motorised Appli-ances

0-240-100V For use with 60 cycles Motorised AppliancesRANGE 1 Fully Shrouded. Complete with 3 -Pin American

Socket. Fitted 6ft 240V Mains LeadRANGE 2 Complete with Carrying Case. 240V Mains Lead.

First 3 items.(*) fitted with one 3 -Pin American Socket, All otheritems fitted with two 3 -Pin American Sockets.

RANGE 1 RANGE 2Values Prices Carr. Values Prices Carr.80 WATTS £7.50 £1.20 *500 WATTS £18.00 £2.50

150 WATTS £9.50 £1.20 *1,000 WATTS £26.00 £3.00300 WATTS £11.50 £1.40 *1,500 WATTS £30.00 OA500 WATTS £15.00 £1.60 1,750 WATTS £35.00 OA

1,000 WATTS £19.00 £2.50 2,250 WATTS £44.00 OA1,500 WATTS £24.00 £3.00 3,000 WATTS £60.00 OA1,750 WATTS £29.00 OA

15%V.A.T. TO BE ADDED TO COST OF ALL ITEMS INC. POSTAGEHOURS OF BUSINESS

WEEKDAYS, 9 a.m. to 5 p.m.; SATURDAYS, 11 a.m. to 2 p.m.


TheProto oardNow circuit designing is aseasy as pushing a leadinto a hole ...No solderingNo de -solderingNo heat -spoiltcomponentsNo manual labourNo wasted time

For quick signal tracingand circuit modificationFor quick circuit analysis anddiagrammingWith or without built-in regulated power suppliesUse with virtually all parts - mostplug in directly, in seconds.Ideal for design, prototype and hobby

NOMODELNO

NO OFSOLDERLESSTIE -POINTS

ICCAPACITY(14 -pin DIP'S

UNITPRICE

PRICEINC P&P15% VAT

OTHERFEATURES

1 PB6 630 6 9.75 12.36 Kit2 PB100 760 10 12.50 15.52 Kit3 PB101 940 10 17.90 22.314 PB102 1240 12 24.95 30.415 PB103 2250 24 39.00 46.576 PB104 3060 32 49.00 58.077 PB105 4560 48 71.00 83.958 PB203 2250 24 61.00 72.95 5V @1A9 PB203A 2250 24 89.00 104.65 5V± 15V

10 PB203AK 2250 24 71.00 83.95 5V± 15V& Kit

Tomorrow's tools for today's problemsGLOBAL SPECIALTIES CORPORATION rG.S.C. (UK) Limited Dept. 7u, Unit 1, Shire Hill Industrial Estate, Saffron Walden, Essex CB11 3AQ.OM=G.S.C. (UK) Limited, Dept. 7uUnit 1, Shire Hill Industrial Estate,Saffron Walden, Essex. CB11 3AQ.Telephone: Saffron Walden (0799) 21682Telex: 817477

I

1Only Reg

2Only Req

3Only Req 4 Only Reg

5Only Reg

6Only Reg

7Only Reg

8Only Req

9Only Req

10Only Rea

Name Address

I

1

I enclose Cheque/P:0. for or debit my Barclaycard. Access, IAmerican Express card no. exp. date

I FOR IMMEDIATE ACTION - The G.S.C. 24 hour 5 day a week service For FREETelephone (0799) 21682 and give us your Barclaycard, Access, catalogue I

I American Express number and your order will be in the post immediately tick box 0mm mm mm m.



15

LINSLEY HOOD CASSETTE RECORDER 2

411111111.1111

Our new improved performance model of the Linsley Hood Cassette Recorder incorporates ourVFL 910 vertical front mechanism and circuit modifications to increase dynamic range. Boardlayouts have been altered and improved but retain the outstandingly successful mother -and.daughter arrangement used on our Linsley -Hood Cassette Recorder 1.This latest version has the following extra features: Ultra low wow -and -flutter of .09% -- easilymeets DIN Hi-Fi spec. Deck controls latch in rewind modes and do not have to be held. Full Auto -stop on all modes. Tape counter with memory rewind. Oil damped cassette door. Latching recordbutton for level setting. Dual concentric input level controls. Phone output. Microphone inputfacility if required. Record interlock prevents rerecordiog on valued cassettes. Frequency generat-ing feedback servo drive motor with built-in speed control for thermal stability. All these desirableand useful features added to the excellent design of the Linsley -Hood circuits and the quality ofthe components used makes this new kit comparable with built-up units of much higher cost thanthe modest, E94.90 V.A.T. we ask for the complete kit.

LINSLEY-HOOD CASSETTE RECORDER 1

We are the Designer Approved suppliers of kits for this excellent design. The Author's reputationtells all you need to know about the circuitry and Hart expertise and experience guarantees theengineering design of the kit Advanced features include: High -quality separate VU meters withexcellent ballistics. Controls, switches and sockets mounted on PCB to eliminate difficult wiring.Proper moulded escutcheon for cassette aperture improves appearance and removes the needfor the cassette transport to be set back behind a narrow finger trapping slot. taw to use, robustLenco mechanism. Switched bias and equalisation for different tape formulations. All wiring isterminated with plugs and sockets for easy assembly and test. Sophisticated modular PCB systemgives a spacious, easily -built and tested layout. All these features added to the high -qualitymetalwork make this a most satisfying kit to build. Also included at no extra cost is our latest HS16 Sendus Alloy super head, available separately at 03.20 but included free with the complete kitat E75 plus VAT.Reprints of the 3 original articles describing this design 45p. No VATReprint of the subsequent postscript article 30p. No VAT.

PRACTICAL WIRELESS 'WINTON' TUNER

LINSLEY-HOOD 300 SERIES AMPLIFIERS

These latest designs from the drawing board of John Linsley -Hood. engineered to the veryhighest standard, represent the very best that is available on the kit market today. The delicacyand transparency of the tone quality enable these amplifiers to outperform. on a side -by -sidecomparison, the bulk of amplifiers in the commercial market -place and even exceed the highstandard set by his earlier 75 -watt design.Three versions are offered, a 30 -watt with Darlington output transistors, and a 35- and 45 -wattboth with Mosfet output devices. All are of identical outside appearance which is designed tomatch and stack with our Linsley -Hood cassette recorder 2.As with all Hart kits the constructors interests have been looked after in a unique way by reducingthe conventional land boring) wiring almost to the point of extinction.Any of these kits represents a most cost-effective route to the very highest sound quality with theextra bonus of the enjoyment of building a sophisticated piece of equipment.30 -watt Darlington amplifier, fully integrated with tone controls and magnetic pick-up facility.Total cost of all parts is E81.12. Special offer price for complete kits E72.35 -watt Mosfet amplifier. Total cost of parts E98.41. Special otter for complete kits, E87.40.45.watt Mosfet amplifier. Total cost of parts E104.95. Special offer price for complete kits E94.80.I Reprints of original Articles from Hi-Fi News 50p. Post free. No VAT.Reprints of MOSFET article 25p. No V.A.T. Post free.

FEED YOUR MICRO BYTES WITH OURSOLENOID CONTROLLED CASSETTE DECK

Front loading deck with full solenoid control of all functions including optional read in fast windmodes. 12 volt operation. Fitted 3 -digit memory counter and Hall IC Motion Sensor. Standarderase and stereo R/P Heads. Cheapest price ever for all these features. Only £98.90 plus VAT. Fulltechnical specification included.

HART TRIPLE -PURPOSE TEST CASSETTE TC1One inexpensive test cassette enables you to set up VU level, head azimuth and tape speed.Invaluable when fitting new heads. Only £2.70 plus V.A.T. and 50p postage.

CASSETTE HEADSHS16 SENDUST ALLOY SUPER HEAD. Stereo R/P. Longer life than Permalloy. Higher output thanFerrite. Fantastic frequency response. Complete with data E8.20HC20 Stereo Permalloy R/P head for replacement uses in car players, etc E4.25HM90 Stereo R/P head for METAL tape. Complete with data ........................ .. E7.20H561 Special Erase Head for METAL tape E4.90H524 Standard Ferrite Erase Head E1.504 -Track R/P Head. Standard Mounting E7.40R484 2/21Double Mono) R/P Head. Std. Mtg E4.90ME151 2/2 Ferrite Erase. Large Mtg. E4.25CCE/8M 2/2 Erase. Std. Mtg E7.90

Brilliant new Ted Rule designed Tuner with everything! Gives you fantastic stereo f/m receptionwith pilot cancelling decoder i.c., fluorescent display, digital frequency readout along with clockand timer functions. In addition to f.m. covers I.w., m.w., s.w. and even TV sound. Further detailsare in our lists; send for your copy.

Part Cost of Post, Packing and InsuranceOrder up to El 0 -50pOrders El 0 to E49- El Export Orders Postage or shipping at cost plusOver E50-£1.50 £2 Documentation and Handling

Please send 9 x 4 S.A.E. or telephone for lists giving fuller details andprice breakdowns.

Instant easy ordering, telephone yourrequirements and credit card number to us on

Oswestry (0691) 2894

AMATEUR RADIOHANDBOOK 1982by A.R.R.L. £8.50

30 -hour Basic by Prigmore £6.50UCSD Pascal Handbook by Clark £13.00Electronic Equipment Reliability by Cluley £7.50Micros in Amateur Radio by Kasser £8.00How to Design, Build Remote Control Devices by Stearne £10.00Modern Communication Switching Systems by Hobbs £8.00Art of Electronics by Horowitz £14.50

* PRICES INCLUDE POSTAGE AND PACKING *

THE MODERN BOOK CO.Specialist in Scientific and Technical Books

15/21 Praed Street, London, W2 1NPPHONE: 01-402 9176: Closed SATURDAY 1 p.m.

Please allow 14 days for reply or delivery

All prices plus VAT

TV TUBE REBUILDINGFaircrest Engineering Ltd. manufacture a comprehensiverange of equipment for processing all types of picture tubes,colour and mono. Standard or custom built units for estab-lished or new businesses. We export world-wide and have anexcellent spares service backed by a strong technical team.

Full training courses are individually tailored to customers'requirements.

For full details of our service contact Neil Jupp

FAIRCREST ENGINEERING LTD.4 Union Road, Croydon, CR0 2XX

01-684 1422/01-684 0246

WW - 058 FOR FURTHER DETAILS16



An entirerange oflow- costhigh-performanceinstruments

sabtronics'Making Performance Affordable

2010A 31/2 -Digit L.E.D. Bench DMM 5020A 1 Hz-200KHz Function Generator2015A 354 -Digit L.C.D. Bench DMM 8110A 100MHz 8 -Digit Frequency Meter2020 394 -Digit L.E.D. Bench DMM 8810A 600MHz 8 -Digit Frequency Meter

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with Temp. PSC-85 600MHz PrescalerLP -10 10MHz Logic Probe 9005 5MHz Single Trace Oscilloscope

Also available in kit form.

Test our low priced test equipment. Itmeasures up to the best. Compare ourspecs and our prices- no-one can beat ourprice/performance ratio.Full colour illustratedbrochure and price list from:BLACK STAR LTD.,9a Crown Street, St. Ives,Cambs. PE17 4EBTel: (0480) 62440. Telex 32339

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selection.* Auto, Normal, TV Triggering.

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SAFGAN ELECTRONICS LTD.OMFGA ROAD, WOKING, SURREY TEL. WOKING 1048621 69560

Carriage: England & Wales £7.50 + VAT.; Scotland E10.50 + VAT.London Stockist Audio Electronics - Tel 01-7243564

North-West Stockist. Darom Supphes, Warrington, Ches. - Tel. Warrington 64764Avon Stockist. 1 F Hannay, Bath. - Tel: Bath 24811

Cardiff Stockist: Steve's Electronics Supply Co, Cardiff - Tel. 10222141905Chesterfield Stockist' Kays Electronics. Chesterfield - 10246131596

Newcastle Stockist. Aitken Bros & Co Newcastle - Tel, 0632 26729Birmingham Stockist: P.A.T.H. Electronic Services - Tel 021-327 2339

Derby Stockist' RTS, Derby - Tel: 103321 41235

MICROCOMPUTER COMPONENTSLOWEST PRICES - FASTEST DELIVERY

MEMORIES21141-200ns 1+0.93

25+01921141-300nsGTE 1.55;FOR ACORN ATOM)2708 450ns 1+2.25

25+1292716 45Ons 1+2.49(single +511 25+2252716 350ns 6.952532 450ns 1+4.50

25+8252732 450ns 1+3.99

25+3.902732 350ns 7.504116 200ns 1+0.74

25+0.70100+0.87

4116 15Ons 1+0.9325+0.89

4118 200ns 1+3.0025+3.45

4118 150ns 6.005516 200ns 12.506116 200ns 7.9561161P 200ns 10.006116LP 150ns 1085

CRT CONTROLLERSEF6845P 9.50EF9364P 5/4EF9365P 62.90EF9366P 62.90EF9365/6 DATA ANDAPPLICATIONS 2.00

BUFFERS811595 0.90811596 0.90811597 0.90811596 2908726A 0998T28A 406195 1.358197A 1.358T98 1 45

DATA CONVERTERSZN425Eb 3.457N4266-8 3.00ZN427E-8 5.99ZN428E-8 4.75ZN429E-8 2.10ZN422CJ.10 28.09ZA-133CJ-10 2.59714440 56.63Z6432E-10 14.75Z1444 9.14ZN448 6.85ZN449 320

cm FLOPPY DISCCONTROLLERSFD1771 17.12FD.1791 32.61F131793 32.01101795 35.33W01391 4510W01393 4580W01395 45.50WD1397 45.50W02143-01 545W01691 10.87

MISCELLANEOUSSUPPORT CHIPSAY -31015 3.25AY3-1270 7.95AY3-8910 6.95AY -5-1013 3.45AV -5-3600 7.95AV -5-2376 195DP8304 850MC1488 0.59MC1489 059MC3446 295MC3448A 4.25MC3480 7.95MC3487 2.95MC14411 6.94MC14412 7.9960-3.25131 6.99R0 -3-2513U 5.99ULN2803/6003 0.84

DVM CHIPSZN450e 7.61ZN450E DAM KIT 25.00

NEW UNEARSLM301AN 025LM308N 0.89LM311N 0.89LM319N 2.201M3245 0.30LM348N 0.59LM555CN 0.16LM556CN 0.09LM725CN 3.20LM741CN 214LM7470N 0.70LM748CN 0.34

its PfCe ea

REGULATORS 4012 0.15 741511 0.127805 0.39 4013 029 741512 0.127812 0.39 4014 0.58 741513 0227815 0.39 4015

COT741_514 0.39

78105 0.29 4016 74LS15 0.12

78L12 0.29 4017 0.45 741520 0.12

78L15 0.29 4018 0.58 74LS21 0.12

7905 0.55 4019 0.29 74LS22 0.12

7912 0.55 4020 0.59 74LS26 0.15

7915 0.55 4021 0.60 74 LS27 0.12

79105 0.5040224023

0.820.17

741528741530

0.150.12

79112 0.59 4024 0.35 74L532 0.1279L15 0.59 4025 0.16 741533 0.18LM309K 0.99 4026 0.99 741537 0.15LM317K 320 4027 0.30 741038 0.15LM323K 4.95 4028 0.55 741540 0.12LM338K 4.75 4031 1.85 741542 0.34

4033 1.60 741547 0.39710 FAMILY 4034 1.55 741548 0.60Z80 CPU 3.49 4035 0.72 741549 0.59Z804 CPU 3.99 4040 0.54 741551 0.14Z80 CTC 2.99 4041 0.89 74 LS54 915Z800 CTC 2.99 4042 0.54 741555 0.15Z80 DART 10.00 4043 0.59 741573 0.19Z804 DART 12.00 4044 0.84 741574 0.16Z80 DMA 9.05 4045 1.65 741575 024Z80A DMA 11.95 4046 0.88 741576 920Z80 PIO 3.49 4047 0.68 741578 aieZ804 PIO 3.75 4048 0.54 741583 0.44Z80 510-0 10.99 4049 0.28 741585 0.65Z80A S10-0 11.99 4050 026 741586 0.15280 510-1 10.99 4051 0.59 741590 0.30BOA 510-1 11.99 4052 0.68 741591 0.75Z80 510-2 10.99 4053 0.59 74LS92 0.34280A 510-2 11.99 4054 120 741593 0.34MK 3886 11.00 4055 120 741_595 0.43MK 3886-4 14.47 4060 039 7415109 021

4063 0.95 741,5112 021WOO FAMILY 4066 0.34 7415113 0236800 2.99 4068 0.17 7415114 0.196802 3.99 4069 0.17 7415122 0.39

FREE OFFERWith each order with a valuein excess of £20* 20 page Component

Catalogue* Reply Paid Envelope* Voucher Value £1

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6803C 11.806809 gee6810 1256821 1256840 4.206850 1.506862 6.916871AIT 18.706880 1.076887 0.6068488 9.116875 4.186843 13.9968800 4.7068802 19.1168821 22968810 2.0068E140 4.706805C 2.156800014 110.00

5500 FAMILY6502 4256520 2.996522 4.756532 6.95

13090 FAMILY8085A 5.500212 1.708216 0.998224 1.958228 3.958251 3.908253 7.958255 3.80

CMOS 4000 '8'SERIES4000 0.114001 0.114002 0.134006 0.604007 0.154008 0.554009 0.284010 0.354011 0.12

4070407140724073407540764077407840814082408540864093450245074508451045114512451445154516451845194520452145224526452745284532454145434553455545564585

0.170.170.170.190.170.620.22

0240.140.190030.690.390.890.391.900.600890.601.491.490.890.400280.891.491.200.702890.700.850290292.900290.44022

74L3 SERIES741500 0.10741_501741502741S03741SO4741505741508741509741510

0.110.122120.12

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741512374151247415125741512674151327415136741513874151397415145/415148741515174151537415155741515674151577415158741516074151617415162741S16374151647415165741_5166741.5173741_5174/41S1757415181741519074151917415192141_5193741_51947415195741519674151977415221741S2407415241741524274152437415244741S245741524774152487415249741525174152537415257

0390.990250250.450280.340350.750900.390290.390.380.310.310.390.390.390.390470990.640700.470.491280490.490490.480.390.390.590150.540.090.890.790.790.850.890.830.830.630.400.390.40

74 LS258 0.397415259 0.797415261 1.957415266 0237415273 0757415279 0.397415283 0.44741S290 0.547415293 0.457415365 0.347415366 0.387415367 0.347415368 0.497415373 0.747415374 0.747415375 0.17741.5377 0.697415378 0.897415379 0.8474 LS386 0287415390 0.547415393 0.59

OIL SOCKETSLOW PROFILE 111

8 pin 0.0714 pin 0.0916 pin 0.0918 pin 0.1320 pn 0.1422 pin 0.1724 pin 0.1928 pin 02540 pr 0.29

CECILOW PROFILE GOLD

Spin 02214 pin 0.2916 prt 0.3118 pin 03320 pin 0.3522 pin 0.4024 pin 0.4228 Om 0.5440 pin 011

ZERO INSERTIONFORCE OIL24 pin 6.3028 pin 7.4040 pn 8.80

CRYSTALS1 MHz 2.9UI 008 MHz 2.9018432 MHz 2.2036864 MHz 2.954 MHz 1.656 MHz 1.908 MHz 1.9514 MHz 3.45

up UHFMODULATORS

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Data ConvenerHandbookInc p&pi 1.58

OATASNEETSPholocope0 DataSheets available Icemost product at 66Per Page ex P&Pand VAT Pleasetelephone for details

KEYBOARDElectrornechancalASCII Encoded1Uppet 8 LowerCasel Keyboard56 Keys Inc She braPrice each 49.95Carnage 2.001

CASEStructured FoamCase for aboveocluding Steel Baselashed in Blackand CharcoalPrice earn 40.05CarHape 10.001

MAINSTRANSFORMFRSuitable for +5Val 25A ±120 atI A Power SupplyUsing BridgeRechhcaloon andLM323NPrice exh 10.95

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PLEASE SEND S.AE.120p) FOR OUR NEW 1982 CATALOGUE. FREE REPLIED PAID ENVELOPEWITH EVERY ORDER. ALL PRICES EXCLUDE P I P ON ORDERS UNDER f 101750 OVER f 10CASH WITH ORDER AT LIST PRICE ONLY AND VAT(1 5%1. ALL ORDERS DESPATCHED ON DAY

OF RECEIPT WITH FULL REFUND FOR OUT OF STOCK ITEMS IF REQUESTED.

MIDWICH COMPUTER CO. LTD.DEPT WW. HEWITT HOUSE, NORTHGATE STREET,

BURY ST. EDMUNDS, SUFFOLK IP33 1 HQTELEPHONE: (0284) 701321 TELEX: 817670




17

e- m utin,t y

Our May issue is a must for all microcomputing enthusiasts:

TIPPING THE BALANCE Can a micro -based system really offer the facilities of amainframe? We investigate.

THE SOFT APPROACH Supercharging the Apple is currently a popular pastime.We look at the CP/M option from Microsoft.

COMPILING THE PROBLEM Use a compiler to accelerate your BASIC! We review acommercial offering.

AFTERMATH With the first screening of the Computer Programmenow complete the BBC's Computer Literacy projectmoves into top gear. We bring you the inside story.

AT YOUR NEWSAGENTS NOWWW - 056 FOR FURTHER DETAILS

PIANOS SPECIALISTS SINCE 1972DOMESTIC OR STAGESIX OR 7t/4 OCTAVESKITS OR MANUFACTURED

DOMESTIC PRICES

SIX 71/4

Comp' 217 244

Full 363.90 399.90

MFD 595 675

The most advancedform of touch senseLive action simulat-ing piano key inertiaby patented tech-nique.

Four mixable voicesfor serious tonevariation pluselectronic chorusand flanger effects.

Component Kits in-clude Keyboard.

Full Kits further con-tain Cabinets, Har-ness, Power Ampand Speaker.

KitKB BAND -BOX' £269 An Electronic Backing

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User ProgrammableVOCAL & INSTRU- for 50-100 scores.MENTAL SOLOISTS! using microprocesso,-

MASTER RHYTHMUser ProgrammableDRUM MACHINE.Twenty-four patterns.Eight parallel tracks.Twelve instrumentssequence operation. £79 KIT £119 BUILT

Write or Phone for full details of our range ofhigh quality Kit and manufactured ElectronicMusical Instruments. Prices include V.A.T., Carr.,& Ins. and we operate Telephone BARCLAY-CARD/ACCESS.Competitive EXPORT Quotations given.

CLEF PRODUCTS (ELECTRONICS)LIMITED

Dept. W, 44a Bramhall Lane SouthBramhall, Stockport, Cheshire SK7 1AH

061-439 3297


SOUND INVESTMENT

QUALITY REEL TO REEL It CASSETTE TAPE HEADSFITTING A NEW TAPE HEAD CAN TRANSFORM THE PERFORMANCE OF YOUR TAPE RECORDER.

OUR FULL CATALOGUE (PRICE 50p) ALSO INCLUDES TAPE TRANSPORTS, DISC DRIVES,PREAMPLIFIERS AND ACCESSORIES

POPULAR UNIVERSAL CASSETTE HEADS TO EIAJ STANDARDSC21RPS18 MONO R/P E4.62 Hole Centres 17mm Apart, 12mm From Head FaceB24-02 STEREO R/P £7.66 C42RPH2O STEREO R/P SENDUST FORB24-07 STEREO R/P FOR DOLBY CHROME/METAL TAPES.. £10.67

SYSTEMS £9.05 C42RPHO4 STEREO R/P GLASS FERRITEC21ES18 MONO/STEREO ERASE THE ULTIMATE LONG LIFE,

HEAD E.2.13 HIGH PERFORMANCE HEAD E13.34POST AND PACKING 40p EX STOCK DELIVERIES, ALL PRICES INCLUDE V.A.T.

The Monolith Electronics Co. Ltd.,5/7 Church Street, Crewkerne.Somerset TA113 7611Tel: 0460 74321.Telex:46306 MONLTH G.

MONOLITHelectronic products


Hitachi Oscilloscopes performance, reliability, exceptional valueand immediate delivery!

Hitachi Oscilloscopes provide the quality and performance that you'd expectfrom such a famous name, in a range that represents the best value for moneyavailable anywhere.

V -152B 15MHz Dual Trace V -550B 50MHz Dual Trace, Dual TimebaseV-202 20MHz Dual Trace V-1050 100MHz Quad Trace, Dual Timebase

(illustrated) Just releasedV -302B 30MHz Dual Trace V-209 20MHz Dual Trace, Battery PortableV-352 35MHz Dual Trace V-509 50MHz Dual Timebase, Portable

Prices start from around E230 and we hold the range in stock for immediatedelivery.

For colour brochures giving detailed specifications and prices, ring 048063570.Reltech Instruments 46 High St., Solihull, W. Midlands B91 3TB



THE CASEFOR

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ACOUSTIC b VIBRATIONBRUEL Et KJAER1621 Tunable Band Pass Filter2113 Audio Frequency Spectrometer2203 Sound Level Meter2215 Sound Level Meter inc. Oct. Filter2218 Sound Level Meter inc. Leg.23056 Level Recorder inc. 50 dB pot.2625 Vibration pick-up amplifier2808 Power Supply/Mains Adapter2972 Tape Signal Gate4230 Sound Level Calibrator4423 Noise Dosemeter4424 Noise Dosemeter

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BRIDGES b V and I STANDARDSADVANCETI la Meter 100 KHz-100 MHz 160

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PHILIPSPM6302 RCL Bridge - direct reading 395

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DYMARBC282 Battery charger for 883 RadioTelephone883 Radio Telephone - VHF band - handheld

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S.T.C. DIGITAL TESTING EQUIPMENT741846 Selective Level Measuring Set 600 HEWLETT PACKARD74216A Noise Generator 300 1600A Logic Analyser 16 ch 20 MHz 140074261A Psophometer 300 1600S Logic Analyser 32 ch 20 MHz 225074262B White Noise Generator 8 Receiver 2000 1602A Logic Analyser 16 ch 10 MHz 90074307C Level Measuring Set 175 1607 Logic Analyser 16 ch 20 MHz 95074834C Distortion Measuring Set 500 TEKTRONIX96016 Selective Null Detector 200

832 Datacom Tester Rg212/V24 1150GTA-2 Quantization Distortion Tester 800

833 As 832 plus BERT/ BLERT feature 1300GTA4B Pattern Generator 900 7DOIF/DFI Logic Analyser/ FormatterTEKTRONIX 16 ch 50 MHz P/ in 26501502 TDR Cable Tester CRT + Recorder 2950 7603/7DOIF/ OF! As above with display

COMPUTER EQUIPMENTmainframe 3600

(90 day guarantee)

CENTRONICS MAINS TEST EQUIPMENT702 matrix printer 500 COLETEKTRONIX T1007 Volt/ Freq/ Spike Monitor Rec 0/P 110

4610-1 Hard copy printer for 4010 series DATA LA Bcomputer display terminals 1800 DL019 Mains Interface for DL905 300

SPECIAL OFFER

FLUKE 8800A51/2 digit digital voltmeter

High accuracy and resolution AC/DC/2.DC resolution 1µV.

AC resolution 10µV.Manual or Auto ranging

£430 (12 month guarantee)(£395 one month guarantee)

COUNTERS Et TIMERSFLUKE1910A-1 125 MHz 7 digit Cntr. AC/ Ban1912 520 MHz 7 digit Counter1912A01 As 1912A but inc. re -chargingbatteries1920A 520 MHz 9 digit Counter inc. Brst.mode1920A14 1250 MHz otherwise as 1920A

HEWLETT PACKARD5243L 20 MHz 8 Digit Counter5245L 50 MHz 8 Digit Counter5300A/5304A 10 MHz 6 Digit CounterTimer5300A/5305B 1300 MHz 6 Digit Counter5345 500 MHz 11 Digit Counter Timer

MARCONITF 2432 560 MHz 8 digit Counter

RACAL -DANA371 18 GHz 11 digit Counter with SourceLocking facility8110 50 MHz 8 Digit Counter Timer9024 600 MHz 71/2 digit Counter9025 I GHz 8 digit Counter9520 10 MHz 4 Digit9905200 MHz 8 digit Counter Timer

SYSTRON DONNER6053 3 GHz 9 digit Counter BCD 0/P51038 Strip Printer for 6053/6054

TEKTRONIXDC501 7 Digit 100 MHz Counter - TM500Plug-in

250425

2000

350

4950320220450

95380

MISCELLANEOUSA.I. INDUSTRIESTCS General Purpose Gas Leak Detector -intrinsically safe

DRANETZ606 3ch Volts Av/ Spike/ Time/ Printer

300 616 2ch AC 1 ch DC Volts/ Av/ Spike/375 Time/Printer

GAY430 LDM AC/ DC/Spike/Time inc. Printer

575750

150200 BRADLEY,

192 Oscilloscope Calibrator

COMARK1601BLS Thermom lOch 87 + 1000°C type KN. B. Thermocouples not included

CROWCON71P Inflammable Gas Detector/Alarm

DATALABDL905 Digital Transient Recorder/ DisplayStorage

FLANN16/11 Rotary Vane Attenuator WG16

HEWLETT PACKARD342A Noise Figure MeterX382A Rotary Vane Attenuator WG16

790 MULTIMETRICS375 AF120 Dual H / Pass L7Pass active

filter 20 Hz -2 MHz

PHILIPS180 PM 5501 Colour TV Pattern Generator

2950

3300

1250

290

825

50

125

1050

250

500175

800

199

PM 6455 Stereo FM GeneratorPM 6456 Stereo FM Generator

RESEARCH INSTRUMENTSMicro manipulator - 4 Probes moveable inall planes. Adjustable test table - WatsonBarnet optics. Complete system mountedin perspex enclosure

ROHDE Et SCHWARZBN252 Transistor Y Parameter Test Set

S.T.C.74600J Attenuator 0-9 dB 505) in 1 dBsteps74616A Attenuator 0-100 dB 60041 in 0.1 dBsteps

TEKTRONIX521PAL Vectorscope528 TV Waveform Monitor575 Semiconductor Curve Tracer1485C TV Waveform Monitor PAL/ NTSC

YELLOW SPRINGSYS157 Water Pollution MeasurementSystem

NETWORK ANALYSERS/PHASEMETERS

GENERAL RADIO1710/11/12/140.4-500 MHz 115 dB range

HEWLETT PACKARD8405A Vector Voltmeter 1-1000 MHz8414A Polar Display for 8410 N.W.A.8745A S Parameter Test Set 0.1-2 GHz11570A Accessory Kit for 8405A11600A Transistor Test FixturesTO18/ TO -7211602A Transistor Test FixturesT05/TO-1211604A Universal extension arm for 8745A11605A Flexible arm for 8743A

OSCILLOSCOPES EtACCESSORIES

CROTECH(New CROTECH Oscilloscopes)3030 15 MHz 1 Trace 5mV built-incomponent tester3033 15 MHz 1 Trace 5mV battery operation3034 15 MHz 2 Trace 5mV battery operation3035 10 MHz 1 Trace 5mV built-incomponent tester3131 15 MHz 2 Trace 5rnV built-incomponent tester3337 30 MHz 2 Trace 5mV with signal delay

GOULD ADVANCE0510006 20 MHz 5mV 2 Trace053000A 40 MHz 5mV 2 Trace 2T base

HEWLETT PACKARD182C 100 MHz Mainframe182T 100 MHz Mainframe with digitalnormaliser interface1804A 50 MHz 20mV 4 Trace Plug-in1825A Dual Timebase Plug-in1805A 100 MHz 5mV 2 Trace Plug-in

PHILIPSPM3207 15 MHz 5mV 2 Trace TV trigPM3211 15 MHz 2mV 2 Trace TV trigPM3212 25 MHz 2mV 2 Trace TV trigPM1713 10 MHz 2mV 2Ch fixed delay DualBeamPM3244 50 MHz 5mV 4 Trace 2T basePM3260 120 MHz 5mV 2 Trace 2T basePM3262 100 MHz 5mV 2 Trace 2T baseTr View

TEKTRONIX465 100 MHz 5mV 2 Trace 2T base4658 100 MHz 5mV 2 Trace 2TB, inc Probes475 200 MHz 2mV 2 Trace 2T base475A 250 MHz 2mV 2 Trace 2T base485 350 MHz 5mV 2 Trace 2T base5642 2 T/ base plug-in 50 MHz Trig for 5000series MainframeDD501 Digital Events Delay - P/in forTM500 series661/453/571A 1 GHz Sampling scope7Al2 105 MHz 5mV 2 Trace Plug-in7A18 75 MHz 5mV 2 Trace Plug-in7A19 500 MHz 10mV 1 Trace Plug-in7A22 1 MHz 100.V Differential Plug-in7A24 350 MHz 5mV 2 Trace Plug-in7A26 200 MHz 5mV 2 Trace Plug-in7653A 2 Timebase Plug-in 100 MHz Trig7680 Single Timebase 400 MHz Trig7885 Timebase with delay 400 MHz Trig7403N 75 MHz 3 slot M/ Frame7603 100 MHz CRT r/ out 3 slot M/ Frame7704A 200 MHz CRT r/out 4 slot M / FrameP6013A X1000 12KV Probe

TELEQUIPMENT1263/V1/V1 15 MHz 2 Trace ImV

Pricesfrom I

220295

475

1500

120

180

2750750425

3100

300

2200

3100750

3100175

125

125250250

145280350

166

230396

500830

1300

1500825500626

270350560

30014501475

1150

14501685175021003500

325

475595300420990595990655530535710990

13501960

96

425

All items have a 12 month guarantee unless otherwise stated.ww - 059 FOR FURTHER DETAILS

CanrSke,YJV Ca Nair re, Ca nkillitv-1117 Ca ntaNirc2/ , , Cal nitalbr/ Cia nOlorriA 7, Ca ft:OW"' r4,44 2

rstottw, ,Cantong%' CarstottmvCarstorrg,9,, CantortwCarstotta!,Carstortwe

3/V5/V5 15 MHz 5mV 2 Trace & fixedlayr5/V4/S2A 50 MHz 1mV 2 Trace 2base3/V4/S2A 50 MHz 1mV 2 Trace 2T/ CRT015 15 MHz 5mV 2 Trace TV trig1 5 MHz 5mV I Trace

EXSCAN1120 Large CRT XY Display withnodulation 280

le: we hold a range of cameras P.O.A.

)SCILLOSCOPES (STORAGEEWLETT PACKARD1A 100 MHz Mainframe 5cm/ms 2500)3A 35 MHz 10mV 2 Tr 2TB 1000 Div/ms 1400

EKTRONIX5 100 MHz 5mV 2 Tr 2TB 1350cm/us 2950

12 10 MHz 2mV 2 Tr ITB 250cm/ ms 895

13 25 MHz 3 slot M/frame split screenm/us 1700

13 100 MHz 3 slot M/frame 4.5cm/us 270034 400 MHz 4 slot M /frame 2500 cm/us 5300

'OWER MEASUREMENT.UKE21A 10 Hz -20 MHz 4% digit Et Analoguens Et dBm 825

EWLETT PACKARD2A RF-Microwave Powermeter for useth 470 series sensors5A Co -ax sensor for 432 meterMHz -10 GHz86A Power sensor for 432 meter W.G. 162A/478A combined price2A/X486A combined price31A Type N Coax sensor for 435A32H Co -ex sensor for 435/436

KHz-4.2 GHz

430

160160550550250

Pricesfrom £

8016A Digital word generator to 50 MHz440 9 x 32 bit

LYONSsso PG73N 20 MHz 10V 502 R.T. 5ns

750 RECORDERS b ACCESSORIES295 BRYANS SOUTHERN135 BS3I4 Chart 10' 4 Pen 16 speed

BS316 Chart 10' 6 Pen 16 speed

Pricesfrom f

3400

390

19002500

DCM8100W Wow Or Flutter Analyser 800

EMLVDT Linear Displacement Or Transducer 50

FYLDE154 Bridge supply and Amplifier

HEWLETT PACKARD7015A XY 1 pen A4 size7046A XY 2 pen A3 size

HONEYWELL56008 Instrumentation tape recorder 14 chFM/ DR 9000

MICRO -MOVEMENTSM10-120/ A Compact UV 10 ch 7 speedrecorder (inc. galvos) 1900

PHILIPSPM8041 XY 1 pen A4 size 750PM/325I Chart 10' 1 pen 12 speed 375

SE LABS9946 ch galvo preamp + DC bridge supply3006 UV chart 6" 6 ch6008 UV chart 8" 25 ch 16 speed6150/51 UV recorder 12 ch-inc 6 ch amps

SMITHS13E541 Chart 8" 1 pen 8 speedRE501/4701 Cht 4" + XY 1ch 10 spdAC Batt

SOLARTRON220 3240 Modular Data Logger system

ARCONI893A 10 Hz -20 KHz Powermeter 13512 R.F. Powermeter DC -1 GHz 10W max 475

R.F. Powermeter DC -1 GHzDW max 800

50/6421 Microwave Powermeter Etnor 0.01-12.4 GHz 500

20WER SUPPLIES etcDVANCE05-20 Switching PSU module 5V -20Aed 90

RANDENBURG0 EHT Power supply 3-30 KV-1mA 450

4RNELL10/5 0 -30V -5A variable 110

10/200 -30V -20A variable 225

SL 5V - 20A PSU module 80

30/25 0 -60V -25A variable metered 420OB 0-30V variable 1A Metered 60

330/100 -30V -10A variable 190)PS/2 Twin 5V @ 5A+ 15-0-15V @ 1A 8535/700 -35V -10A or 0 -70V -5A variablestored 320

EWLETT PACKARD688 0-40 V variable 30 A Metered V+ I 57566A 0-36 V variable 10 A Metered 450

IARCONI540-30V variable 2A metered 75

HILI PS1646 0-75V variable 6A Metered V + I 496

PULSE GENERATORSDVANCE3 52A Modular pulse generator system -de range of configurations - costpendant on modules - typical 650350020 0.1 Hz -1 MHz 50V 1002 DoubleIlse R.T. 15ns 290

H RESEARCH210 Hz -3.5 MHz 50V 500 RT 10ns 2 pulse 190

EWLETT PACKARDi11A 0.1 Hz -20 MHz 16V 502 RT 1Ons incHsi mode 475

RANK1740 Wow & Flutter meterNote: UV recorders are priced less galvos

SIGNAL ANALYSISEQUIPMENT

AIRMEC210 AM/ FM Mod Meter 2.25 MHz -300 MHz 235248A Wave Analyser 5-300 MHz 200853 Wave Analyser 30 KHz-30 MHz 200

MARCONITF791D FM Mod meter 170TF2304 Mod meter AM/ FM 475TF2330 Wave Analyser 20 Hz -50 KHz 475TF2330A Wave Analyser 20 Hz -76K H z 900TF2331A Distortion meter 770

RADFORDDM52 Distortion meter 20 Hz -20 KHz 200

SOUND TECHNOLOGY1700A Distortion Meter 10 Hz -100 KHz inc.oscillator 800

WAYNE KERRA321 Wave Analyser 20 Hz -20 KHz 180Note: see also "Spectrum Analysers"

SIGNALJFUNCTION/ + SWEEPGENERATORS

GENERAL RADIO1362 Generator 220-920 MHz

GOULDJ3B Generator 10 Hz -10 MHz 0/P levelmeter & Attn.J4 Generator as J3 but no output levelmeterSG21 Generator - Square Wave only0.3-100 MHz

HEWLETT PACKARD204C Oscillator 5 Hz -1.2 MHz204D Oscillator 5 Hz -1.2 MHz inc. 80dBattenuator6080 Generator 10-480 MHz AM/Pulse

450370960

1000

250

200

P.O.A.

8601A Gen/ Sweeper 0.1-110 MHz Attn.AM/FM8614A Generator 800-2400 MHzAM/FM/Pulse8660C/86632A/86603A Synthesised SignalGenerator 1-2600 MHz AM/FM digitalreadout, push button controls, BCDprogrammable86408 Generator 500 KHz-512 MHzAM/FM Phase Lock618B Generator 3.8-7.5 GHz612 Generator 450-1230 MHz614 Generator 0.8-2.1 GHz

IECF51A Function 1 mHz-10 MHz

110 Sin/Sq/Tri/ Pulse/ Ramp

LEVELL700 TG150DM Generator 1.5 Hz -150 KHz995 battery operated

MARCONITF144H/4S Generator 10 KHz-72 MHz AMTF8O1D Generator 10 MHz -470 MHz AMTF955/2 Generator 0.2-220 MHz AM/FMTF1066B /1 Generator 10-470 MHz AM/ FMTF2000 Generator 20 Hz -20 KHz-111 dBattenuatorTF2002/3MI Generator 10 KHz-72 MHzAM onlyTF2011/5 Generator 96-140 MHz FM onlyTF2012 Generator 400-520 MHz FMTF2015 Generator 10-520 MHz AM/ FMTF2015/1 Generator as 2015 with narrowFM deviationTF2015/2171 Generator system with phaselock synchroniserTF2015-1/2171 Generator system withphase lock synchroniserTF2171 Synchroniser for 2015

PHILIPSPM5108L Function 0.1 Hz -1 MHzSin/ Sq/Tri 0/P meter -50 and 6002

85 PM5127 Function 0.1 Hz -1 MHz Sin/Sq/Tri/ RmpPM5129 Function 1 mHz- 1 MHz Sin/ Sq/Tri/ Ramp/Pulse + Sweep + Burst

TEKTRONIXFG503 Function 1 Hz -3 MHz Sin/ Sq/Tri -P/in for TM500 series

TELONIC2003 Sweeper system 0.1-130 MHz withAttn.

TEXSCAN9900 Sweeper 10-300 MHz 6/in CRT dispVS60 Sweeper 5-1000 MHz

WAVETEK143 Function 0.0001 Hz -20 MHzSin/ Sq/Tri/ Pulse

SPECTRUM ANALYSERSHEWLETT PACKARD141T/ 855213/6553B 1 KHz-110 MHzsystem141T/8552B/8554B 100 KHz-1250 MHzsystem141T/8552B/8555A 10 MHz -18 GHzsystem3580A 5 Hz -50 KHz with digi store disp8445A Pre -selector 0.01-18 GHz8558B 0.1- 1500 MHz Plug-in for 180 series

375 MARCONITF2370 30 Hz -110 MHz Digi-store displaybuilt-in counter and tracking gen

350 TEKTRONIX7L131 KHz-1800 MHz Plug-in for 7000

220 series M/ Frame7L18 1,5-18 GHz Plug- in for 7000 series.

80 High resolution. Digital storage display.Built-in pre -selector7603/7L13 System with display 0.1-1800MHz7613/7L13 System with storage/var.persist. display

210

250400

Pricesfrom

1950

2800

15000

4500975750825

375

60

550180670690

750

560550550

1150

1350

1900

19501050

425

450

645

250

750

525890

695

7100

9050

10700295024004450

7500

7700

10100

8900

9900

Pricesfrom £

7603/7L18 System with display 1.5-18 GHz160 GHz with external mixers) 11100

VOLTIMULTI-METER(ANALOGUE

BOONTON92C AC/ RF 10 KHz-1.2 GHZ mV -3V 250

HEWLETT PACKARD400E 10 Hz -10 MHz ImV-300V DC 0/P 285

400H 10 Hz -4 MHz 1mV-300V 75

411A 0.5-500 MHz 10mV-10V DC 0/P 175

427 AC/DC/V/4 196

3400 TRMS 10 Hz -10 MHz 1mV-300VDC -0/P 390

LEVELLTMI 1 Analogue Multimeter AC/DC/V/142 115

M. L. ENGINEERINGNAMV - DC sensitive u Volt/ nAmp metercentre zero 45

MARCONITF2600 10 Hz -10 MHz 1rnV-300V AC + DC0/P 230

TF2603 50 KHz-1.5 GHz 3000/-3V 300

TF2604 20 Hz -1.5 GHz 300mV-300V 425

PHILIPSPM2404 Analogue MultimeterAC/DC/V/1/2 100

RACAL -DANA9301 R MS 10 KHz-1.5 GHz 100pV-300V 550

VIBRON/E.I.L.33B-2 1mV-1V Electrometer 200

VOLT/MULTI-METER (DIGITAUBOONTON92AD 1999FSD 10 KHz-1.2 GHz 10r.V res 525

FARNELLDM131D 1999 F.S.D. AC/DC/V/142 OrTemperature. Mains/battery - Tempprobe included 135

FLUKE8010A 2060 FSD TRMS AC/ DC/VII2 140

8010A01 As 8010A + re -charging batteries 159

8020A 2000 FSD HandheldAC/ DC/V12 + cond. 89

8022A 2000 FSD Handheld AC/ DC/V112 65

8030A-1 2000 FSD AC/DC/5/112 Batt + AC 165

8050A 20000 FSD AC/DC/VII-2 dB TRMS 2158050A-01 As 8053A + re- chg batteries 245

8200A 16000 F.S.D. DC only fast readingsystem Voltmeter 8508300A 120000 F.S.D. DC only fast readingsystem Voltmeter 1100

8600A 200000 FSD AC/DC/V2 660

GOULDDMM7 1999 FSD AC/DC/V/1/f2 80

HEWLETT PACKARD3490A 100000FSD AC/DC/V/2 550

SOLARTRONA200 19999FSD DC only 1uV-1 KV 65

A203 19999FSD AC/ DC/V/S2 160

A205 19999FSD TRMS AC/DC/Vat 175

=1...11.11=MieNLOW COST CORNER

Items in this box have 30 dayguarantee only.

M.L. ENGINEERING NAMVD.C. Sensitive nAmp/uVolt meter -centre zero

TEKTRONIX547/ 1A450 MHz Dual Trace Dual Timebase4 channel oscilloscope

TEKTRONIX575 Transistor Curve Tracer

TAYLOR62A AM/ FM Signal Generator 4-120 MHz

150

21ull details and specification'of equipment listed, available. Because of long copy dates this list is not comprehensive - ring for inventorypdate or tell us your SPECIFIC NEEDS. Hours Monday to Friday 9.30 am -5.00 pm (lunch,1-2 pm). Prices exclude delivery and VAT.Je take Access or Visa.

Carlton Electronics Ltd01.267 5311

hirley House, 27 Camden Rd, London NW1 9NR. Telex: 23920

/Contact us for a cash quote on your under utilised test equipment

ftm/7 Ca StOC aQ CotvCas CaeiCatr:vtanr xlrtorwtmrsorY

LP POWERSUPPL ES

MOST WITH ILPTORO l DAL

TRANSFORMERSpace -saving,

efficient ILP power suppliesare designed to give youflexibility in planning audio -, - ...Orassemblies. Nine of the

l!..., if,frfl"eleven models have toroidaltransformers manufactured on ....new cost-efficient high technologymachines in our own factory. So we keep thequality up, and the price down.

ILP power supplies are compatiblewith all other ILP modules - combine them toproduce almost any audio system. All carry the ILPyear no quibble guarantee and include full connection

So send your order on the Freepost coupon

POWER SUPPLY UNITS

5

data.below today,

Model No. For use withPrice

inc. VATPrice

es VAT

PSU 30 ±15V combinations of HY6/66 series toa maximum of 100 rnA or oneHY67.

£5.18 £4.50

The following will also drive the HV6/66 series except HY67 whichrequires the PSU 30.

PSU 36 1 or 2 HY 30. £9.32 £8 10

',Su 50 tor 2 HY 60. £12.58 £10.94

PSU 60 1 xHY 120/HY 120P/HD 120/HD 120P. £15.00 £13.04

PSU 65 1 x MOS 120/1x MOS 120E £15.32 £13.32

PSU 70 1 Of 2 HY 120/HY 120P/HD 120/HD 120P. £18.31 £15.92

PSU 75 tor 2 MOS 120/MOS 120P . £18.63 £16.20

PSU 90 1 xHY 200/HY 200P/HD 200/HD 200P. £18.63 £16.20

PSU 95 1x MOS 200/MOS 200P. £18.77 £16.32

PSU 180 2 x HY 200/HY 200P/HD 200/HD 200P orLxHY 400/1 x HY 400P/HD 400/HD 400P

£24.54 £21.34

PSU 185 1 or 2 MOS 200/ MOS 200P/1 x MOS 4001 x MOS 400P.

£24.68 £21.46

All models incorporate ILP toroidal transformers except PSU 30 and PSU 36which include our own laminated transformers.

Now to order Freepost:Use this coupon. or a separate sheet of paper, to order these modules, or any

products from other ILP Electronics advertisements. No stamp is needed if you address toFreepost, Cheques and postal orders must be crossed and payable to ILP Electronics Ltd, cashmust be registered. C.O.D. - add Et to total order value. Access and Barclaycard welcome.All UK orders sent post free within 7 days of receipt of order.

Imo

Please sendILP modules

Total purchase

I enclose Cheque

Please debit

Name

ii

me the following

price

Postal Orders Int. Money Order

my Access /Barclaycard No,

IAddress

Signature

I

IELECTRONICS LTD./

STAYAHEAD.STAY WITH US

WW6/5

Post to ILP Electronics Ltd. Freepost 2. Graham Bell House Roper Close.Canterbury CT2 7EP. Kent EnglandTelephone 10227154778: Technical 10227) 64723 Telex 965780

KONTAKT

O

The European name of AerosolExcellence. Special cleaners for allelectrical contacts and switches.

Kontakt 60Dissolves oxides and sulphides,removes dirt, oil, resin and tracesof metal abrasion. Protectsagainst erosion. Ensures perfectcontacts.

Kontakt 61Special cleaning, lubricating andanti -corrosion fluid for NEW (nonoxydised) and specially sensitivecontacts. An excellent lubricantfor all electrical and electromechanical systems.

Spray Wash WLA rapid cleaner for reliable wash-ing and degreasing of electricalequipment and components. Forremoval of dirt, grease, oil, solder-ing residues and other impurities.

ALSO AVAILABLE:A COMPLETE RANGE OF INDUSTRIAL AEROSOL SPRAYS

SK10 Soldering Lacquer, K75 Cold Spray, K70 Plastic Spray, K88 OH Spray, K701Vaseline Spray, K90 Video Spray, K33 Graphite Spray, K100 Antistatic Spray,K101 Fluid Spray and, of course, Positiv 20 positive photo resist for printedcircuits.

Details from:

Special Products Distributors Ltd.81 Piccadilly, London, W1V OHL

Tel: 01-629 9556. Telex: 26500 lanswerback RACEN). Cables: Speciprod, London,W1


TRANSDUCER and RECORDER

AMPLIFIERS and SYSTEMS

0

41*

reliable highperformance &practical controls.individuallypowered modules -mains or dc optionsingle cases and upto 17 modules instandard 19" cratessmall size -lowweight -realisticprices.

L49/51 Fylde Road PrestonPR1 2XQ

\Telephone 0772 57560

1 FyldeElectronicLaboratoriesLimited.

22

WW - 053 FOR FURTHER DETAILS WW - 025 FOR FURTHER DETAILS


AUDIO El ECTRA.11CPRETAILMAIL ORDER.EXPORT LONDON'S TEST EQUIPMENT CALL IN AND SEE FOR YOURSELFINDUSTRIAL. EDUCATIONAL CENTRES OPEN SIX DAYS A WEEK t`` MODEL

fp'. .1 CROTECH 30350-* ® 10 MHZ Scope0 Plus Component0Wo-. Tester

5" - 130mm Flat Face_I Tube DC - 10 MHZ

5mV/DIV 220/240V AC Trig. to 20 MHZ

As advertised by us at £189.75 inc VAT

4.* E168.50 Inc.VAT

)UK c/p £3.501 Exclusive to Audio Electronics

PROFESSIONAL 100 K OHM/VOLTMULTIMETER30 ranges 15A AC/OC1.5 KV, 200 meg ohms.

Features mirror scale.polarity reverse, electronicoverload protection, taut bandsuspension.As advertised by us at £67.50+ case i.e. £84.00

49 Inc. VAT[UK c/p £1.501with leather caseExclusive to Audio Electronics

LCD LOW COST MULTIMETERS05601 3'4 chgrl LCD 26 range push button 2A £36.50AC/DC 20 meg ohm basic 0.5%2033A Sabtronics version of above £39.95NC703 0.1% version of above £54.00DIA001 ia/ 3), digit LCD 15 range push £43.50button plus Hle Tesler 10A DC INo AC AlHam 3'/2 choir LCD 30 range Rotary switch plusSte Tesler 10A AC/DC E69.95

Callers will always find a range of low cost testequipment accessories tools irons andboards in stock also special offers for certainequipment which will vary from time to time

Price correct at time of preparation FADEAll prices include VAT

CHOOSE FROM UK's LARGEST RANGE

STOP PRESS Fart only BM 23 range 10A AC/DC rangehold continuity buzzer plus much more Rotary switch £59 95

TRIO OSCILLOSCOPESRange of mains operated Scopes with 5" displays, triggeredsweep (UK c/p £3.50)

DUAL TRACE

CS1562A 10 MHZ. 10 MV; 1 micro sec. £267.95CS15604 11 15 MHZ, 10mV; 0.5 micro sec. £341.55CSI566A 20 MHZ: 5mV, 0.5 micro sec. £363.40CS1577A 35 MHZ; 2mV: 0.1 micro sec. £523.25CS1820 20 MHZ, 2-5mV 1 micro delay sweep £483.00CSI830 Mk 11300 MHZ. 2mV, 0.2 micro sec £626.75(fitted delay line)CS1575 5 MHZ. ImV, 0.5 micro sec. Multi display Audio scope.

£312.80SINGLE TRACEC013030 5 MHZ. 10mV, low sweep for observation below 1 HZand up to 450 MHZ. 75mm display (UK c/p £2.00) £124.20

DIRECT READ OSCILLOSCOPE PROBE KITS

HV PROBE(ukcip 6.5p)(UK c/p 50p per 1 to 3) Available BNL plugor Banana X1 £7.95 xi° £9.45 X1-010

'0 /40KV 20K Volt £18.40 £10.50Aiso 0100(BC only) £16.95

CROTECH OSCILLOSCOPESRange of Portable Scopes mains and battery operated.Plus special features (UK c/p £3.00)

3030 Single trace 15 MHZ, 5mV, 0.5 micro secs. Plus built incomponent tester 95mm tube £172.503131 Dual trace 15 MHZ. trg to 35 MHZ. 5mV. 0 5 micro sec130mm tube, plus component tester. £276.003034 Battery -mains dual trace 15 MHZ, trig to 20 MHZbuilt in Nicads. 5mV. 0.5 micro secs £356.50(Eliminator charger optional £28.75)

Also Available 3033. single trace 3034 £322.003337. dual MHZ. 130mm £454.00

STOP PRESS £168.50Model 3035 was £189.75 - Special Offer

MULTIMETERS

(UK c/p 65p or £1.00 for two)CHOOSE FROM UK's LARGEST RANGE

KRT101 10 range pocket 1K /VoltKRTI00 12 range pocket 1K /Volt1101 12 range 1K/Volt overleadNH55 10 range pocket 2K/VoltST5 11 range pocket 4K /VoltAT1 12 range pocket Deluxe 2K/VoltNH56R 22 range pocket 20K /Volt0P1360111 19 range plus Hfe test 20K/VoltKRT6001 16 range 10 amp DC range

double 50KNolt f17.95ST303TR 21 range plus Hfe Test 20K/Volt £18.95ATI020 19 range Deluxe plus Hfe Test 20K/Volt £18.95ECT5000 As KRT5001 plus colour scales 50K/Volt

£18.957081 18 range double 10A DC 50K /Volt £23.75TMK500 23 range plus 12A DC plus cont buzzer30K/Volt £24.50I 68m 36 range large scale 10A AC/DC 50 K /Volt £28.50AT2050 17 range Deluxe plus Hie tester 50 K/Volt

£29.95AT2I0 23 range Deluxe 12A AC/DC 100K /Volt £32.50380TR 23 range large scale 10A AC/DC Hfe test50 meg ohm 1KV AC/DC 100 K /Volt £39.95

£4.95£5.50£5.75£6.50£7.50£8.95£11.50£14.95

SCOPE ADD ON UNITSSUITABLEFOR ALL SCOPES

LTC905 Semiconductor Curve tracer £95.45(post 85pl

HZ65 Component Tester £29.95(Post 55p)

CLAMP -ON -METERSINSULATION TESTERS

Multi -range clamps all with resistancerange. carry case & leads Also digitaland DC clamp in stock IUK c/p 75p)

ST300 300A 600V 9 ranges £25.95ST3I 0 300A 600V 9 ranges £28.95K2602 150A. 600V. AC 7 ranges £35.95'K2606 300A. 600V. AC 8 ranges £49.5002803300A. 600V. AC 9 ranges £59.95K2903 900A. 750V. AC 9 ranges £77.50021031000A. 750V. AC 9 ranges £95.00'Optional temperature probe £13.80ELECTRONIC INSULATION TESTERSBattery operated complete with carrycase (UK c/p £1.001YF50131. 500V/ 100Meg Plus 0-100 ohm

£65.00K3I03 600V/100Meg Plus 0-2 6K ohm

£109.0003106 500V & 1000V. 1000 & 2000M eg

£119.00K4I01 Earth resistance tester £149.00M506 Hand cranked insulation tester500V/ 100Meg £79.50

THANDAR - SINCLAIRReliable low cost portable instruments, bench models all25 5 x 15 x 15cm. Generators mains operated rest battery(supplied) UK c/p Hand models 65p bench £1.151

DIGITAL MULTIMETERS (31/2 digit LCD)TM354 Hand held. DC 2A. 2m ohm. 1mV - 1000V DC. SODS AC.

£45.94TM352 Hand held, DC 10A. Hfe test. Continuity test £57.44TM353 Bench 2A AC/DC 1000V AC/DC 20M ohm. Typical 0.25%

NEW LOW PRICE £86.25TM351 Bench. 10A AC/DC. 1000V AC/DC. 20M ohmTypical 01°r° £113.85FREQUENCY COUNTERS (8 OHM

PFM200A Hand held LED 200 MHZ 10mV 1600 MHZ with TP600)New Model fitted BNC sockets. £67.50TF040 Bench LCD. 40 MHZ. 40mV (400 MHZ with TP6001 £126.50TF200 Bench LCD 200 MHZ. 10-30mV (600 MHZ with (TP6001/

£166.75TP600 600MHZ 10 Prescaler 10mV £43.13GENERATORS (All bench models) mains operatedTG100 Function 1HZ-100 KHZ. Sine /SO/Triangle/TTL £90.85TG102 Function 0.2 HZ -2 MHZ Sine /S0 /Triangle /TTL £166.75TG105 Pulse. 5 MHZ-5HZ (2000S-200mS) various outputs £97.75

OSCILLOSCOPE (Bench model low power portable)10 MHZ 7' trace. 10mV. 0 1 micro sec All facilities.Model SC 110 £159.85Rechargeable battery pack £8.63. AC adaptor/charger £5.69OPTIONAL ITEMSCarry case (bench only) £6.84 AC Adaptors (state model) £5.69

t- luD'OCOuu I ..unnoLoc,6

LOGIC PROBE ," 0P450Leader LDP076 50 MHZ10MEG ohm. tOn Secwith carry case. LP1610Mhz probe f211.50 £56.90

KEITHLEY PROFESSIONALDIGITAL UK c/p 75pMULTIMETERModel 130 25 range Easy to hold and useLCD DMM Size 7 x 3 1 x 1.5Ranges

DC Volts 200mV-1000V 0 5% 100 micro voltAC Volts 200mV-750V 1% 100 micro voltDC current 2mA-10AMP 1-2% 1 micro ampAC current 2mA-10AMP 2°,, 1 micro ampResistance 200 ohm -20 Meg 0 5% 0 1 ohm

£102.35Model 129 as above £79.35

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TV COLOURGENERATORSPAL UHF and VHF ModelsLCG3113 VHF 6 pattern £143.75LCG392u UHF 15 pattern £228.85I.C6392v VHF 15 pattern £231.15I.C6399 VHF/UHF 13 pattern £57270

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444

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WIRELESS WORLD MAY 1982 WW 040 FOR FURTHER DETAILS 23

NRDC-AMBISONICUHJ SURROUND/SOUND DECODER

s.NArruundsoltBdIS00.N.41C.,

The first ever kit specially produced by Integrex for this British NRDC backed surround sound system which is the result of 7 years' research by the Arnbisonic team W W July. Aug '77The unit is designed to decode not only UHJ but virtually all other 'quadrophonic' systems (Not CD4), including the new BBC HJ. 10 input selections.The decoder is linear throughout and does not rely on listener fatiguing logic enhancement techniques Both 2 or 2 input signals and 4 or 6output are provided in this most versatile unitComplete with mains power supply, wooden cabinet, panel, knobs, etc.

Complete kit. including licence fee £57.70 VAT or ready built and tested £76.95 VAT

INTRUDER 1 Mk. 2 RADAR ALARMWith Home Office Type approval

The original 'Wireless World" published Intruder 1 has been re -designed by Integrex to incorporate several new features, along with improvedperformance. The kit is even easier to build. The internal audible alarm turns off after approximately 40 seconds and the unit re -arms. 240V acmainsor. 1 2V battery operated. Disguised as a hard -backed book. Detection range up to 45 feet. Internal mains rated voltage free contacts for external bellsetc

Complete kit £52.50 plus VAT, or ready built and tested £68.50 plus VAT.

Witk

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Complete Kit PRICE: £49.95 + VAT (3 head model available)

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All kits are carriage free

INTEGREH LIMITED

Typical performanceNoise reduction better than 9dB weightedClipping level 16 5dB above Dolby level (measured at 1 'tf, thirdharmonic content)

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ACCESS and VISA welcomePlease send SAE for complete lists and specifications

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TEMPERATURECONTROLLED

SOLDERING IRONS

Control range 200PC to 400T set byhexagonal key, upplied. Factory set to320°C.

£13.75

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STANDARDSOLDERING IRONS

ANTEX Type C 15w £4.50CCN 15w E4.70*CSBP 17w E5.30CX 17w E4.00

E80£5.30

X25 25wXSBP 25w

`New types with moulded 13A plug

ANTEXStand £1.70

IMPORTANTAll solderingequipment ispriced NETT. Add

VAT at 15%

ELECTROVALUE LTD., 28a St. Judos Road, Englefield Green, Egham, Surrey TW20 ORBPhone Egham 33803 (STD 0784, London 87). Telex 264475.Northern Branch: 680 Burnage Lane, Burnage, Manchester M19 1NA. Phone (061) 432 4945.

TELEMET AB164COUNTER TIMER

a professional, portablelow cost unit

liglemet ABI64 COUT1tC31" rrna'

,

00011%11%11

3 frequency ranges DC to 180MHz with1 Sec gate including phase locked loop1Hz-1KHz providing 0.01Hz resolution within10 seconds.Period/Time ranges to 1i./Sec, 1mSec and 1 Secresolution.Manual and logic gating on the time and eventranges.

13mm 8 digit display with leading zerosuppression.Internal charger and NiCad batteries.

Price £195.00 plus VAT (carriage incl.) from

TelemetUnit S17, Europa House,Fraser Road, Erith,Kent DA8 1QL.Tel. (03224) 39677.

WW - 050 FOR FURTHER DETAILSWIRELESS WORLD MAY 1982

A new generation of drive units from KEF is nowavailable to the home constructor.

KEF's drive units have been improved in terms ofreducing audible colouration as a result of the detailedanalysis of speaker vibrational characteristics, using

computer aided techniques.Now the improved units and complete technical data onthem are available to you to build a system to your own

design or to use in any prescribed combinations tocomplete a system designed by KEE

DRIVE UNITS

Manes dome high frequency unit with extended Low colouration dome high freq urn. s unit withfrequency response and wide dispersion. extended frequency response.

Compact, bass mid range unit.suitable for use In either a compact lull rangesystem, or es a specialised mid range unit in amulti -way system.

B13913=

obi ;

Long throw bass mid range unit. suitable for usein either a compact full range system, or esspecialised mid range unit In a multi -way system.

107 B200G

Low frequency unit with toll -stressed expanded Low mid range unit with visco-elestir dampedpolystyrene diaphragm end highly compliant Bextrene diaphragm and high temperature voicesurround. suitable for totally enclosed box, reflex. call assembly, suitable for use where lowtransmission line, horn end other specialised low distortion and high power handling are requiredfrequency applications.

KEFEKIThe Speaker Engineers

KEF Electronics Ltd., awn, Maidstone, Kent ME15 6QP.Thlephone: (0622) 672261. Telex: 96140.

- MIN EN MN MIN MN MIII

Please send me complete technical data ofKEF Drive Units

Name.

Address.

\'I\A,582- IMM Mi 1=I ME NM ME MOWW - 032 FOR FURTHER DETAILS

25

26

The Professionals VALVES ,SEMICONDUCTORS&COMPONENTS for: -

Communications, Displays,Radar, Computer,Audio etc.

Hall Electric LimitedElectron HouseCray Avenue, St. Mary CrayOrpington, Kent BR5 30.JTelephone: Orpington 27099Telex: 896141

MIN DEF APPROVAL 0529/0531

WW 009 FOR FURTHER DETAILS WIRELESS WORLD MAY 1982

TEST COMPONENTSON THIS NEW OSCILLOSCOPE

USE READER CARD FOR DETAILSWW - 001 FOR FURTHER DETAILS

IRVINE BUSINESSSYSTEMS LTD IB

NEW PRODUCTSI.R.S. now manufacture Industrial quality 5100 products in Scotland.I.R.S. 1903 and 1906. S100 19" Sub Rack System.These racks were designed originally to the exacting specification of the ElectricityGenerating Board for use on nuclear power stations.1903 is a 3U high card cage and 8 -amp power supply and will take 6 5100 cards.1906 is a 6U high card cage and 16 -amp power supply and will take 12 5100 cards.* IEC mains connector, filter, fuse and tap change switch on rear panel.* Key operated ON/OFF/RESET for maximum security.* Heavy duty painted front panel.* Carrying handles.* Supplied assembled complete with Power supply, IEEE 16961 motherboard, cardguides, and cooling fans.

I.R.S. 1903 .0299.00I.R.S. 1906 1399.006 -slot Card cage, card guides, mother board and fan £119.0012 -slot Card cage, card guides, mother board and fans £249.00

64K CMOS Static RAM/PROM Board for 5100.

This is a superior quality Ram/Prom board for the industrial user, the board will accepteither H6116 -312K x 81 Ram chips or 2716 EProms in any combination.

* S100 IEEE (6961 Compatible. * Will run at 6Mhz with standard Rams.* 24 Bit Addressing. * Wait state generation for Proms.* Can be used with any CPU. * Phantomable.* Prom/Ram selectable on 2K boundary.* Prom/Ram can be disabled to suit popular memory mapped devices.* Low power.

PRICES:BARE BOARD Assembled/ 16K 32K 48K 56K 64K

tested £65.00 £179.00 £239.00 £299.00 £329.00 £359.00

Educational and industrial discounts available.

SOFTWARE SALE (whilst stocks last).

Microsoft Basic 80 WAS E175 NOW £149.00Microsoft Basic Compiler WAS £180 NOW.. ............._ £159.00

Introductory offer

MicroPro CALC STAR WAS £175 NOW £149.00

* Visit our stand at the Thames Valley Business Show, on 23/24/25th March '82* Stand H50/51 * Slough* The Fulcrum Centre

The above prices exclude VAT at 15%

IRVINE BUSINESS SYSTEMS LTD.P.O. BOX 510 NORTH VENNELBOURTREEHILLIRVINEAYRSHIRE KA11 1NE

TEL. 0294 218888Telex 777582Mark: attn. IBS

1111111CLAVCARD

The ideal design of a loudspeaker system involvesthe detailed and scientific study of the enclosure,drive units and crossover network. By applyingcomputer aided techniques to the questions of

enclosure volume, band width, efficiency, powerhandling capacity, probable system location andrequired directional characteristics, KEF have

prepared detailed designs for the home constructor.All this experience is now available to you - to

help you build your own system - successfully andat the right price.

LOUDSPEAKER DESIGNS4"-Pciagiweffmkghailvter

Eiichrguiv.13...frr

8006

Model CS5This floor standingloudspeaker, based onthe KEF Carlton, canprovide remarkably sharpstereo imaging due to anovel method ofminimising inter -unit timedelay, and will produce afull frequency range withoutstanding clarity andlow distortion.

Model CS7A new three way designincorporating the B139,which was the world's firstflat diaphragm loudspeaker.The system offers anextended bass response andexcellent power handlingcapability, with the threedrive units being combinedthrough a computerdesigned crossover networkto give a very smoothfrequency responsecharacteristic with finelydetailed reproduction ofcritical mid -range information.

KEFEllMaking it together

KEF Electronics Ltd., Tovil, Maidstone, Kent ME15 6QP.Telephone: (0622) 672261. Telex: 96140.- .111 111M NM NI 1111 II.

Please send me details of KEF Systems Designs

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UM NM 01111 M MO



27

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)4100, %'7f;%:' d 0.1'

*

The Sound of the Professionals,

1---I 1.J FREShure Electronics Limited Eccleston Road

Maidstone ME15 6AUTelephone Maidstone (0622) 59881

roazOW EVLiqx269) 1/1 ri3g0000Xlagi 10)brings a new dimensionto a hand-heldcondenser microphone

This new high technology Shure microphone will changethe way people think of condenser microphones. TheSM85 is designed especially for on-stage. hand-held use.Its sound is unique-far more tailored to the special needsof the vocalist: sizzling highs and a shaped mid -range forsuperb vocal reproduction. and a gentle bass rolloff thatminimizes handling noise and boominess associatedwith close-up use. Ultra -low distortion electronics make theSM85 highly immune to stray hum fields. An integral, dual -density foam windscreen provides built-in pop protection.

What's more. the'SM85 Condenser Microphone mustpass the same ruggedness and dependability testsrequired of Shure dynamic microphones. Asa result. theSM85 sets a new standard of reliability for hand-heldcondenser microphones.

The SM85 is extremely lightweight, beautifully balan,ced-it feels good. looks good on-stage, on -camera, on -tour.Ask your dealer for a demonstration of the new SM85 PROTECH Sound, or write to us (ask for AL664) for full details.

SM85Cardioid Condenser

Hand -HeldProfessional Microphone


wirelessworld

Editor:PHILIP DARRINGTON

Technical Editor:GEOFF SHORTER, B.Sc.01-661 8639

Communications Editor:MARTIN ECCLES01-661 8638

News Editor:DAVID SCOBIE01-661 8632

Design EditorALAN KERR

Drawing Office Manager:ROGER GOODMAN

Technical Illustrator:BETTY PALMER

Advertisement Manager:BOB NIBBS, A.C.I.I.01-661 3130

DAVID DISLEY01-661 8641

BARBARA MILLER01-661 8640

Northern Sales:HARRY AIKEN061-872 8861

Midland Sales:BASIL McGOWAN021-356 4838

Classified Manager:BRIAN DURRANT01-661 3106

OPHELIA SMITH01-661 3033

Production:BRIAN BANNISTER(Make-up and copy)01-661 8648

Arms and the manA great many words have been written inthe last year or two on the amorality andexpediency of engineering. On the onehand, some engineers have come to believethat the responsibility for rendering thebellicose ambitions of political leaderscapable of realisation lies squarely with thedesigners and makers of lethal hardware -engineers themselves. If it were not for thecomplaisance of engineers, they say, themeans to wage war in the modern mannerwould not exist.

Those who do not embrace this belief(or who choose to disregard itsimplications) point out that if "defencesystems" - a weasel expression, referringto all military equipment, including thatwhich by no stretch of the imagination canbe seen in a posture of defence - were notavailable, then one "side" would subduethe other and impose its own ideology onthe defeated. The solution to this problem,the holders of this view assert, is for eachcamp to arm itself to the teeth at an ever-increasing rate, threaten to irradiate theplanet if provoked, but only to do so if theother side does it first. The unspeakable,impenetrable folly of such an attitude isalmost too obvious to warrant argument:its holders would scarcely deny that thatthis method of preserving life and liberty ishardly compatible with the pursuit ofhappiness.It is perfectly true, as apologists for the

arms race often point out, that some of theeffects of the insane compulsion toaccumulate weapons are not at all asunsavoury as their raison d'etre. "Spin-off" has provided most of the advances in,for example, electronics in the last fewdecades. Innovation and development areaccelerating at such a rate that it is barelypossible to see five years into the future,assuming there is one. But to what effect?After the expenditure of so much effortover so many years, with neither East orWest yet persuaded that that an unstableequilibrium is a poor way to avoidcatastrophic failure, are we being asked tobelieve that the possession of homecomputers, video games and digitalwristwatches makes the whole thing worthwhile?

Some of the greatest scientists andengineers in the world, in both East andWest, have laboured their entire working

lives to produce hellish machinery, thewhole point of which is that it shall neverbe used. Hospitals, schools, universitiesare closed or run down so that moreweapons can be bought or made and theonly benefits in our own field that we haveto show for all this misdirection of effortand resources are a few gadgets.Admittedly, communications haveimproved immeasurably in response to thestimulus of military requirement, but agood deal of the improvement is taken upby the provision of entertainment.

It is a specious argument, which takesno account of the time scale involved: evenin the absence of military urgency, the"improvements" and engineeringadvances would most probably occur intheir own good time, and who is to say thatthat sooner is better than later when thepace of progress outstrips ourunderstanding of it?

Much that has been written on thistheme has not dwelt on the inconvenientlylarge question of waste. Materials, theefforts of gifted men and women,irreplaceable earth resources, time and thewealth of nations are all squandered toproduce equipment which, if employed inthe manner for which it was designed,would have failed in its purpose. And thiswhile millions of people in all continentsare deprived of the simplest staples of life.The contrast between profligacy in thehighly developed and privation in theprimitive is too stark for us to contemplatethe continuation of useless armedposturing into the indefinite future: forthat is the outlook - either a sudden andcomplete end to humanity or aninterminable attitude of menace betweenEast and West. Scientific American haspointed out that there are now more thanthree TNT - equivalent tons of nuclearexplosive for every single person on earth.

It has been said before on this page, andit will bear repeating, that engineers in allthe developed countries have made theconfrontation possible. It is thereforeengineers who are in the best position tobring it to an end, by simply refusing towork on armaments. Call it rebellion orsimply common sense, but sincepoliticians the world over seem bent onkilling us all, it is the only way to avoidcollective suicide.


ORCHESTRAL SOUND,HALLS AND TIMBRE

or -'why does it sound so beautiful?'This article examines aspects of the appreciation of orchestral sound, with particularreference to the transfer characteristics of the outer ear and its influence on timbre in

various directions and on our sense of orientation. New subjective criteria are proposed.The Kingsway Hall is used as a model in the discussion

by Denis Vaughan*

For several decades the most sought-aftervenue for recording orchestral music inEngland has been the Kingsway Hall inLondon: legend has it that Sir ThomasBeecham was the first to identify this hallas particularly suited for the purpose. Arethere some identifiable reasons for itssuperior warmth and clarity? Could theybe applied elsewhere.

My interest in acoustics was stimulatedby a request from the AustralianBroadcasting Commission. The quest tofind a common denominator for warm,rich string tone in a hall and in a recordinghas led me to study many halls, and toanalyse musical qualities and our hearingcapacities. These analyses have broughtseveral surprises. First of all come ourhearing capacities.

TimbreOur localization of sound is based on threemain complementary systems: only two of

*Musical Director, State Opera of South Aus-tralia

Horseshoe balcony in the Kingsway Hall isonly 17m wide, giving early reflectionsback at the orchestra.

these have been used so far in stereorecording techniques. The first is based onthe exact timing of impulses to each ear. Adifference of 0.63 milliseconds weinterpret as a change of angle of 90° in thedirection of the earlier impulse. So we can,miraculously, recognise a timingdifference is small as 0.007ms, the timenecessary to move the sound source onedegree to the side. The second is based onloudness and intensity: a softer sound willseem farther away. We apply this inlocalization: just a small change in volumeon one channel will shift a stereo picture tothe left or right and a general rise in levelbrings an instrument nearer to us. But thethird system, timbre, has yet to beexplored.

We hear a different timbre from everyangle. Move a small clock around close toyour ear, and you will notice that you canalways tell where it is, and that the sound

is never identical. If the clock is near yourear but always equidistant from it, this testexcludes the possibility of the impulse orintensity methods contributing to theeffect: we recognize each and everydirection partly by its own particulartimbre. If you change the timbre, theapparent direction changes. The filteringeffect of our external ear, illustrated byFig. 1 and Fig. 2, causes us to hear a veryodd balance in sound reaching us face -on.The left-hand column of Fig. 3 shows that,with 400Hz as OdB, there is a strong peakat 3kHz of 12dB and a deep trough at10kHz of -10.5dB. So we hear certainupper -high frequencies (e.,:cept 14 and15kHz) frontally very much weaker thanthose at 3kHz.

timbre n. Characteristic quality of soundsproduced by a particular voice or instru-ment, depending on the number and char-acter of the overtones


20cn

D 10

0a_

<02-1

lwPresent dataiener 194610"

Jahn 1960

Shaw 1974

11111

J

05 1 2 5 10 15

FREQUENCY (kHz)

Fig. 1. Filtering effect of the ear canal,showing peaks near 5 and 10kHz, commonto all that we hear. All frequencies above11kHz are much weaker.

10dB

0°

18°

36°

54°

72°

F- 90°xx108°

126°

144°

162°

180°

1 -

02 05 2 5 10 15

FREQUENCY (kHz)

Fig. 2. Filtering effect of the outer ear onsounds arriving in the horizontal plane. 0°corresponds to a point straight in front.

Horizontally to the side at 90° thebalance is more even. The upperfrequencies become as much as 15dBstronger than the frontal spectrum and thevarious peaks at lower pitches aresmoother, thus reducing the rangebetween the extremes to only 15dB asopposed to the 22.5dB range of the frontalspectrum. But the sensitivity which wehave at 90° for 12 and 13kHz starts todisappear already at 54° and 144°. Figures4 and 5 summarize the table of Fig. 1

graphically.You may have noticed another aural

characteristic. We tend to identify bassnotes as coming from below our ears; also,the higher we sit in a hall, the warmer itsounds. I believe that we react similarly toloudspeaker placing. Surprisingly, aboveour heads we can hear a strong peak at 8and 9kHz, as shown by Fig. 6. In fact wecan only hear 8kHz as coming from thatdirection, no matter where the soundsource. But further up the spectrum,above 10.5kHz, we hear very little fromover our heads. Therefore in a low room ora hall, where the predominant earlyreflections come from the ceiling, we canperceive very little refinement, delicacy ortexture in the sound. Figure 7 is thegraphical representation of Fig. 6.

Musical qualitiesIt is no easy task to prepare a preferentiallist of musical qualities in sound.Celibidache and other conductors, andseveral recording engineers and producershave approved the following list, whichshould only be regarded as tentative, andwide open to improvements:richness - powerful multiple reflections;density - many reflections across the hallwithin one second from a single impulse;warmth - a strong bass -heavy frequencyresponse curve, with a plateau in the tenoroctave (125-250Hz) tapering off smoothlytowards the top;clarity - medium high frequenciesarriving from all directions shortly afterthe original sound;intimacy - an adequate supply offrequencies between 11 and 15kHzarriving early at the ear between 54° and144° horizontally, and below 60° vertically;weight - low frequencies arriving shortlyafter the original sound;singing tone - a growth in thereverberation reaching a peak about 100milliseconds after the original sound, thendying away smoothly over about 1.8 secs.

One reason why richness - and not along reverberation - tops the list isbecause a variety of reflections comingfrom many angles close upon each othergives our ears a full frequency coverage.With our aural limitations of timbre in anyone direction, the deficiencies can be madegood only by receiving sound from allsides. In Avery Fisher Hall in New York,you can hear that in some upper/frontbalcony seats, where richness is present,any lack of the other qualities is much lessnoticeable.

Impulses

Another reason for our appreciation ofrichness is our astonishing capacity forquickly perceiving separate impulses in

sound. Tests have shown that all listenersprefer to hear orchestral sound impulseswhich do not arrive simultaneously in bothears - hence the preference for stereo overmono. This scattering of the impulses iscalled 'binaural dissimilarity'. In a concerthall, it is the extent of the initial time -delaygap between the original sound and thefirst reflection - often about 40ms in amedium-sized hall - which gives much ofthe character to the acoustic. (Intimacy hasbeen associated with this gap, but my listsuggests other requisites.) Our earsappreciate these reflections most whenthey arrive close to horizontally from theside. My timbre lists show that the timbreof a hall is influenced for us first by theangle at which we hear the strongest firstreflection, and then by the shape andmaterials of the hall, or room, and thereverberant spaces beneath it.

When we receive a lot of earlyreflections, one shortly after another, theseimpulses come in an arpeggiated form -in slow motion rather like the thrummingof a chord on a harp. This sequence ofimpulses we perceived as being muchricher than an instantaneous reflection. Adigital delay unit demonstrates thisquickly, by making two or three stringinstruments sound like a rich chorus. Hallsare preferred where the sequence ofimpulses, whether first or later reflections,dies away evenly. It is called a 'smoothdecay curve'.

Home simulationThese two keys to richness, namely timbreand impulses, are demonstrable in thehome with a system which I hope will bedeveloped in the phonographic industry,as soon as the field of the external ear iscompletely measured. The system wouldneed at least ten loudspeakers: one largeone on the floor to represent the orchestra,and the smaller ones set around the roomabove and below the ear level, with theapposite timbre applied to each speaker

FRONTAL

SPECTRUMFREQUENCY 0° 18° 36° 54° 72° 90° 108° 126° 144° 162° 180°

OPPOSITESound coming

to right

FIELDfrom

earPeak+2

0

-2

left

Low Angle-3 -108

-25 -140/60

-4 -140/-45

Angle-36

-90

-90

-0.5 dB

+0 5

+1

200 Hz

500

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-05-2 1kHz 0 25 4 45 65 7.5 7 65 55 5 4 -6 -30 +15 -90+10 2 0 2 2 15 15 05 0 -15 -2 -2 -3.5 -12 -110/-75 -7 -90+12 3 0 1 2 3 2 -1 -2 -2-5 -25 -3 -35 -15 -110 -8 -90+5 4 0 3 4 35 15 -2 -5.5 -85 -8 -65 -55 -15 -120/-75 -9 -90-1.5 5 0 3 5 4 5 45 3-5 O5 -55 -9 -8 -7 -135 -120/-75 -12 -90-0.5 6 0 4 65 7 IS - 7 SS 2.0 -3 -45 -5 -13 -110/-60 -12 -85+15 7 0 4.5 8.5 10 10 8.5 65 25 -1 -25 -13 -110/-50 -10 -90-2 8 0 4.5 8 11 14 15 14 5 12 7.5 3 5 25 -10 -120/-75 -5 -90-8 9 0 35 55 7 85 11-5 11 8 ,..5 1 -05 -7.5 -130/-50 -5 -90-105 10 0 3 55 7 7 65 7 84 45 25 -25 -6 -135/-9D-50 -3 -1101-75

-10 11 0 3 35 6 75 7 75 7 65 2 -2-7 12 0 5 1.5 35 7< 55 e 65 : 35 15 25 -7.5 -130/-90 -3 -75

-2 13 0 15 5 SS.. 6 5 1 0 -45+2 14 0 'Of.,. 2 2 25 2 15 -05 -25 -4 -7 -11 -120/-50 -3 -75+35 15 0 iSS. 2.5 3 1.5 0.5 -1 -2 -as -5 -75

_ .

rong h.f. sensitivity Negative quantities

Fig. 3. Lateral differences in timbre for one ear, compared to sound reaching us fromstraight ahead at eye level (from Mehrgardt and Mellert).


according to its direction (to help to lockthe stereo image) and with increasing time -delays on each speaker, equivalent to thosewe hear in a fine hall like Kingsway. A six -track tape or cassette could probablysupply sufficient source material. Allinitial tests I have made in this directionimprove the timbre and richness farbeyond the one -plane, identical -timingand timbre of the quadrophonic system.Without dropping hints, we might call thenew system 'clecaphonic'. It develops theBose system of reflections from all sides,which works best for me in rooms withlittle or no damping. Both point to theincreased physical satisfaction when ourorientation filtering system is being fullyutilized in the appreciation of musicalsound. The main problem lies in fixing thedelicate balance between focused imageand general immersion in the sound.

I have always found a stereo image toimprove greatly when the frontal speakersstand at least three feet in front of a wall, asthe timing of the frontal wall reflectionseems to give full depth to the image.Thus, under ideal circumstances, anorchestra seems to be the same distancebehind the speakers as the orchestra wasbehind the microphones in the studio -hence the need for simple microphonetechniques. To obtain this effect in aroom, I have often needed to set thespeakers parallel and not angled towardsme. In general, and sometimes despitemanufacturers' advice, the adage of theRCA engineer Albert Pulley seems to workwell in practice - that is, to set thespeakers at a quarter of the width in fromthe sides and a quarter of the length of theroom from the end. (Domestic bliss can be'-reserved with this obstructive placing if

0.5

06

08

10

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1-6

18

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30

12(..-2..../"N.------------------

1 I 1

1

1 i 1-I i

....

....11.....

1... ....................

.......---t--...-

..

......

- 1 I

-180° -120° -60° 0° 60° 120° 180°Left side Right side

Fig. 4. Graphical summary of lateraldifferences in sound pressure for the rightear. Negative angles refer to sound comingfrom the left side of the head. Range isfrom 500Hz to 3kHz.

the speakers are disguised as occasionaltables.)

Long reverberationUntil such a time as a `decaphonic' systemis common currency, it is fairly obviouswhy very reverberant halls will befavoured for recording. Present systemsuse mainly microphones which pick upfrontally frequencies that we can neverhear there (with our 3kHz peak, 10kHztrough, and general cut-off in the ear canalabove I 1 kHz). Also the loudspeakers areusually placed at angles where we cannotperceive several other frequencies verywell, showing a 20dB range between the3kHz and 11kHz readings. The simplestway of covering up these two auralmismatches is to add reverberation to dif-fuse and thus beautify the sound.

This has the unfortunate effect ofrobbing the interpreter of a number ofbreathtaking dramatic effects, because hecan never achieve a quick silence, until thecommon 2.5s of reverberation has diedaway. That would never have done forVerdi, Toscanini or Callas.

Instead we should seek out a true andsatisfying way to give us global (360°)reflections in the reproduction, and thus anatural, full -frequency spectrum,concentrating on our most sensitive area,between 40° and 140° laterally. Even mostheadphones are unnatural (save those withmulti -speakers) in that they eliminate thewhole of our own aural frequency filtersystem. The great advances in`Kopfbezogene stereophonie' (binauralrecording) fall back at this point.

Architectural prerequisitesThe quest for the physical conditionsnecessary to produce warm, rich stringtone in a concert hall was sparked off bythe decision of my home town,Melbourne, Australia, to spend 33.5million dollars (A) to build a 35 metresquare, virtually all -concrete hall for thatpurpose. Of the many indications given tome, two of the most revealing were fromVillein Jordan and Derek Sugden. Jordancould not obtain 'lateral efficiency' in a hallwider than 27 metres, and observed that allthe famous halls had smaller widths.Sugden stated:

"A hall must have 'presence' so that younot only preserve clarity in a reverberantfield but the music will have 'weight'. Apowerful sound in the first 100milliseconds in necessary. This can beachieved preferably with a width of about18 metres, and if this is not possible thendeep balconies must be used, or thetechnique of putting the audience interraces and providing large surfaces forlateral reflections. There must be rapidlyfollowing early reflections to really achieveintimacy or presence."

A third useful piece of wisdom camefrom Decca's former chief engineer,Kenneth Wilkinson:

"I have recorded in many hallsthoughout Europe and America and havefound that halls built of mainly brick,wood and soft plaster, which are usuallyolder halls, always produce a good,

-180° -120° -60°Left side

0° 60° 120° 180°

Right side

Fig. 5. Continuation of Fig. 4 in range3.5kHz to 14kHz. Small peak at -90° on leftside persists up to 9kHz, then moves to-75°.

natural, warm sound. Halls built withconcrete and hard plaster seem to producea thin, hard sound and always a lack ofwarmth and bass. Consequently, whenlooking for halls to record in, I alwaysavoid modern concrete structures." Thisstatement has been endorsed by most ofthe other large record companies.

First reflectionsIn all the famous orchestral halls, the firstlateral reflections come from the sidebalcony faces. Their timing is exactlycontrolled by the width (1 foot = Is). So acentral seat in the Leipzig Gewandhaus,with only 12.5m between the balconyfaces, had an initial time delay gap ofaround 41ms. Vienna Musikvereinsaal with15m had 49ms, Boston Symphony Hall(17/19.3m) 56/63ms, and the AmsterdamConcertgebouw (19.3m) 63ms. Thosefigures give a very good idea of the relativeclarity and definition, intimacy anddensity of sound in each of the above halls.As upper -high frequencies fall off audiblythrough atmospheric absorption afterabout 15 metres, Leipzig and Vienna musthave the best quality.

Looking at the Kingsway Hall, it is easyto see where it satisfies the mainrequirements. Its full width is at the upperlimit, 27 metres, with inner walls set onpillars at 19 metres width. But the widthbetween the horseshoe balcony faces, with.a very useful curved reflecting surfacebeneath them, is only 17 metres at itswidest point. The balcony surrounds theorchestra at a height of 3.5 metres. To behonest, I think that such a horseshoewould bring any large symphony orchestragood acoustical luck. It gives all theplayers reflections back early enough, andat the right angle, to allow them to obtain


good ensemble. The unbroken surfaceallows early bass reflections to come backto the microphones (not too strong, mindyou) because the long bass waves arereflected intact, and from a shapeconsonant to their own. It might be worthcopying this reflecting shape in AbbeyRoad, Maida Vale, Henry Wood,Walthamstow, Brent and Watford, toname but a few London recording halls.The shape is reminiscent of thosemarvellous small Italian theatres.

In recent years, the Kingsway lease hasbeen shared by EMI and Decca, also sub-letting it to RCA and other companies.Virtually all the seats have been removeddownstairs and many upstairs coveredwith cloth. At the moment itsreverberation time with an orchestrapresent is about 2.5 seconds.

Hall background noisePoor Wagner cannot have guessed that in`Tristan and Isolde', by giving hisshepherd on the rocks a woodwind solowhich lasted more than four minutes, hewas condemning one of his greatestinterpreters - Furtwangler - torecording a duet for English Horn andPiccadilly Line Train. Unfortunately,collaboration between EMI and LondonUnderground is not yet such that theengineer's `red light area' can extent tosuch nether regions. The rumble of thetube trains would not be so noticeable,were Kingsway not such a good hall.Moreover the cavernous storerooms andairducts beneath the main floor, whichundoubtedly contributes to the warmth ofthe sound there, develop the tube rumblewith equal generosity - a sound which iscruelly revealed by digital recordingtechniques. The hall is very much alive atall frequencies, even when no-one is in it.The presence of 80 musicians is somethingwhich you not only feel there, but whichgives the indispensable and audible humanelement to the music, with myriad smallhigh -frequency extra -musical sounds. Theease of tone and spaciousness achieved inBeecham's `Scheherezade' andFurtwangler's 'Tristan' have to my ears yetto be bettered on disc. Both recordingsmanaged to reproduce the 'hush' whichwas present during the sessions, and whichis an integral part of the greatness of themusical interpretations. A bald silencebehind the music is the antithesis of thisspell -binding, breathless hush, andunfortunately I fear that Dolby techniquesso far, in their valiant battle to eliminatetape hiss and mechanical noise, have alsoeliminated some of this integral part of themusic. Digital recording is proving to beone of the better ways, which do notreduce the human element in aperformance, and the comment of theacoustic on this human element.

'Singing' decay curveIt would be fascinating to know just whythe string sound at the beginning of thethird movement of the Beecham`Scheherezade' is so natural. To write thisarticle, I went down on my hands and

FRONTAL

SPECTRUMFREQUENCY 0° 9° 27° 45° 63° 85°

(Ove99°

head)117° 135° 153° 171° 180°

(behind)

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+10 2 0 -2 -4 -5 -5.5 -65 -7 -5.5 -4.5 -4 -4.5 -3-5

+12 3 0 -0-5 -2 -3 -4 -45 -5.5 -6 -5.5 -5 -3.5 -3.5

+5 4 0 -0.5 -1 -2 -25 -4 -5.5 -6.5 -7 -7 -6 -5-5

-15 5 0 -75 -1 -0-5 -2 -4.5 -5.5 -65 -7 -7 -7 -7-0.5 6 0 1 3 2.5 2 -05 -2 -2.5 -3.5 -4 -45 -5

+1.5 7 0 1. 5 7 55 1.2.: 2 2.5 2 0.5 -2 -2.5

-2 8 0 2 8 12 125 12 10 9 10 ' 4 2.5

-8 9 0 1,5 7 10 12.5 135 12 11.5 11 7 15 -0.5

-10.5 10 0 1 5 55 8 8.5 7-5 7 r 35 0.5 -1.5 -2.5

-10 11 0 0.5 1 -1 2 4-5 0-5 -1 -1-5 -45 -2 -2

-7 12 0 0.5 2 -1 -2.5 0 -3 -5.5 -25 -3 -2.5 -2.5

-2 13 0 1 2 -35 -75 -4 -75 -10 -6 -8 -7 -45+2 14 0 0.5 1 -3 -7 -2 -8 -10 -8 -7.5 -7 -7+3q 15 0 0 0 -35 -8 -0-5 -8.5 -115 -8 -7 -7.5 -7-5

Positive quantities Outlined area -_, stronger sensitivity at 7 to 10 kHz

Fig. 6. Vertical differences in timbre (equal for both ears) compared to sound reaching usfrom straight ahead at eye level. From Mehrgardt and Mellen.

knees, and with the generous help of theKingsway caretaker, measured the variousdistances, counter -checking them againstthe few remaining plans of the hall. Soplease do not expect total accuracy.

All the great halls have a certain`singing' tone, characterized by acrescendo in the decay curve. Just as wecan all sing better in the bathroom,because the acoustic supports us, so the`singing' curve gives a lift to theperformers, and allows the music to takewing, without need for forcing. (I thinkthat adding a short peak of this nature to adry recording would give more musicalresults than the general confusion causedby the usual long reverberation.) No onehas the formula for its production in a hall.Guildford thinks that it needs a large areaof parallel surfaces above the highest seat,as in Vienna, Boston, Amsterdam, etc.Joan Sutherland (and I) think that it needsalso a set of hard surfaces around the hallat the level of the performers. Schultz thatit needs a filigree of smaller surfaces for thevery first reflections. It is probably acombination of all three.

For the Beecham sessions, with theorchestra facing the organ, themicrophones were about 2 metres in frontof the stage. For an instrument just underthe microphone this gives the followingsequence of delays in the reflections fromvarious parts of the hall after the originalsounds:Stage front, 14ms; upper stage front,30ms; side balconies, 48ms; back balcony,54ms (first frontal reflection); ceiling,57ms (larger); diagonal walls beside organ,73ms; side walls down stairs, 81ms(larger); arches between side pillars andinner walls, 93ms (et seq.); ceiling curves,100ms (larger); backwall downstairs,105ms (larger); curves organ ceiling,1 1 1ms; side wall upstairs, 133ms (larger);back wall upstairs, 147ms (larger).

Some of these figures should be higher,where the reflection can only come back to

- 1 2

1-

t' 1.6

LL 1.8

2-0

25

30

0.8

the microphone with the help of asecondary surface, such as side wallupstairs/lower ceiling. As the microphoneis not very sensitive on top (and ficklememory suggests that the stereomicrophones were hung upside down for`Scheherezade'), this means that theeffectively larger reflections start about18ms after the original sound. Boston'ssinging tone is based on a growth up to apeak in the decay curve, the peak reachingfrom 100 to 150ms. Amsterdam puts iteven later. By Sugden's standards of`presence' and 'weight' Kingsway hasquite a lot of powerful reflections to offerwithin the first 105ms, because the largerreflections continue to return up to 14ms,the substantial and lengthy support of themusicians is assured, before the riotousping-pong of the subsequent reverberation

10dB_:05

Ti I T

1.0 50

I FI I

J2\1LL,"tth

0° 60° 120° 180°

10 dB

3.5

4-0-1-1

45

7.0

8-0

90

10

12

I

0- 60° 120° 180°

Fig. 7. Vertical differences in soughtpressure perceived equally by both ears.90° is overhead, 180° behind.


in every direction sets in. All laterrefections are naturally weaker.

CurvesRobert Lloyd, the bass, has observed thatwherever these are a lot of curved surfaces,the acoustic tends to be very good. Whenthe curves are concave, they may matchthe shape in which the sound waves firstreach them, and thus reflect them well.When the curves are convex, they distri-bute the sound waves evenly over wideareas. Kingsway is rich in both types ofcurve. Nearly all the stage -end surfaces arecurved one way or the other, with manyinterim small reflections, such as curvesover doors, etc. I hope sincerely that thisarticle may stimulate others to copy them,above all because of the full -frequency -range efficiency of the initial longhorseshoe curve of the balcony face and itsundercurve. For a full symphony orchestrait comes at an ideal moment to break upthe sound, and is as worthy of respect asthe exact measurements of the orchestralshell in the Boston Symphony Hall. If youwish to copy a Stradivarious, all details arerelevant!

ReversalIt would be interesting to know whethersharp -eared listeners with refinedequipment can detect the differences inrecordings made in Kingsway the otherway round, with the orchestra's back tothe organ. Many recent opera recordingsuse this setup, which puts the singers in abetter relationship to the orchestra, andallows them to move as though on a stage.It also allows the full depth of the voices todevelop, in the essential 8-10 metredistance to the main orchestralmicrophones.

But this way round, the reflection pat-tern for the orchestra is changed. The lowfront of the stage and the small upper stagemust substitute for the 3.5m high curve ofthe long back balcony face. The frontal,early deep -bass reflection at microphoneheight at 54ms has been replaced by a veryearly one at about 8-10ms. The differenceought to be noticeable to keen listeners asthis new reflection is behind themicrophones.

AwarenessPerhaps the foregoing analyses of severalaspects of hearing will help listeners

towards a greater appreciation of colourand texture in sound. The measurementsof timbre are far from complete, and moredetails are due to be published next year,covering the whole of the upper righthemisphere of our field of hearing.

When stereophony was introduced,analyses of aural localization mentionedthe three systems available to our body -giving the greatest importance to thetiming of impulses, much less to intensity,and virtually dismissing timbre differencesas inessential. It remains to be seenwhether in fact timbre is not the Cinderellaof the trio, ready to blossom into the mostbeautiful attribute when it is identified,recognized and espoused for its trueworth.

Further readingAnalyses of musical qualities and hear-ing:1 J. Sound and Vibration, 1980, vol. 69pp 110-138. Musical Times, Jan./Feb./-Mar. 1981. Studio Sound, J y 1981, pp62-66.

Timbre lists; Musical Times,Jan./Feb./Mar. 1981.

Langmuir thin-filmtrough for molecularelectronicsCollaboration between scientific instru-ment makers Joyce Loebl and a number ofresearch establishments, especially Dur-ham University, RSRE Malvern and ICI,has resulted in what is believed to be theworld's first commercial ultra -thin film"growing" equipment. The films in ques-tion are monomolecular layers of a class ofmaterials floated on a liquid surface,usually water transferable to a solid surfaceby passing it through the liquid. Thematerial originally used by the pioneer ofthis technique - Irving Langmuir ofGeneral Electric back in 1917 - was thesoap -like fatty acid salt sodium stearate,but other materials and their deposition onsolid surfaces were subsequently investi-gated by Langmuir and Blodgett, one resultbeing the development of glass anti -reflec-tion coatings. Chief property of thematerials used is a rod -like molecule, oneend of which is attracted to water and theother end repelled so they stand end -on(assuming the material is correctly com-pressed). But the trough is aimed at pos-sible new applications of L -B films thatarise largely out of microelectronics tech-nology. Such layers, one molecule thick,are becoming important in what is calledmolecular electronics - the "science of

BernerMonolayer

Eiectrobalance Comparator

Subphase leg purified eater)Burnermotor

-Trough

clever chemistry and electronics". Appli-cations include insulating layers as thin as10-9 metre in gallium arsenide devicesand as a resist in electron -beam lithogra-phy. Organic layers may have applicationfor gas detection, while biological mole-cules such as antibodies and enzymes maymake field-effect devices feasible for invivo monitoring. In integrated optics theyoffer a route to the precise building ofmultilayer films to one tenth of an Ang-strom unit, perhaps with the molecularaddition of metallic atoms to tailor res-ponse to radiation.

"Molecular Lego", as it has beendubbed, also has potential application toenergy conversion devices, photosynthe-sis, magneto -optics, three-dimentionalmemory devices, and to display devices,where high electric fields may allow a high-speed alternative to current technology.

Molecules are compressed in the Lang-

muir trough with a constant -perimetervariable -area boundary which encloses themonolayer and prevents film contami-nation. A sensitive microbalance with sen-sor in the liquid surface monitors differen-tial surface tension, and links through acontrol system to the barrier drive. Amotor -driven micrometer screw automat-ically drives a substrate in and out of theliquid. Constant surface pressure is pro-vided by a differential feedback system tomaintain film integrity. A pre -determinednumber of monolayers can be programmedby a control unit using a range of dippingspeeds, and a two -pen recorder charts sur-face pressure and area during deposition.

The trough is made by Joyce-Loebl, asubsidiary of Vickers Instruments, ofTeam Valley, Gateshead.

Enter WW 500 on reply card for furtherdetails.


NETWORKING SMALLCOMPUTERS

Simply transferring a program or data from one computer to another by telephone is nottoo great a problem, but if a number of remote computers are to work together regularlyin a network, relatively complex software is required to organize received informationefficiently. This article describes such software designed for Pet microcomputers and

outlines networking generally.

As personal computers become morepopluar, the need for simple methods ofexchanging programs and data betweenthem increases. Eventually, it may bepossible to exchange this informationthrough some form of readily accessibleglobal communications network, but atpresent, we have to make the best possibleuse of the facilities available. Some of themore important information disseminationtechniques currently being explored are- teletext broadcasts- viewdata systems, such as Prestel- and distributed computer networks.

Each of these approaches has itsadvantages and disadvantages. In the UK,experiments have been carried out usingCeefax and Oracle as a means of dis-tributing software' but these methodscan only be used to access informationfrom a central point. With Prestel, two-way information exchange is possible, butthere are two categories of 'user' - theordinary customer, who can only receiveand examine pages of stored material, andinformation providers. The majordrawback of this method is that not allusers can be information provident. TheCouncil for Education Technology iscurrently investigating this type ofinformation dissemination in conjunctionwith a number of schools and colleges2.'

A truly distributed computing network3'4is the third approach to program and datadistribution. Such a system has theadvantage of allowing totally unrestrictedbi-directional data exchange between anytwo parties. In this article I describeusing the public switched network (p.s.n.)as a means of distributing programs anddata between owners of personal com-puters.

Source program transmissionThe distributed computing system'sarchitecture significantly influences thetype of data it can accommodate. Broadlyspeaking, these systems fall into one of twocategories - one in which intermediatedata storage is available, and one in whichdata transfer is direct.

In Fig. 1(a), the microcomputer ownerat site X is able to dial the telephone

t British Telecom say that potentially all userscan be information providers so presumably DrBarker refers to cost limitations. - Ed.* Dr Barker is a Principal Lecturer at theDepartment of Computer Science, TeessidePolytechnic.

by Philip G. Barker*number of the owner at site Y and thentransmit information to him/her. In thecontext of data exchange, transmissiontakes place as if the two microcomputerswere linked together directlys. Nointermediate data storage is available soerror detection and correction procedureshave to be incorporated in the softwareused for receiving the data. Messagespassing over the communication networkare susceptible to corruption by noise orcrosstalk and as a result, if the receiverfails to respond to the transmitter, datatransfer is inhibited.

In Fig. 1(b), the microcomputer ownerat point X can store material in amainframe at site V or W for laterretrieval. Provided that the computers atpoints Y and Z can meet all the necessary

(a) Direct transfer

MICROX

( b) Transfer via intermediate mainframe

MICROX

MICRO

access control requirements, they too cangain access to the data. With this kind ofnetwork, information can be shared easilyand distribution to other geographicallocations is simplified.

Details of using a microcomputer as aninteractive terminal, in conjunction withthe public switched telephone network 6' 7,

and of using a microcomputer as anintelligent terminali have been presented.In reference 8, algorithms for information -file transfer between a mainframe andmicrocomputer are discussed in detail.These files may contain machine -codeprograms, high-level (source -language)programs or data. Using the softwaredescribed, communicating programsbetween one microcomputer and another(via a mainframe) is reasonablystraightforward but a decision has to bemade regarding whether the programs are

MAINFRAMEV

MICRO

MICRO

MAINFRAME

Fig. 1. In (a), the public switched network is used to link two computers together directly.Messages passing over the network are susceptible to corruption by noise or crosstalk - ifthe receiver fails to respond to the transmitter, data transfer is inhibited. Data from any ofthe three microcomputers shown in (b) may be stored in a mainframe computer andretrieved later. Using this type of network, certain codes can be imposed to restrict accessof information from the mainframes to those microcomputer owners with knowledge ofthe code.


to be transmitted in machine -code orsource -language form.

Factors influencing the ease with whichprograms may be communicated are- the level of language used- the availability of internationally

accepted language standards and theability of programmers to keep withinlimitations imposed by these standards

- compatibility of the computers used.These factors alone are probably

sufficient to justify transmitting programfiles in source language form rather than asmachine -code memory images. In thiscontext we have been examining theproblems associated with transmittingboth Pascal and Basic programs over thep.s.n. between microcomputers andmainframes. Some interesting results havebeen obtained - a few of which aredescribed here.

Files transmitted between the twocomputers consist of a contiguous set ofcharacters. Certain special charactersinterspersed in the sequence, for exampleend -of -line $0D*, impose a simple recordstructure on these files. That the files maynot be physically stored in this way ineither the source or destination computeris of little consequence as far as this articleis concerned.

Loading Basic from secondarystorageOnce a Basic program has beentransmitted from a remote computer andstored locally on a secondary storagemedium such as a tape or disc drive, it is asimple matter to load the program intomemory for subsequent execution. Howthe program is loaded will depend on thetype of microcomputer used. To illustratethe purpose of this article, specificdescriptions pertaining to the 3000 seriesCommodore PET microcomputer areincluded.

The function of a loading program is torecognize Basic statements contained in asecondary storage file, convert them to theappropriate format, and store them at thecorrect location in the memory spaceavailable. Functional requirements of sucha program for the PET are summarized inFig. 2(a), where it can be seen that thestorage area for Basic programs starts at$0400 and ends at $7FFF where 32K ofmemory is available. Obviously, theloading program at the top end of thememory will slightly reduce the amount ofspace available for other programs.

One of the loading program's main tasksis to convert the incoming source code to acode which can be stored in the computer'smemory, the two forms of which arerepresented in Fig. 2(b). When the sourcecode is stored, each statement consists of atwo -byte pointer, a two -byte encoding ofthe statement number, a sequence ofbytes representing the original source lineand a byte containing the 'end -of -line'marker. Further details on how Basic

*The 'dollar sign' indicates that the numberimmediately following it is in hexadecimal form.This is not the standard method of indicatinghexadecimal numbers, but is familiar to mostusers of the microcomputer concerned. - Ed.

(a) Principle

Secondary Storage Device

BASIC Program insource code format

PET Memory Space

Reserved Area

Loader Program

Screen Memory

)b) Comparison of internal and external forms of Basic

$0400

$7E00

$7FFF

SOURCE CODE INTERNAL FORMAT

10 PRINT"HELLO" 0400 00 OE 04 OA 00 99 22 4820 X= 3+ 2 0408 45 4C 4C 4F 22 00 18 0430 Y =3*240 = PRINT X,Y 0410 14 00 58 B2 33 AA 32 00

22 0450 PRINT"GOODBYE" 0418 1E 00 59 B2 33 AC

0420 32 00 2C 04 28 00 99 20

0428 58 2C 59 00 38 04 32 00

0430 99 22 47 4F 4F 44 42 59

0438 45 22 00 00 00 AA AA AA

lc) Memory map for a typical loading program

RAM ROM$0400

Operating System

$C3AB

$7E00

User Written Code

$7E50Borrowed Code

$7EE4

$7F01

$7FFF

Fig. 2. The function of a source -languageloading program. These diagrams,although specifically relating to the PET,are typical of most microcomputers.Underlined sections in (b) indicate thepositions in memory of the Basic statementnumbers.

programs are stored in memory can usuallybe found in the computer's manuals9.

Once a statement has been converted, ithas to be placed in the correct memorylocation. Both conversion and insertion areusually carried out by routines built intothe computer's operating system, which inthe case of the PET are locations $C34B to$C43F, and there is no reason why theseroutines may not be used in the programsconcerned. But for most readers, copyingthe relevent r.o.m. information into r.a.m.will be more practical than altering thesystem's r.o.m. A simple assemblylanguage program will serve this purpose.The loading program's basic structure is asfollows;Step 0: borrow code from the operating

systemStep 1: initialize Basic (usually using

NEW)Step 2: read input file (get next source

character)

Step 3:Step 4:Step 5:

Step 6:

Step 7:

Step 8:

if 'end -of -line', go to step 6if 'end -of -file', go to step 8store source character in Basicbuffer then go to step 2prepare for operating -system en-try routinesconvert source statement held inbuffer, enter into Basic memoryarea, then go to step 2pass control back to Basic com-mand mode with a 'READY'message.

As was suggested earlier, step 7 willprobably be carried out by a 'borrowedcode', and the remaining steps will beimplemented by the operator, see Fig.2(c). An assembly -language program forthe above algorithm - for Basic sourcefiles on cassette - is shown in Fig. 3, anda complementary flow diagram is shown inFig. 4. When invoked, the initializationcode copies $94 bytes, starting from$C34B, in the slot reserved for it throughmanipulation of the assembler locationcounter. When this is completed, theloading operation starts. The program usesa subroutine called TPREAD to transfer ablock of data from cassette into therelevant buffer area. In turn, this routinemakes use of the operating utility codecommencing at $F855. Characters are then


Fig

. 3. B

asic

sou

rce

-cod

e lo

adin

ggi

prog

ram

writ

ten

in a

ssem

bly

lang

uage

for

rt.7

,ca

sset

te -

base

d sy

stem

s.U

)U) K >

0001

0002

CO

0003

")

0004

0005

0006

0007

0008

0009

0010

0011

0012

0013

0014

0015

0016

0017

0018

0019

0020

0021

0022

0023

0024

0025

0026

0027

0028

0029

0030

0031

0032

0033

0034

0035

0036

0037

0038

0039

0040

0041

0042

0043

0044

0045

0046

0047

0048

0049

0050

0051

0052

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

7E00

7E02

7E05

7E08

7E09

7EOC

7EOE

7E11

7E14

7E17

7E19

7E1B

7E1E

7E20

7E20

7E22

7E24

7E26

7E29

7E2C

7E20

7E2E

7E30

7E32

7E35

7E38

7E3A

7E3D

7E3F

7E42

7E44

7E46

7E48

7E4A

7E4D

7E50

7E50

7EE4

7EE4

;TAPE LOADER PROGRAM

********** *********

TAPERD=$F855

DEVICE=$D4

BASBUF=$0200

BUFFER=$027A

NEWSYS=$C55D

CHRGET=$0070

OSCODE=$C3AB

BAS1C=$C389

*=$7E00

AO 00

START

LDY #50

B9 AB C3

COPY

LDA OSCODE,Y

99 50 7E

STA INSERT,Y

C8

INY

CC FE 7E

CPY NUM

DO F4

BNE COPY

20 50 C5

STEP1

JSR NEWSYS

20 FO 7E

JSR TPREAD

20 FO 7E

JSR TPREAD

-

A2 00

LOX #$O

AO 01

LOY #$1

89 7A 02

STEP2

LDA BUFFER,Y

C9 OD

CMP

FO 19

STEP3

3EQ STEP6

C9 CO

CMP #$00

DO 03

STEP4

BNE STEPS

4C EC 7E

JMP STEPS

90 00 02

STEPS

STA BASBUF,X

E8

INX

C8

LY

INY

CO CO

CPY #$C0

FO 03

BEQ GBLOCK

4C 18 7E

JMP STEP2

20 FO 7E

GBLOCK

JSR TPREAD

AO 01

LDY #$1

4C 1B 7E

JMP STEP2

A9 00

STEP6

LDA #$00

90 00 02

STA BASBUF,X

A2 FF

LOX #$FF

86 77

STX $77

A2 01

LDX #$O1

86 78

STX $78

8C 00 7F

STY YIND

20 70 00

STEP?

JSR CHRGET

INSERT=* *=*+$94

;TAPE READ ROUTINE

;INPUT DEVICE NUMBER

;BASIC BUFFER

;TAPE BUFFER

;PERFORM "NEW"

;LINE FETCH ROUTINE

;START OF CODE TO BE COPIED

;BACK TO BASIC

;COPY OS CODE

;INTO THIS PROGRAM

;ALL DONE?

;NO - GET SOME MORE

;INITIALISE SYSTEM

;READ A TAPE BLOCK

;READ A TAPE BLOCK

;INITIALISE X -REGISTER

;INITIALISE Y -REGISTER

;GET A CHARACTER FROM TAPE BUFFER

;IS IT END OF LINE?

;YES

;IS IT END CF FILE?

;NO

;YES

;STORE IN BASIC BUFFER

;INCREMENT X -REGISTER

;INCREMENT Y -REGISTER

;END OF DATA BLOCK?

;YES - GO GET ANOTHER

;NO - GO GET NEXT CHARACTER

;GET ANOTHER BLOCK

;INITIALISE COUNT

;RETURN TO MAIN LOOP

;PUT EOL INTO BASIC

;BUFFER AREA

;SET UP POINTERS TO THE

;ADDRESS OF BASIC

;SOURCE TO BE PROCESSED

;SAVE CONTENTS OF Y -REGISTER

;INVOKE CHRGET ROUTINE

;TOKENISE STATEMENT

;AND INSERT RESULT INTO

;BASIC PROGRAM AREA

;GET READY TO GO BACK AND

0053

0054

0055

0056

0057

0058

0059

0060

0061

0062

0063

0064

0065

0066

0067

0068

0069

0070

0071

0072

0073

0074

7EE4

7EE4

7EE7

7EE9

7EEC

TEED

7EFO

7EFO

7EFO

7EFO

7EF2

7EF4

7EF7

7EFA

7EFD

7EFE

7EFE

7EFE

7EFE

7EFF

7F00

7F01

AC 00 7F

LDY YIND

A2 00

LDX #50

4C 2D 7E

JMP LY

EA

STEPS

NOP

4C 89 C3

JMP BASIC

AO 01

TPREAD

LDY #51

84 D4

STY DEVICE

8E FF 7E

STX XIND

20 55 F8

JSR TAPERD

AE FF 7E

LDX XIND

60

RTS

94

NUM

.BYTE $94

00

XIND

.BYTE 0

00

YIND

.BYTE 0

.END

Fig

. 5. T

his

asse

mbl

y la

ngua

ge p

rogr

am, a

mod

ified

ver

sion

of t

he p

rogr

am s

how

n in

Fig

. 3, i

s fo

r lo

adin

g so

urce

-co

de p

rogr

ams

in a

dis

c -b

ased

sys

tem

.

0001

0002

0003

0004

0005

0006

0007

0008

0009

0010

0011

0012

0013

0014

0015

0016

0017

0018

0019

0020

0021

0022

0023

0024

0025

0026

0027

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

000Q

0000

0000

0000

0000

0000

;PROCESS NEXT STATEMENT

;RESTORE Y -REGISTER

;INITIALISE X -REGISTER

;GO BACK TO MAIN LOOP

;END OF FILE

;RETURN TO BASIC

;ROUTINE TO READ A TAPE BLOCK

;LOAD INPUT DEV

;PASS TO OPSYS

;SAVE X -REGISTER

;READ A TAPE BLOCK

;RESTORE X -REGISTER

;RETURN TO CALLER

;DATA STORAGE AREAS

;NUMBER OF BYTES TO COPY

;PLACE FOR X -REGISTER

;PLACE FOR Y -REGISTER

;DISK SUPPORT ROUTINES FOR LOADER PROGRAM

************* ******* ********* ***********

;RESERVED LOCATIONS

LONAM=SDA

HINAM=$DB

L0=$02

PA=$D4

SA=$D3

FILEN=$D1

ST=$96

BUFFER=$027A

;ADDRESS OF FILE NAME -LOW

;ADDRESS OF FILE NAME -HIGH

;LOGICAL DEVICE NUMBER

;PRIMARY ADDRESS

;SECONDARY ADDRESS

;LENGTH OF FILE NAME

;STATUS CODE

;TAPE BUFFER

;SYSTEM SUBROUTINE ADDRESSES

PRINT=SCA1C

READY=$C38B

INPUT=$C46F

FOPEN=$F524

CHKIN=$F770

INBYTE=$F18C

FCLOSE=SF2AE

CLRCHN=$FFCC

;PRINT A STRING

;READY

;INPUT FROM KEYBOARD

;OPEN FILE

;SET INPUT DEVICE

;INPUT SOURCE BYTE

;CLOSE FILE

;CLOSE I/O CHANNELS

cont

inue

d

Fig.

5: c

ontin

ued

0084

0085

706D

7070

20 1C CA

60

JSR PRINT

RTS

0086

7071

OD

PROMPT

.BYTE $00,$0A,'FILE NAME? 1,$0

0086

7072

OA

0028

0000

;DEFINED SUBROUTINES

0086

7073

46 49

0029

0000

****** ***..*********

0086

707E

00

0030

0000

0087

707F

CD

MESS1

.BYTE $0040A,'FILE OPEN ERROR',$0

0031

0000

*=$7000

0087

7080

OA

0032

7000

0087

7081

46 49

0033

7000

;DISK OPEN ROUTINE

0087

7090

00

0034

7000

0088

7091

OD

MESS2

.BYTE $00,$0A,'FILE OPENED OK',$0

0035

7000

A9 01

OKOPEN

LDA #$01

;OPEN ERROR AND DISK

0088

7092

OA

0036

7002

85 D1

STA FILEN

;COMMAND CHANNEL

0088

7093

46 49

0037

7004

A9 00

LDA #$00

;LOW BYTE OF FILE NAME ADDRESS

0088

70AI

00

0038

7006

85 DA

STA LONAM

;STORE IN POINTER LOW

0089

70A2

0039

7008

A9 02

LDA #$02

;HIGH BYTE OF FILE NAME ADDRESS

0090

70A2

;DISK READ ROUTINE

0040

700A

85 DB

STA HINAM

;STORE IN POINTER LOW

0091

70A2

;- EMULATES

A FAST CASSETTE

0041

700C

A9 49

LDA #'I

;INITIALISE DISK COMMAND

0092

70A2

0042

700E

80 00 02

STA $0200

;STORE IN FILE NAME

0093

70A2

8D FD 70

DKREAD

STA ACCUM

;SAVE ACCUMULATOR

0043

7011

A9 OF

LDA #$OF

;LOGICAL FILE 15

0094

70A5

8E FE 70

STX XREG

;SAVE X -REGISTER

0044

7013

85 D2

STA LD

;STORE IN LOGICAL DEVICE BYTE

0095

70A8

8C FF 70

STY YREG

;SAVE Y -REGISTER

0045

7015

A9 08

LOA #$08

;DISK IS DEVICE 8

0096

70AB

A2 02

LDX #$2

;SET NUMBER OF FILES OPEN

0046

7017

85 D4

STA PA

;PUT IN PRIMARY ADDRESS

0097

70AD

86 AE

STX 174

;IN LOCATION 174

0047

7019

A9 OF

LDA #$OF

;LOAD SECONDARY ADDRESS CF 15

0098

70AF

A2 02

LOX $02

;SELECT LOGICAL CHANNEL 2

0048

7018

85 D3

STA SA

;STORE IT

0099

7081

20 70 F7

JSR CHKIN

;SET INPUT DEVICE

0049

7010

20 24 F5

JSR FOPEN

;INITIALISE DISKS - OPEN 15,8,15,"I"

0100

7084

A2 01

LDX #$01

;LOAD POINTER

0050

7020

A9 71

LDA #<PROMPT

;LOAD ADDRESS

0101

7086

AD FC 70

LDA EOF

;HAS EOF BEEN PREVIOUSLY DETECTED?

0051

7022

AO 70

LDY >PROMPT

;OF PRCMPT MESSAGE

0102

7069

DO 22

BNE CLOSE

;YES - GO CLOSE FILES

0052

7024

20 1C CA

JSR PRINT

;GO PRINT IT

0103

7088

20 8C Fl

LOOP2

JSR INBYTE

;GET A BYTE FROM DISK FILE

0053

7027

20 6F C4

JSR INPUT

;GET FILE NAME FROM USER

0104

70BE

A4 96

LDY ST

;END OF FILE?

C054

702A

A9 02

LDA #$02

;SET LOGICAL FILE NUMBER 2

0105

7000

DO GB

BNE END

;YES - GO CLOSE THEM BOTH

0055

702C

85 D2

STA LD

;STORE IN LOGICAL DEVICE BYTE

0106

70C2

9D 7A 02

STA BUFFER,X

;NO - SO SAVE CHARACTER IN BUFFER

0056

702E

A9 08

LDA #$08

;SELECT DEVICE 8 FOR DISK

0107

7005

E8

INX

;INCREMENT POINTER

0057

703 0

35 D4

STA PA

;PUT IN PRIMARY ADDRESS BYTE

0108

7006

EO CO

CPX #$C0

;BUFFER FULL YET?

0058

7032

A9 02

LDA #$02

;LOAD SECONDARY ADDRESS OF 2

0109

7008

FO 28

BEQ FULL

;YES - GO BACK TO CALLER

0059

7034

85 D3

STA SA

;STORE IN SECONDARY ADDRESS BYTE

0110

70CA

AC BB 70

JMP LOOP2

;NO - SO GET ANOTHER BYTE

0060

7036

A2 00

LDX #$00

;SET INDEX TO ZERO

0111

70CD

A9 OD

END

LDA #$OD

;PASS EOL OVER TO BASIC BUFFER

0061

7039

0112

70CF

9D 7A 02

STA BUFFER,X

0062

7038

BD 00 02

LOOP1

LDA $0200,X

;GET CHARACTER FROM INPUT BUFFER

0113

7002

E8

INX

0063

7038

FO 04

BEQ NEXT

;IF ZERO THEN END OF FILE NAME

0114

7003

EO CO

CPX #$C0

;BUFFER FULL?

0064

0065

7030

703E

E8 4C 38 70

INX

JMP LOOP1

;INCREMENT X -REGISTER

;EXAMINE NEXT CHARACTER

0115

0116

7005

70D7

DO 06

8C FC 70

BNE CLOSE

STY EOF

;NO - SO OK, ALL IS WELL

;YES - SO NO ROOM FOR EOF MARKER

0066

7041

86 01

NEXT

STX FILEN

;SET FILE NAME LENGTH

0117

70DA

4C F2 70

JMP FULL

;REMEMBER EOF HAS COME

0067

7043

20 24 F5

JSR FOPEN

;OPEN FILE:

OPEN 2,8,2,"//777/?"

0118

7000

A9 00

CLOSE

LDA #$00

;LOAD EOF MARKER

0068

7046

A2 OF

LDX #$OF

;TEST FOR ERRORS

0119

700F

90 7A 02

STA BUFFER,X

;PASS IT OVER TO BUFFER

0069

7048

20 70 F7

JSR CHKIN

;SET INPUT FILE TO 15

0120

70E2

A9 02

LDA #$02

;LOAD LOGICAL FILE 2

0070

7048

20 8C Fl

JSR INBYTE

;GET A BYTE FROM DISK ERROR CHANNEL

0121

70E4

20 AE F2

JSR FCLOSE

;GO CLOSE FILE 2

0071

704E

C9 30

CMP #$30

;IS IT ASCII ZERO?

0122

70E7

20 CC FF

JSR CLRCHN

;SET DEFAULT I/O DEVICES

0072

7050

FO 17

BEQ OPENOK

;YES - FILE OPENED OK

0123

70EA

A9 OF

LDA #$OF

;LOAD LOGICAL FILE 15

0073

7052

A9 7F

LDA #<MESS1

;GIVE DIAGNOSTIC

0124

70EC

20 AE F2

JSR FCLOSE

;GO CLOSE FILE 15

- COMMAND CHANNEL

0074

7054

AO 70

LDY #>MESS1

;MESSAGE TO USER

0125

70EF

20 CC FF

JSR CLRCHN

0075

7056

20 1C CA

JSR PRINT

0126

70F2

AE FE 70

FULL

LDX XREG

;RESTORE X -REGISTER

0076

7059

A9 02

LDA #$02

;CLOSE CHANNEL 2

0127

70F5

AC FF 70

LDY YREG

;RESTORE Y -REGISTER

0077

7058

20 AE F2

JSR FCLOSE

0128

70F8

AD FD 70

LDA ACCUM

;RESTORE ACCUMULATOR

0078

705E

A9 OF

LDA #$OF

;CLOSE CHANNEL 15

0129

70FB

60

RTS

;GO BACK TO CALLER

0079

7060

20 AE F2

JSR FCLOSE

0130

70FC

00

EOF

.BYTE $0

;PLACE FOR EOF STATUS

0080

7063

20 CC FF

JSR CLRCHN

;SET DEFAULT I/O DEVICES

0131

7CFD

00

ACCUM

.BYTE $0

0081

7066

4C 8B C3

JMP READY

;GO BACK TO BASIC

0132

70FE

00

XREG

.BYTE $0

;SAVE AREA FOR REGISTERS

0082

7069

A9 91

OPENOK

LDA #<MESS2

;TELL USER THAT THE

0133

70FF

CO

YREG

.BYTE $0

0083

7068

AO 70

LDY #>MESS2

;FILE OPENED OK

0134

7100

.END

lowing table their load size differed by onlyfive bytes.

TapeCassette

c?

REMOTECOMPUTER

DirectLoad

TPREAD

Tape 1 buffer - BUFFERY -Register $0274

OUTCHAR

DKREAD

$0339

BASBUF - BASIC Input buffer

kA A

Accumulator

Maincode

DKOPEN DKREAD Totalstore

Flexible Tape loader 257 257Disk Disc loader 1 257 152 95 504

Disc loader 2 242 152 115 509

DKREAD(Version No. 2)

BASIC Program Area

The loading programs can be located ine.p.r.o.m. or in any part of the memoryspace available for program loading. Whensiting these programs, two importantfactors must be considered;- that the programs do not over -write

themselves while running (this isusually caused by locating them toonear the low end of memory), and,

- that they do not interfere with any ofthe operating system support softwarethat may be partly in r.a.m. (forexample, DOS support uses r.a.m.above $7EAB in 3040 disc -based 32PET systems).

Each of these restraints can be avoidedT /4 $0400

rk9- -by using an appropriately structurede.p.r.o.m. However, if the loadingprograms are to be stored in r.a.m. theirsecurity and effectiveness depends on

FF 01 finding a suitable memory space into$77$78 X -Register which they may be loaded and run.

$7FFF Unfortunately, disc loader 2 is too large to

Fig. 4. Data flow diagram for the source code loading program shown in Fig. 3.

copied one at a time from the tape buffer,$027A, across to the Basic input buffer,$0200 - $0250, using the Y and Xregisters respectively as pointers in theindexed load and store operations. Eachtime an end -of -the -line character, $0D, isencountered in the input data -stream(INCHAR) an end -of -statement marker,$00, is sent to the output stream(OUTCHAR) for placement in the Basicbuffer. Subsequently, at step 6, thepointers at $77 and $78 are set to point tothe memory area containing the newstatement. A subroutine call to theoperating system utility CHRGET is thenmade. This is essentially a line -fetchroutine that sets up the next Basicstatement for processing. More details onhow the routine operates are given

Once the CHRGETelsewhere l ,I2.

routine has been primed, the code forconverting/inserting the new line into theBASIC program area can commence.Further source statements are thenprocessed one at a time until an end -of -filecode, $00 for tape files, detected onINCHAR terminates the loading processand passes control back to Basic direct -command mode with the prompt"READY".

A major disadvantage of the loadershown in Fig. 3 is its lack of identitychecking. Inherent in the program is theassumption that the tape will be positionedat the point from which loading is tocommence; the first block (programidentity) is then skipped over. Ifnecessary, it would be a simple matter toreplace the first reference to TPREAD(line 21) by a call to asubroutine thatallows the operator to interact. This


subroutine could be used to ask theoperator for the name of the file to beloaded and then automatically position thetape ready for loading. A routinetype is essential in a loading programdesigned for handling source programsfrom discs.

To enable the loading program shown inFig. 3 to handle disc files, two additionalsubroutines are needed: one to open thedisk file, DKOPEN, and another to readand close it, DKREAD. Implementationsof each of these are presented in Fig. 5.DKOPEN fulfills the requirementsoutlined above, that is, it prompts theoperator for the name of the file to beloaded, checks its validity and then returnsan appropriate message. The DKREADroutine emulates the action of the tapecassette thereby minimizing the number ofchanges necessary to the code listed in Fig.3. Indeed, only three changes are required;the reference to TPREAD in line 21 mustbe changed to DKOPEN and that toTPREAD (line 65) must be altered toDKREAD. Finally, the device number inline 62 must be changed from 1 to 8.

As a means of checking that tapecassette emulation was a reasonable approachto use, a second version of the disc loadingprogram was written using a different ap-proach. This involved reading the whole ofthe disc file into memory, storing it, andthen processing it as an internal file. Otherthan the slight modifications needed forthe revised input method, no majorchanges to the logic of the program shownin Fig. 3 were required and no detectabledifference in performance between the twodisk -loading programs was observed.Furthermore, as can be seen from the fol-

fit into the tape cassette buffer areas,$027A through $03F9, but its main bodyand the smaller of the two input routines(DKREAD) easily slot into this area;DKREAD could now reside at the highend of r.a.m. above about $7E10, the exactlocation depending what other software ispresent in this area. Because the version ofthe loading program for handling tape -based source files is too large to be storedin cassette buffer 2, as with the DKOPENroutine, it would also need to be positionedsomewhere above memory address $7E10.Similar arguments apply in the case of diskloader 1. Whatever parts of high r.a.m. areused, the limit of Basic memory wouldneed to be lowered by suitably adjustingthe pointers held in zero page locations $34and $35.

Each of the software systems describedabove successfully loads Basic programsfrom tape/disc files into memory ready forexecution. These files will usually havebeen created by program transfer fromanother remote computer through thepublic switched network or a privatecommunication system. Alternatively,they may have been prepared by an editingsystem or as a result of LISTing to eithertape or disc. Because these files are inconventional ASCII form rather than ininternal machine -code form they are moreeasily exchanged between different typesof personal computer.

Comparing load timesGiven that there are now several ways ofloading Basic programs into memory someconsideration of loading times would beappropriate. There are two importantcomparisons to make- the relative speed of loading source

programs compared with memoryimage programs, and

- the relative speed of tape loadscompared with those from disc.

39

To carry out the above comparisons asimple program generator was con-structed. This consisted of a series of Basicstatements which when executed produced(as output) another Basic program. Thiscould be written as an ASCII file to tapeand/or disk. Furthermore, once processedby either of the loaders described above,this program could also be saved in theconventional manner using a SAVE com-mand. The program consisted of 1000statements whose average length was about22 characters. Its load size was 19K bytes.Measures of the time required to load thisprogram under different conditions are- time to load source program from tape,

1037 s- time to load source program from disk,

260 s- tape load time for SAVEd program,

357 s- disk load time for SAVEd program,

1 Os .

There are two observations immediatelyapparent. Firstly, loading source programsis much slower than loading memoryimages; secondly, loading from disc is verymuch faster than loading from tape. Theserelationships could have been predictedintuitively and so the only value of theabove figures lies in the quantitivecomparisons they permit. From the valuesshown it can be seen that disc loading isabout 35 times faster than tape loadingwhere memory images are concerned but

only about four times faster in the case ofsource -code loading. In the latter case, ittook only 11 seconds to read the sourceprogram into memory from disc. Thiswould suggest that about 96% of theprogram loading time is devoted toconverting source statements into a formsuitable for storage, and storing them.Similarly, in the case of tape loading, ittakes about six seconds to read a blockfrom tape into memory. The test programcontained 131 blocks, i.e., 192 x 131characters, and so its input/output timewould be about 786 seconds. This meansthat only 24% of the program loading timeis spent on conversion operations. It isinteresting to note that the time spentconverting and inserting programs inmemory is the same for both programs -249s for the disc loading program and 251sfor the tape version. This means that themodifications converting the tape loadingprogram into its disc equivalent do notinfluence the program's performancecharacteristics. These results illustrate theadvantages of memory -image loading oversource -code loading, but most readers willprobably prefer to sacrifice some efficiencyto make their programs more compatiblewith computers of a different type.

References1 Hayman, M., Brighton project sets out on

the micro road, Practical Computing, Aug.1981,pp. 75-76.

2 Technical Developments Programme -Telesoftware Project, paper CID 81.2, 1981,Council for Educational Technology.

3 Cannon, D. L., and Luecke, G.,Understanding Communications Systems,Radio Shack, ISBN: 0-89512-035-6.

4 Davies, D. W., and Barber, D. L. A.,Communications Networks for Computers,Wiley, ISBN: 0-471-19874-9.

5 Campbell, G., Commodore 8010 modem,Commodore Club News, July 1981, p.18.(Nick Hampshire Publications, 19Hobhouse Court, Whitcombe St, LondonWC2).

6 Barker, P. G., Using a Microcomputer as anInteractrive Terminal, Interactive SystemsResearch Group Working Paper, Apr. 1981(Dept. of Computer Science, TeessidePolytechnic, County Cleveland).

7 Barker, P. G., Using the PET as anInteractive Terminal, Interactive SystemsResearch Group Working Paper, Jun. 1981.

8 Barker, P. G., Algorithms for IntelligentTerminal Operation, Interactive SystemsResearch Group Working Paper, Jul. 1981.

9 Donahue, C. S., and Enger, J. K.,PET/CBM Personal Computer Guide,Osborne/McGraw-Hill, ISBN: 0-931988-30-6, pp. 312-314.

10 Hampshire, N., The PET Revealed,Computabits Ltd, pp. 77-78.

11 Doyle, D., DIMP: A Machine LanguageRoutine for the PET to Handle AlgebraicInput, Commodore PET Users ClubNewsletter, vol. 2, issue 8, 1980, pp. 19-20,(ICPUG, 109 York Road, Farnborough,Hants).

12 Doyle, D., DIMP Revisited, CommodorePET Users Club Newsletter vol. 3, Issue 2,1980, p.31.

Teledon videotex in UKThe first private viewdata system based onTeledon technology has been introducedby Poulter Computervision, a new com-pany in the Poulter advertising and mar-keting group. Developed by the CanadianDepartment of Communications, Teledonis an easy -to -use system to enable text andhigh -quality animated images to betransmitted to tv sets. It was chosen foraudiovisual communication by Poulterlargely because of its impressive graphiccapability.

The company have moved fast sincethey discovered it late last year. In factGraham Poulter told WW he didn't evenknow of it until 14 weeks prior, whenPeter Ashley (now a director) told him of itafter seeing it on an Australian NEB trip.They now have sole UK rights to Teledon,negotiated with the CDC licensee Norpak.

Two equipments are available, the sim-plest being a decoder with 64K of usabler.a.m. (there is further memory for screenmapping and holding software) controlledby a 6809 microprocessor and fed from acassette player. Up to 200 frames or"slides" can be displayed in any order,each one appearing either instantly or pro-gressively. With a modem attached, 10pages of information can be recorded in 60seconds - ten times faster than otherviewdata systems of the alpha -mosaickind. The other terminal is an informationprovider's graphic creation unit with digi-tizing tablet, colour monitors, two floppydisc drives and PDP11/03 computer. With

about ten minutes' learning time, it isclaimed, images can be created by retriev-ing an image from a library to edit, bysketching or tracing drawings on thetablet, or by using high-level commandsdefined as geometric elements. Animationsof any length are possible and the combi-nations of colours with grey shades areunlimited. A page of text takes about 5minutes to assemble while a chart mighttake 10 to 15 minutes.

Secret of Teledon is the picture descrip-tion instruction coding that describesimage content by co-ordinates - two for

lines and rectangles, three for arcs, morefor polygons, hence the name alpha -geo-metric. Images can also be described byscanning point-to-point, and they are re-constructed to whatever resolution the re-ceiving equipment allows. Among claimsmade for it are future equipment compati-bility as well as future information compa-tibility, easy conversion to alpha -mosaicor d.r.c.s. and it is said to handlemore CCITT videotex -attributes than anyother scheme. Teledon is in regular use inCanada, on trial in the USA, and Europeanrights have been bought by Siemens.

ao WIRELESS WORLD MAY 1982

DIGITAL TELEVISIONSTANDARDS

Towards a worldwide compatibility for broadcasting studio equipment at recentmeetings of the CCIR in Geneva, decisions were taken which will have an

important bearing on the introduction of digital systems into television studiosthroughout the world.

Discussions on digital video coding havebeen going on for many years; in Europethey have taken place mainly in the EBU.In fact, the CCIR was largely respondingto a submission from the EBU reachedafter extensive consultations among itsmembers and with industry, other broad-casting unions and the AmericanSMPTE.

It had long been accepted that to ob-tain the maximum benefit from digitaltechnology one should handle the threecomponents of the video signal (e.g. lu-minance and colour -difference signals)separately throughout the digital studiorather than combined into the compositePAL, SECAM or NTSC composite formas in most of the analogue studio opera-tions of today. The use of componentcoding will also ensure commonality ofequipment design throughout the 625 -line world and to a valuable degree withthe 525 -line world - assuming agree-ment on the basic parameters definingthe video signal.

There may be a case for establishing indue course a compatible family of codingstandards to suit different quality re-quirements, e.g. of ENG at one extreme

by A. Howard JonesBBC Research Department

and high -definition television at theother. But the most urgent requirementwas to specify the standard that will beused within all of the main studio equip-ment and at the inputs to the recordingand transmission equipment used for in-ternational programme exchange.

It was agreed at Geneva that the mainstudio standard would use sampling ratesof 13.5 MHz for luminance and 6.75MHz for each of the two colour -dif-ference signals. This corresponds to 864and 432 samples per line respectively in625 -line countries and 858 and 429samples per line respectively in 525 -linecountries.

8 -bit linear p.c.m. coding will be usedand it was agreed by most delegationsthat the coding ranges should be set asindicated in Fig. 1.

There is a good chance that thesefigures will have been formally writteninto the Recommendation by the time of

The author is chairman of EBU Specialist Group VI-VID in which much of the discussion on standardiza-tion has taken place.

CODING RANGES

255 111111111)

235- White - 111101011)

16 Black (00010000)

0 100000000)

LUMINANCE

255 (11111111)

239- Maximum -111101111)

128- Zero uvolts -110000000)

16 -Minimum-(00010000)

0 (00000000)

COLOUR DIFFERENCE

Fig. 1. Coding ranges for the 8 -bit linear p.c.m. system

15

-309

64

10.5

9.8

720 12 132 720 12 132

Fig. 2. The EBU proposal for 625 -line signal and nominal analogue timing for referencewith 864 luminance samples for each line.

the Plenary Assembly next year, togetherwith a statement to the effect that in both625- and 525 -line areas the circuits whichprocess only the active part of the televi-sion line should accommodate 720 lumi-nance and 360 colour difference samplesper line.

At a sampling frequency of 13.5 MHz,720 samples occupy somewhat more thaneither of the nominal active line periods.The intention is that the latter will bedefined by a blanking operation to becarried out when the signal eventuallyemerges into the analogue compositeworld. Meanwhile, an appropriate posi-tioning of the 720 samples (Fig. 2

shows the EBU proposal for 625 -line sig-nals and digital and nominal analoguetiming for reference) will ensure that thesystem will accept the whole of an anal-ogue active line at its input regardless ofthe actual timing within permittedtolerances.

The adoption of this specification willensure maximum compatibility of equip-ment throughout the world and will laythe foundation upon which further speci-fications, covering studio interfaces, digi-tal video tape formats, and the multiplexstructure to be used on international digi-tal links, can be built.

CorrectionsRemote control for a hi-fi system. Unmarkedcomponents in Steve Kirby's article in theMarch issue, page 54, are p -n -p transistor inFig. 1 and 3.9kf1 for its base -emitter resistor.Transmitter diodes are high -power types - RSComponents 308-512 or equivalent. Labels"standby" and "normalise" should betransposed on the keyboard. Notes on settingup the link, a simplified tone control summingcircuit, and p.r.o.m. listing will be publishednext month In the mean time they can be ob-tained by sending a stamped, addressed enve-lope to Steve Kirby at the Department ofElectronics, University of York, Heslington,York Y01 5DD.Heating -fuel saver. The introductoryparagraph states that the outdoor temperaturesensor is not essential but in fact, the schemewould not work without it. The non -essentialpart is the meter to indicate the reading of thesensor. If this is not required, the milliameterand IC2b can be omitted. In the first paragraphof the main text a d -to -a converter has beenmisprinted as a 'data -a converter'.Digital, multi -track tape recorder. Contrary tothe impression by the April part of this article, itwas not the final section. A further part on theplayback facility will be published in the nextissue.

BBC micro. See News of the month.


Tracking vehiclesDisclosure of hitherto secret Home Officeguidelines on the police use of "bugging"and other electronic equipment has drawnattention to a form of surveillance that haslargely passed unnoticed: the "tracking"of suspect vehicles by the attachment of aminiature transmitter which can then belocated using sophisticated fixed or mobileDoppler -type v.h.f. and u.h.f. direction -finding equipment that overcomes many ofthe usual problems of accurate d/f in built-up areas. Equipment of this type is madein several countries, and indeed two yearsago Rohde & Schwarz specifically des-cribed their PA002 and PA005 systems assuitable for "specialized applications in thefield of personal protection or even intrailing 'prepared' vehicles". From fixedbases such equipment can locate an urbantransmission to within about 100 metres.At least one American firm makes mobileequipment that would have little difficultyin following a vehicle at a discreet distance.

Direction -finding, the first applicationof a radio navigational aid early this cen-tury is once again in vogue. Marine v.h.f.d/f systems in the English Channelsupplied by Racal have proved their use insea rescues. American portable (man -pack)d/f equipment is currently being promotedfor military detection and tracking ofarmoured vehicles.

Broadcast relaysFor several years, some of the Europeanexternal broadcasting services have beenusing satellite circuits to carry programmesto their overseas relays. But most of thesehave made use of Intelsat earth stationsbuilt primarily for telecommunicationsservices.

However, Marconi CommunicationSystems have recently announced a£500,000 -plus order from the Foreign andCommonwealth Office for a 10 -metre, re-ceive -only, Standard B earth station to belocated on Masirah Island, off the eastcoast of Oman, to be completed this year.This station is expressly to receive the BBCOverseas Service programmes forretransmission on the high -power FCOtransmitters forming the Middle East Re-lay Station, including two 750 kW m.f.transmitters.

The users of extremely high -power h.f.over -the -horizon radar and broadcastingstations may have noticed with someconcern a report of recent joint -work of theMax-Planck-Institut fur Aeronomie andthe University of Leicester (Nature, 25February 1982). This shows that the ionos-phere has non-linear characteristics suchthat above a certain optimum power, sig-nals received at remote sites decrease with

additional power. The optimum power isusually not much more than about 6.5MW e.r.p. - a power less than that cur-rently used by some broadcast and radarstations.

Mobile radio and s.s.b.The outlook for the use of v.h.f. single-sideband with 5 kHz channelling inthe private -mobile radio or in theRadiophone services cannot be regarded asbright - and seems to depend on whetherthe fast -acting, companding-type a.g.c.system being developed by Dr McGeehanat Bath University proves suitable for in-corporating into s.s.b. mobile phones.

The intensive work in the UK over thepast few years on the Wolfson project formobile s.s.b. has failed to produce theclear-cut results needed to convince users.Completely independent user -trials byBritish Telecom Research and by theHome Office, and related trials by manu-facturers, all seem to have shown that onfrequencies of the order of 160 MHz,s.s.b. equipment (without companding)does not provide fully equivalent perform-ance to that of 12.5 kHz channelling f.m.systems and is significantly degraded incomparison with 25 kHz channelling f.m.The British Telecom results suggest thats.s.b. also requires a much higher co -chan-nel interference protection ratio (about 20dB) which would mean that there could bemuch less re -use of channels, substantiallyreducing the theoretical spectrum -savingadvantages of s.s.b. The earlier HomeOffice trials highlighted the problem ofDoppler frequency shift and the need foran extremely good a.g.c. system if speechquality is to be maintained above 200 MHzwith vehicles travelling at more than 30km/h.

The BT trials (Electronics Letters, Octo-ber 29, 1981) used s.s.b. equipmentspecially designed to assess the suitabilityof the mode as a replacement for f.m. inthe Radiophone service, with tests carriedout under carefully controlled conditions.Speech of a well defined level wastransmitted simultaneously over threeradio links (12.5, 25 kHz f.m. and s.s.b.)and recorded in a moving vehicle. Therecordings were later carefully assessed inan acoustic room with simulated vehiclenoise, under conditions of fading, interfer-ence and signal level. The conclusion wasthat s.s.b. subjectively degraded the per-formance compared with 12.5 kHz f.m. byas much as a change from 25 to 12.5 kHzf.m. With co -channel interference, "meanscores" were: s.s.b. 1.8, 12.5 kHz f.m.2.1, and 25 kHz f.m. 2.4.

Unless the Bath University work ona.g.c. reverses the situation, early wide-spread adoption of s.s.b. seems unlikely.

Marine communicationsThe official opening of the Marecs-A mari-time satellite communications system onMarch 1 provided a notable technical hic-cup. The planned inaugural call by Ken-neth Baker, Minister for InformationTechnology, had to be called off at the lastmoment due to the aftermath of "intensesolar activity".

While we all know how easy it is forpress and public demonstrations to goadrift, this incident must have been parti-cularly galling for those promoting asophisticated system that seeks to high-light and then supersede the radio propa-gation vagaries of traditional marine radio!

Shipping companies have seldomproved eager to introduce new commu-nications or navigational systems unlessthe costs can be off -set by lower marineinsurance rates - so that 24 -hour reliabil-ity must be counted a vital consideration.

There can be little doubt that marinesatellite systems offer many advantages fordeep-sea vessels, and will eventuallysupersede long-distance h.f., just asmarine v.h.f. has gradually won throughfor short-range operations. But I wonder ifI am alone in recalling the high commu-nications efficiency of the old pre-war pas-senger ships using "long waves" above2000 metres?

When static was not too bad, the highlyprofessional radio officers and coast sta-tions could handle traffic in a manner sel-dom heard on the other marine frequen-cies. Today, with few large passenger -carrying ships, marine traffic tends to belighter and largely confined to the runningof the ships or personal messages of thecrew. As with all radio communications"progress" seems to be a matter of ever -higher frequencies - though marine ra-dars have long paved the way tomicrowaves.

Topics in the airM. Hansen and J. P. Loughlin of theAmerican Naval Ocean Systems Center,San Diego have described (IEEE Trans.,Vol. AP, No 6, November 1981) a four -element adaptive aerial array that automat-ically minimizes multipath reception.Typically, at frequencies between 3.4 and9.3 MHz over a 234 km over -ocean path,unwanted modes were reduced by morethan 15 dB.

George J. Flynn of Washington Univer-sity, St Louis, Missouri has forecast that ifthe rate of increase of objects in orbit con-tinues to increase, the first collision be-tween satellites can be expected in the next10-15 years. He warns: "A reversal of thistrend is required to prevent a serious


hazard to orbiting satellites in the twenty-first century". Although the number ofobjects in near -Earth orbit decreased be-tween 1978-1980, they have since in-creased rapidly to an all-time high of 4,740objects, in October 1981. 137 new objectswere associated with the US Landsat 3satellite, launched in 1978, and 118 withCosmos 1275, launched in June 1981.

Licence snafuFollowing meetings between the R.S.G.B.and the Home Office, the Home Officeconfirmed officially that the new amateur -radio licence schedule, as published in TheLondon Gazette on February 12, containederrors and a revised schedule would bepublished with a minimum of delay. TheHome Office also issued a statement thatthey had had "no intention of changing thebasis of amateur radio operation in theU. K." .

In other words, the sensation caused bythe February 12 schedule was ascribed toyet another "snafu" on the part of thelicensing authorities - although to thecredit of the officials concerned they re-acted promptly and fairly when the conse-quences of the error -prone schedule werebrought to their notice by the R.S.G.B.and by many horrified amateurs!

Perhaps a light-hearted side of the inci-dent was that, by omitting a key line, theGazette unwittingly deleted all regulatorydifferences between Class A and Class Blicences. Any Class B amateur could havelegally operated on h.f. etc., until anamending notice was hastily published onFebruary 26. The Home Office hasaccepted that the introduction of newpower restrictions and mode restrictionson 3.5 MHz and 432 MHz, etc., wereerrors and may revert to traditional powerregulations above 1 GHz at least while thequestion of "equivalent isotropic radiatedpower" is reconsidered further.

The world sceneNo firm announcement about the release,on a non-interference basis, of the 18 and24 MHz bands had been made at the timesthese notes were written. All three newbands, 10.1, 18 and 24 MHz, were re-leased to amateurs in South Africa on Jan-uary 18.American c.b. licences are reported tohave fallen from 16 million to about 10million during the past two years. There

are just over 400,000 amateur licences inthe USA. A recent survey indicates thatonly about one -in -eight instances of radio -frequency interference (r.f.i.) problemsfrom all types of transmitters (but basicallydue to inadequate electromagnetic compa-tibility in consumer electronic appliancesetc) are reported officially to FCC - aratio that is believed to be roughly compa-rable with similar interference problems inthe UK.A 16 -year -old instructor for the December1981 Radio Amateur's Examination -John Morris, GU6BG1, of the GuernseyAmateur Radio Society - coached six can-didates. Five passed both sections whilethe sixth passed one section. One whopassed, Tim Hodkinson, will have to waitfor his licence until his 14th birthday nextJune, when he is likely to become (at leastfor a time) the UK's youngest licensedamateur.

Here and thereFifty -years ago, during 1932, the internati-nal Madrid conference resulted in the firstclear recognition of amateur radio by de-fining in the international radio regulationswhat amateurs could and could not do.The Madrid conference was one of the lastof the international conferences in whichno major changes were made to the fre-quencies allocated to radio amateurs -although it was already clear that pressureon their frequencies from rival users wasmore intense in Europe than in NorthAmerica and only with difficulty was the

1.7 MHz" band retained in Europe. Atthat time the major ITU conferences wereheld every four years.

Detailed observations on and conclusionsabout the remarkable 5000 -mile 145 MHzEuro-Asia to Africa paths by transequato-rial ionospheric reflection during Solar Cy-cle 21 have been reported by RayCracknell, Z22JV in Zimbabwe, Fred An-derson, ZS6PW in Pretoria, and CostasFimerelis, SV1DH in Athens (QST, De-cember 1981). They show that high -den-sity, ionized zones exist 10 to 15 degreesnorth and south of the magnetic dip equa-tor capable at times of providing circuitsbetween stations up to 5000 miles apart atfrequencies up to 432 MHz. They believethat amateurs in suitable locations "have aunique opportunity to engage in pioneerresearch".

Amateur satellitesIvan James, G51J has described, in OscarNews No 36, a novel form of 145 MHzcrossed -delta loop aerial suitable foruplinks to amateur satellites in low orbits.The aerial is based on the principles of the

broadband, apex -fed, polygonal loop asdescribed by T. Sukiji and Tou (IEEETrans AP -28, No 4, July 1980). Thesystem provides some horizontal gain, re-quires no impedance transformer and canreadily be made from soft 8mm diametercopper tubing. It has been tested on Oscar9.

The six Russian amateur satellites, RS3 toRS8, launched last December have allbeen transmitting telemetry data but RS3and RS4 are not expected to be fully activ-ated until later in the year. The satellitesare in a nearly circular orbit about 1700 kmabove Earth (periods of about 118.5 toabout 119.8 minutes). As with other satel-lites in relatively low orbits it is provingdifficult to provide accurate predictions formore than a few days at a time. The Rus-sian transponders have uplink frequenciesin the band 145.86 to 146 MHz and downlinks 29.36 to 29.5 MHz.

In briefThe 10.1 MHz band has still not beenreleased to American amateurs and there isopposition from other users . . . A "dia-mond jubilee hamfest" to mark the settingup of the original "Lincoln & DistrictAmateur Wireless & Scientific Society" inFebruary 1921 is being organized by Lin-coln Short Wave Club (G5FZ, G6COL) atthe Lincolnshire Showground, 4-5 milesnorth of Lincoln on the A15, on SundayMay 9. The Club is aiming at a 5000 at-tendance, with trade and "bring and buy"stands plus family attractions . . . DerbyDale & District Amateur Radio Societyhas its 2nd mobile rally at Shelley HighSchool, June 20 . . . The Worcester Clubhas its annual radio rally on July 11 at theHigh School, Ombersley Road, Droitwich. . . The RSGB has forecast 80 trade standsat the 1982 National Amateur Radio Exhi-bition at the New Alexandra Pavilion,Alexandra Park, north London from April15-17 . . . Mobile rallies at Harrogate andBarry (May 23), Hull and Plymouth (May30), Elvaston Castle, MHS Mercury (June13) . . . With the legalization of c.b. radioit would seem that some of the formerusers of 27 MHz have moved elsewhere.Recent reports indicate that an illegalgroup of so-called "InternationalBreakers" have been active on about 6.6MHz, a frequency that was a "pirate -

haunt" several years ago . . . . The Mar-coni Group recently noted the 60th anni-versary of the 2MT Writtle broadcasts in1922 paying tribute to the efforts of theamateurs, grouped in wireless clubs,recognizing that it was their petitioning ofthe Post Master General that helped set offregular broadcasting in the UK.

PAT HAWKER, G3VA


MICROCONTROLLED

LIGHTING SYSTEMHardware for the input side of the lighting system - the control desk.

Modular construction is suggested to allow for variations in total system size

The input portion of the lighting system -the control desk - transforms the posi-tions of the numerous faders into data inthe processor memory. To maintainprocessing speed and hence the interactivenature of the system input and outputoperations are designed so that no proces-sor WAIT states are required. This is read-ily achievable in the output to the dimmersby ensuring that the access time to eachdimmer is less than 410 ns (the maximumdata bus access time permitted by theprocessor) and the use of a mapped -memory input technique was chosen.However, the analogue -to -digital conver-sion of the fader positions is inherentlyslow, and so some method of increasingtheir apparent conversion speed is re-quired. Three possible methods can beconsidered. Allocate a slow a -d converter to eachfader which continuously tracks the anal-ogue level of the fader and then the proces-sor addresses each converter in turn toobtain data. The large number of faders ina lighting desk means that this wouldprobably be a very expensive solution. Use an a -d converter which is fastenough to perform a conversion in themaximum access time of 410 ns. Thepractical conversion time must be muchshorter than this to allow for the multiplex-

, 100k toe

1

Cs -c7,:;7*

1

T

John D. H. White andNigel M. Allinson

ing of the faders and the sampling of theanalogue levels. The cost of high-speedconverters and multiplexers means thissolution is also expensive. Rather than set the conversion speed bythe processor requirements, set the speedby the desk operator's requirements. Forinstance, the maximum useable "responsetime" of the system should be about 20ms. Hence use a converter which is fastenough to perform all the conversions re-quired in this maximum response time.The faders can then be scanned by ananalogue multiplexer, converted to digitalcode and stored in a block of memorylocations. The processor is then able toaccess this block of memory. The majordifficulty with this method is the unambi-guous access to a block of memory by boththe processor and the converter.

The final method was chosen for use inthe control desk because of its lower cost.The fader units in this prototype systemwere designed on a modular basis. Eachmultiplexer connects one of 16 faders to a

The authors are at Keele University.

2k7

A

8

+15V

"r rout0

0 +V f

0 Vref

CD 4016

7406

4-15V

0 Analogue bus

20

71,154C

2 0 Counter '2bus it22

230OC

Fig. 11. Address decoding is performed by a 4 -bit code.

44

common analogue bus and the fadersaddressed via a 4 -to -16 line decoder by a 4 -bit digital address bus. One a -d converterwas allocated to each of these 16 fadermodules; however, the converter andsample -and -hold circuit used have a totalconversion time of 26 !is at a 500 kHzclock frequency so one converter canaccess over 600 faders within a responsetime of 20 ms.

The input circuits can be split into threeparts - an analogue multiplexer whichconnects the faders to the a -d converter,the converter itself and associated sample -and -hold and timing circuits, and theshared memory with access control logic.

Analogue multiplexer moduleThe fader connected to the common anal-ogue bus is determined by a four -bit code,and address decoding is performed by a 4 -to -16 line demultiplexer (74154), Fig. 11.Analogue switch control inputs are buf-fered by level -shifting inverters. Fader po-tentiometers are connected to a bipolarreference bus derived from the a -dconverter internal reference voltage, Fig.12.

As the lighting system scales the channelpresets by a master preset control, asmentioned in the first article, this requiresthe multiplication of stored data. For anyreasonable interaction time between faderposition and light output, softwaremultiplication by the processor is out ofthe question. As described in the finalarticle, fader levels are stored in log form;multiplication and division become simpleaddition and subtraction, and an anti -loglook -up table r.o.m. is used to provide thecorrect code for each output dimmer. Un-usually, log -law potentiometers are usedfor the faders.

The potentiometers can be considered asa voltage source with an internal im-pedance which varies with slider position.The highest internal impedance is (trackresistance)/4, that is 25 kfl in this case. Asthe output capacitance of each c.m.o.s.switch is about 5 pF, the worst -caseswitching time constant for 16 switches ona common analogue bus is 2µs. With asample time for the a -d conversion of 6µs,this gives a significant sampling error. Thesolution is to introduce a capacitor Cs tothe input side of each switch. The percent-age error in the final output voltage is100% x Co/(C's + Co) so for Co = 100 nFthe error is only 0.08%. The switchingtime constant is now about 25 ns; t is


+Vre0

+15V

9.134-

11 747

2

22p

10k

-Vref0 1 -1-27474

10k4k7

24k7 S

+5V

10

9

4- -15v

+15V --

010n1 p

Analogue0bus

+5V

'1/4 7400

LF398

7

10p

5

§ 3 k 9

470p

5

ZN427E -8

OE

EOC SC CK

11

12

13

14

007OO

15

16

17

18

240k

4 3

0O

DO

ADCdata bus

15V

0 Write request

1/4 7400

CLR PR

0-1D 1/2 7474

CK

PRa

'12 7474

aCK CLR

PR

0 1,2 7 474

CK CLR

CLR PR

1/2 7474

aCK

0Systemclock 620

Fig. 12. Control signals are generated bytwisted ring counter comprising two D -type flip-flops.

switch on -resistance x Co. However, thereis now a significant time constant asso-ciated with the potentiometer resistanceand Cs, but the worse -case value is 2.5 mswhich does not effect operation of thecontrol desk.

AD conversion and timingmoduleThe ZN427E 8 -bit converter of Fig. 12is clocked at 500 kHz, derived from theterminated processor system's 1 MHzclock (generated from the 3 MHzmicroprocessor clock in the Quarndon de-velopment system). The various controlsignals and associated sample -and -hold,are generated by a 2 -bit twisted ring coun-ter, comprised of two D -type flip-flops(7474). This type of counter was chosenfor its simplicity and that all states can bedetected by two -input NAND gates. Thefirst state of the sequence enables thesample -and -hold circuit, the second stateis used as a write request for the memoryaccess logic, and the final state is used toclock a third D -type flip-flop. The output

+5V100-9

7 P

ENT CK

LOAD 74161A

ENCIA 0)3 05 ap

K

114 13 12 11

0 0 00 C3

Counter bus

of this flip-flop is used as the start conver-sion pulse of the a -d converter. The end ofconversion signal (EOC) goes low, and isused to hold the counter in its reset state.The positive -going edge of EOC clocks a 4 -bit counter (74161A) used to address theshared block of memory and the analoguemultiplexer. The data outputs are always

147400

^ ^

enabled, by holding OE (pin 2) low. TheLF398 sample -and -hold circuit has morethan adequate specifications for 8 -bit ac-curacy at 6 us sample time.

The 2.55 V a -d converter referencevoltage is used to bias the fader potentiom-eters. To reduce processing time, fadercodes (positions) are first checked to deter-mine if they are zero (i.e. channel not inuse); only if they are non -zero will furtherprocessing be performed. Contact andend -resistance in the potentiometers givesa small d.c. offset, even when the channelis not being used. Hence a bipolar voltagereference is supplied to the faders to give asmall "deadband", for which the outputcode is zero. These references are obtainedby buffering and inverting the converterreference voltage by a 747 dual op -amp.

Shared memory and access controlThe memory can be accessed by either themicroprocessor or the a -d converter, andhence the data and address buses must bemultiplexed between the microprocessorand converter. It differs from conventionaldirect memory access techniques in thatthe converter and processor have separatebuses and operate independently, Fig. 13.

The shared memory consists of twoAM27S07 (16 -word x 4 -bit Schottkyr.a.m.), and as these devices have separatedata inputs and outputs and the a -dconverter only writes to this memory whilethe processor -only reads from it, no databus multiplexing is required. Data outputsare tri-state which allows direct connectionto the processor data bus. Address busmultiplexing is performed by two 74125tri-state buffers; the appropriate one isenabled for read or write operations. Forlarge systems standard 250 ns memorychips may be used instead of theAM27S07's, but they will require addi-tional data bus multiplexing.

The eight high -order bits of the proces-sor address bus are compared with a bitpattern set by eight wire links to determinethe page location in the memory map ofthe input data addresses, Fig. 14. This isachieved in the same manner as the outputaddressing decoding described in Part 1.When the processor needs to read from theshared memory, a read request signal isgenerated before the system enable signalE goes low, achieved by AND-ing theaddress decoder output, M/I0 and W/Rsignals. The output is latched by the 8085

P

System clock l 1t11 -1z

ADC clock

Start conversion

End of conversion

Sample enable

Write request

WIRELESS WORLD MAY 1982 as

1,4,10,13

C 4 11 13 A 1/4 740 0

Addressbus

A30 2

O

O

00

C30

Counter 0bus 0 - 5

[00 2

9

5

12

74125

A

Y

8 14

6 15

3 1

9

74125

4Y

Y

11

12

10

6

A

3

9

0 D7

0O

Am 27507

WE CS

3 2

I-113

data bus

1/4 7400

5 7400

8

6

4

15

1, 4 ,10, 13

12

10

6

A

WE CS

3

3

03

°O

Am27507

DO

11

9

7

14 7414

0 D3

-0data bus

14. 7400

Fig.13. Memory access method differs fromconventional d.m.a. technique in that a -dconverter and processor have separatebuses.

address latch enable signal ALE to ensurethat the read request signal is low before Egoes low. Timing diagram: Fig. 15. Theread request signal enables the appropriateaddress buffer and sets the memory to readmode.

1

0 000 0 0 (2))D7 Do

ADC data bus

The absence of a read request signal setsthe memory to write mode and enables thea -d converter address buffer. A write re-quest signal from the converter timingcontrol enables the memory and data isclocked into the memory by the system

+5V

K 1k

Highorder

addressbus

- A150

O

O

14

11

9

A110

Bo

6

A -B

7485

A

A>I3 A.B Ac6

15

13

12

10

4

5

3

6

2

7

O 14

0 11

A 0

A>13 A.B A<B13 A3

7485

Bo AC

A<B A)13 A=B

15

13

12

10

2 14 13

.sy 999994000000000

IFig. 14. Eight high -order bits of address busare compared with bit pattern set by eightwire links to determine page location inmemory map.

M/100

W/RO

ri4 ALE0

1/17410

1/3 7410

CK

1/27474

READ

REQUEST

3 7410

0

1/47414

1/67414

WRITE0REQUEST

620

o20

READ

REQUEST

enable, E. The duration of the write re-quest is long enough to ensure that anydata is always stored in the memory. Sincethe processor controls access to thememory at all times, no conflict of simul-taneous access requests occur.

Continued

The authors ask us to point out that ElandE2 in Fig. 9 should be inverted, for whichthe two spare 7400 gates may be used.

CK

A8-A15 X High order address valid

AO - X Low order address valid

ALE

W/R

M / 10

DO - D7

I

READ

REQUEST

Fig. 15. READ REQUEST enables theappropriate address buffer and setsmemory to read mode.


16 -CHANNEL DATAACQUISITION SYSTEM

The article concludes with a continuation of the circuit description, its operation and asample program for scanning through sixteen channels.

Figure 8 is the timing diagram for thelistening sequence. On power -up, theReset line is brought low forapproximately 150 ms via R3 and C2 toreset the address latch IC7 and the address -enable flip-flop IC5.

To select a channel and start an a -to -dconversion, the Basic statement below isexecuted:PRINT # DN, "an"where DN is the device number (0-30)

* is the ASCII character "*"n is the ASCII equivalent of therequired channel "0" to "F".

When the system receives a device number(DN) corresponding to that selected on theaddress switches (S5 - S1 in Fig. 7), the%LS488 will initiate a timing sequence, asshown in Fig. 8 (not to scale). The r.o.m.(IC6) decodes ASCII information to binarydata, its contents being outlined in Table1. Four outputs of the r.o.m. give thebinary data obtained by converting ASCII"0" - "F" to binary 0000 - 1111 andadditional outputs are used to detect a "a"character and a carriage return (CR) -data outputs 06 and 05 are used for thispurpose.

When the first "*" character is sent (2 inFig. 8) the * line goes low (3) and theRXST and RXRDY are pulsed (4) and (5)in accordance with Fig. 5. As the data isremoved (6), * detect goes high and setsthe address enable FF - Q* goes high (8).The next data byte is presented (9),representing one of 16 address channels,and as RXST goes high (10), CLK goeshigh (11) and latches the address latch(12). RXST and CLK than go low (13) and(14), and data is removed (15).

A Carriage Return is now presented atthe data bus (16) and the CR detect (or GOsignal) goes low (17), and starts conversionin the AD7555 (to be discussed later). Thissignal also resets the address enable F -F(18), while RXST pulses (19) and (20),CRD is removed (21) and GO is returnedhigh.

The result of all this activity is that oneof 16 channels is enabled in the AD7506(16 channel multipleker) and a conversioncycle of the appropriate channel is started.

Talking sequence(conversion cycle)The AD7555 is a 41/2/51/2 -digit a -to -dconversion subsystem. A free -runningclock (DMC) strobes out the b.c.d. datafrom the AD7555 in a 4 -bit -wide bus. In

* Analog Devices, Limerick, Ireland

by Pat Hickey*

this application, the DMC signal iscontrolled by the 96LS488 handshakesignals to transmit the information to theGPIB. Each b.c.d. data byte is signalled bya digit line which goes low when that byteis being outputted, DO going low for themost significant digit (sign and first digit),DI for the next significant digit, etc., andD5 for the least -significant digit. In thisapplication, D5 going low is used to send acarriage return code on the IEEE -488 bus.Although this loses one digit of resolution,it considerably eases the interfacecircuitry.

Figure 9 highlights the conversiontiming sequence. Upon receipt of a GOsignal (2) (from the listening sequence inFig. 8) HOLD goes high (3) whichinstructs the AD7555 to start conversion:the free -running DMC clock is also

enabled (4). Upon comparator crossing atthe end of phase 0, (the beginning of thequad -slope a -to -d conversion procedure)SCC goes low (5), enabling the 1.024MHzclock to pin 12.

At the end of the conversion, SCCreturns high (6) and on the next DMCrising edge (7), DAV goes high andremains high for two DMC pulses (9):during this period, the internal buffers areupdated with the latest data. After this,DAV returns low (10) and brings HOLDLow (11). This is known as the masterreset and disables the free -flowing DMCclock. From this point control of DMC istaken over by the TXST handshake duringread -back.

At this stage, the data presented by theAD7555 is the most significant digit;TXRDY is high, indicating that data isready; and SRQ has been brought low (12)telling the controller that a conversion hasbeen completed and the new data is ready.

Fig. 8. Timing diagram for the listening sequence.

RESET

RXRDY

RXST

of

G0

Data

* Detect

ELK

A3 -AO

0 0

011110_011111=0111111=6,

Address 0

Fig. 9. Conversion cycle timing sequence.

WEFT

GO

HOLD

DMC

SCC

DAV

SRQ

Address n

tt

_II C2

tz


PARTS LIST 4 150 (5%) 1

Integrated circuits 6-20 10k (5%) 15

1, 2 MC3441 21 lk (5%) 1

3 96LS488 23 10M (1%) 1

4 74C08 24 5.1k(1%) 1

5, 10 74C74 25 6.8k (1%) 1

6 6331 26, 29, 30 10k(1%) 3

7 74C175 27 1M (1%) 1

8 74C04 28 20k (1%) 1

9 AD755511, 23, 24 74C157 Potentiometers12 74C30 Rp1 500 multiturn 1

13 74CO2 Rp2 200 multiturn 1

14 AD750615 74C901 Capacitors16 7493 1, 4, 6, 11 0.0111 4

17 LM399 2 0.47µ 1

18 AD517 3 150p 1

19,21 AD301 5 1011 1

20 AD542 7 0.211 1

22 74C10 (polystyrene)25 74C14 8, 10 33p 2

9 0.1n. 1

Diodes1-4 led 4 Miscellaneous5 1N914 1 Xi 4.096MHz 1

6 4.7V 1 Si -S5,1,2, 5,22 470 (5%) 4 S6 -S9 d.i.l. switch 23 39k (5%) 1

Readback cycleData is transferred to the controller via theinput instruction INPUT # DN, R$,where DN is the device number, and R$ isan ASCII string. When this statement isexecuted, the 96LS488 checks thatTXRDY is high (indicating that the firstcharacter is ready). It takes the byte andbrings TXST in Fig. 10 high (1) to showthat it has received the data. This clocksDMC high (2), which brings DO back highand loads the next data byte (4), and bringsTXRDY low (5), acknowledging that thelast byte has been received. TXST goeslow (6), completing the sequence. Thisclocks DMC low (7) which brings D1 low(8). TXRDY goes high (9) indicating thatthe second data byte is ready.

TXST

TXRDY

DMC

DO

SRQ

Data

48

The sequence is repeated for D1, D2,D3 and D4 (10)-(23). TXRDY goes low(23), acknowledging that D4 has beenreceived, and TXST goes low (24) tocomplete the handshake. This clocksDMC low (25) and brings D5 low (26).The output from the AD7555 is D5 at thisstage (the last and unused digit of the 51/2digits). However, a carriage return istransmitted to the controller instead,indicating the end of the string, via thedata selector (IC11). As D5 goes low, acarriage return (ASCII 13) is presented tothe %LS988 (27) and TXRDY goes high(28), indicating that it has a byte (CR) tosend. D5 going low also resets the SRQ

Fig. 10. Timing of the readback sequence.

flag (29). The CR is loaded during therising edge of TXST (30) and the usualhandshake follows.

The data string received by thecontroller is a 5 character string encoding a41/2 digit word. The first character is anencoded version of the sign and mostsignificant digit as outlined in the table.

The program shows a simple method ofconverting the input string R$ to a numberR. A positive or negative over -range(caused by a voltage greater than ± 1.999volts) is transmitted as "0<<<<" and"2<<<<" respectively.INPUT # 27, R$IF R$ = "0««" THEN PRINT"+ VE OVERRANGE" : ENDIF R$ = "2««" THEN PRINT"-VE OVERRANGE" : ENDX$ = LEFT $ (R$, 1)IF X$ = "0" THEN X$ = "+ 1."IF X$ = "2" THEN X$ = "-1."IF X$ = "<" THEN X$ = "+0."IF X$ = "7" THEN X$ = "-0".R$ = X$ + RIGHT $ (R$, 4)R = VAL (R$)PRINT "READING = ";R; "VOLTS"END.

Service request and status byteBit 6 of the status byte, shown in Fig. 11,contains the service request bit (needed inthe case of a serial poll), high when aservice is requested. The rest of the statusbyte contains information as to why aservice was requested. (In this case there isonly one reason, an end of conversioncaused by Bit 4 high.) The four l.s.bscontain the address of the last selectedchannel. The status byte is read during aserial poll and handshaking is performedby STRDY and STST similar to Fig. 5.

System performanceAs discussed, the a -to -d converter isoperated as a 51/2 -digit system, but only41/2 digits are used. The a -to -d conversiontime varies from 1.3 seconds for full-scalenegative input, to 1.7 seconds for full-scale

36

12

17

11

51

51

21

0

DO D2 04 DO


7 6 5 1. 3 2 1 0 -4-Bit number

Address of the lastselected channel

0 Converter is busy

, Converter has1 finished converting0 No service request

1 Service requested

Fig. 11. Service request and data byte.

positive input. The conversion time can bereduced by a factor of ten by operating thea -to -d converter in the 41/2 digit mode.Some minor changes in circuit values andpin -straps are necessary.- Change R27 to 3601(11 and C7 to

0.22µF.- Disconnect wire from pin 22 of IC9 to

pin 1 (ICI') and pins 2, 5, (IC24).- Connect wire from pin 23 (IC9) to pin 1

(ICI i) and pins, 2, 5, (IC24).- Disconnect pin 8 (IC9) from +5V and

connect to GND.In the 41/2 digit a -to -d conversion modeonly 31/2 digits of information aretransmitted on the bus.

The a -to -d converter handles input sig-nals in the range ± 1.9999 volts. Resolu-tion is 10011V and accuracy of the proto-type wire -wrap system was ±200µV. Theconverter exhibits no flicker or offset. Ac-curacy would be improved by using aprinted -circuit board and by paying moreattention to leakage paths through i.c.sockets, etc: it is also recommended that

Sign and most Output ofsignificant digit AD7555

nput tocontroller

ASCIIequivalent

+1 0000 00110000 0-1 001 0 00110010 2+0 1100 00111100-0 0111 00110111 7

the operational amplifiers and reference(IC17-IC21) be kept as close to the AD7555as possible, and as far as possible from thedigital circuitry. The AD7555 data sheetgives information on appropriate p.c.b.layout. Calibration procedure:- Adjust RP1 until pin 1 (IC9) is at

+4.096V.

10 REM***PROGRAM FOP SCANNING THROUGH20 REM+++USING 'COMMODORE PET-.***20 REM***PAT HICKEY***40 REM+++19 OCT 19810+50 PEM100110120130140150160170180190200210 PRINT:PRINT220 GOT01301000 REM+++LOOR FOR1010 I=FEEK59426)1020 I=PEEK(59427)1030 L=I AND I2a1040 IFLC,128THEN10201050 PEMO+READ STATUS EYTE+++1060 AD=103:PEMOtAD=SERIAL POLL

REMO+MAINLINE PROGRAM***OFEN15,15PRINT"n"FORX=07015C..,IFO9THENC=C+7Cl."+"+CHRt(C+48)PRINT#15A:4GOSUD1000GOSUE2000PRINT"CHANNEL"CH:"NE4TX

- Adjust RP2 until pin 2 (IC20) is at+ 2 .0480V.

Correction. Four errors occurred in Fig. 7of the April part of the article: diode D4should go to +5V, instead of ground; ICiiis a 74C157; IC2 on pin 42 of IC3 should beC3. It is not clear on the drawing that R15 -

R20 go to +5V.

Two programs, for Commodore Pet and Fluke1720A, to scan 16 channels.

16 REM***PROGRAM FOR SCANNING THROUGH 16 CHANNELS***20 REM***USING'FLUKE 1720A CONTROLLER '+++SO REM*OPAT HICKEY***40 REM*4419 OCT 19810*50 REM100 TERM CHR4,(13%) !TERMINATION CHARACTER IS CR110 FOR=0% TO 157. ! SCAN 15 CHANNELS120 C:7=!:130 IFC%>9%THENC7:=C7:+7% !CHANNEL IIUMBEP IN HEX140 Cl=wV+CHR3(0:+48) !"0" TO "F"150 PRINTIM51,C1 !SELECT CHANNEL160 WAIT FOP SF0170 INPUT@16,Pt !READ REPLY180 REM+OPPOCESS REPLY***190 X4,=LEFTt(PT.1%)200 Y4-.FIGHT$(Pt,4%)210 P.T="OVEPPANGE"220 IFY17="THEN280 !OVER:RANGE230 IRA-.="0"THEM240 IFX$="2"THEN it=" -1."250 IPA'=""THEN ::l="+0."250 IFX-1."7"THEN Xt="-0."270 Rt=l+Y1+" VOLTS"280 CH%=SPL(16%) AND 15% !DEVICE 15 STATUS BYTE290 PRINT"CHANNEL"CH%;":- RS300 NEXTX%310 PRINT320 0070110

READY.

16 CHANNELS.***

- ";RC" VOLTS"

SERVICE REQUEST***

ENABLE ( SPE

1070 GOSUF12001080 GE T *15 , St : REM++ST=STATUS BYTE1090 AD=102 REM**AD=SER I AL POLL DISAELE(SPD)1100 GOSUD12001110 CH=ASCAS$)AND151120 RETURN1200 REM*4+SEND ADDRESS,TOMMAND1210 POKE534560 :REM++ATN LOW1220 FOrE59425AD:REM++SEND COMMAND1220 FGKE59427,52,REM**DAV LOW1240 POKE53427,50:REM**DAV HIGH1250 PCUE59455.4 :REMOATN HIGH1260 RETURN2000 REM***READ DATA FROM BUS***2010 INPUT#15,Pt2020 X$=LEFTS(R$.1)2030 YS=RIGHT$(RS,4)2040 IFX4"="0"THENXW+1."2050 IFX$="2"THENX$="-1."2060 IF4,="<"THENX4"="+0."2070 IFX$="7"THENX4,="-0."

2080 P$=X-.1,+Y$2090 IFY$="<<(<"THENRS="OVEPPANGE"2100 RETURN

READY.

TO OP I B BUS***

Elements of Microprogramming, by D. K.Banerji and J. Raymond. 434 pages, hardback.Prentice -Hall, £18.70.The advantages of microprogramming overhard -wired control logic systems are describedfrom a historical viewpoint prior to a thoroughtreatment of the theory, practice andapplication. A microinstruction is at a lowerlevel than a machine -code instruction; an Add,for example, requires four microinstructions.Microprogrammed control possesses theadvantages of flexibility and economy and thepossibility of changing the instruction set orarchitecture of a computer by altering themicroprogram.

Digital Control Using Microprocessors, by P.Katz. 293 pages, hardback. Prentice -Hall,£16.95.Differences in emphasis between digitalprocessing of signals and the digital control ofprocesses are stressed in this book, which is at asuitable level for final -year degree students andengineers who are already familiar withanalogue control. Sample 8085 programs areincluded.Computers and the Radio Amateur, by P.Anderson. 208 pages, hardback. Prentice -Hall,£14.20.A thorough and well presented introduction tocomputers in amateur radio. Presents a veryreadable explanation of Basic and assembly -level programming, and goes on to describeinterfacing to amateur equipment and to detailelectronic keying and Morse reading.

World's Radio Broadcasting Stations, by C. J.Both. 214 pages, paperback. Newnes TechnicalBooks, £5.50.European f.m. radio and television transmittersare included in this comprehensive listing ofstations. The book, first published in Holland,presents the relevant information to enable alistener to identify or locate stations in the long,medium and short wavebands, giving frequencyand wavelength, power, co-ordinates of thetransmitters and their place names. In the caseof television and f.m. radio, there are columnsto indicate channel number, aerial polarizationand whether the station transmits in stereo. Anumber of appendices list the addresses ofbroadcasting stations and DX clubs and there isa five -language glossary, a frequency/wavelength conversion table and a table givingthe characteristics of tv transmitters.


Waveform synthesizerHere, an X/Y matrix is used to plot a givenwaveform. The waveform to be synthe-sized is divided into a number of timedomains and the voltage at the end of eachdomain is set on a diode -chain potentiome-ter. If the length of the time domain is lessthan half the period of the maximum fre-quency present in the waveform and thenumber of discrete levels is large, accuratereproduction of the original can beachieved. This circuit lends itself to com-puter control and expansion.

By varying the 555 -clock frequency, theoutput waveform frequency may be ad-justed proportionally. A 7493 counterconverts the clock signal into 4 -bit binaryto drive a 4 -to -16 -line decoder, which inturn drives 16 output transistors throught.t.l. buffers. Each transistor output is fedto a common point through a resistor. Forcertain waveforms, an integrating capaci-tor may be connected accross the output tofilter out steps and switching pulses.P. D. SomervilleCrawleySussex

NiCd battery protectionEssentially a fold -back current limiter witha low -voltage detection capability, this cir-cuit draws less than 300 µA and drops lessthan 0.35V on full transmit load.

The low loss on load, important in manybattery applications, is due to the use ofgermanium as the control element. Onlyone control transistor is shown in the sim-plified diagram although two in parallel areused. The germanium control transistorTr1 is held on by a silicon transistor, Tr2,whose base current flows through zener D1and R1. With a 12V battery D1 is 9.1V. Inthe event of an overload or short circuit thep.d. across Tr1 rises and on reaching 0.6Vis detected by silicon transistor Tr3 withemitter -base connected across the emitter -collector of the germanium control tran-sistor. Tr3 turns on, raising the junction ofD1 and R1 to battery voltage. This actionturns off Tr1,2 and they remain off whileany load is connected.

A similar action occurs if the voltage onor off load falls below 1V/cell, i.e. below10y. In this case the battery voltage fails tosupport a current through Tr2 (requiring0.6V) and D1 (requiring 9.1V) and Tr1starts to turn off, initiating the same fold -back action. C1 is included to damp thefold -back loop. A low -value resistor R2 isused to control thermal run -away of Tr1.J. B. H. SteadSalisburyZimbabwe

50

+5V

3k3

5k

470

6

114 12 11 9 18

B C D

SN7493

5106

TlOn

All 7404

ti

LM555

J1 L.3

24 23122 21 20 19 18

SN74154

2 3 5

F-1flAll 6k8

Output

All 3k9

waveform

+15V

0

0+


Input o

Line

FirstmonostableSecondmonostable

AND out

Latch

Firstmonostable

ECL inverter

Secondmonostable

ECL AND /Latch I 14 o+Sv

1

Reset

IL

Glitch detectorUsing two fast monostable multivibrators,such as e.c.l. MC10198's, it is possible todetect extremely short glitches. These de-vices provide a very short pulse, but al-though the pulse is short, it is at least twiceas long as anticipated glitches. As thetiming diagram shows, normal pulses arerejected using an AND gate.D. VialettoCastellanzaItaly

Wideband f.m.demodulatorOperation of the demodulator relies on thelinear relationship between power con-sumption (IDD where VDD is fixed) andoperating frequency of c.m.o.s. logic cir-cuits. A 4013B D -type flop -flop is usedbecause the internal clock elements have ahigh clock rate capability which extendsbeyond the normal range of usage. Mea-surements indicate that the demodulatorwill work satisfactorily from d.c. up to andbeyond 20MHz.

The flip-flop is clocked by logic leveltransitions and the resultant current flowconverted to an output voltage by the cur-rent mirror and output components. The

current mirror ensures a minimal interac-tion between supply voltage and current inthe flip-flop - a higher performance mir-ror could be constructed using spare de-vices in the 3046 array if required.

The resistor is chosen to suit the maxi-mum input frequency (the output canswing the full supply voltage, limited onlybe quiescent device consumption and Vcesaturation) and the capacitor provides low-pass filtering to remove input frequencynoise. Values shown have been used in a10.7 MHz f.m demodulator prior to"birdy" filtering and stereo decoding.G. C. HammondWhitestoneNuneaton

+12V

Variable S R Vss Demodulatedfrequency signal 0-12Vinput(0-20MHzI

Constant -current supplyThis circuit is extremely simple, uses nospecial components, yet has a very widerange of output currents, 2µA to 100 mAin six ranges. The only limitation to outputis component ratings. It also has a per-formance that is comparable to more ex-pensive equipment.

Tr', Tr2 and ICI comprise a constant -voltage supply that can be varied from 0 to100 V by varying Vf.i. When testing thissection, no change in the output voltagecould be detected on both analogue and31/2 -digit voltmeters with change of supplyvoltage from 150 V to 250 V and withsudden application of a 100 mA load.

Tr3 and IC2 comprise the constant -cur-rent section, R, is the current sensing re-sistor. By choosing the appropriate valueof It, or switching different values, therequired current range is obtained.

The voltage drop across &which equalsVref.2 was chosen to be about 0.7V so thatthe error in voltage measurement will notexceed this value plus the drop in the am-

meter circuit, a total of less than 1V. Amulti -turn potentiometer to obtain Vf.2enabled accurate current adjustment.

Capacitors C1 and C2 suppress oscilla-tions that would otherwise occur; Di andD2 protect Tr2 and Tr3 from possible nega-tive voltages that may occur due toswitching transients. Switching It, during

160V

24k2W

Tr1

operation proved to be of no harm, but IC2may need some extra protection if in-termittent loading with outputs greaterthan 30V is used frequently (a diode be-tween pins 3 and 7 might help. Ed).Hussein A. EassaCairo UniversityEgypt R6

TIP662

BF299

Tr2

3N 3

62k

+15V

ICI7

741

4

0111N914

0 ()Out

+15V

IC2BF299

'12k2W

R56

742

V 1

2 V ref .23R3ref

4

R4 330 C2 0211N914_15v

3)113

Rc


DIGITAL FILTER DESIGNIn the next few years digital filters will be increasingly used in place of their analogue

counterparts, not only on account of their accuracy and versatility but also their rapidlydeclining cost. Authors Cheetham and Hughes introduce the basic theory in this article,

give design techniques for a useful class of filters in the next, and describe theirimplementation by special-purpose microprocessor in a third article.

The conversion of an analogue signal intodigital form requires a process of samplingat successive points in time separated byequal intervals, say T. Each sample is thenconverted to a binary number proportionalto the sampled voltage. The samplingprocess requires that the analogue signalbe bandlimited to below the Nyquist fre-quency 1/2fs, where Ar-----1/T. This may beachieved to an acceptable accuracy by low-pass filtering the analogue signal beforesampling. Failure to do this will result infrequency components above the Nyquistfrequency being folded back into the rangebelow 1/2f causing a form of distortionknown as aliasing.

Further distortion is introduced by theprocess of representing each sample by afinite wordlength or number of bits; thetrue voltage must be truncated or roundedto one of the discrete levels which corre-spond to a permissible binary number. Thenoise introduced by this quantization errormay be reduced to acceptable levels bya judicious choice of wordlength andsampling rate.

The discrete -time signal produced bysampling an analogue signal is defined tobe an infinite sequence of numbers eachcorresponding to a sampling point at timet=nT for - <n.< oc. Such a sequence isalways referred to by its value at t=nT.Thus the sequence {x(n)} is defined as

{. . . x( - 2),x( - 1), x(0), x(1), x(2), . . .1

with element x(n) occuring at t=nT. Bythis definition, {x(n-k)} denotes the se-quence whose value at t=nT, is x(n -k).Hence k>0, {x(n-k)} is a delayed ver-sion of {x(k)} where each element isshifted k places to the right and is thusdelayed by k sampling intervals. It is oftenassumed, and arranged in practice, thatelements of a discrete -time signal are zerofor n<0, but this would not always be thecase. A discrete -time signal becomes adigital signal when its elements are repre-sented by fixed-wordlength binarynumbers. Not all signals encountered inthe study of digital filters originate as anal-ogue signals. Many digital signals, such asthe discrete time impulse {o(n)} illus-trated, are readily generated in digital formbut would be unlikely to occur in thatprecise form as sampled analogue signals.Further, a perfectly rectangular digitalsquare wave is not necessarily the sampledversion of a bandlimited analogue squarewave.

Conversion from a digital to an analoguesignal involves reconstituting the sampled

by B. M. G. Cheethamand P. Hughes*

The importance of digital filters asdevices for processing digitized sig-nals is rapidly increasing now with theintroduction of special-purposemicroprocessors and integrated cir-cuits specifically designed for signalprocessing. Using the numericalprocessing power of such circuits,digital filters are able to performoperations corresponding to those ofanalogue filters. For example, the In-tel 2920 analogue signal processorwith its analogue/digital convertersacts as a one -chip replacement for ananalogue filter.

In addition to their uses in emulat:mg the frequency responses of estab-lished forms of analogue filters, digi-tal filters have a wide range of otherapplications which take advantage ofthe much greater power and flexibilityof numerical processing as comparedwith analogue methods, and the filtermay not easily be described as havinga particular type of frequency res-ponse. Digital filter inputs need notoriginate from analogue sources, andnumerically generated signals are en-countered in many applications. Indeveloping the basic theory of digitalfilters, therefore, it is best to considerthem as general devices for processingsequencies of numerical data ratherthan as digital realisations of analoguefilters. But before doing this, this arti-cle briefly considers the samplingprocess often used to produce digitalsignals and introduces notation forrepresenting such signals.

voltage levels as electrical pulses at thesampling instants, and low-pass filtering toremove frequencies at and above the Ny-quist limit. In practice, the sampling rateemployed for analogue to digital conver-sion is normally considerably greater thantwice the highest frequency of interest toensure that the analogue low-pass filtersrequired may be relatively simple andinexpensive.

A digital signal may be subjected tonumerical operations such as addition,subtraction and multiplication by passingthe sequence of numbers (referred to assamples) throujh some form of digital

*P. M. Hughes B.Eng. and B. M. G. CheethamPh.D., M.I.E.E. are lecturers at the Universityof Liverpool.

processing system. Such a system could bea program implemented on a main-framescientific research computer normallyused to process blocks of stored digitalsignal samples for analysis some time later.Alternatively, the system may be a piece ofspecial-purpose hardware consisting ofsome digital integrated circuits and/or amicroprocessor. With such a dedicatedhardware system the processing may becarried out in real time so that an outputsignal is generated as an uninterruptedstream of samples with at most a smallfixed delay between each input sample andits corresponding output sample. In thiscase the digital system, with associatedanalogue to digital converters, may act as adirect replacement for an analogue systemsuch as a filter or a modulator.

Digital processing systems can be de-signed to carry out a very wide range ofoperations on digital signals. A digitalfilter is a processing system which gener-ates the output sequence {y(n)} from aninput sequence {x(n)}

M Ny(n)= E a,x(n-i) -E biy(n -j) (1)

i=0 j=1at time nT for - co<n< cc . This is a dif-ference equation of order M or N,whichever is the larger. When N>0 thefilter is said to be recursive as previousoutput samples are used in the calculationof the present output sample. Coefficientsao, al, . . . am and bt, b2, . . . 6N are fixed(time invariant) multiplication constantswhich characterize the effect of the filter.The design of a useful digital filter requiresthe selection of these constants using de-sign techniques corresponding to thoseadopted for calculating component valuesin analogue filters, and an example for aclass of digital filters is given in a subse-quent article. As a simple example, con-sider the digital filter defined by the first -order difference equation

y(n) = x(n) + by(n - 1) (2)

where b is a constant. This filter is shownin diagrammatic form in Fig. 1, illustrat-

Adderx(n) yln)

Fig. 1. First -order digital filter appliesnumerical operations to the sampled inputsignal x(n) to produce an output y(n).


Stnl

a art am as am am saw mew am. mom .me, an ..../e.

0 T TIME

Fig. 2. The discrete -time impulse 8(n) isdefined only at sampling points t=nT,

J 0, t= nT,' 1, t=0

ing the three basic operations required forany digital filter: addition, multiplicationby constants and delay. Make the inputsequence {x(n)} equal to the discrete -timeimpulse sequence {8(n)) of Fig. 2, with

1, n=0b(n)= {0, n*0

The output from this simple filter may becalculated by hand. Assumingy(- 1) to bezero, then

y(0) = x(0) + by( -1) = 1

Following on from this

y(1) = x(1) + by(0) = by(2) = x(2) + by(1) = b2, and so on.

Hence the output will be the real exponen-tial sequence:

{y(n)} = {. . 0, b, b2, . . b', . . .} (3)

illustrated below in Fig. 3 for b=0.7. Ifbl> 1 , the sequence {y(n} would

increase without limit and the digital filterwould then be said to be unstable. A stablefilter is one which produces a boundedoutput sequence, i.e. a sequence whoseelements do not increase without limit as nincreases or decreases (looking backwardsin time) for any bounded input sequence.As the input signal in the example above isthe discrete -time impulse (8(n)) the out-put obtained is termed the impulse res-ponse of the filter. If the input had been{8(n-k)}, a delayed version of thediscrete -time impulse, the output wouldhave been (y(n-k)) a similarly delayedversion of {y(n)}.

Assuming the impulse response of a gen-eral filter, as given by equation 1, to bethe sequence {h(n)}, consider its responseto an arbitrary input sequence {x(n)}.Such a sequence may be expressed as theweighted sum of delayed unit impulses

oo

{x(n)} ={ E x(k) . 8(n-k)} (4)k=-00

If only bounded input and output sequ-ences are allowed, it may be shown that thedigital filter defined by equation 1 islinear in the sense that if input sequences{xi (n)} and {x2(n} produce outputs{yi(n)} and {y2(n)} respectively, the res-ponse to (Xxi(n)-Fux2(n1 will be {Xyl(n)-11Y2(n)) for any values of X and u. Byextending this property to the infinite sumof scaled impulses as given by (4) one de-duces that the response to {x(n)} is

co

{y(n)} ={ E x(k) . h(n-k))k=-co

The right hand side is the convolution of{x(n)} with {h(n)} , often denoted by{x(n)} * {h(n)}. By a simple change ofvariable it may be shown that an entirelyequivalent expression is

{y(n)} {h(n)} *{x(n)}

00

E h(k).rn-k)}k= - 00

The impulse response of a filter thereforeprovides a complete characterization of itsbehaviour, allowing the response to anyinput sequence to be deduced from thesetwo equations.

Alternative characterizationAn alternative method of characterizing adigital filter is to specify its effect on sinu-soidal input signals over a range of fre-quencies. A fundamental property of fixedlinear systems in that their steady-stateresponse to a sinusoidal input is a sinusoi-dal output of identical frequency but mod-ified amplitude and phase. Define a sinu-soidal sequence of radian frequency w tobe the sampled version of a sinusoidalfunction of time, with frequencyF=w121tT; for example (A cos (con)).The response of a filter with impulse res-ponse {h(n)} to this sequence as inputmay be readily calculated by first consid-ering the theoretical response to the com-plex -valued exponential sequence {el.},where j= VI -1. The response is an outputsequence:

00

{y(n)} = E h(k)e."("-k)}k= -

co

= {el" E h(k)e--"k}k=-00

= {e lw"H(e

where H(e")= E h(k)e-Iwk (5)k= -co

The function H(ej.) is defined as the fre-quency response of the digital filter and isa complex number for any value of w(subject to the convergence of the series inequation 5; by the definition of stability

AM,* INN OM

yIn)

iiTIME

Fig. 3. Output sequence obtained by feed-ing 8(n) in Fig. 2 into the digital filter shownin Fig. 1 with b=0.7 is the real exponentialsequence y(n)=0.7" for n>0.

given earlier, convergence is assured for astable filter).

The response to cos (con)} is a

sequence {y(n)} with

y(n)= 1/2A (H(ei )e""+H(e-'we-"")

Denoting by 4)(w) the argument of H(e")and noting that since all values of h(k) inequation 3 are real, Vicenl=11/(e--")1 andthe argument of H(e-")= -4)(w):

y(n)=1/2A I H(e) Ix

(e i(wn+cl:(w))+e-j(eion+ 4)(w)))

=A H(e") cos(con+.0(w))

Hence the modulus and argument of thecomplex -valued frequency response H(e")give the gain and phase shift of the filteroutput relative to a sinusoidal input ofradian frequency co. Bearing in mind that

n

jw(n-k)tho

-it

it may be deduced from equation 3 that

f 2Jt if n=ktO if

1

h(n)=2n H(eiw)eiwndw for -co <n< co

- (6)

The transformation from the sequence{h(n)} to the complex function H(e") ofw defined by equation 5 is a Fouriertransform; the reverse process given byequation 6 is an inverse Fourier transform.

As an illustration of frequency response,consider again the simple digital filter de-fined by equation 2. By equations 3 & 5

00

H(e")= E bke-"kk=0

which may be summed for lb <1 as a geo-metric series, giving

H(e /w)= (1 -be-iw)-1 (7)

Evaluating this expression for b=0.7 gives

H(e") = (1.49 -1.4cosw)- 1/2

and ii)(0))= tan -1( 0.7sinw0.7cosui - 1)

Frequency response graphs of gain,11-1(en , and phase 4)(w) over radian fre-quencies 0 to it, corresponding to analoguefrequencies from zero to the Nyquist, areshown in Fig. 4(a) and (b).

z -transformsAnalysis and design of digital filters isgreatly simplified by the use of the z -transform which is analogous to theLaplace transform for analogue filters.


3

-0, 2

z 02a 04ce

.-R -06is

-08

rz

111111/%1111

0

w

Fig. 4. Frequency response of a digitalfilter (in this case Fig. 1 with b=0.7) charac-terizes its response to sampled sinusoidalinputs of the form Acoswn. Amplituderesponse at top, phase response bottom.

The z -transform of the sequence {x(n)} isdefined as the infinite sum

cx

x(,)= E x(n)z-'n= -co

for a complex variable z. Notice thesimilarity between this expression andequation 3; setting z=e" gives X(z) as theFourier transform of {x(n)}. The z -

transform of the impulse response {h(n)}is H(z) and hence the setting of z= e" inthis case gives the frequency response al-ready defined as H(e"). The equationabove may therefore be thought of as ageneralization of the Fourier transform.Also, the z -transform of the delayed sequ-ence {x(n-1)} is z-1X(z) as each coeffi-cient of z -n is shifted along by one place.In general the z -transform of {x(n-k)} isz-kX(z). Also notice that the z -transformof the impulse {o(n)} is 0(z)=1.

Applying the z -transform to the outputof a digital filter as defined by equation 1gives

M NY(z)= E ajz-'X(z) - E kz-inz)

i=0 j=

which may be rearranged and expressed inthe form

Y(z)=[(1±4 aiz--1)1(1+ biz-1*(z)i=0 j=1

The expression in square brackets above isequal to H(z) as if the input sequence

{x(n)} = {i5(n)} then Y(z) becomes equalto the z -transform of the impulse response.Hence H(z) may be expressed directly interms of the multiplier coefficients, andthe frequency response may be obtaineddirectly from this expression by settingz=e". This may be verified for the simplefilter defined by equation 2 whereH(z)=11(1-bz-1) and hence an expres-sion for H(e") identical to equation 7.

The transfer function of a filter, H(z),has now been expressed as the ratio of twopolynomial expressions in z- I, the roots ofwhich are the poles and zeros of H(z).Hence

H(z)=a0 3 (l -Piz- I) (8)i=1 j=1

assuming a0=0, where the poles are p, andthe zeros by z,. Expanding by partial frac-tions (assuming there are no repeated rootsother than at z=0),

M-NH(z)= E Biz-i+ E Aio-piz-1)

i=0 j=iwhich expresses H(z) as the weighted sumof sequences whose z -transforms are z-1and 1/(1-A z--1). Clearly z-1 correspondsto a delayed impulse {8(n -1)} . By refer-ring back to the example of a first -orderfilter whose transfer function is

1/(1- bz-1) it may be deduced that1/(1-pi z-1) is the z -transform of an expo-nential sequence of the form

{. . 0, . . . 0, 1, pi, pj2, pir, .} (9)

The roots of a polynomial may of course becomplex numbers and therefore the sequ-ences above may be complex. As complexroots occur in conjugate pairs, the sequ-ence obtained for {h(n)} is always real. Anon -recursive filter, i.e. one with N=0,will have an impulse response withh(n)=B for and zero otherwise.Such an impulse response is termed finiteas only a finite number of elements are

Imaginary Iz)

Fig. 5. Argand diagram shows pole andzero positions for H(z) obtained from Fig. 1

which determines the frequency responseH(e)

non -zero. The impulse response of a recur-sive filter (N>0) will include at least onesequence of the form in equation 9 and cantherefore be of infinite duration. For sucha filter to be stable, the above sequence 9corresponding to each of its N poles p,must be a decaying exponential. Hence astable filter must have Ipil<1 for allits poles.

Considerable insight into the behaviourof digital fileters may be gained by plot-ting. Argand diagrams showing the posi-tions of poles and zeros as values z. Such adiagram is shown in Fig. 5 for the transferfunction H(z)=11(1-0.7z-I) which has apole at z=0.7, and a zero at z=0. Thepoints for which z=e" on this plane corre-spond to the unit circle with centre z=0and radius 1. The frequency responseH(e") is obtained by an evaluation of H(z)for values of z on this unit circle, where wis the angle subtended from the real axis tothe point corresponding to z=e". Fre-quencies zero and the Nyquist appear atopposite sides of the unit circle on the realaxis.

A stable filter will have all its poles in-side the unit circle <1). Fromequation 8 the value of 1H(e")1 atany point on the unit circle is equal to a0multiplied by the product of the distancesfrom that point to each of the zeros,divided by the product of distances to thepoles. The phase of H(z) may also be read-ily calculated. Consequently zeros close tothe unit circle correspond to frequenciesfor which 1H(e") is close to zero.Poles close to the unit circle produce largevalues of 1H( e n the closer thepole, the larger the modulus. Such polescan also affect 4(.o) resulting in severephase non -linearity.

The design of digital filters withspecified frequency responses is often car-ried out by locating zeros and poles atappropriate points on the z -plane. Designtechniques exist for both recursive andnon -recursive filters: refer for details toany of the standard references, some ofwhich are listed below. Non -recursive filt-ers have certain advantages of guaranteedstability and easily specifiable phase char-acteristics, but tend to involve a largenumber of arithmetical operations whichcould make them more difficult to imple-ment. Recursive filters are perhaps stillmore commonly used, and therefore thenext article will introduce a design proce-dure for this class of filters.

continued

Further readingDigital Signal Processing, by A. V. Oppenheimand R. W. Schafer, Prentice -Hall, 1975.Theory and Application of Digital SignalProcessing, by L. R. Rabiner and B. Gold,Prentice -Hall, 1975.Digital and Kalman Filtering, by S. M. Bosic,Edward Arnold, London, 1979.Introduction to Digital Filters, by T. J. Terrell,Macmillan, 1980.Digital Signal Processing Thoery, Design andImplementation, by A. Peled and B. Liu,Wiley, 1976.


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IL_ __IL_1

A CHARTER FORISOLATIONI wish to quote from your editorial "A Charterfor Isolation" in the December issue:

"It leaves us, says Hartley, with a 'conceptionof the engineer as no more than a high-gradetechnician, a functionary not fully professional

5 99

This conforms to a view held in this countryin a previous age - 1920-50. But it surprises methat you did not correlate the holding of thisview with the photo on page 37 of that issue,where "engineers practice climbing on theseshort poles". By our definitions, if British engi-neers still spend time climbing poles then wewould have to say they are technicians.

The engineering profession down -graded it-self for too long be accepting such jobs, even intraining; besides who can afford such at presentstarting salaries of US $22,000 or thereabouts?J. D. Ryder,formerly Dean of Engineering,Michigan State University.

THE DEATH OFELECTRIC CURRENTIvor Catt's letter in the February issue onlyserves to illustrate the deficiences in hisknowledge of mathematics and conventionalEM theory and the confusion of his own theory.

Can he not see that E1H=VW is wrong andH=B1µ is right for mathematical reasons?There is indeed a small chance that the latterdoes not describe correctly the true physics ofmagnetism but at least it is dimensionallysound.

His difficulty with step waveforms on trans-mission lines becomes clearer. Of course theconduction and displacement currents are bothpresent in the line together, but only as the waveadvances. The displacement current dD/dT isassociated with the wave front only (D is con-stant elsewhere). If the wave reaches a (correct)resistive termination dD/dT ceases, the step isterminated and the resistor begins to absorb theenergy in the wave. It is precisely because thedisplacement current flows across the transmis-sion line that the wave is called a transverse EMwave and the displacement current is distinctfrom the conduction current. The energy asso-ciated with the displacement current is storedand can be recovered later (cf. radar pulse gen-erators). It can be seen from Mr Catt's ownillustration (Fig. 3, p.68 March, 1979) that theE vector (dB/dT) and the displacement currentvector (dD/dT) are at right angles, thereforeExH is purely reactive. This is analogous withreactive power (VAr), where current and voltageare 90° out of phase. The H vector associatedwith the conduction current is also at 90° to theE field and again no energy is dissipated; thepower flow is in the direction of the conductioncurrent. In a third case, the transmission line isresistive and there is a component of the E fieldalong the line in a direction opposite to thecurrent flow. Here some of the power is dissi-pated.

Mr Catt is further confused with regard toelectric charge. The existence of electric chargeis not a theory; it is a fact like the sun and coal inSouth Wales. Since one of the manifestations ofelectric charge is electric potential, any theory ofelectric waves that dispenses with electriccharge must be rubbish. It is the objective of

EM theory to explain the various manifestationsof electric charge.

Mr Catt's mathematics is wrong; he does notunderstand the application of vectors to TEMwaves and he does not distinguish fact fromtheory.

I'm sorry if he believes his version of Maxwellis correct; it isn't. If he was right in his beliefsome changes would indeed be needed andradios would not work.Dermod O'Reilly,Antwerp,Belgium.

RECHARGING DRYCELLSWith reference to the letter from Mr D. F.Caudrey (Letter, August 1981) I should like tooffer my findings on the subject, and also begmore information from the author.

I have been using the same four SP2 cells forabout 11 weeks, five days a week, approxi-mately 1 hour per day. At first I would rechargethem (using the circuit and method due to MrCaudrey) for an hour or two, twice a week butnow I need to re -charge every day for about 2-3hours to get an hour's use from the cells. Al-though I am convinced that the method is feas-ible in practice, I do not seem to have had thesame success as Mr Caudrey, and so I would liketo hear from Mr Caudrey his recommendationsabout charging, i.e. when and for how long.S. P. Narey,Idle,Bradford.

MILLIMETRE -WAVELENS AERIALSI have read Dr K. L. Smith's article on milli-metre wave lens aerials with interest (and somenostalgia as I was in the lens business in theearly 1950s) and congratulate him on an excel-lent reintroduction to an almost forgotten topic.

Has it occurred to Dr Smith that his methodof fabrication would be equally applicable toanother of Winston Koch's inventions, the ser-pentine lens? This form of lens can be assem-bled from a set of plates which have beencrimped into sinusoids. Propagation is in theTEM mode and the quasi -refraction index issimply the ratio between the widths of crimpedand uncrimped sheets. Dr Smith has only tostack a set of crimped sheets and machine aprofile to produce a set of path -length lenses.

The serpentine lens has two advantages overthe Hot wave -guide lens. It is unaffected by thespacing between plates, so tolerances are easier,and by arranging for the surfaces of the sinusoi-dal sheets to be normal to the phase surface ofthe lens where they meet this surface, the lens -medium will be matched to free -space, avoidingthe alternating X/4 and X./2 transformers whichdegrade the side -lobe performance of a wave -guide lens in which the refractive index has beenpushed too far from unity.

The path -length lens may have disadvantagesas well, but since to the best of my knowledgeone has never been produced for operationaluse, perhaps Dr Smith will identify them byinvestigating the first thirteen models?S. S. D. JonesMalvernWorcestershire

The author replies:I was pleased to hear that Mr Jones enjoyed thearticle on mm -wave lens aerials. He has raised avery interesting point regarding the de-velopment of the serpentine plate lens aerial,which he is right in ascribing to Winston Koch.I agree on the added advantages of the corru-gated conductor planes, but I did not consideremploying them in the lens I made. Mr Jonesraises a very interesting possibility, as I alsoagree with him that there would not be anyfundamental problem in turning out such mod-ified lenses by the same method I originated.

It would be most interesting to see an attemptmade practically on such a design. We shouldthank Mr Jones for the suggestion.

LINEAR POWERAMPLIFIEROperation of the output transistors at an ap-proximately constant low voltage, as recom-mended by D. Rawson -Harris (Letter, Jan.1982, p.40), can be used to give a class -A ampli-fier which retains to a considerable extent theefficiency of a class -B amplifier.

The low -voltage transistors are operated inclass A from a low -voltage supply, perhaps +2,0, -2 as suggested by Mr Rawson -Harris, andthis supply is carried up and down by a slaveclass -B amplifier of gain +1. The class -B ampli-fier may produce noticeable crossover distor-tion; but as the effect of the distortion (or error)is only a small modulation of the almost con-stant c -e voltage of the class -A transistors itseffect on the performance of the complete am-plifier may be expected to be very small. Anoutline of the system is shown in the diagram.

As a piece of engineering the system cannotbe rated very highly: Peter Walker's Qurd am-plifiers are much simpler, and their distortion isso low that they sound like a piece of wire. Butthe economics of producing an amplifier may bedifferent for the amateur constructor and expe-rimenter, and this alternative class -AB systemmay therefore be of interest. It has been used insome expensive Japanese amplifiers, but may benew to many Wireless World readers.

pnpequiv

nrb

b npnequiv

e

Floating powersupply, low voltage

nonequiv

b

popequiv.

LOAD

o t

1

Class Bpower amppill +1


_JL_ __J

Mr Rawson -Harris calls his triples currentamplifiers. Certainly their current gain is high;but it is poorly defined, having at least thecurrent -gain spread of their first transistors, andthey have high inlet resistance. I feel that acurrent amplifier should approximate to a shortcircuit and present a low resistance. To me thetriples are enhanced transistors giving a voltagegain of many hundreds as a common -emitteramplifier, or enhanced emitter followers givinga voltage gain very closely.

E. F. GoodNeashamDarlingtonCo. Durham

CLANDESTINE RADIOPat Hawker's review in the January and Feb-ruary, 1982 issues ably covers an area of interestto technical people which is noticeably omittedin the many books dealing with Resistance andIntelligence activity in World War II. In-evitably, in a collation from many sources, er-rors appear and among many statements of factone finds items which are the opinions or deduc-tions of a particular source. Some correctionswhich I am qualified to make, will, I hope,contribute to a valuable summary.

SOE began to design and make radio equip-ment before mid -1942, particularly the Type AMkl and the B Mkl in 1941. The "early FrenchResistance suitcase set" illustrated in p.82 of theFebruary issue was indeed the Type A MkII,which I designed in late 1941, just after thecompletion of the B MkI. This set was producedby Marconi, first at Writtle then at Hackbridgein quantity believed well over 1000. Many wereallocated to Russia as well as to France andother areas of Occupied Europe, but details ofdistribution and usage are not available so far.The modular form of the A MkII, like that ofthe later B MkII, was to assist in assembly ontovarious housings, transport and concealment, aswell as service by substitution.

Operational demand for a one-piece unit ofthe smallest size led to the re -engineering of theA MkII into the A MkIII, by Marconi produc-tion engineers. The main difference in the de-sign was in the replacement of the TT11 Txvalve by the 7C5, which had then become avail-able. Volume production from about the end of1942 onwards totalled, I believe, over 4000.

The "A" series was designed for short tomedium -range communication particularly toUK from France, Belgium, Holland, Denmarkand Norway. While the "B" series was intendedfor medium to long range in Balkan, MiddleEast and African countries as well as fromSouthern France. A "C" series was consideredbut not developed, but a B MkIII was producedespecially for the Far East and long-range junglepatrols. The transmitter was c.w. and a.m./r.t.,and like the receiver, was hermetically sealed,positively buoyant, and entirely powered by apedal -generator. The station was in two man -packs. The tendency of technical people tocontract titles led to the general use of "A2","B II" etc., but the term "B2 minor" is amisleading post-war usage.

SOE development was not centred on Gor-hambury at St. Albans, which was only one ofmany large country houses used, but at theFrythe in Welwyn. Producton of the B MkIIwas entirely by the ISRB (ie. SOE) factory atStonebridge Park, employing mainly Servicespersonnel: RAF, Royal Signals, REME, ATS

58

and FANY. About 7000 sets were made, withoutput reaching 400 per month in 1944.

I will not contest the relative merits of SIS/-SOE/Polish sets since I am as biased to one asPat Hawker is to another, following our respec-tive wartime employment and loyalties, butwould beg to differ, since the operational re-quirements differed. The SOE sets were essen-tially para-military, with far wider applicationthan to agent use in Northern France, and for agreater variety of operators. Too little has beensaid of the Polish sets and the Polish contribu-tion, for which I have the greatest admiration.The OSS started development of suitcase setsfrom about mid -1942, learned rapidly, fromBritish and their own experience, and madetheir contribution world-wide. Naturally, eachhistorian tends to present the story as seenthrough the records and reports of his coun-trymen, and frequently dates are omitted, sothat the order in which facts are presented im-plies their precedence. Reading G3VA's accountof air -to -ground links (February, p.83) hequotes first MI -6 use of "early American f.m.equipment on 30MHz" then "SOE developedthe 450 MHz S -Phone" and gives one date -August 1944. I have no information of the use ofthe American R/T sets before 1944, about thetime of the "Joan -Eleanor" project, but the S -phone was working in 1941, and my colleague,Charles Bovill tested the first airborne equip-ment on a flight in Wellington No. L7772 onOctober 6th 1941. The air -set was a prototypesuperhet tuning through 60-70cm. It was usedin Operation "Claude" on October 28th in aWhitley Mk.V. The S -Phone ground -set wasdeveloped by Capt. Bert Lane and the airset byMajor Hobday, both of Royal Signals. The air -set was destroyed in a crash later in 1941, butreplaced by a super -regenerative air -set ten dayslater, by a rapid development by F/Lt Bovill.This remained standard operational equipmentby 138 and 161 Squadrons until the productionof the Homing Aircraft-superhet in 1943. InJanuary 1944, a USAF Liberator was fitted withHoming S -phone gear, and in summer of thatyear F/Lt Bovill equipped and flew with thirtyC47 aircraft of the American 60th Group TroopCarrier Sqdns, at Brindisi. These aircraft usedS -phone continuously in operations until theend of the war, mainly over Albania, Yugoslaviaand N. Italy. This is only a small part of the S -phone story, appropriate now in context withPat Hawker's article.John I. Brown, G3EUR,S. Ockendon,(late Major R. Signals).

THE NEWELECTRONICSI am afraid that my own experiences with in-terviewees is closely similar to that described byMr Jaques in the January 1982 issue. I couldhear an echo of my own comments and exper-iences as I read it through.

I like to finish an interview with a few simpletechnical questions, not to cause the intervieweeany difficulty but to ensure that his under-standing of the fundamentals of the subject isadequate. In the situation, slick, polishedtextbook answers are not expected but the rightapproach to achieving a satisfactory answer isexpected. At this stage of the interview the in-terviewees are likely to be reasonably relaxed,and frequently have done a good job on selling

themselves, so that the situation for both partieslooks good.

My opening question starts with a batteryfeeding a capacitor through a resistor and switchin series. Assuming the capacitor is dischargedat time zero, tell me how the capacitor voltagevaries with time? All too frequently we do notget on to the second part (adding a series induc-tor) or the third part (replacing the battery witha sine -wave generator). Perhaps the interviewsituation is too upsetting, I try to provide nottoo serious help and guidance. Nevertheless onehopeful believed that the linear network with asinusoidal input produced squarewaves.

It is very difficult explaining to the MD that,in spite of the excellent paper qualifications ofthose already interviewed, further interviewingwill be necessary.N. A. Haran,St. Albans,Herts.

INTENTIONAL LOGICSYMBOLSIn reply to Christopher Hudson (Letters, Feb-ruary 1982) the question as to whether a NANDgate is performing the function of positiveNAND or negative NOR is to me as daft asasking whether a bucket is half full or halfempty. The answer is both, not merely becausethe truth table says so but because, as an exper-ienced logic designer I can, and do think of it aseither with complete dexterity, although morefrequently I think of a gate in terms of its truthtable. If then I, as the designer of a circuit,cannot identify an intention, how can there beone?

Logic 1 and 0 are two states of completeequality: one is not merely the absence of theother. Some inputs, a 'clear' on a flip-flop forexample, may be responsive to one state ratherthan the other, but this is a function of the inputnot of the signal feeding it. Mr Hudson does not

la)

F

(b)


m,n may be 00, 01, 10 or 11

if all inputs = m, output = n

if any inputs # m, output =

define what he means by the assertive state, Ican only assume that he means the state whichasserts itself, but that gets me no further. Evenin the case of flip-flop 'clear' inputs, one couldhave an active -high and an active -low flip-flopconnected to the same signal. How can the sig-nal itself be thought of as having an assertivestate? Mr Hudson illustrates the point himselfin the mess he gets into over his Fig. 2. Essen-tially a 1 or 0 on the select are equally assertiveand I maintain that, far from being unusual, itrepresents the general case.

In a practical design what may start out in thedraft design as Fig. 1(a) may finish up as Fig.1(b). The question is, is the two -input NORperforming the function of low -assertiveNAND or high -assertive NOR? If Fig. 1(a)represents the intention then it is performingboth. Should we draw it twice? Well why not,we are already being asked to show the outputson flip-flops twice, use twice as many logicsymbols as before, accept that identical devicesmay have different symbols, that a connectionmay be shown broken with a naming ceremonyin between and even to accept that an inherentlysymmetrical device like a two gate latch shouldbe drawn so as to make it look asymmetric, (seeCassera, November 1980) all inthe name of sim-plification.

The AND and OR names are a useful aid tomemory as to the truth table of the gates sodescribed. The predominance in practical logicof NANDS and NORs spoils the essential sim-plicity of the concept to the point where thenames may be more of a hindrance. Intentionallogic symbols are an attempt to restore theoriginal simplicity. Mr Hudson's letter is in myopinion ample proof that they have failed miser-ably to do so.

My proposed logic symbols exploit the factthat if one is forced to live with negative andpositive logic, one does not need to also live withboth AND and OR because we can redefine theOR as a negative AND. As we now have onlyone type of function that function does not needa name, it is only necessary to define whether itis positive or negative logic, inverting or non -inverting. This is most easily achieved by put-ting the simplified AND truth within thesymbol, thus nothing need be committed tomemory: it speaks for itself.

By way of a field test I introduced my 10 yearold son to my logic symbols. Within half anhour he could derive the waveforms out of anygate combination I gave him. (Previousknowledge of logic nil). With intentional logic itis necessary to define eight types of gate, withtruth -table logic symbols, Fig. 2 gives a fulldefinition. Simplicity is the name of the game.J. E. Kennaugh,Callington,Cornwall.

I disagree with your correspondent, C. Hudson,over his proposal for intentional logic diagrams.

Whilst these may at first seem attractive froman academic viewpoint, in practice such cir-cuitry can cause a good deal of confusion, parti-cularly where multiple gate packages are in use.Consider for instance, a 7400 NAND gatesplit up in a circuit such that part is usedas NAND, part is used as low -activeOR, and the remainder as inverters.Under Mr Hudson's instructions, thisresults in three different drawings for the samedevice. A service technician trying to relate thedrawing to a particular chip pack would havedifficulty, without a great deal of cross-referenc-ing. In addition, an increasing number of com-plex devices have inputs in which clock highand low could be equally considered to be ac-tive, since important but differing instructionsare conveyed by each polarity. How would suchan input be drawn?

Even if the traditional method of drawingdiagrams is for some reason to be deplored, Iconsider that it should be retained on the basisthat it is at least an established standard. Tochange symbols every time someone has a newidea is a recipe for annoying confusion.

To sum up, I would say that I consider MrHudson's proposals a change for the sake ofchange - rather like using Hertz for theperfectly acceptable c/s, and changing the spel-ling of enquiry to inquiry.L. HaywardWarehamDorset

TWINS PARADOX OFRELATIVITYI refer to L. J. Higgins' letter (April 1981) inwhich I am accused of addressing myself to a"fundamental flaw" and also of imagining a"miraculous coincidence".

The first is easily disposed of, since the accu-sation is quite false and originates in Mr Hig-gins' failure to pay close attention to the textbeing discussed, in particular W. W. Oct. 1980p.56., the first column of which cites Einstein'sown activities and his words to which the secondparagraph of my letter (January 1981) alluded.Thus Mr Higgins accuses Einstein, not me, ofcontriving a fundamental flaw.

I come now to the matter of coincidence andall that ensues.

The equation FL/1/2v = my shows how mo-mentum is achieved. Unfortunately Newton didnot know that material particles are heldseparate by interatomic forces and that, in con-sequence, all force acts at a distance, but todayany competent radio engineer knows that the1.h.s. of the above equation represents the cu-mulative Doppler modification to an impressedforce acting from a distance and having itsorigin fixed to some arbitarily stationary datum,motion and energy being of course related tothat datum.

So we have two methods of obtaining the KEequation, the classical which is based upon ananalogue with friction and this present onewhich depends upon Doppler. Being a physicaldescription, the latter represents the applicationof negative feedback to ancient hypothesis, serv-ing to convert that hypothesis into the form ofunassailable physical description and allowingdirect comparison with modern experimentalresults. This is an addition to the scientificmethod.

Even though the two methods of obtainingthe KE equation differ so widely, each notmentioning what the other contains, they yield

the same result which in its turn accords withexperiment. The fact that the original derivationof the KE equation is in accord with experimentand also with the physical description is purecoincidence, nothing more.

I come next to the experimental facts whichlead to the falsification of both the concept ofvariable time and the light postulate, therebyputting an end to the twins controversy.

When referring to J. C. Maxwell (Letters,February 1982), P. G. M. Dawe tells us that themass increase hypothesis has been verified byexperiment. He also inverts history by putting E= MC' before mass increase. In a linear particleaccelerator the origin of the motive force is atrest relative to the machine and since the forceacts at a distance its effect must be subject tofirst -order Doppler. This is a physical fact,which is never mentioned. If the force travelledat infinite velocity then the experiment wouldyield the Newtonian energy equation as its re-sult.

However, in reality the force is known tomove at the lesser velocity C and hence thedeclining effectiveness of the force with relativevelocity is modified by a second -order term -coincidentally identical to the Lorentztransform.

Electron beam and linear particle acceleratorexperiments prove quite conclusively that massis velocity -invariant. If, as Mr Dawe would haveus believe, mass increase can be derived from E= MC2 then either the mathematic or the deri-vation or the equation itself is wrong. Thefalsehood is proven by experiment.

Let us now contemplate the consequences ofthese things.

Mass increase is justified by the considerationof the elastic collision of two projectiles. Withinthis scenario the conclusion that mass is veloc-ity -variant rests solely upon the stationary ob-server 'knowing that the clock of the movingparticipant of the experiment runs slower'.

If, as has earlier been shown, mass is velocityinvariant then time is, inevitably, velocity -inva-riant as well.

In its turn the derivation showing time to bevelocity variant rests entirely upon the assump-tion that the light postulate is true.

Because time is in fact velocity invariant thereis no alternative but to accept that the lightpostulate is false.

The fact that an experimental result canappear to confirm the end product of a flight ofpure fancy is indeed a miraculous coincidence.Should anyone question the fact that E = MC2is disproven, other than in the limited sense ofmathematic equivalence, I would point out thatthe matter has never been tested directly due toinsurmountable technical problems'.

I suggest that Prof. H. Dingle's misgivingsabout atomic experiments were entirely justifiedbecause it has been shown that matter hasnever, on this planet, been converted intoenergy. We are left with the distinct risk thatinterconversion might one day accidentallyoccur and there exists neither mathematic norexperience to predict the outcome.

A valid alternative has been provided to re-place S.R.T. and it is to be hoped that thescientists will emerge from behind their wall oficy silence and discuss the matter in termswhich do not involve the double standards thatthave been observed by I. Catt (Letters, Feb-ruary 1982).Alex Jones,Swanage,Dorset.ReferenceJ. Chappell. S.S.T. Vol. 2., No. 3, p.316-317.


HIL_ HL JE-41 67)

AMATEUR LICENCES INGERMANYJust in case nobody else objects, may I correctV. A. Sancto's statement in your February is-sue.

Licence Morse Amateur bandsClass requirement

B 60 lettersp.m.

A 30 lettersp.m.

C none

H. Borsutzky,Cologne,W. Germany.

All amateur bands,most modesincluding telephonyexcept 1815-1832and the new10, 18, 24 MHzbandswhich are telegraphy(A1A) only

3520-3700 telegraphy3600-3700 alsotelephony21090-21150telegraphy28.0-29.7 MHz alsotelephony

v.h.f./u.h.f. only

POWER TRANSISTORFAILUREI have some pulse -width -modulated switchingoutput power amplifiers which deliver up to18A at ± 170V into a d.c. motor and inductor ofabout 5 mH. The amplifiers have been unrelia-ble over a long period, apparently randompower -transistor failures occurring even afterseveral hundred hours of operation.

The output stage uses parallel pairs of2N6547 transistors (others have been tried),switching the load alternately between thesupplies. Unmodulated switching rate is about 4kHz, rise and fall times are typically 51.ts, andthe collectors are clamped at the total supply,i.e. 340V. During part of the cycle the collector -base junction is forward biased. There is activeturn-off of the transistors.

Any light on the possible causes of failure willbe appreciated.I. E. ShepherdHydraulics Research StationWallingfordOxfordshire

ORIGINS OF THE HIGH -POWER TRANSMITTERIt is now 90 years since Nicola Tesla delightedthe eyes of engineers in Europe with demonstra-tions of high -frequency discharges in gases. Toobtain a voltage sufficiently high, he used whatwe now recognise as a loose -coupled transfor-mer with tuned primary and self -resonantsecondary, to step up the more modest levelsobtainable from a high -frequency alternator and

power transformer. To the more critical eye of,today his circuit with its two spark gaps mayseem a trifle over -complicated; but he also useda simpler arrangement with only one spark gap,powered from a low -frequency generator. Read-ers familiar with the circuits of early wirelesstransmitters, for example, that of Poldhu de-signed by Fleming ca 1900, would undoubtedlyrecognise some antecedent features. It may notbe generally appreciated that Tesla himself sug-gested such an alternative application for hisdischarges: "I think that it may find practicalapplications in telegraphy. With such a brush itwould be possible to send dispatches across theAtlantic (sic) . . ." It is clear from the contextualwording that Tesla was thinking more in termsof an ion or plasma beam than of any "ethericforce"; and his later patent2, though it includeswhat is recognisably an antenna, confirms this.He was probably aware of the telegraph basedon atmospheric conduction proposed by Loomisand Ward3 in the previous decade, which wouldcertainly have benefited from a transmitter ofphenomenal power. Though Tesla here seemsto have had his head in the clouds, the practical-ity of his transformer engineering shows that hisfeet were certainly well grounded.

Hard on his heels we find another American(though Tesla was in fact Yugoslav), the engi-neer Elihu Thomson, describing 4 a similar cir-cuit capable of providing the high potentialsneeded for testing electrical apparatus. This cir-cuit appears to correlpond to the simpler one ofTesla, and actually uses an air -blast at the spark -gap as suggested in Tesla's paper. As neither ofthese two engineers acknowledges the work ofthe other, we are left in some doubt as to whichof them invented what. Unless earlier contend-ers appear, it is not unreasonable to allow themboth to share the honours. Again, there is nomention of etheric telegraphy in Thomson'spaper, nor in his subsequent patent 5. And thisindifference to the communication potentialitiesof his apparatus is the more surprising in that hehad himself (it is alleged by Snyder') practicalexperience of "Maxwell Electro-MagneticWaves", and also had published 7 a joint ac-count of his work with Edwin Houston on "TheAlleged Etheric Force" demonstrated by Edi-son's experiments.

Wireless, therefore, waited for others todemonstrate viable communication, Lodge withhis "syntonized" tuning and the entrepreneurialMarconi with an aerial. And only then, as wire-less took off, did companies in search of higherspark power embody features of Tesla andThomson circuits in almost every transmitter ofconsequence. With the subsequent demise ofspark telegraphy, these features eventually va-nished from wireless transmitters, though theblown spark -gap surfaced again in radar mod-ulators in World War II 8' 9 and later still inphotographic flash -gear 1o. Where then can welook today for the Tesla-Thomson "coil". Openup a "tickler" vacuum tester and you will findone; start up a xenon arc lamp and you will beusing another. "Tesla Lives" is my centennialtoast!Desmond ThackerayMusic DepartmentUniversity of Surrey

References:1. lour. I.E.E. 21, (1892), Lecture of 3

February by N. Tesla2. U.S. Patent 645,576 of 20 March 1900

(filed 2 Sept. 1897)3. E. N. Sivowitch, Jour. Broadcasting, IS,

(1970), pp. 3 to 5

4. E. Thomson, Electrical World, 19, (1892),116

5. U.S. Patent 500,630 of 4 July 1893 (filed 18July 1892)

6. M. B. Snyder, General Elec. Rev. 23,(1920), 208

7. E. J. Houston & E. Thomson, lour.Franklin Inst. (April 1876), 270

8. J. D. Craggs, M. E. Haine & J. M. Meek,lour. I.E.E. 93, IIIA, (1946), 963

9. K. J. R. Wilkinson, ibid, 109010. R. H. J. Brown & J. A. Popple, Med. &

Biol. Illustr. 5, (1955), 23

HORN LOUDSPEAKERDESIGNBernard Jones' thoughtful letter (January, 1982)prompted me to re-examine my 1974 articles onhorn loudspeaker design*, and in particularFig. 13. The intention of this figure was toillustrate how a treble horn could be given adegree of directivity in the horizontal plane bymodifying the standard circular cross section tobe rectangular, with aspect ratio 2.5:1, but stillensuring that the area profile from throat tomouth followed a true exponential law (it couldhave been a tractrix law, but there are goodreasons for avoiding tractrices at high audiofrequencies).

I have re -checked my design calculations, andmust agree with Mr Jones that on strictly ma-thematical grounds, neither vertical nor hori-zontal profile should fall inside the circular hornprofile (in fact, the two sides of the rectangleshould respectively be 1.12 and 2.8 times theradius of the circular horn). I began this particu-lar design of horn with a circular throat to suit acircular loudspeaker, and my imperfect attemptat "fairing" from circular to rectangular cross-section has resulted in this anomaly. In practice,I can see that my artwork with damp plaster -of -Paris probably made the profile even more ap-proximate at this point, but horns and ears areremarkably tolerant, and I doubt whether anycolorations thus produced are audible, or if aud-ible are at all obtrusive.

I can confirm Mr Jones' suspicions that treblehorns give disappointing results unless mountedon baffles (hemisphere loading) to minimise dif-fraction effects. The sound quality from smallpiezo-electric tweeters (those fitted with integralplastic horns a few inches across) is very de-pendent on the mounting topography within aradius of up to 12 inches from the mouth.Jack DinsdaleCarltonBedfordshire*March, May and June, 1974. Reprinted inHigh Fidelity Designs, volume 2.

CARTRIDGEALIGNMENTGood grief, Mr Frost (Letters, January), howwill Wireless World ever graduate to promulgat-ing the concept of pickup arm rigidity as anover-riding design concern if you want to intro-duce further, unnecessary bearings? It's notquite so specious an idea as the infamous thread -suspended pickup arm, but . . . As a finaltouch, perhaps the APT design team shoulddevelop it.Keith HowardTeddingtonMiddlesex


DIGITAL OPTICAL RECEIVERSDr Garrett concludes his review of receivers for optical fibre communication

with the theory of digital reception and gives practical achievements withp-i-n diode/f.e.t. receivers

In a receiver for a binary digital system,the aim is to process the signal in such away as to be able to distinguish betweentwo hypotheses, which we label zero andone, with the minimum possible error. Inthis way we seek the best estimate of theoriginal message from the attentuated,distorted and noisy signal in the receiver.Commonly the signal is detected, ampli-fied and filtered and then presented to adecision gate which is opened for a shortinterval at the centre of each bit period bya pulse from a clock circuit. This intervalis called the decision time. Assume that,for a received zero bit, the receiver outputvoltage v(0) at the decision time has a meanvalue mo and variance so, while for a re-ceived one, the mean is m; and thevariance s1, Fig. 9. Because the quantumnoise is signal -dependent, so and s1 aredifferent, in contrast to microwave trans-mission systems. Assume also for simplic-ity that v(0) has a Gaussian distribution,although the multiplied quantum noise hasin fact a compound Poisson distribution.The error probability is then

Pe= 1/2erfc (Q/V2)where mi- mo= Q(si+ so). (1)

Graduating from Trinity College,Cambridge in 1965, lan Garrett completeda PhD on radiation damage in metals in1969. He joined the Post Office ResearchDepartment, now British TelecomResearch Laboratories, as a ResearchFellow working on the theory of chemicaltransport reactions. In 1971 he becamegroup leader responsible for thepreparation of compound semiconductingfilms and crystals. Since 1976 he has lead asection responsible for optical transmittersand receivers and integrated opticaldevices.

by Ian Garrett

This says what difference there must be inoptical power between the zero and onebits in terms of the noise (variances) andQ, which is related to the signal-to-noiseratio (in fact, 4(22). The equation gives thevalue of Q needed for a given acceptableerror rate. For example, Q=6.00 forPe= 10-9; small changes in Q producelarge changes in error rate. For designerror rates of this magnitude, errors arisefrom the far tails of the noise distribution- six standard deviations away from themean. That is why accurate models ofnoise statistics are important in opticalsystems. In fact the Gaussian approxima-tion used here is successful at predictingerror rate as a function of mean signalpower, but is poor at giving the correctsignal threshold level and the optimumavalanche gain, for this reason.

The theory of optical receivers enablescalculation of mo and ml, so and s1, in termsof the received optical waveform and thecomponent values of the receiver. One canthen predict the sensitivity of the receiverand model how it is affected by changes inreceiver or system parameters. Detailstheoretical analyses are listed in the bibli-ography, and is only the very simplest caseis considered here. If the received opticalpower p(t) is p during a one -pulse and zeroduring a zero -pulse, the pulse energy for aone -pulse b1 is pT and for a zero -pulse bo iszero. The photocurrent (in) is theniqMp/hy during a one -pulse and zero dur-ing a zero pulse. This current is filtered bythe receiver front-end.

A typical circuit is shown in Fig. 9 withthe equivalent circuit for noise analysis.The photocurrent is then amplified andpassed through an equalizing and band -limiting filter H(f) resulting in an outputvoltage<v,>, which corresponds to m1Or mo.

The noise sources which contribute to soand s1 are the amplifier thermal noise, themultiplied quantum noise and excess ava-lanche noise, and the shot noise on thephotodiode dark current. The mean -square noise voltage at the receiver outputmay be expressed as:

<v2,,>=(iivri)2[MxTI2(<if,>+Id)/q+Z/M2](2)

in which T is the bit -time, M is the currentgain of the photodiode, 12 is a dimension-less bandwidth integral of order unity, /dis the dark current, and Z is a dimension-less parameter characterizing the amplifiernoise. In fact, Z is the r.m.s. amplifiernoise voltage normalized with respect to

Decision time

bit -time T

Fig. 9. In the unfiltered output pulse froman optical receiver, the shaded regionindicates the variance (mean -square noisevoltage), shown to depend on signal level.Mean levels m1 and m I correspond to zeroand one bits (spaces and marks). Pulse isslightly dispersed so that some energy isoutside the bit -time T.

the receiver's response to one photo-electron. Typical values are 105 at a fewMbits/s to 107 at a few hundred Mbits/s.This equation also assumes that m1 hasbeen normalized to be equal to b1, theoptical energy for a one pulse.

Shortly before this article went topress, British Telecom ResearchLaboratories at Martlesham Heathannounced the transmission in thelaboratory of an optical signal cap-able of carrying nearly 2000 simul-taneous telephone calls over 102km of optical fibre, without theneed for intermediate repeaters.Operating at 160Mbaud, this is thelongest single -span fibre systemyet demonstrated. Many of thecritical components were made inBritish Telecom's laboratories atMartlesham, including the verylow -loss fibre and the receiver,which is the most sensitive in theworld at wavelengths between 1.3and 1.6 p.m. A InGaAs/InP p-i-ndiode, of the sort described in thisarticle, with a Plessey GAT4m.e.s.f.e.t. were used for thecritical first -stage amplifier.


p(t)

a.g.c. loop

Voltage reg. Peak det.

rig. 10. In this typical circuit for an optical receiver the broken -line connections and the peakdeioctor and voltage regulator are only necessary if an avalanche photodiode is used tocontrol the gain. Noise model of the receiver shows principle noise sources and equalizingfilters (see text).

More detailed treatments listed in thebibliography take into account the shape ofthe received pulses, pulse spreading intoneighbouring bit -times because of disper-sion, and other system impairments, andgive detailed expressions for Z in terms ofthe receiver components. Here consider asimple case first and then look at some ofthe results of the detailed theories.

Consider a p-i-n photodiode which hasunity gain only. The quantum noise isinsignificant, so from equation 2:

S1 = SO = vZ11 V

so from equation 1:

mi= 101=2Q-hv

With typical component values, Z mightbe 106. So with Q=6, we need 12,000photogenerated electrons per one -pulse, inagreement with the earlier rough calcu-lation. Using discrete components, a

unity -gain photodiode provides a receiversensitivity typically 10 to 15 dB worse thanan avalanche diode. However, by hybridintegrating the p-i-n diode with the firstamplifier stage using a gallium arsenidem.e.s.f.e.t., the input capacitance of thereceiver can be reduced so that Z falls to

Fig. 11. Hybrid p-i-n f.e.t. integratedoptical receiver for high data rates,say 30Mbits/s upwards in astandard 14 -pin d -i-1 package is themost sensitive so far for the range1 to 1.6µm. Input fibre tail, visibleat the top left, enters package andpasses through glass blocksupporting the photodiodevertically so that it can beilluminated through the substrate.The thick -film circuit comprises aGaAs m.e.s.f.e.t. input stage withbipolar shunt feedback andemitter -follower stages.

10,000 or less. The receiver noise parame-ter Z is proportional to C2/gm, at high datarates where C is the total input capacitance(photodiode, gate -source and stray capaci-tance) and gn, is the transconductance. Instate-of-the-art receivers, C is around0.5pF and gm is 20 ms. Such receivers havea sensitivity of -44.2dBm at 160Mbaudand -40.1dBm at 294Mbaud, at 1.3umwavelength, and similar sensitivity at1.55um, better than that of a.p.d. re-ceivers. The p-i-n/f.e.t. hybrid approachalso offers the advantages of low -voltageoperation, no need for feedback to controlthe avalanche gain, simpler device tech-nology and probably greater reliability.Typical photodiodes, for use in p-i-n/f.e.t.receivers are shown in the first part of thisarticle. The receiver uses a high impedance(integration) front-end amplifier for thebest performance, although a trans -im-pedance amplifier could be used with aslight penalty. The integrating characteris-tic (time constant typically 1000 times thebit period) has to be equalized, which canbe done simply by differentiating with acapacitor -resistor arrangement. Fig. 11

10k

5k

0

LA..1

2kofa_

;71

ata..1

CO L.A.J

M

z500

1k

shows a typical receiver module.Look now at how the sensitivity is re-

duced by the reverse bias leakage of thephotodiode. Fig. 12 shows some theoreti-cal results for the mean number of photo-electrons required per bit time n and opti-mum avalanche gain M as a function of thenumber Nd of dark current electrons perbit -time. Parameter x is the excess noiseexponent of the a.p.d. and Fig. 12 is calcu-lated assuming Z=106, typical of a receiverusing discrete components at a fewhundred Mbaud, and with zero opticalpower on zero -pulses and no pulse spread-ing.

It can be seen that when the dark cur-rent is negligible, we need about 300 to1500 photons per bit -time, depending onthe noise properties of the photodiode.When the dark current is large, thenumber of photons per bit -time which isneeded is roughly proportional to thesquare root of the number of dark currentelectrons. The noise properties of thediode become far less important. This ishardly surprising as the dominant noise isthen the shot noise on the dark current,and both are subject to the excess noise ofthe photodiode. The optimum gain de-creases markedly once the dark currentbecomes a significant noise source.

Clearly it is important to minimize Ndand to a lesser extent to reduce x. Notethat a leakage current of 160 nA gives Ndof 1000 at 1Gbaud, which is large enoughto affect the optimum gain and the receiversensitivity. At lower data rates the effectwould be greater still.

Fig. 13 shows how n and M vary withextinction ratio E and pulse spreading(extinction ratio is the mean power onzero -pulse divided by the mean power onone -pulse; if it is not zero the optical poweron the zero level contributes to the noise

200 -

1°C'o

1.0

10

0.3

0.7

0.7

1

10 103 104DARK CURRENT ELECTRONS PER BIT-TIME

100

50

20

10

5

-2

105

Fig. 12. Receiver sensitivity and optimum avalanche gain as functions of the number of darkcurrent electron per bit -time (see text)


50k

20k

Cc

10k

u_

ao

z2k

1.1.1

X

5k

1k

5000 01 0.2 03 0.4

SOURCE EXTINCTION RATIO0.5 06

Rg. 13. Receiver sensitivity and optimum avalanche gain as functions of the sourceextinction ratio, assuming a value of unity for the excess noise factor exponent x. Parametera is the r.m.s. width of the impulse response of the fibre normalized to the bit -time T, andassumed to be Gaussian for convenience in calculation, ie it is a measure of the bandwidthof the fibre.

so). The pulse spreading is represented bya, the normalized r.m.s. width of the fibreimpulse response, assumed to be gaussian.The pulse originally launched into thefibre is taken to be rectangular and tooccupy half the bit -time, and the darkcurrent is assumed to be zero. Notice thatthe receiver sensitivity is strongly affectedby pulse spreading and by non -zero extinc-tion, and the optimum gain is reduced byzero -level noise and by fibre dispersion,the effect being greatest when x is small.

This type of calculation, which assumesgaussian noise statistics, tends to over -esti-mate the optimum gain although relativemagnitudes are predicted more accurately.Obviously, combinations of appreciablepulse spreading, non -zero extinction andconsiderable dark current (Nd=100000)reduces the receiver sensitivity very much,and also reduce the optimum avalanchegain to near unity.

Future developmentsThere are some obvious approaches to im-proving the sensitivity of present opticalreceivers. The p-i-n f.e.t., currently themost suitable for the important wavelengthrange 1 to 1.6 um, can be improved byreducing c2/gm; that is by developingsmall -area photodiodes (30 !Am diameter),very short f.e.t. gates (0.3 utn), and byincreasing the transconductance. Themixed compound InGaAs may be a betterf.e.t. material than GaAs in the futurebecause of its high carrier mobility, parti-cularly if it can be cooled, and it would alsopermit monolithic integration of the f.e.t.,

the photodiode, and eventually other re-ceiver components. Between 5 and 8 dBcould be gained here. Avalanche photo -diodes could offer some improvement, atleast over present day p-i-n f.e.ts, if a low -noise material could be found. Recentwork on (CdHg)Te looks promising, al-though it is at a very early stage of de-velopment yet.

A third possibility is to amplify the opti-cal signal before detection, using a Fabry-Perot or a travelling -wave amplifier. Thesedevices would be similar in structure toinjection lasers; their biggest problems arenoise due to spontaneous emission whichcan be reduced only with a very narrow -band optical filter, and gain saturation inthe case of the Fabry-Perot amplifier. Anoptical amplifier is an almost essentialcomponent for optical integration of anyuseful complexity, so there is considerableincentive to overcome these problems.

Finally, one may consider coherent opti-cal transmission systems with heterodynedetection. The outstanding problems hereare: divising an optical source and localoscillator with sufficiently narrow line -width; tracking the local oscillator; ob-taining spatial coherence of the signal andlocal oscillator when they are mixed on thephotodiode; and controlling the polariza-tion of the receiver optical signal. The pay-off for overcoming this daunting list ofproblems is not only increased receiversensitivity (10 to 15 dB possibly), but thefamiliar advantages of using the frequencyand phase information on the carrier whichis present optical communication systemsis lost.

Further readingPhysics of Semiconductor Devices, by S. M.Sze. Wiley, 1969.Optical Fibre Communications, S. E. Millerand A. G. Chynoweth. Academic Press, 1979.Optical Fibre Communication, by the TechnicalStaff of CSELT. McGraw-Hill, 1980.Receiver Design for digital fibre opticcommunication systems, by S. D. Personick.Parts 1 and II, Bell Sys Tech, vol. 52 1973 p.843-86.Simplified approach to digital optical receiverdesign, by D. R. Smith, R. C. Hooper and I.Garrett. Opt Quant Electr vol. 10 1978 p. 211-21.Properties of avalanche photodiodes, by P. P.Webb, R. J. McIntyre and J. Conradi. RCARev, July 1974.Receivers for optical communications: acomparison of avalanche photodiodes and p-i-nf.e.t. hybrids, by D. R. Smith, R. C. Hooperand I. Garrett. Opt Quant Electr vol. 10 1978 p.293-300.InGaAs p-i-n photodiodes for long -wavelengthfibre -optic systems, by R. F. Leheny, R. E.Nahory and M. A. Pollack. Ekctr Lett vol. 151980 P. 713-5.III -V alloy hetero structure high-speedavalanche photodiodes, by H. D. Law, K.Nakano and L. R. Tomasetta. IEEEQuantum Electr vol. QE -15 1979 p. 549-58.InGaAsP heterostrucnire avalanchephotodiodes with high avalanche gain, by K.Nishida, K. Takaguchi and Y. Matsumoto.App! Phys Lett vol. 35 1979 p. 251-3.Avalanche multiplication and noisecharacteristics of low dark -currentGaInAsP/InP avalanche photodetectors, by V.Diadiuk, S. H. Groves and C. E. Hurwitz. ApplPhys Len vol. 37 1980 P.807-10.Band structure dependence of impact ionizationby hot carriers in semiconductors: GaAs, by T.P. Pearsal, F. Capasso, R. E. Nahory, M. A.Pollack and J. R. Chelikovsky. Solid -StateElectron vol. 21 1978 p. 297-302.Required donor concentration of epitaxial layerfor efficient InGaAsP avalanche photodiodes,by Y. Takanashi, M. Kawashima and Y.Horikoshi.japan3 Appl Phys vol. 19 1980 P.693-701.PIN-FET hybrid optical receivers for longerwavelength optical communications systems, byR. C. Hooper, M. A. Z. Rejman, S. T. D.Ritchie, D. R. Smith and B. R. White. 6thEuropean Conference on OpticalCommunications, York, Sept 1980.

In brief .

Technician engineers change their image. Theterm 'technician engineer' was coined to caterfor the non -chartered electrical and electronicsengineer. But the IEETE feel the name hasbecome confused with the general description`technician' and that this may be a stumblingblock to the understanding of the role played bytheir corporate members. So they will call them-selves the Institution of Electrical and Electron-ics Incorporated Engineers, as a reflection of aprofessional body incorporated other than bycharter, and which requires a specific level ofachievement and qualification for its mem-bership. Corporate members are now entitled tocall themselves Incorporated Engineers (Electri-cal and Electronics) and to use the letters FIEIe-cIE or MIEIecIE.


Cables and politicsA broadband cable system connected to allhouses in urban areas and covering about halfthe population is the recommendation of theGovernment's IT Advisory Panel. Although allthe services to be provided are not specified, it issuggested that the system should include tvchannels, f.m. radio channels, and the panelalso recommends that the system should have atwo-way link which would allow any informa-tion service to be interactive, to include suchfacilities as links with a bank account orelectronic shopping. There could also be moni-toring of premises against burglary or fire andthe emergency services could be summonedautomatically if needed.

The scheme involves an entirely new networkas the existing telephone network does not offersufficient bandwidth. It could link in with thoseBritish Telecom networks which are of suffi-

cient bandwidth and thus be provided withpacket switching. Each home would be fedthrough a cable, probably coaxial, with channelselection provided at the distribution pointwhich would have the full bandwidth serviceand would be able to serve up to 100 houses.

In arguing for urgency, the panel say thatexisting cable distribution networks are ceasingto have much value when the country is wellprovided with broadcasting transmitters. Thepanel believes that cable would be the best wayof distributing the direct broadcasts from satel-lites; the PAL system comes out of patent res-trictions at the end of 1983 and could lead to aflooding in the large -screen tv market of cheapsets from the Far East, leading to the downfallof our domestic tv manufacturing industry. If adecision were taken for an early launch of thecable system, the telecommunications industries

involved would get a boost and a world leadwith the possibility of high exports.

One of the pre -requisites for such a system isthat current restrictions should be withdrawnand that potential information providers orbroadcasters be allowed to transmit whateverthey like, within the bounds of decency or sedi-tion. There should be a self-regulating bodysimilar to those in advertising and in newspap-ers.

But as the panel believes that the systemshould be self-financing, requiring no publicfunds at all, it sees a further need for urgency.The system should be at an advanced stage ofplanning before the next General Election be-fore a possible change of Government could leadto a change in policy, so that potential investors,especially programme providers, can be assuredof a return on their investment.

Satellite tv gets go-aheadOn the fourth of March, the Home Secretary,William Whitelaw, announced in the House ofCommons that the country should make anearly start with direct broadcasting by satellite(DBS), with the aim of having a service inoperation by 1886. Because of the importance ofmaking this early start, the Government hadconcluded that the best course would be to startwith two channels initially, though this could beincreased later to the maximum of five channelspermitted by international allocation. The ser-vices would be transmitted at powers sufficentfor individual reception and for community re-ception with cable distribution.

The system is to be financed privately, andthere were indications that there were interestedparticipants in the aerospace and electronicsindustries who were ready to pay a part.

As far as the programmes were concerned ithad been decided to award both DBS channelsto the BBC as they had already formulatedproposals for the programming of such chan-nels. One channel would be a subscription ser-vice including a substantial element of featurefilms and major sporting, cultural and otherevents not presently available for transmissionthrough the usual channels. The other would bea service which would draw on the best tv pro-grammes from around the world, and wouldprobably be financed by a supplementarylicence fee.

The Home Secretary said that although theIBA and commercial television companies hadalso shown some interest in providing DBS ser-vices, "their plans were less well advanced.Additionally, more time would be needed todevise the right framework, which would belikely to involve legislation".

But the IBA say that their proposals for satel-lite broadcasting are as well prepared as anyfrom the BBC. Following the Governmentstudy document on DBS last year, the IBA hasargued for the use of satellites to improve pic-ture quality and for the need to have uniformstandards throughout Europe, because of theoverlap of satellite footprints. IBA engineershave developed the multiplexed analogue com-ponent technique for satellite broadcastingwhich overcomes the problems of incompatibil-ity between the different colour systems in

Europe, providing a single 625 -line system withclearer pictures than are presently available ontelevision receivers, and with multi -channelsound. Only one design for an adaptor unitwould be required throughout Europe. Theyalso argued that they had more commercial ex-perience which would be useful for organising asubscription service.

tary's announcement, British Aerospace, Mar-coni and British Telecom made a joint an-nouncement that they would take equal sharesin a new company, United Satellites, to provideBritain's first national broadcasting and tele-communications satellite system. The threecompanies had already investigated potentialmarkets, and the technical and operationalmeans needed both in the long and short term.The system would probably have the capacityfor two tv channels and three or four commu-nications channels. There could be sufficentbandwidth to transmit high -definition tv anddigital sound channels and the possibility oftransmitting a Prestel-type service this waycould also be possible. Discussions with broad-casting and telecommunications organisationswill define the facilities to be provided. Thesatellites will be leased to the users.

The satellite, to be known as Halley 1, as the1986 launch will coincide with the appearance ofHalley's Comet, is likely to be of a similar typeto the European Communications Satellite(ECS) and it is planned to have two satellites inorbit, with the second as a standby and a thirdon the ground ready for launching.

United Satellites hope to sell their satellitesaround the world and believe there is a potentialmarket for up to 100 of them.

The IBA is participating in the experimentalEuropean service, organized within the EBU.The five -week tv experiment, to start at the endof this month, includes four sound channels,each with a different language and the IBA'steletext system for sub -titling. The closed-cir-cuit service is to be transmitted using a mobiledish antenna via the ESA orbital test satellite.

A Pan -European service is due to be launchedin 1986 and the IBA has suggested that the all -British satellite should carry that service.

Maritimesatellite getssunstrokeWhat was to have been a blaze of publicity whenthe Minister for Information Technology, MrKenneth Baker, was to have made the firstshore -to -ship telephone call by way of the newMarecs-A maritime satellite, turned into a bit ofa damp squib when it was announced that thesatellite had certain anomalies which needed tobe sorted out before it became fully operational.

The anomalies had been caused by an over-active sun which had produced an unusuallyhigh number of sunspots. Sunspots emit high-energy particles which when they encounter asatellite can electrostatically charge the outerthermal blanket of the spacecraft. As differentsurfaces are charged at different levels, this cangive rise to arcing and if any electromagneticdisturbance penetrates the screening this cancause spurious pulses in the electronics. Thefirst occasion on which this happened in Ma-recs-A, it caused the orientation system to thinkthat it had lost contact with the earth. It auto-matically went into a 'search' mode when itrotated slowly to find the earth again. This ma-noeuvre took eight hours before contact was re-established and this caused a whole series ofchecks to be carried out to assure the groundcontrollers and users that all was well. It was notpossible to complete these checks before theofficial inauguration of the service. Since then,there have been further small 'glitches' causedby sunspot activity.

A major event during the initialisation of thesatellite was the failure of two modules in thebattery discharge regulator. Standby moduleswere switched in, but there is no further re-placements for these components. A spokesmanfrom British Aerospace told us that although itwas worrying to lose the redundancy factor soearly into the mission they were confident thatthis would have no effect on the planned life ofthe satellite of seven years and more. They wereinvestigating the cause of the failure, and of theanomalous behaviour of the vehicle in order tobuild additional safeguards into Marecs-B


Marecs -A maritime communicationssatellite suffering from anomalies causedby an overactive sun.

which is to occupy a geosynchronous orbit overthe Pacific Ocean.

The two Marecs spacecraft in conjunctionwith an Intelsat V over the Indian Ocean offer aship -to -shore telecommunications system whichcovers all the oceans. Marecs-A is the firstEuropean Space Agency's communications sa-tellite to enter commercial service. It is also thefirst to be dedicated to merchant shipping, andthe first to be leased by ESA to an internationalorganisation, Inmarsat.

Marecs offers some 40 telephone circuits,four times the capacity of the Marisat satellite it

replaces. It is also 11 degrees further west thanMarisat and so can cover the western part of theGulf of Mexico and some of the eastern Pacific.In addition to telephone contact the satellite canbe used to receive and transmit telex, facsimileand digital data links. There is also a specialemergency signal link.

In order for the satellite to operate efficiently,as much attention needs to be made to thecoastal receiving stations as to the on -boardsystem. Europe's first maritime communica-tions station has been inaugurated at Eik, south-west Norway. Eik is the fifth in the global satel-lite system of earth stations and another 14 areplanned including one at Goonhilly, Cornwallwhich will be commissioned by mid 1982.

3-D spectacleThe first British broadcast of 3-D tv takesplace on May 4th at 19.00h over the transmittersof TVS, the Southern region ITV company.This follows the four 3-D tv programmestransmitted over Norddeutscher Rundfunk inWest Germany, the first of which was on Feb-uary 28th. TVS is negotiating rights to some ofthe German material, and also producing someoriginal British material. The British pro-gramme, one of the weekly series The RealWorld, deals with three-dimensional images ingeneral, and the 3-D inserts are being used forillustrative purposes.

The system being used for these transmis-sions is the old and imperfect method of 'anag-lyph stereo': that is, separation of the twoimages is achieved by colour coding, and theviewer has to wear red -and -green spectacles.This is clearly not a system with any prospect offuture acceptance as a practical method forbroadcast stereo. It is however at the presenttime the only method by which stereo imagescan be broadcast, pending future technical de-velopments. Consent has accordingly beengiven by the IBA to TVS transmission as a one-off experiment.

IBA consent was required because the anag-lyph system is non -compatible: 3-D can only beseen by viewers with colour receivers. Viewerswith black -and -white sets will merely see a pairof overlapping images, whether or not they lookthrough the spectacles. And viewers who don'thave the anaglyph specs will also see merely apair of flat images.

Colour scenes cannot be transmitted, sincethe colour -coding is already being used for 3-Dseparation. The left -eye image is put out on thered channel and the red tube phosphors, and theright -eye view in green plus blue.

In fact, if a colour scene is coded in this way,a certain sensation of the colours of the scene isretained even through the red/green glasses, asthe brain attempts to add together the differinginformation received from each eye. But ambi-guity and some discomfort is caused by anybrightly -coloured objects; for instance a reddress will appear bright to the left eye but darkto the right eye. Without spectacles however thescene appears relatively normal in colour values.Experiments are now being made in the transferof colour scenes, but none are expected to lxincluded in the first British transmission.

The research behind the German pro-grammes has been carried out in the Eindhoven

laboratories of Philips Ltd. Anaglyph imageseparation on tv is at best imperfect, since thegreen phosphors on tv tubes have quite a highred content. This means that 'crosstalk' is intro-duced: the left eye sees some of the green image,which should be confined to the right eye. Inaddition, colour coding within the PAL trans-mission system is itself imperfect, and allowssome spread of colour information to the wrongguns. Philips have developed a method of cod-ing the master video tapes, which at presentremains secret, to eliminate this overlap andensure the best possible separation of the twoimages that can be obtained within the PALsystem.

IfThegreatest problem remains the provision

the red/green anaglyph spectacles. TVS hasobtained half a million of these cardboard lorg-nettes, and are distributing one in every copy ofTV Times in the Southern region. Even so, itseems there will be at best one viewing device toeach set, so the programme is being scripted toallow time for it to be passed from hand to hand.The programme cannot of course be networkedoutside the Southern region, because of the lackof sufficent spectacles. Lucky viewers outsidethe region who are able to pick up TVS pro-grammes will have to make their own arrange-ments to get hold of a pair of anaglyph specs.

Viewers who have seen the German pro-grammes agree that in spite of the limitations,the results are remarkably successful; the cross-talk or double -imaging only becomes worryingwhen the normal, rather restricted, depth rangefor any scene is exceeded. And the 3-D scenes,particularly in the 'live' studio sequences, arecertainly good enough to serve as a glimpse intothe future. The people in the studio scenes,even in black -and -white, look much more likerounded human beings than the usual 'flat' tvimages.

Mercury andBritish TelecomThe consortium of Cable and Wireless, BritishPetroleum and Barclays Merchant Bank havebeen given a licence to operate a private tele-communications system in the UK. The system,to be known as Mercury, will have access to thepublic switched network when 'appropriateterms' have been established. It will also pro-vide an earth station for business telecommuni-cations via satellite. The licence has beengranted for a period of up to 25 years withprovisions for review. Patrick Jenkin, Secretaryof State for Industry said that "the BritishTelecommunications Act 1981 and the licencehave been structured in a way to enable theGovernment to ensure that both BritishTelecom and the licensee co -exist and competeto generate new services and job opportunitiesand to enhance customer choice within the UKwhile increasing the national share of the worldtelecommunications market".

It seems that the competition has alreadystarted with BT cutting its charges on some ofthe main trunk lines joining the main businessand industrial centres. The principal reason forinstituting Mercury was the high cost of trunkcalls.

All this may be thrown into the melting pot ifthe telecommunications network is to be boundin with the proposed tv cable system. lain Car-son reports in The Observer that the Government


is to introduce a new Telecommunications Billtowards the end of the year. The Bill will pro-pose the selling of about half the shares of BT tothe public and to establish a new telecommuni-cations authority to oversee the provision ofcable tv, telephone, data and electronic maillinks. The so-called Busby Bonds, announcedby the Chancellor in the Budget with which itwas planned to inject public investment intoBT, are now likely to be replaced by the muchwider de -nationalisation. BT say the report is"pure speculation".

BildschirmtextAt the heart of Prestel is the GEC 4080 compu-ter which uses its own language, Babbage. Witha five-year lead over any rivals, GEC must havefelt that they had a very good chance in theworld's markets and particularly in Europe.Their confidence received a severe blow,however, when the West German Bundespostplaced an order worth several millions withIBM. What was even more galling was that IBMhave not demonstrated any system in public.

The GEC equipment has undergone a fieldtrial in Germany, and the Bundespost has selec-ted a Prestel-compatible system, as recom-mended by the CEPT, but the selection of anIBM system means that IBM will have to writeall the software by the contract deadline in 1983.

Sweden in spaceby 1984

Sweden's Space Corporation is likely to be giventhe krona it requested for this year's space re-search programme, more than double the1979/80 figure. About half of this will be contri-buted to the European Space Agency whereSweden collaborates actively in the programmesof research. But its national programme in-cludes its own space research where the largestproject is the Viking satellite, to be launched byAriane in 1984 for North Pole magnetospherestudies, as well as the industrial Tele-X project.Due for launch in 1986 from Guyane SpaceCentre, South America, Tele-X is an experi-mental telecommunication satellite that willhave pre -operational direct broadcast applica-tion. And it will provide high-speed digital com-munication for inter -office links, a teletype ser-vice to mobile stations in vehicles, andpropagation measurements in the 20-30GHzband for high-speed digital data communica-tion, as well as wideband services.

Monitoring oil spillages is the chief applica-tion of the Corporation's other main programme- in remote sensing. Marine surveillance fromaircraft determines oil thickness and volume, amicrowave radiometer while a laser fluorosensorclassifies oil type, this information beingtransmitted to oil combat vessels. Remote sen-sors also monitor ocean ice distribution andthickness, atmospheric pollution and map vege-

Auditoria designers are often "very surprised" with the results they obtain, said HughCreighton, acoustical consultant to London's latest concert hall in answer to our questionabout reverberation time turning out lower than planned. "Hall acoustics is not a completescience" he reminded us, "but design guided by science". For although r.t. had beencalculated from the hall's volume and absorbencies to be 1.8 seconds, it turned out tomeasure only 1.4. But the simple expedient of adding hardboard to the backs of the (fixed)seats increased the figure to 1.6 seconds, or 1.9 with an audience. And that seems to satisfythe LSO, according to a spokesman, for whom it was designed. A height restriction meantthat the concrete roof beams protrude into the auditorium, their disruptive effect beingreduced by the suspension of some 1,000 diffusing spheres (some also acting as lightingfittings) open at both ends to prevent undue aborption. And while siting the hell close tothe foundations of the Barbican complex may reduce the vibration due to the nearbyunderground railway, it didn't obviate the need to re-lay the tracks and mount them onrubber.

tation, deserts and lake water to study seasonalchanges. The Corporation manages the Esrange stationwhich receives, processes, stores and distributesimages from ESA satellites in the Earthnetscheme, and regularly collects data fromLandsat. The station conducts ionosphericsoundings to give investigate electron densityprofile (see WW February issue, page 37).

Where isChernobilsky?The position of the Russian electronics engineerBoris Chernobilsky who, as we reported in Oc-tober 1981, page 70, was being harassed by theKGB, is giving his wife Elena great cause foralarm. After his harassment and arrest on arelatively trivial charge (hitting a policeman)Chernobilsky was sentenced to one year's im-prisonment in a corrective labour camp, muchagainst the wishes of the court, who came undera great deal of public pressure to relax the in-tended five-year sentence. The court sentencewas that Chernobilsky be taken to the labourcamp immediately, but instead was held in pri-son for two months, whereupon he disappeared.According to our informant, he started his jour-ney to the camp many weeks ago, but neitherhis destination nor present whereabouts areknown, in spite of a telegram from his wife to L.Brezhnev, and other Soviet leaders, to whichshe has had no reply. His wife and friends fearthat the KGB are victimizing Chernobilsky be-cause he was awarded a 'light' sentence, andthat his health will be damaged by the extremelysevere conditions on the journey and in thelabour camp.

BBC microThe gremlins got into the BBC micro programlistings at the Paisley Microelectronics Educa-tional Development Centre, John Gordon tellsus. Routine (f) on page 82, March issue, shouldbe

500 PROCTAXCAL0(450, 100)600 PRINT tax to_pay700 END

1000 Dia' PROCTAXCALC ( total_pay, tax allowance)

1010 LOCAL pay_lef t , pay_this_rate , rate

1020 tax to_pay=0 : pay left=total_pay - taxallowance: rate.° . 1

1030 REPEAT1040 IF pay lof t>100 THEN

pay this_rate= 100ELSE pay this_ratpay left

1050 tax to_pay=tax to_pay + rate*pay this_rate

1060 rate= rate+0.11070 pay 1 ef t=pay left -

pay this_rate1080 UNTIL pay_lefo40.116)0 '

It is useful to use lower-case characters for data -names he points out: this gets round the prob-lem of BASIC keywords appearing at the begin-ning of a dataname.

Also in this issue . .

Book notes 49Communication news 42Corrections 41In our next issue 77Langmuir thin film trough for"molecular electronics" 34Teledon videotex in the UK 40


EPROM PROGRAMMERMost commercially available e.p.r.o.m. programmers are expensive as they includesoftware and other facilities to enable them to be used on their own. The cost of aprogrammer can be significantly reduced if it is designed for use with an existing

microprocessor system as shown in this second of two articles. The design presented isfor 2708, 2716 and 2532 e.p.r.o.ms, but with small modifications other devices may be

programmed.

On entering the program one is given thesystem options and prompted to replyeither Y (yes) or N. Next the addresses arerequested in hexadecimal numbering,starting from 0000. If the e.p.r.o.m. al-ready has data in the first 256 locations thestarting address must be given as 0100,even though it is intended to reside at,say, DCBO. Options and addresses aredisplayed on the monitor screen. Whensufficient information has been given theprogram repeats the e.p.r.o.m. type andprompts you to press G (go). At this pointthe scratchpad has been loaded with datarelevant to the e.p.r.o.m. selected andwhether it is in read or write mode, asdefined by the options on entering theprogram. (A changeover d.i.l. switch isneeded to select the 2708 rails; for conve-nience this was fitted to the plug-in cardcarrying the socket together with a jack forthe program voltage.)

Scratchpad data is loaded by the indexregister as though it represented addresses;this seems to be the quickest method ofloading for the 6800. Data stored in thescratchpad is given in the panel and ex-plained as follows. The device code in AS-CII enables it to be displayed on the moni-tor screen and serves as a check that thescratchpad has been loaded correctly.Number 04 signals the end of the ASCIIdata. The term "pin profiles" is one I'vecoined to define the logic levels on a portwhich are independently varied within aprogram. The existing address port is in-sufficient to drive the e.p.r.o.m., whichneeds 12 lines, so some are borrowed fromthe control port. By OR-ing the pin -profilewith the other data the port will supportthe two functions. For example, during aread operation the address part of the portwill be changing and the levels on thecontrol will be static, during write thecontrol part will change from pulse-off-)pulse-on--,pulse-off during eachchanged address. The loops will normally=1, except when the 2708 is being pro-grammed which requires 200 loops. It isnot permissible to apply N pulses to onelocation and move on. The number ofloops may be varied in the range 100 to1000, depending on the pulse width; N =200 was chosen for convenience in generat-ing the timing. Locations E,F contain anumber which is used with the index regis-ter and decremented to zero. The time atthe pulse output (port) should be mea-sured with a universal counter or an accu-rate 'scope since it depends on the softwareroute taken by the programmer, as well asthe system clock frequency. RandomWIRELESS WORLD MAY 1982

by H. S. Lynes

access memory addresses determine thearea of the system memory that will bewritten to or read from. The e.p.r.o.m.start/finish enables part -used ones to beadded to. This is not to be done with 2708sas already explained. The control word iseither 80 (port B is output, so writee.p.r.o.m.) or 82 (port B is input, so reade.p.r.o.m.) which shows the ease of usingthe 8255 in mode 0. (Other numbers in thecontrol register will cause all kinds oftrouble).

The shorthand CAD and CAP were use-ful since they are frequently referred to inthe software. The "loops left" is loadedwith the value of the loops at location Aand decremented on starting at the firste.p.r.o.m address, i.e. when CAP is set tothe address at 14,15. In the case of a 2708,this will now represent a value greater than1, so the same addresses must be pro-grammed again until lE reaches zero. Forreading an e.p.r.o.m. whether dumpingthe contents into r.a.m. or checking aprogram cycle, the loop facility is notneeded as the program will exit wheneither CAD or CAP reach the respectiveaddresses in 12,13 or 16,17. Thus the pro-grammer should ensure that whichever isthe smaller number of locations will causethe program to exit. The last three loca-

tions are loops -left, as explained, and theerror address, to be explained later.

Port control. Since the software controlsthe 8255 it is essential to check that all iswell before proceeding. The sequence is asfollows. Select the e.p.r.o.m. type, themode (read/write), as well as the addressesfor both e.p.r.o.m. and system r.a.m. Theprogram responds by displaying the typein four decimal figures followed by theprompt to press G. There are two chancesto get this right: it's frustrating to enter thedata again just because you accidentallytouch the space -bar. Before the programstarts the control port is checked for either80 or 82, since other numbers will causechaos. At this point the scratchpad hasbeen checked twice; once visually by theuser and once in software to fairly tightmargins (2/256). Any error should be re-solved by starting again. After a programsequence the 8255 is put into the readmode and the data is compared with ther.a.m. area specified. Any error will storethe error address at the scratchpad 1F,20locations. A message is written on thescreen to invite inspection - the systemèrrors' each time at the last address (whichproves it's working) since to program onee .p .r.o.m. location, say 01F2, requires theuser to enter ep.r.o.m start = 01F2 and,logically, e.p.r.o.m. finish O1F3.

Reading an e.p.r.o.m. This is the easiestpart. Select the appropriate pin supplies

Scratchpad data defined. Location of the scratchpad is at the option of theprogrammer.

0, 1, 2, 34, 567

89ABCD

E

F

10, 1112, 1314, 1516, 1718191A, 1B1C, 1D1E

1F, 20

Device code in ASCII 32 37 30 38 for 2708EOT code and blank 04 00'read''progam' pin profiles e.g as in Table 1

'pulse -on'

Loops = 1 except for 2708 = hex equivalent of 200- (normally biank, except during verify)

Maximum bytes, could be used to check 'space available'

delay = pulse time

r.a.m. start addressr.a.m. finish Entered by user; 'start' must be lowere.p.r.o.m. start number than the 'finish' numbere.p.r.o.m. finish8255 control word

Current address data (CAD)Current address p.r.o.m. (CAP)Loops leftError address - in hex (could be converted to ASCII if screen displayrequired)

67

using the small d.i.l. switch next to thesocket, and enter the necessary informa-tion to fill the scratchpad. After pressing Gset-up the 8255 ports by sending 82 (hex)to the control register at X503. Thestarting address of the e.p.r.o.m. is placedin the address ports A and C. The controlpin -profile is OR-ed with the address inport C and the data read by the c.p.u. fromthe address of port B. This is stored in thearea of r.a.m. pointed to by CAD using theindexed mode of addressing. CAD andCAP are checked to make sure they are notoutside limits and only then will they beincremented until the e.p.r.o.m. data isplaced in system r.a.m.

The time taken is quite short, but it isnot possible to run a program from ane.p.r.o.m. in the programmer withoutsome considerable delay and a dedicatedprogram to do it. In my system a facilityexists to move some of the system r.a.m.,having set up the new start address ond.i.l. switches. Thus by moving a toggleswitch the r.a.m. can be made to behave asthough it was a programmed e.p.r.o.m.,residing at the same address as thee.p.r.o.m will in the finished system. Thismay be write -protected if desired. Ensurethat only one device is enabled when shift-ing.

t ttestpoint

Link 1

see

Note 3/4

PC5

PC4

PC7

1100n I

Programming. This is more difficult,since the e.p.r.o.m needs to be given aprogram pulse for a defined time. Anexternal voltage is required, about 27V toallow for losses, and on my system a circuitmeasures this voltage and turns on anl.e.d. if it is correct. Thus the light indi-cates that the e.p.r.o.m can be pro-grammed. The use of a built-in programvoltage is left to you; if the ports are likelyto be used for general use I think it is saferto bring it in separately. Pin selection d.i.l.switch, address entry, etc is as explainedfor reading. After pressing G the e.p.r.o.mis placed in the write condition using thepin -profile described. A program pulse isapplied by OR-ing CAP with the pulse -on pin -profile and placing it at the port.This is timed using the delay routine, afterwhich the address is OR-ed with the writepulse -off pin -profile and stored at the port.Thus the port is in the write mode all thetime, some of which is in the pulse -onmode; the e.p.r.o.m. address is onlychanged when the port is in plain writemode.

The choice of software timing for thepulse or the use of a monostable is left toyou. If you choose monostable timing theclock frequency is not important; but amonostable is another i.c. to wire and

T TuP

10k

1k

10k

//Red fed.see

Note 4

10k 47

10k

1k

2 x 120

0+265Program supply to provide a minimumswing of 25V see Note 1

n p n 2N3904p n p 2N3906 11 I

2 x 3900 Output

2000p

Fig. 6. In this transistor interface and resetlogic PC7 is used to detect the highimpedance state after reset occurs. Thisprevents unwelcome voltage appearing onthe e.p.r.o.m. socket. Normal operationwith PC7= output, logic 0 is Vp = 26V withPC5 = logic 1. Notes:1. Pulse output is critical and should be

checked against manufacturer's data.Measurements must be from e.p.r.o.m.socket. For Co 1800pF, Tr1µsT11.2fis.Co 2800pF, T, 1.5µs Tf2ps measured on50MHz 'scope TTL input waveform 1:3ratio, 1 cycle 25µs.

0 0 V

+12V

n/WE2708 onlysee Note 2

2. The CS/WE pin needs to be taken low atthe finish of programming before theaddress is changed. Since PC4 is onlyused with 2708 this can be done at theend of any programming sequence, as aforerunner to the verify routine.

3. Test point is a convenient place to drivethe interface, with link 1 open.

4. LED is on when V,, is high. If no 'scope isavailable V,, should be set to 26V usinga 20kI2/V multimeter. Test point = 3.5Vwith link 1 open.

could be susceptible to interference. Soft-ware timing has its critics too, but whenother e.p.r.o.ms as well as 2708s are to becatered for it is justified in my view. Pro-gramming does take time - typically oneminute for every 1024 x 8 bits. Thus fora 4K e.p.r.o.m the processor is tied -up forat least four minutes. If any interferenceoccurs during this time it could causetrouble, so there may be some advantage tobe gained by switching off any well-knowngenerators of interference. In the homethis can include anything with a thermo-static control inductive load.

Software development. Some of the de-velopment, done in hex machine code, wasmade easier by using the sub -routinesavailable in the monitor, such as the "printASCII string" sub -routine, and the "inputcharacters from keyboard" sub -routine forsetting -up the scratchpad data. If you wishto develop your own programs for anyc.p.u. type, I recommend that you includea facility for additional features you maywish to try. For example, my program asksif the user wants to "read?" and if theresponse isn't 59 (ASCII for Y) it goes to"write?", after which it exits. There wouldbe some advantage in writing "extra facili-ties; enter facility number"; you then enterdifferent routines, to be developed later,without rewriting the remainder of thesoftware. What you do is to reserve twomemory locations at the end of theprogram (in the final e.p.r.o.m. for themoment a 2716) and set the index registerto the address of the first, less two. Thus ifthe number entered is 1 the index registerwill be incremented by 1 x 2, so by goingto this location a new starting address maybe inserted. By leaving say six memorylocations all FF they may be programmedlater. Arrange the address routines as asubroutine so they may be used in laterdevelopments.

Infrequent users may find some advan-tage in making use of a 37 -way D -connector and a small plug-in p.c.b. withthe socket on it. This is only plugged inwhen an e.p.r.o.m. is to be programmedor read. The diagrams show the wiring forthe d.i.l. switches connected to pins 18-21,Fig. 6 It is essential that such switches aresuitable for the low -power duty that isrequired. Protect the wiring on this p.c.b.from handling; an unetched piece of cop-per laminate is ideal for the purpose as itmay be connected to OV.

Erasing e.p.r.o.ms. It is essential thate.p.r.o.ms are correctly erased before pro-gramming is started. This means exposingthem to "hard" ultra -violet light for aperiod of between 5 and 20 minutes, de-pending upon the strength and closeness ofa suitable source. So-called u.v. tubes withfluorescent coatings inside glass will not besatisfactory; this rules out disco black -lighttubes and soft tubes used to generate art-work. The correct tubes are usually small,low -wattage with a quartz tube thatpermits the transmission of the mercury -vapour radiation of 254nm wavelength.Although satisfactory erasers are availablecommercially, you may be tempted tomake your own using a replacement tube.


Fig. 7. In the prototypeprogramming board the78L05, which shouldhave been shown herewith a diode in its groundlead, was mounted onthe programming boardtogether with a z.i.f.socket, d.i.l. switch andprogramming pulse jacksocket. The diode in theregulator's ground leadraises its output to 5.7V.Current limiting at 50mAis used on the '30V'supply, which shouldnever be less than 26Vand without overshoot.The line at the junction ofthe two diodes is at either5 or 25.25V, dependingon the device to beprogrammed.

-12V smoothed

OVO

+17Vsmoothed

CS/WE (PC4)0

PC60

0PC2

78L12

79L05

79[05

R <

r I

S

Si V

C 100n discR 41(7 "2W

4 -pole 2 -wayi.l. switch

21

20

019

0+26V switched ( PCS)

COP3

0+30V (25 to 30V(

El VA

10

10k

1 Ov

18

socket

Take care in the design of a close -fitting lidor drawer to prevent the incidence of u.v.burns to eyes or skin. It is a sine qua non toinclude an interlock which breaks thetube -current in the event of the lid (ordrawer) being opened during the eraseperiod. The addition of a timer is a usefulrefinement as the tube has limited life.Clean the i.c's window before erasure -afterward it may be covered to guardagainst possible loss of data when it hasbeen programmed. And keep thee.p.r.o.ms in conductive foam whenever

possible to prevent electrostatic chargecausing degradation or destruction.

Whilst this programmer satisfies the ini-tial design requirements there is no reasonwhy other e.p.r.o.m. types should not becatered for. Probably the easiest method ofaltering the pin requirements is to bringthose pins which are likely to need changesto a separate header which may be used asa patch -board, in the same way that thed.i.l. switch was necessary in Fig. 6.

The 26V transistor interface, Fig. 7, istolerant of the value of output capacitance

although I recommend that the outputwaveform is checked. The l.e.d. is illumi-nated when the output is at high potantial,which should be typically 26V to ensurethat the miminum swing of 25V is met.

Reset logic prevents unwelcome voltageappearing on the e.p.r.o.m. when an out-put port is arranged so that logic 0 = OV. Ifthis is inverted then the problem may beresolved and the port PC -7 becomes spareand could be used to perform some otherfunction. Personally I like to have ports atlogic 0 meaning no output.

1

1

April 23-25The Computer Fair, at Earls Court, (sponsoredby Practical Computing and Your Computer).Details from Exhibition Manager, IPCExhibitions Ltd, Surrey House, 1 ThrowleyWay, Sutton, Surrey.April 25Audiojumble: sale of audio equipment at theGandhi Hall, YMCA, 41 Fitzroy Square,London W I. Organised by Ed Lord, 67Liverpool Road, London Ni.April 26Amateur radio satellites; IEE lecture foryounger members. IEE, Savoy Place, LondonWC2P OBL.April 27Recent developments in the measurement ofweak magnetic fields and associatedapplications: IEE colloquium.April 29Software engineering: IEE lecture.April 29UOSAT - a low cost spacecraft for professionaland amateur scientists: IEE lecture.

April 29-30Spectral analysis and its use in underwateracoustics: Institute of Acoustics/IEEconference. Imperial College, London SW7.Details from: Dr T. S. Durrani, Department ofElectronic Science and Telecommunications,University of Strathclyde, Glasgow G1 1XW.April 30Up-to-date applications of dataview systems:IEE colloquium.May 3-6Video '82: Trade fair and Congress:International Congress Centre, Berlin.Organised by AMK Berlin, Postfach 19 17 40,Messedamm 22, D-1000 Berlin 19.May 4Human factors in word processing: IEEcolloquium.May 5-7Videotext Systems '82: Conference andExhibition. Cunard International Hotel,London. Organised by IPC Exhibitions Ltd,Surrey House, Throwley Way, Sutton, Surrey.May 6Digital tv effects: IEE Younger Member'slecture. Ship Hotel, Duke Street, Reading,Berks.

May 11-13Micro City '82: Information technologyexhibition. Bristol Exhibition Complex. Detailsfrom Tomorrows World Exhibitions Ltd, 9Park Place, Bristol BS8 1JP.

May 12Microprocessor projects for the plasticsindustry: Seminar at the National ComputingCentre, Manchester. Organised by the BritishPlastics Federation, 5 Belgrave Square, LondonSW1X 8PH.May 12Electrostatics and optical effects: IOP Meeting.Institute of Physics, 47 Belgrave Square,London SW1X 8QX.May 12Time delay systems control: IEE colloquium.May 12Effects of obstacles and dielectric structures inthe near -field on antenna performance: IEEcolloquium.May 12Teletex and its protocols: IEE lecture.May 13Development environments for microprocessorsystems: IEE colloquium.


Within 80ms a mass of I/4kg can be moved a distance of four inches and stopped to withina quarter micron of a specified point - this article shows how.

From disccontrollogic

CYLINDER

DIFFERENCE

4N.

Cylindercrossings

TRANSDUCER

d -to -a Scheduled velocit

DISC DRIVETRANSDUCER

AMPLIFIER

-SNSMI6.2116110==,

ERROR

AMPLIFIER

Actualvelocity

POSITIONERSACTUATOR POWER

AMPLIFIER

Velocityerror

In any positioning system the most crucialcomponents are the prime mover and thetransducer used to describe the positionand velocity of the element under control.Here, the main features of disc -drive posi-tioners, including feedback loops andcontrol circuits, are described.

With the exception of fixed head andWinchester type disc drives, the read/writeheads are mounted on a rigid platformcalled the carriage. This carriage has onedegree of freedom radial to the drivespindle and is restricted by guideways,usually in the form of rails or bars; in mostcases, the carriage runs on ball bearings,one or more of which is spring loaded totake up play and ensure that the bearingsroll instead of skidding. Not all carriagesrun on ball bearings - some run directlyon the guideway - but the way in whichfour types of those that do are constructedis shown in Fig. 1. Rotary positioners,such as those used in Winchester discdrives, will be described in a subsequentarticle.

In multi -platter drives, the heads areusually mounted side -by -side between theplatters to reduce the overall height of thepack and minimize the weight of the car-riage. The part of the carriage to which theheads are attached is often called the T -block because more often than not it is T-shaped. For convenience, the two sides ofthe T -block are designated A and B, andeach side will have upward and downwardfacing heads. So in this case there are fourread/write head labels; A -up, A -down, B -up and B -down. A and B heads designedfor opposite directions are similar in ap-pearance but if they are mistakenly in-terchanged, slipper aerodynamics will be

*B.Sc., M.Sc., Digital Equipment Co.

by J. R. Watkinson*

ij -w401,

Fig. 1. Four methods used for mounting disc -drive positioner carriages. Common purposeof these is to allow only one degree of freedom, ideally along radius of the disc.

Actual positioner path

Ideal posihoner path

Fig. 2. Mounting read/write heads side -by -side in multi -platter drives reduces height of thedisc pack and hence weight moved by the positioner, but alignment between carriagecentre line and disc radius becomes more critical. Here, the heads are aligned at track A andthe error caused by carriage/track-radius misalignment becomes apparent at B.


affected, so the head type is usually clearlymarked. Slots in the T -block allow radialadjustment of the heads.

As the heads are in two rows, it is vitalthat the centre line along which the car-riage travels is precisely on the disc radius.Figure 2 shows why. Alignment fixturesprovided with the drives allow the heads tobe accurately aligned and, equally impor-tant, keep the head adjustment standardbetween drives using interchangeablediscs.

Motive powerThere are three main methods of drivingthe carriage- hydraulically- by moving coil- or by electric motor.

Hydraulics. The first moving -head discdrives stored data at very low density bymodern standards, so if large amounts ofdata had to be stored, large discs had to beused. Some of these discs measured severalfeet in diameter. The carriage was equallylarge, and the only practical way of movingit was by hydraulics. Much research intohydraulic systems for applications such aspower -operated gun turrets on military air-craft had already been carried out so thedesign of a system for driving the carriageof a disc drive was simplified.

Figure 3(a) shows the essentials of anhydraulically powered positioner, in whichthe pump may be driven either by thespindle motor or by a separate motor. Theaccumulator is required for rapid seeks,when the peak -flow requirement is greaterthan the pump can deliver; the analogywith a power -supply capacitor is clear.Fluid pressure is regulated by a bypassvalve, the fluid equivalent of a zener diodeand a series of solenoid -operated valveswith calibrated orifices are used to move

(a)

Pump

(b)

Spring

Ram- -1 To carriage

ALcumulator Controlblock

Regulator

Control signals

1

Fig. 3. Essential elements of an hydraulic positioner are shown at (a), in which the pressurefrom the fluid pump is regulated by a bypass valve and control signals from the drive logicoperate solenoid valves in the control block. Accumulator permits high peak -flow rateswithout large pressure fluctuations. In (b), two opposed positioners are used to cancel outreactions caused by fast carriage acceleration.

the carriage at different speeds. Somedrives with hydraulic positioners wouldmove from their position in the computerroom, because of the reaction from fastcarriage acceleration, and had to be movedback into place from time to time. Behe-moth drives had two parallel spindles with

se format

ack or head, and sector. A malfunction inorks from three dimensions: cylinder,e access mechanism of a disc drive

any of these could bring the heads to thewrong data block. In the interests of dataintegrity, each block of data is preceded bya header which contains the disc address ofthe block. Before a data transfer can take

ace, the disc address according to the'cess mechanism is compared with thesc address in the header. If the two aree same, the data transfer proceeds, if

ot, the transfer is aborted and a misposi-oning condition exists, usually referred to

a header mismatch error. The header:.

HetlOr DISC

Pr COI biE odrirp,s,

Syncnit&

He'l/er

are usually written once when the disc isfirst used, by a process known as format-ting, and are then subsequently only read.Because of this, the header and the asso-ciated data require individual preambleswhen used with an encoding techniquerequiring phase -locked recovery, as theheader and the data have not necessarilybeen written at the same time, or for thatmatter, on the same disc drive. Somedrives, however, treat the header and thedata as an entity, such that the header isrewritten every time a block is written.The diagram shows a fairly common disc -block format and lists the functions of eachelement.

Oat,:;,recTI-

er7or

Representative disc -data block. Header cyclic -redundancy check (c.r.c) and data -error correction words will be discussed later. The postamble is included toprevent data corruption when the write current is switched off.

opposed positioners between them to can-cel out this effect, Fig. 3(b).

Moving coil. As head and medium designimproved the storage density increased,allowing the platters to be made smaller.This made the carriage smaller and lighterso less power was required to move it. Atthe same time, advances in semiconductortechnology brought down the price ofpower transistors. It thus became feasibleto use a moving coil to drive the carriage,with the further weight reduction of thecarriage that the principle allows beingused to reduce access time.

A typical coil has a diameter of threeinches and works in the radial flux from apermanent magnet weighing about 50pounds. Smaller drives use a copper wirecoil on a glass fibre former, but larger unitsmay use self-supporting coils wound fromrectangular -section aluminium strip. Alu-minium has a higher strength -to -weightratio than copper, and this considerationoutweighs the disadvantage of higher resis-tance. The coil frequently requires forcedair cooling in large units. The assembly isusually described as an e.m.a. (electro-magnetic actuator), Fig. 4.

Electric motor drive. There are two maintypes -one is as shown in Fig. 5. In thefirst, the motor drives a leadscrew whichmoves the carriage as it turns. In somecases a stepping motor is used, where thestable positions of the rotor correspond tothe positions of disc cylinders.


Fig. 4. Essentials of a disc -drive positioner.

headcantilever

motor spindle

tacho magnet

motor

headpigtails

Fig. 5. One type of motor -driven positioner. This assembly illustrates how apositioner using steel wires to drive the carriage looks.

(a)Fig. 6. Mechanical detenting. Detent pawl is split and has two sets of teeth at 180° to eachother. At (a), the carriage is detented to an odd numbered cylinder and the upper pawl teethare engaged. The lower pawl, represented by the broken line, rests against the topsof therack teeth. In (b), the carriage is detented at an even cylinder and the lower pawl is engaged.Tooth pitch on the rack is twice the cylinder spacing.

tacho

.4/`/ I I AO

(b)

A Input

Case ANull

Case BIn -phase

Case C

Antiphase

!

Fig. 7. Carrier -wave cylinder transducer. Oscillator feeds the transducer primary coil and thetwo secondaries are connected in opposite phase. Output signal phase, determined by therelative reluctance of the magnetic circuit's two limbs, is a function of the rack position.Three examples are given with associated waveforms.

Fig. 8. Para lel bar and Moire type gratingsused to modulate a light beam producetriangle and sine -wave outputsrespectively. These gratings are used todetect position and velocity.

The motor in the second type drives adrum which imparts linear motion to thecarriage through flexible steel wires. Thesetwo types are normally used only in smalldrives.

DetentingWhen the carriage is held at rest with theheads correctly aligned above the disktracks, it is said to be detented. Earlydrives used mechanical detenting wherepawls on a detent actuator move to engagea rack on the carriage. Figure 6 shows atwo-phase detent mechanism, where thespacing between cylinders is one half therack pitch. Mechanical detenting can befound on both hydraulic and moving coilpositioners, and the pawl will be operatedby a ram in the former case, or by a sole-noid in the latter. The teeth on the rack areasymmetrical so that after the detent hasengaged, some forward drive can be ap-plied to take up any backlash without fearof the pawl jumping out of engagement.The detent actuator is a fine piece of preci-sion engineering, and as such is expensive.Recent drives take advantage of the fallingcost of electronic circuitry and employelectronic detenting, where the carriage isheld by a feedback loop using a positiontransducer. Should for any reason the posi-tioner find itself off track, the positiontransducer generates an error voltagewhich will drive the carriage until the erroris cancelled. When operating in this waythe carriage servo system is said to be indetent mode, track following mode, finemode or linear mode, depending on thespecific documentation consulted. Duringa seek, the servo system changes to veloc-ity mode, also known as coarse mode.These are the two major operating modesof the servo.

TransducersThe purpose of a transducer will be one ormore of the following- to count the number of cylinders

crossed during a seek,- to generate a signal proportional to car-

riage velocity,- or to generate a position error propor-

tional to the distance from the centre ofthe desired track.


Gratingsignals

sindt

-cos

Adt

-sin

dtcos

Velocityoutput

LFig. 9. Optical velocity transducer. Four quadrature signals are produced from the two-phase transducer. Each of these is differentiated, and the four derivatives are selected oneat a time by analogue switches. This process results in a continuous analogue -outputvoltage proportional to the slope of the transducer waveform, whish is itself proportional tocarriage velocity. In some drives one of the transducer signals may also be used to countcylinder crossings during a seek and to provide a position error for detenting.

Sometimes the same transducer will beused to provide all three signals. For thisreason, transducers are best classified byprinciple of operation, rather than by func-tion.

Magnetic transducers. There are threedistinct types- moving coil- moving magnet- carrier wave.The first two types simply give an outputproportional to the rate of change of flux.The only difference is whether the coil orthe flux moves. Moving -magnet types of-ten have the coil concentric with the actua-tor, which provides good noise shielding.Moving -coil types sometimes have a buck-ing coil connected in phase oppositionwhich does not link the magnetic circuitin order to cancel out induced noise. Thesetwo types of transducer can only generate avelocity signal, but have the advantage thatno precision alignment is necessary; aworking clearance is all that is required.

The third type is illustrated in Fig. 7.The flux path of the transducer is com-pleted by a rack on the carriage, often the

same one as is used by the detent actuator.As the rack moves, the reluctance of thetwo limbs will rise and fall, and as thesecondary coils are wound in opposition toeach other, the output will be alternately inand out of phase with the input. A phase -

Sign bit

[yldiff

Differencecounter Decrement pulses

from cylindercrossing detector

sensitive rectifier gives a binary outputwhich can be used to count cylinder cross-ings during a seek. As no accurate positionerror or velocity information can beextracted, this type of transducer is res-tricted to use in mechanical detent drives,in conjunction with a magnetic -velocitytransducer. Adjustment of carrier -wavetransducers is critical, as the signal be-comes rapidly attenuated if the distancefrom the rack is too great, but thetransducer may be damaged by the rackteeth if the clearance is too small.

Optical transducers. These devices con-sist of gratings, one fixed and one mova-ble. The relative positions of the two willcontrol the amount of light from an 1.e.d.or bulb which can pass through to one ormore photo -transistors.

Referring to Fig. 8, it can be seen thatthis class of transducer falls into two cate-gories- Moire -fringe- parallel -grating.In a Moire -fringe transducer the bars onthe moving grating are not parallel withthe bars on the fixed grating. Relativemovement causes a fringe pattern whichtravels at a right angle to the direction ofmotion. This results in sinusoidal modula-tion of the light beam.

In the second type, all the bars areparallel so the sensor's output is a trianglewave. In both types of optical transducer,the spacing between the two gratings iscritical.

Whether the waveform used forcounting cylinder crossings is sinusoidal ortriangular is not important, so the choicebetween the two transducers is governedby whether a position error or a velocitysignal is required. The slope of a sine waveis steeper in the zero region than an equi-valent triangle wave so it is more useful fordetecting position error. Conversely theconstant slope of a triangle wave is easilydifferentiated to produce a velocity signal.Because the differential of a triangle wavechanges sign twice per cycle, a two-phaseoptical system is often used to give a con-tinuous velocity -output signal. Thestationary grating has two sets of bars witha 90° phase relationship and the resultant

Inverter

Actualvelocity

Scheduledvelocity Velocity

error

B

Fig. 10. Carriage velocity control by cylinder difference. Cylinder -difference value is loadedinto the difference counter, A. A d. -to -a. converter generates an analogue voltage, called thescheduled velocity, from the cylinder difference. This is compared with the actual velocityfrom transducer B to generate a velocity error signal which drives the servo amplifier.


Scheduled velocityand

actual velocity( broken line)

MAX CYLINDERDIFFERENCE

A

B

(a)

Positionercurrent

MAX CYLINDER ,

DIFFERENCE

A

( b)

8

Fig. 11. In example (a), dissipation in the positioner is continuous, causing a heatingproblem. The effect of limiting the scheduled velocity above a certain cylinder difference isshown in (b), where heavy current only flows during acceleration and deceleration. Inbetween, only enough current to overcome friction is required. Back to e.m.f. causes thecurver acceleration slope.

waveforms are referred to as sin and cos,even if they are triangle waves. The twowaveforms and their complements, knownas -sin and -cos, are differentiated andthe four differentials selected in turn attimes when there is no sign change. Thisprocess of commutation is achieved byf.e.t. analogue switches controlled by com-parators looking for points where the inputwaveforms cross. The result is a cleanoutput signal proportional to velocity.

Where one transducer has to generate allthree of the required parameters, Moiretype gratings are preferable because oftheir better position -error detecting per-formance. A certain amount of ripple onthe velocity output derived from a sinusoidhas to be accepted.

Optical transducers often contain addi-tional light paths to aid carriage -travellimit detection. The resulting signals maybe used during the head -loading sequenceto position the heads at cylinder zero, asthe sine or triangle outputs are cyclic anddo not give an absolute cylinder address.Mechanical detent drives pose the problemof finding an absolute reference to the cyc-lic output from the rack transducer. Onesolution is to drive the carriage forwardslowly until it contacts the forward stop,and then to preset the cylinder count totwo or three cylinders more than the maxi-mum.

SeekingA seek is a process where the positionermoves from one cylinder to another. Thespeed with which a seek can be completedis a major factor in determining the accesstime of the drive. The main parametercontrolling the carriage during a seek is thecylinder difference:

cylinder difference =desired address - current address.

The cylinder difference is a signed bi-nary number representing the number ofcylinders to be crossed to reach the targetcylinder, direction being indicated by thesign. The cylinder difference is loaded into

a counter which is decremented each timea cylinder is crossed. The counter drives ad. -to -a. converter which generates an anal-ogue voltage proportional to the cylinderdifference. As shown in Fig. 10 thisvoltage, known as the scheduled velocity,is compared with the output of the car-riage -velocity transducer. Hence any dif-ference between the two results in a veloc-ity -error voltage, which is then used toreposition the carriage hence cancelling theerror. As the carriage approaches the tar-get cylinder, the cylinder difference be-comes smaller with the result that the run-in to the target is critically damped (veloc-ity a - distance) to eliminate overshoot.

Figure 11(a) shows graphs of scheduledvelocity, actual velocity and actuator cur-rent with respect to cylinder differenceduring a seek. In the first half of the seekthe actual velocity is less than thescheduled velocity causing a large velocityerror. This saturates the servo amplifier,providing maximum current to the actua-tor which in turn accelerates the carriage toreduce the error. In the second half of thegraph, the scheduled velocity falls belowthe actual velocity generating a negative

To

servo

b

a

a+b

I

Fig. 13. Staircase from a d. -to -a. smoothedby adding a sawtooth waveform.

velocity error, and the servo amplifier isnow driving a reverse current through theactuator to decelerate the carriage inaccordance with the scheduler. Thescheduler deceleration slope can never besteeper than the saturated accelerationslope. Areas A and B on the current graphwill be almost equal, as the kinetic energyput into the carriage has to be taken out.Any difference will be due to friction andother losses. The current through the coilis continuous which would result in aheating problem, so to counter this the d. -to -a. converter is made non-linear so thatabove a certain cylinder difference no in-crease in the scheduled velocity occurs.This results in the graph of Fig. 11(b). Theactual -velocity graph is called a velocityprofile, and consists of three regions: ac-celeration, where the system is saturated, aconstant -velocity plateau, where onlyenough current is required to overcomefriction, and the scheduled run-in to thedesired cylinder. Dissipation is only signi-ficant in the first and last regions. Theeffect of carriage velocity on dissipation isas follows.

Scheduledvelocity

MAX CYLINDER DIFFERENCE 0

Fig. 12. Voltage -dependent feedback around the operational amplifier permits a piecewiselinear approximation to a curved velocity profile. This speeds up short seeks withoutcausing dissipation problems on long seeks.


Carriage acceleration, a, is cc actuator cur-rent, I, and

a=st2

where t is the seek time. Dissipation is12R, which is proportional to a2R

a2R12R=4-s2Rt2 e

Average carriage veolocity vac lit,therefore, dissipation cc e.As a result, it is necessary to limit themaximum velocity of the positioner veryaccurately or severe overheating of the coilor amplifier may result.

A consequence of the critically dampedrun-in to the target cylinder is that shortseeks are slow. Sometimes further non -linearity is introduced into the velocityscheduler to speed up short seeks. Thevelocity profile becomes a piecewise linearapproximation to a curve by using non-linear feedback. Figure 12 shows the effectof using a shaper or profile generator, asthis device is known.

Servo amplifiersIn small disk drives the amplifier is usuallylinear in all modes of operation, resem-bling nothing more than an audio outputstage. As the scheduled velocity signalcomes from a d. -to -a. converter, the dece-leration ramp is depicted by a staircasewaveform. When the staircase is comparedwith the actual velocity signal, the result-ing velocity -error signal contains an a.c.

Fig. 14. Comparison of velocity error with asawtooth waveform results in a pulse -width modulated output which can be usedto reduce dissipation in the servo amplifier.

In this photograph of a moving -coil transducer, the magnet under the coil can be seenclearly.

component due to the steps. This increasese.m.a. dissipation and can cause an audibleoutput from the coil - a problem that issometimes solved by adding a saw -toothwaveform, at the same rate as the steps, tothe shaper output. This approach is shownin Fig. 13.

Larger units employ pulse -width mod-ulation to reduce dissipation in the servoamplifier. The duty cycle is establishedtypically by comparing the velocity errorwith a sawtooth waveform. A simplifiedexample of this process is shown in Fig.14. Appreciable electromagnetic radiationis caused by p.w.m. servo systems, butthis is generally of no consequence as nodata transfer takes place during a seek. Intrack following mode, p.w.m. servos re -

00 "'11011011%11111111111111111 0111111111111101111111110 #04/40

Fromshaper

'-Regularvelocitytransducer

Retracttransducer

Positionerror

Forwardseek

Velocity modeInverter

Retract made

(t) a-)

Error amp.

Positionerror

Servo amp

Cylindercentres

Flg. 15. Typical servo -amplifier input stage. In velocity mode, the shaper and velocitytransducer drive the error amplifier. In track -following mode, position error is the onlyinput.

vert to a linear amplifier configuration,which is why the term linear mode is oftenused to describe the detented state of thepositioner.

The input of the servo amplifier nor-mally has a number of analogue switcheswhich select the appropriate signalsaccording to the mode of the servo. As theoutput of the position transducer is a

triangle or sine function, the sense of theposition feedback loop has to be invertedon odd numbered cylinders, to allow de -tenting on the negative slope. In somecases a different velocity transducer is usedwhen the heads are being retracted fromthe pack. Figure 15 shows a typical servo -amplifier input -selection circuit.

Fig. 16. Alignment disc has flux patternsdisplaced alternately about the centre lineof the reference track. In the resultingoscillograph at (a), the head is too close tothe spindle, at (b) too far from the spindle,and at (c), in the correct position.

Head alignmentOn drives where interchangeable discs areused, the distance between the read/writeheads and the spindle axis is critical. So toset the heads, an alignment disc(sometimes called a 'custom engineer')containing prerecorded flux patterns at areference cylinder is used. Figure 16 showsa typical alignment -disc pattern and result-ing oscilloscope waveforms for correct andincorrect head alignments.

Disc rotation, cooling, filtration, powersupplies and safety will he discussed in thenext chapter.


DESIGNING WITHMICROPROCESSORS

Linking a mocroprocessor with a printer directly is wasteful: much time can be saved bysending data to a buffer for reading at a slower rate. Professor Zissos concludes his serieswith two articles on programmable i/o chips, this first on basic concepts, and the second

on design procedure and implementation.

It is not always necessary or indeed de-sirable for two devices to communicatedirectly, particularly if one device is muchfaster than the other. For example, amicroprocessor transmitting data directlyto a slow character printer will be idlingwhile a character is being printed. In thissituation much time can be saved by thefast device transmitting each item of datato a port (in practice a data buffer) andallowing the printer to read the data fromthe port in its own time - see Fig 1. Sucha scheme would release the microprocessorfrom the unproductive task of waiting andallow it to look after other tasks while theprinter is printing.

Input/output ports are normally imple-mented with programmable chips, that ischips whose operations can be specifiedwithin limits by the user. Designing suchsystems involves two steps. First, the i/ochip is programmed. And second, the in-terface between the i/o chip and the peri-pheral unit is designed. Although thesecond stage presents no difficulty, pro-gramming the chip in practice is not al-ways a trivial task, because of lack of asystematic method. This often preventsone from taking full advantage of the mainproperty of such chips - that their termi-nal characteristics can be specified to someextent by the designer.

Clearly the source must not send data tothe port until it can accept it. For thispurpose the port sends a signal (h1) to thesource indicating its status, namelywhether it is empty or full. Signal hl mustalso be sent to the acceptor to prevent itfrom reading old data that jt has alreadyread, as shown in Fig. 2 (h1 = 0 indicatesthat the port is empty, and hl = 1 that theport is full). Reference to Fig. 2 shows thatstatus signal hl must be turned on by thesource when it sends data to the port, andturned off by the acceptor when it readsthe data; variables h2 and h3 denote these"handshake" signals.

In practice signal hl is generated by aflip-flop, the status flip-flop. A JK flip-flop implementation is shown in Fig. 3. Bypulling its J terminal high and the K termi-nal low, a pulse on its clock terminal sets it(h1 = 1) and pulsing its clear terminal resetsit. That is, a pulse on line h2 sets the flip-flop and a pulse on line h3 resets it. Thefunction of the AND gate is to terminatethe clear signal (CLR) immediately afterthe flip-flop is reset, CLR = hl.h3 = 0when hl = 0. In practice, the port is abuffer which requires a strobe pulse with

by D. Zissosand Jane Pleus

every new item of data before it accepts it:the pulse on handshake line h2 can be useddirectly for this.

In summary the step-by-step operationof the handshake system in Fig. 2 is asfollows. The source monitors status line hl

Fast dev,ceSlow link

to determine whether the port is full orempty. If empty, it outputs the next itemof data and pulses line h2, which strobesthe data into the port and sets the statusflip-flop (h1 = 1) by pulsing its clock ter-minal. This constitutes the write opera-tion; the read operation is initiated by theacceptor when line hl is high. When thedata is read it resets the status flip-flop bypulsing its clear terminal.

Fast deviceFast link Port

( buffer I

Slow device

Stow linkSlow device

Fig. 1. Fast device feeding a slow device needs buffer stage to avoid microprocessorwasting time.

Source

Data

h1

h2

Port

( buffer)

Data/hl

h3/Acceptor

Fig. 2. Handshake signals are exchanged before data is transferred from source to bufferand buffer to acceptor. Source monitors status lines 1 to see if port empty: Line h2 thenstrokes data into port. Read operation is intended by the acceptor when hl is high.

hi II

Source

h2

1 -

0-CLR

hl

Ihi

- hihl

Acceptor

h3

Fig. 3. Status flip-flop generates signal hl. With J high and K low, pulse on line h2 setscircuit and on h3 resets it.


S

E in

Data

Port

h2/ /h1 h1/ /h3

Interface 1

Data

A

C

in

Interface 2

Fig. 4. A handshake system requires two interfaces, one to coordinate source/buffer activityand the other acceptor/buffer activity.

Inputport

h1 h2

p t r(or anysource

Statussignals

Cd

Command

signals

Interface

Outputport

WI/ h 3

Printer(or any

acceptor)

Status / /Commandsignals signals

Interface

Fig. 5. Microprocessor -based system with input port and source (paper tape reader), top,output port and acceptor (printer), bottom.

To implement a handshake system re-quires two interfaces, one to coordinate theactivity of the source with the activity ofthe buffer, and the second to coordinatethe activity of the acceptor with that of thebuffer, Fig. 4.

Because most commercially -availablemicroprocessor systems are normally pro-vided with ports which are already in-terfaced to them, one need only consider

interfacing peripheral devices to theports. Therefore microprocessor -basedsystems with fo ports can be representedby the two block diagrams in Fig. 5. Apaper tape reader and printer act as sourceand acceptor because their action is easy tovisualize - they can clearly be replaced byany other device, equipment or process.

Next article - Design steps and imple-mentation.

IN OURNEXT ISSUE110 -100 -wattaudio amplifierJohn Linsley Hood's new am-plifier is described in a three-part article, beginning with anexplanation of design prob-lems in relation to the charac-teristics of mosfets. The de-sign will be closely followedby a new, modular preampli-fier, the pair forming possiblythe best amplifying equipmentyet described in these pages.Microprocessor -controlledradio -code clock. Using the60kHz standard -frequencytime -code transmission fromRugby, this clock providesdate and time informationautomatically, in that thedisplay is continually corrected by the transmission.Particular attention to receiverdesign has greatly reduced theeffects of interference, and a6502 microprocessor is usedto perform the d..:coding func-tion.Heretics guide to modern phy-sics is a controversial reviewof current doctrine, set at thelevel of the sixth -form studentor educated layman. Enor-mous gaps exist in our under-standing of Nature and manyof our fundamental theoriesare not very credible, says W.A. S. Murray, who in nine arti-cles investigates electromag-netic theory, photons, duality,quantization, matter wavesand haziness, and reviews thestate of physics today.Control technology andsafety. Presenting informationon large systems - oil rigs,nuclear power stations, air-craft - to control engineers isnot a simple matter of layingout alarms and indicators on alarge panel. The psychology ofcrisis control, the requirementfor new types of equipment fordata marshalling and methodsof training personnel are exa-mined by R. E. Young.Radio in tunnels by leakyfeeder. D. J. R. Martin, aspecialist in undergroundradio communication, reviewsdevelopments in the use ofleaky, or radiating, cables.

ON SALEMAY 16


CEPSTRUM ANALYSISThis final part of the review gives uses in speech analysis and machine diagnostics, as well as

calculation with an FFT analyser using the digital form. Part 2 gave application to signalscontaining echoes (March), while part 1 derived the cepstrum as the spectrum of a logarithmic

spectrum.

The applications of the cepstrum to speechanalysis are mainly connected with its abil-ity to separate source and transmissionpath effects, provided they have differentquefrency contents. This is usually thecase with speech where the source spec-trum is very flat, containing a largenumber of harmonics of the voice pitch,but is modified by the resonance character-istics of the vocal tract, the so-called for-mants, which determine which vowel isbeing uttered. Fig. 13 shows spectra andcepstra for the vowels "oh" 1OI and "ee" ailand illustrates how the differences mainlylie in the low quefrency part of the ceps-trum, which is dominated by the formantcharacteristic. Non -voiced sounds, such asmany consonants and whispered speech,do not give peaks in the cepstrum corre-sponding to the voice pitch, and one of theearliest applications of the cepstrum was toseparate voiced and non -voiced sounds andto measure voice pitch '°

It is also possible by editing in the ceps-trum to remove one effect completely, forexample the voice, and thus simplify thetracking of the formants. Fig. 14 from ref.11 shows a typical situation, a three-di-mensional representation of the section"ea" from the word "Montreal". The pic-ture is confused but by short -pass lifteringeach of the spectra to remove the voicecomponents, as shown in Figs 15 and 16,only the formants are left and the picturebecomes much clearer.

The cepstrum can be used for efficientvocoding and transmission of speech. 12

Most of the intelligence is contained in thelow quefrency part of the cepstrum so onlythis is transmitted, along with informationas to whether the speech is voiced and if sothe voice pitch. At the receiver end thespeech is reconstituted using the low quef-rency information to generate a filter char -

Fig. 13. Spectra and cepstra for "ee" [II vowel

by R. B. Randall and J. Hee

acteristic or impulse response for a sourcewhich would either be a variable frequencypulse generator for the voiced sections or anoise generator for the unvoiced sections.Despite the synthetic voice the speech wasreported as sounding natural.

It can also be useful to include it alongwith spectral and other information in pat-tern recognition algorithms for speakeridentification. Inclusion of the cepstral in-formation improved the ability of the tech-nique to exclude impostors.13

Machine diagnosticsThe applications of the cepstrum tomachine diagnosis are mainly based on itsability to detect periodicity in the spec-trum, e.g. families of harmonics and uni-formly spaced sidebands, while being in -

Fig. 14. Scan spectrum of "ea" in "Montreal"

sensitive to the transmission path of thesignal from an internal source to an exter-nal measurement point.

The cepstrum technique has been pro-posed to aid detection of missing blades inturbines. Such blade anomalies give rise toa large number of harmonics of the shaftrotational speed in measurements14 madeboth internally and externally on the cas-ing in the vicinity of the affected bladerow. Even though the harmonic patterncan be seen by eye, the whole family ofharmonics is reduced in the cepstrumbasically so one component which is mucheasier to monitor.

Similar reasoning is applicable to gear-box diagnosis; tooth anomalies have a verysimilar influence on gearbox vibration sig-nals, as do blading anomalies on turbinesignals.15 A very detailed discussion isgiven in reference 15 of the application ofcepstrum analysis to gearbox diagnosis andso here the discussion is limited to a coupleof typical examples. .

Frequency 5kHe

112 nu

In gearbox vibrations deviations fromexact uniformity of each toothmesh showup partly as harmonics of the shaft speedand also as sidebands around the tooth -meshing harmonics caused by modulationof the toothmesh signal by the lower rota-tional frequencies. The sideband spacingthus contains valuable information as tothe source of the modulation and can beextracted using the cepstrum. The ceps-trum has the two advantages of being ableto detect periodicity not immediatelyapparent to the eye, and of being able tomeasure it very accurately because it givesthe average sideband spacing over thewhole spectrum.

The first advantage is illustrated in Fig.78 WIRELESS WORLD MAY 1982

Spectrum a) Cepstrum b)

f1 50 He

ti

Frequency

Short pass later

7, 6,616s

OuefrencY

Fig. 15. Cepstrum lifteringa) log power spectrum of vowelb) magnitude of cepstrum

I NOOuefrency

Frequency

c) short pass lifter characteristicd) short pass liftered log power spectrum

80 de

E

Frequency 5 PH,

112 ms

Fig. 16. Short -pass liftered scan spectrum of

17 and was made using an FFT analysertype 2033 in conjunction with an HP9825desk -top calculator. A 2000 -line spectrumincludes the first three harmonics of thetoothmeshing frequency of a single reduc-tion gearbox (a). It purposely excludes thelow harmonics of the shaft speeds sincethese may have other causes than thetoothmeshing. The spectrum was obtainedby performing five 400 -line zoom analyseson the same data and storing the interme-diate results in the calculator memory. The2000 -line spectrum was then read digitallyback into the 10K input memory of theanalyser and frequency analysed oncemore using the scan average procedurewith 75% overlapping Hanning windowsto obtain the cepstrum. Fig. 17 (b) repre-sents the average of five such cepstra. Eventhough it is difficult to see any periodicstructure in the spectrum, it is apparentfrom the cepstrum that there are two fami-lies of sidebands with spacings of 85 Hzand 50 Hz respectively, the rotationalspeeds of the two gears. All significantcomponents in the cepstrum stem fromone or other of these two shaft speeds.

The other advantage is illustrated in

"ea" in "Montreal"

Fig. 18 which shows spectra and cepstrafor two truck gearboxes, in good and badcondition respectively, running on a teststand. The good gearbox shows no markedspectrum periodicity, but the spectrum ofthe bad one contains a large number ofsidebands with a spacing of approximately10 Hz. The cepstrum gives this spacingvery accurately as 10.4 Hz and thus ex-cludes the possibility that it was the secondharmonic of the output shaft speed 5.4 Hz.

Ran, of400 -Dineoom spectrum

- 0 Toothnrsh00 lio9100 110.

' 0

Fig. 17. Example of a cepstrum analysis ona gearbox vibration signal(a) 2000 -line logarithmic power spectrum(b) Average cepstrum calculated from

It was traced to the rotational speed ofsecond gear, even though this was idlingbecause first gear was engaged.

References

10. Noll, A.M. Cepstrum pitch determination,J.A.S.A. vol.41. 1967, pp. 293-309. Schafer, R.W.& Rabiner, L.R., Digital representations of speechsignals. Proc. IEEE. 1975, pp. 662-77.11. Thrane, N. Application of a long memory FFTanalyser in speech analysis. B&K application note066-81.12. Schafer, R.W. & Rabiner, L.R. System forautomatic formant analysis of voiced speech.J.A.S.A. 1970, pp. 634-48. Oppenheim, A.V.Speech analysis -synthesis system based on ho-momorphic filtering. J.A.S.A. 1969, pp. 458-65.13. Luck, J.E. Automatic speaker verificationusing cepstral measurements. J.A.S.A. 1969, pp.1026-32.14. Sapy, G. Une application du traitementnumerique des signaux au diagnostic vibratoirede panne: La detection des ruptures d'aubes mo-biles de turbines. Automatisme - Tome XX, no.10, October 1975, pp. 392-9.15. Randall, R. B. Cepstrum Analysis and GearboxFault Diagnosis. Bruel & Kjaer application noteno, 233-80.16. Thrane, N. Discrete fourier transformer andFFT analysers. B & K Technical Review, no. 1,

1979.

Itoa) Gearbox 1 (Bad condition)

lop. , Spectra (1st gear engaged)

VdB

100

90

80

70

b) Gearbox 2(Good condition)

100 200 300

Frequency (Hal400 500

28,1 ms135,6 Hz)

95,9 ms(10.4 Hz) Cepstra (1st gear engaged)

0:2Ouefrency Is)

Fig. 18. Spectra and cepstra from truck gearboxes in good and bad condition

Or3


Appendix ACalculation using FFT analyser and cal-culator.Even though the analyser basically performs aforward transformation of 1024 real data points,the results can be modified in the calculator soas to obtain the inverse transform of up to 1024real or complex values thus giving the possibil-ity of calculating both power cepstra and com-plex cepstra. The actual algorithms used aremore generally applicable and so are detailedin Appendix B.

The digital version of eqn 3 for the powercepstrum is

Cp(n) = { log F,,,,(k)}where n stands for n At (At is the samplinginterval) and thus indicates the time. n runsfrom 0 to 1023. Likewise k represents the fre-quency k Af (Af is the line spacing in the fre-quency spectrum) and in principle also runs

from 0 to 1023 even though only the values from0 to 512 are calculated. Because of the implicitperiodicity of all functions calculated by theFFT process the values of k from 512 to 1024also represent the negative frequency compo-nents (from -512 to 0) and can usually be

derived from the positive frequency values.16 AsF(k) is a real even function, the inverse trans-formation can be replaced by a forward transfor-mation (Appendix BI). In general only the one-sided power spectrum is given, and the simplercalculation method of Appendix B2 will be ad-vantageous. With this method, only the one-sided spectrum is transformed, and the real partof the transform gives the desired cepstrum.Another advantage of this method is that theenvelope cepstrum (amplitude cepstrum of theone-sided spectrum) of Fig. 4 may be obtainedat the same time. In fact the analyser itselfautomatically calculates this and displays it asthe instantaneous spectrum, which can beviewed on a linear amplitude scale. The enve-lope cepstrum is

Ce(n)=17-1{logG(k)}1where G(k) is the one-sided power spectrum.The formula for the complex cepstrum is

Ce(n)= 7-1(logeAx(k)+A(k)).Because the logarithmic spectrum is a conjugateeven function, the calculation method of Ap-pendix B3 may be used. Note that the phasefunction (1)x(k) must be unwrapped to a contin-uous function of frequency in place of the prin-cipal values modulo 2 .7 which are calculatedfrom the real and imaginary parts of the com-plex spectrum. Moreover the log amplitudemust be scaled in nepers (natural log of theamplitude ratio) to correspond to the radians ofthe phase spectrum.

The analysers in general are a.c. coupled,so the zero frequency value in the powerspectrum is not calculated. It is therefore neces-sary to insert a value before calculating the ceps-trum. In practice best results are obtained bysetting the zero frequency component equal tothe value of the neighbouring line.

As the FFT algorithm used in the Analyserstypes 2033 and 2031 is optimized for signalswith no d.c. component, it is advantageous tosubtract the mean log spectrum value beforecalculating the cepstrum. This optimizes thesignal noise conditions in the cepstrum, and isparticularly valuable when editing and transfor-mation in both directions is to be performed.In calculation of the complex cepstrum it isadvisable before attempting to unwrap thephase spectrum to remove any simple delay,which gives a linear slope to the phase spec-trum. This should be done to the maximumextent possible in the time signal before trans-formation, and then in the phase spectrum itselfby varying the linear component until thenumber of "jumps" over 2a is minimized.

Appendix BCalculation of inverse Fourier transformThe forward and inverse discrete Fouriertransforms, as calculated by the FFT analysers,are defined as

1

N-1X(k)=N x(n) exp-j2nknIN

n=0

N-1

and x(n)= E X(k)expj2nkteNk =0

where X(k) the discrete complex spectrum x(n)the sampled time function and N number ofsamples in the time record.

The Fourier transform implemented inthe analysers types 2033 and 2031 is designed tobe used forward transformation of real -valuedtime signals, but by using some of the propertiesof the Fourier transform, as listed in thetables, it can also be used for forward andinverse transformation of any complex signals.The inverse transformation of the three types ofsignals: real -valued, real and even, and conju-gate even are described in the following. The

Algorithm

'{X(k)}=(N f {X*(k)})*' {X(k)} = N {X*(k)}'{X(k)} = N {X(k))

-'{X(k)}=(N {X(k)})*

Conditions

any X(k)x(n) realx(n) real, evenX(k) real

Time signalreal and evenreal and oddimag and evenimag and oddrealconjugate even

Spectrumreal and evenimag and oddimag and evenreal and oddconjugate evenreal

results are sketched where the vertical lines in-dicate the result of the FFT calculation and thesolid lines the desired result. Not that zero isshown in the centre of the diagram. Duringmany of the operations, zero frequency or timewill be located at the start of the record, butbecause of the periodicity of all functions thenegative frequencies or times will be located inthe second half of the record.

Bl. Real -valued spectrumFrom the table it follows that

-1{X(k)} =N[ {X(k)}]*.

The calculation procedure for positive time isthen- forward transform- form complex conjugate- multiply by N.The result for both positive and negative time isseen in Fig. B 1. For the special case of evenspectra it is possible to omit the second step, butin that case the next procedure will normally bepreferable anyway.

N FFT

k >

B2. Real and even spectrumFrom the original symmetrical spectrum a newone-sided spectrum is formed which has theoriginal spectrum as its even part and is zero fornegative frequencies. The real part of theinverse transform of such a spectrum is identicalwith the inverse transform of the original spec-trum. As normally only the positive frequency

components of the original spectrum are givenin any case, this saves forming the symmetricalspectrum for negative frequencies. It followsthat

7 - 1 {X(k)} =NRe[,7 {X(k)}]

12X(k),0<k<512

where g(k)= X(k) , k=0,k=5120 , -512<k<0

Xe(k)=X(k).The calculation procedure, Fig. B2, is thus- form X(k)- forward transform- extract and scale the real part.

N. FFT

(B3. Conjugate even spectrumAny complex spectrum can be inverse -trans-formed by transforming the real and imaginarycomponents separately by the procedure Bl.However, this requires two Fourier transfor-mations as well as some extra storage capacityfor the intermediate results. In the situationwhere the spectrum is conjugate even, i.e. corre-sponding to a real time signal, the followingprocedure can be used. This requires only onetransformation and a minimum of storage space.

- {X(k)} = - {XR(k)+ iXi(k)}=N[ {XR(k)} -1 7 {Xl(k)}1

=N[R(n)+ i(n)]

Also .7 {XR(k)+Xl(k))=--R(n)+ ji(n)

where R(n)= {XR(k)}

and jl(n)= 7 {X1 (k)}The calculation procedure, illustrated in Fig.B3, is as follows.

Add the real and imaginary parts for positiveand negative frequencies. In practice this meansadding the imaginary parts to the real parts (ofthe positive frequency spectrum) for the firsthalf of the record and subtracting the sameimaginary parts from the real parts for thesecond half in reverse order.

x.

K. a,

N. FFT

A 11111V ir

Forward transform. Add the real and imagi-nary parts for positive and negative time. Thenegative time section will be located in thesecond half of the record and can be removed toits correct position before the first half. Zerotime will then be in the centre of the record.


SPECTRUM/NETWORKANALYSERFrequencies in the range 50Hz to1.8GHz are covered by Takeda Ri-ken's combined spectrum/networkanalyser, with which a dynamicrange of 100dB may be displayed.The TR4172 has a built-in trackinggenerator, a four -channel memory,eight tunable markers and is GPIBcompatible. Facilities for mea-suring phase and group delay, witha simultaneous display of ampli-tude, are included. This instrumentis for use in both production andresearch and development applica-tions. Chase Electronics Ltd,Church Lane, Teddington, MiddxTW11 8PA.WW301

BLUE L.E.D.This is a 490nm gallium nitride1.e.d. intended primarily as a colourreference source in chromatogra-phy applications. Light output, in aviewing angle of 4°, is typically2mcd at lOrnA, which is also themaximum forward -current rating.Forward voltage varies betweenaround 4.5V at 0.5mA and 7.5V at10mA. The ESL50B2 is housed in astandard 1.e.d. package. AngliaComponents Ltd, Burden Road,Wisbech, Cambs PE13 2PS.WW302

WAVEFORMMONITORThe V-098, designed for broadcastand professional video applications,is a waveform monitor that can beset to give a flat response, an IRE(Institute of Radio Engineers) res-ponse, or display waveformssubjected to a 4.43MHz bandpass


filter. In addition, two line andfield sweeps can be selected andvarious other adjustments made.This monitor is from Hitachi In-struments, a new division of Hita-chi Denshi, and can be obtained formounting in a 19in rack or as aportable unit running off batteries.Hitachi Denshi (UK) Ltd, 13-14Garrick Industial Estate, GarrickRoad, Hendon, London NW9WW303

PORTABLE VIDEORECORDERAccording to Sulkin (UK) Ltd whoimport the Technicolor 212E, it is"the world's smallest, lightest and

WW304

simplest" video cassette recorder.It uses 6.3mm tape cassettes notmuch larger than a standard audiocassette, for either 30 or 45 minutesof play, and weighs around 3.2kgwith rechargeable batteries. Madeby Funai and designed by Futec ofOsaka, the mechanism is similar tothe one used in the Grundig VP100recorder and mentioned in last De-cember's issue (New Products,page 87). But Grundig now say theywill not market their recorder inthe UK because of supply shortage.The 212E two -head recorder usesan Hitachi -made colour camera,though almost any other can beused via a simple adapter, with anelectronic viewfinder, zoom lens,and close-up x6 "macro" setting.A u.h.f. television tuner will beavailable shortly. Sulkin (UK) Ltd,73 Grosvenor Street, London W1X9DD.WW304

TEACH YOURELFAn introduction to digital electron-ics suitable for beginners is givenby a kit from Cambridge Learningcovering such subjects as booleanalgebra, gating, flip-flops, shift re-gisters, ripple counters and half ad-ders. Problems, with solutions, andan appendix covering basic prin-ciples are included in the manual.At £19.90, the kit comprises logici.cs, a `solderless' breadboard,l.e.ds, a handful of other compo-nents and, of course the manual -all in a pocket -sized wallet (for14cm-wide pockets). A powersupply or 4.5V battery is required.Supplementary kits delving furtherinto digital electronics are pro-posed. Cambridge Learning Ltd,Rivermill Lodge, St Ives, Hunting-don, Cambs PE17 4EP.

WW30581

UN INTERRUPTIBLE

P.S.U.No-load to full -load voltage and fre-quency fluctuations of this uninter-ruptible power supply and regula-tor's output are ±1% and ±0.1%respectively. Maintenance -free bat-teries, normally under charge,drive the 240V/50Hz output duringmomentary or total mains failureand large mains fluctuations from 0to 270V and from 40 to 70Hz havelittle effect on the output. Theswitch from mains to battery back-up is not apparent at the output.Surge currents up to five times thenominal rating are provided forstarting inductive motors, etc.These units can supply from250VA to 2kVA, handle 100%overloads for 30 minutes and in-clude comprehensive overload pro-tection. T.h.d. is 2%. CompecSystems Ltd, Welton, Brough, N.Humberside HU15 1PT.WW306

12 -BIT D -TO -ALinearity error of this 12 -bitmicroprocessor compatible digital -to -analogue converter is 0.01%.The HS9338 has its input registersorganized as three independent 4 -bit elements each with its own re-gister -loading enable input. Outputvoltage is programmable in ranges

from 0 to 5V to ±10V and an in-ternal reference is available; out-put -settling time is quoted as 5p.s.A 24 -pin d.i.l. package is used andthe device operates on 5V and±15V supplies. Hybrid SystemsUK, 12a Park Street, Camberly,Surrey.WW307

FLUX -DENSITYMETERA small meter for checking mag-netic fields up to 19.99 kilogauss(1G=10 -4T) in three ranges ismanufactured by Redcliffe. Read-ings - down to 0.1G on the mostsensitive range - are given on a 31/2 -digit I.c.d. and the meter has apeak measurement function forchecking and locating maximumflux areas in pulse -magnetisedcoils. Two probes are available, onefor transverse fields and the otherfor axial fields, and a batterycharger is supplied. Reference mag-nets are also available. RedcliffeMagtronics Ltd, 24 Emery Road,Brislington, Bristol BS4 5PQ.WW308

ACRYLIC FILTERSExpansions in Chequers' range ofacrylic filters for light -emitting de-vices have been made. Red, greenand grey filters are available in fourshades, amber and blue filters intwo. There are also yellow andpurple filters. In addition, de-signers can obtain a sample walletcontaining four shades or colours offilter. Each sample has a sectiontreated with Glarecheq - a coatingfor reducing glare and reflection.Chequers (UK) Ltd, 1-4 ChristinaStreet, London EC2A 4PA.WW309

CALIBRATABLESTROBOSCOPEThis type of instrument is used inevery field of engineering and hasmedical applications, yet we seesurprisingly few new designs. Fir -nor Misilon has introudced a stro-boscope which it claims has, "fea-tures usually associated with unitscosting twice as much." Retailingat £198 excluding v. a. t . , the WM10

has three ranges covering ratesfrom 0 (off?) to 16000 flashes perminute. When used without exter-nal triggering, the flash rate can beset to within 1% at certain points onthe continuously -variable scaleusing a mains -frequency dependentcalibration method; a t.t.l. compat-ible output is provided. Maximumlight output of the unit is lOW andmains inputs from 110V to 240Va.c. can be used. Firnor Misilon,Unit 49, The Makings, StansteadAbbotts, Herts.WW310

ATOM SOURCEFOR VACUUMDEPOSITIONResearchers at UMIST's chemistrydepartment developed a fast -atombombardment (f.a.b.) source formass spectrometry now availablefrom Ion Tech Ltd. The saddle -field gas gun provides an intenseneutral beam of fast atoms and doesnot require the use of a charge ex-change cell to neutralize the gasions produced with an electrostaticsaddle field oscillator. The coldcathode ion gun also has applicationin thin-film vacuum deposition and

in substrate cleaning. Much betteradhesion between a surface and,say, copper is obtained if it is firstbombarded with the atom gun, themakers say. Known as the FAB-GG, the gun is available from IonTech Ltd, 2 Park Street, Tedding-ton, Middx TW11 OLT.WW311

Professional readers areinvited to request further de-tails on items featured hereby entering the appropriateWW reference number(s) onthe mauve reply -paid card.


for onlyBE A SHARP BUSINESSMAN £278 +VAT

The sensationalnew PC -1500 Pocket Computer

approaches the Personal Computer in ability. Add the revolutionaryCE -150 Graphic Printer

COMPUTER AND 4-COLOUR PRINTER

and a cassetterecorder and you have a complete, battery powered, Business

Computer Systemthat travels in your briefcase!

--------

SHARP CE -1504 -colour GraphicPrinter£130.39 + VAT;Total £149.95

Li10 lit 0 0 111 0 0

0 00[itCt0000 0 0 0 0 0 0 WI

CE)'Zi3 CI3

Price includes SECURICOR 24 HOUR DELIVERY*.Same day despatch, subject to availability.

BUSINESS APPLICATIONS

pC:--1510 Jr 4F4January Sales Ana.nen i. 11554.

Quick and accurate data processing in daily business. Estimates,records and charts of sales, salaries, invoicing and all other datacrucial to efficient business operations can be easily programmed,calculated and summoned.

ENGINEERING APPLICATIONSTechnical calculations in fields suchas mathematics, statistics, measurementsand mechanics are done superbly andeasily. The calculator more than meetsthe requirements of engineers andscientists.

A 11-20 ....ovaB 21-30C 31-40 ....19%D 41-50

Sales Chart tprrntoutl

Equational Graph (printout)

MANAGEMENT APPLICATIONSBalance sheets, so crucial to management analysis, and profitcalculations by break-even point analysis are instantly yours withthe PC -1500. By using the integral clock, calendar and alarmfunctions, this computer can also be used as a schedule reminder.

Computer Graphinlpnntou0

HOBBY APPLICATIONSMany popular computer games canbe played, including Blackjack,utilising the random numberfunction. Use the clock and alarmfor speed games. The ComputerGraphics will draw virtually anypattern.

Tram (display,

TEMPUSDept WW, 38 Burleigh Street, Cambridge CB1 1DG

Tel: 0223 312866

SHARP PC -1500'Basic' PocketComputer£147.78 + VAT;Total £169.95

BASIC LANGUAGEThe most simple computer language is used for programming ease.Additional BASIC terms provide variables including two-dimensionalarrays, variable strings and many other advanced features.LARGE MEMORY16K bytes of ROM and 3.5K bytes of RAM, with 2.6K bytes in theuser area. Adding the optional CE -151, 4K byte memory module,expands the RAM to 7.5K bytes. An 8K byte memory module willbe available soon. The PC -1500 is battery powered and program anddata memories are fully protected, even when switched off.MINI -GRAPHIC DISPLAYThe 7 x 156 dot matrix allows almost any display, including gamesymbols. Line width is 26 characters and/or numbers.HIGH SPEED DATA PROCESSINGThe C-MOS 8 -bit CPU enables swift data processing. Complicatedtechnical or business calculations require far less time.QWERTY TYPEWRITER KEYBOARDTh oneofpirtsitinala pocket computer. Lower case letters are available. Withthe CE -150 colour graphic printer, the PC -1500 can serve asa small personal typewriter. Word Processor software will be available

SIX SOFTWAREKEYSThese can serve as reservable keys, or as definable keys to defineprograms.CE -150 4 -COLOUR GRAPHIC PRINTER/CASSETTE INTERFACEAutomatic program, data and calculation printing. It printsvirtually any drawing in either red, black, green, or blue. Charactersare printed in nine different sizes and in lines ranging from 4 to 36digits in length. You can control the printer completely and directthe printing either up, down, left, or right. As a cassette interface itwill connect up to two cassette recorders, one for data and programstorage, the other for their recall. The CE -150 has a built-in recharge-able battery and is supplied with a mains adaptor, type EA -150.AVAILABLE SOON RS -232C interface. Software board to serve as input keys ingraphics, or pictures, previously drawn on a template. ROM (MASKROM) module also applicable. " A wide range of business software. '

DIMENSIONSPC -1500. 195Wx25.5Hx860mm 17-11/16x1x3-3/8"l Wt 3759(0.831b)CE -150. 330Wx50Hx115Dmm 113x2x4 inches). Wt 900g I1.981bs1.Full 12 MONTHS guarantee, with EQUIPMENT LOAN SERVICEduring downtime.°SAME DAY DESPATCH of orders - Systems by SECURICOR 24hour service, Ito attended premises only) or by first class registeredpost. AT NO EXTRA COST'SEND FOR FULL DETAILS to TEMPUS, the Portable ComputerSpec:alists.

To: Tempus, FREEPOST, 38 Burleigh St, Cambridge CB1 1 BR.

INFO. ITEM QTY PRICE TOTAL

PC -1500 Pocket Computer £169.95

CE -150 Four Colour Printer £149.95CE -151 4K Byte RAM Module £ 49.95

Total inc VATFor it formation only tick appropriate box

I herewith enclose a cheque or Postal Orders value £or I wish to pay by Access B'caid Visa.My number is:Name:

Address:



---= 01-723 1008/9Callers to: 404 EDGWARE ROAD, LONDON W2 1ED -

ALL MAIL ORDERS/EXPORT ENQUIRIES 11/12 PADDINGTON GREEN, LONDON, W2

ItemNo.

1 TEKTRONIX PORTABLE OSCILLOSCOPE type 422. Dual Trace .................................13502 TEKTRONIX STORAGE MONITOR type 613 _...................

'Fiug-in

ItemNo.

5354

POLARAD MICROWAVE SIGNAL GENERATOR Model MSG -1 950-2400MHZ.........£150POLARAD MICROWAVE SIGNAL GENERATOR Model MSG -2 2150-4600MHZ.......£150

MARCONI AM/FM SIGNAL GENERATORtype TF106613/65

10-470 MHZ in 5 bands£275 each

WAYNE KERR COMPONENT BRIDGE3 TEKTRONIX Dual Trace OSCILLOSCOPE type 581A with CA .1160 55 GENERAL RADIO MICROWAVE OSCILLATOR type 13608 1.7-4.1GHZ4 TEKTRONIX CURVE TRACER type 575.. .11505 TEKTRONIX AMPLIFIER type 11216 TEKTRONIX SAMPLING PLUG-IN type l

56

57GENERAL RADIO FREQUENCY/DISCRIMINATOR METER type 1142A.0-1.5MHZ.....£96GENERAL RADIO OSCILLATOR 1209C; 12090L; 1215C with Power Unit type 1263B 50-

'14'13

type 8521 (CT 375)Resistance 1mOhm - 1000 MegOhm

.....-.........--.....-........-... .11757 TEKTRONIX PLUG-IN type D Single Trace High dein DC Differential........................120 58 GENERAL RADIO DECADE CAnafoa ;Wit. ANAlidG LIMIT COMPARATOR Capacitance 50 KuF - 500 pF8 TEKTRONIX PLUG-IN type E Single Trace Low Level AC Differential9 TEKTRONIX PLUG-IN type G Single Trace Wide Band DC Differential ......................£25 59

1782 and IMPEDANCE COMPARATOR 1654STODDART RADIO INTERFERENCE & FIELD INTENSITY METER type N -M 52A.....£195

Inductance 101 - 500 kHwith copy of manual

10 TEKTRONIX PLUG-IN type L Single Trace 30MHZ High Gain ............... 60 KEITHLEY REGULATED HIGH VOLTAGE SUPPLY type 241 __________________ .£145 ONLY £40 each11 TEKTRONIX PLUG-IN type M 4 Trace DC-20MHZ .112512

61

62BRANDENBURGH HIGH VOLTAGE GENERATOR typeBRANDENBURGH HIGH VOLTAGE P.U. Model 705 Metered 0-15KV. +/- AVO VALVE TESTER type CT160

13 TEKTRONIX PLUG-IN type 0 Transducer & Strain Gauge ...........................................£75 63 BELIX POWER UNIT type CMT3001. +/- 0-1000 Volts in 3 ranges (22 valve bases) with copy of manual14 64 PLESSEY TELEGRAPH SIGNAL GENERATOR TSGIO with TOMS type 70. Speed 50-75- £20 each15 TEKTRONIX PLUG-IN type W Differential Comparator ...............................................112516

17

6566

As Above but SPEED Copy of Valve Data £5(only available with unit)

18 HEWLETT PACKARD QLC METER type 4342A __________'_________.

11,15019 HEWLETT PACKARD OCCURRENT SOURCE type 618160.100V; 0-250MA............£12520 HEWLETT PACKARD WIDE RANGE OSCILLATOR type 2000021

6768

6970

RACAL AUTO FREQUENCY CONVERTOR type 8133A ........................................£20RHODE & SCHWARZ NOISE GENERATOR SKTU 654151/2/60

AVO TRANSISTOR ANALYSERtype CT446 with copy of manual

£20 each22 71 Copy of Transistor Data £523 HEWLETT PACKARD DC MICRO VOLT AMMETER type ___140 72 R & S FREQUENCY METER VHF UHF 30-300MHZ type W1D 13N442. 140 (only available with unit)24 HEWLETT PACKARD OSCILLOSCOPE 182A with 1808A and 1825A. 75MHZ Dual

TraceDelayed Sweep ....................._...................................._.........._.............................195025

73

7475

& S RESONANCE FREQUENCY METER 3o-Siimiiz WAM ElF44.51i2 .150 AVO SIGNAL GENERATORNo. 2 AM/FM

26 HEWLETT PACKARD VACUUM TUBE VOLTMETER type 4108 with 76 AM 0.45-225 MHZ; FM 20-100 MHZ27 MARCONI IN SITU UNIVERSAL BRIDGE type TF2701. Battery Operated................£95 77 R & S CAPACITANCE METER BN5201 with copy of manual28 MARCONI WIDE RANGE OSCILLATOR type TF1370. 10HZ-10MHZ .£65 78 ISOLATING TRANSFORMER 240V Input 240V Output 1300 £75 each29 MARCONI (SANDERS) MICROWAVE POWER METER type _115030 MARCONI UHF SIGNAL GENERATOR type TF1060... .E95

7980

AUTO TRANSFORMER +/- KVA Pri Volts 90/240 Sec Volts 115DC SERVO MOTOR 110V 2.5A Cont. Double Shaft. 4 wire 4 brush. New MARCONI COUNTEFt/FREQUENCY METER

31 MARCONI FM SIGNAL GENERATOR type TF1077/1 81 CLAUDE LYONS AUTOMATIC VOLTAGE STABILISER. Input 204-252 Volts Output TF1417/2 with Convertor type32 MARCONI UNIVERSAL BRIDGE type TFI313. 0.25% .........___________________1185 ...............................................£75 TF 2400/TM7164 - 500 MHZ33 MARCONI VARIABLE ATTENTUATOR type TF1073A/25 ICT42i)34 MARCONI UNIVERSAL BRIDGE type TF2700.35 MARCONI AM/FM SIGNAL GENERATOR TF995A/3/S

828384

PHILIPS VIDEO COLOUR TEST eENERideR type 1445522As above but NO CABEPHILIPS FM STEREO GENERATOR. tape PMG.456. Separate 'Signals Carrier Freq

_£35SINE & SQUARE WAVE AUDIO GENERATOR

36 MARCONI AC MILLIVOLTMETER type TF2600 10HZ-5MHZ; 1125 type TE-22, 20HZ-200KHZ. Portable as new37 B & K ACCELEROMETER PREAMPLIFIER type 262. 85 f30

*Yiki .14.12105ONLY £35 each. P&P £4

38 B & K DEVIATION BRIDGE type 150339 B & K DEVIATION BRIDGE type 150440

66

8788

PHILIPS AUTOMATIC ELECTRONIC OHM. METER typeKAY ELECTRIC VARI-SWEEP Model 400 15-470MHZ ______________________1193HEWLETT PACKARD DC POWER SUPPLY type 64488.0.600 Volts 0-1.5 Amps.......£295

MULTIMETERRussian Type 4324

41 89 ADVANCE UHF SIGNAL GENERATOR SG69 370-1040MHZ ________________£125 AC/DC volts; AC/DC current; ohms, etc.42 90 Brand new, boxed.43 B & K BEAT FREQUENCY OSILLATOR type 1018..44 B & K AUDIO FREQUENCY SPECTROMETER type 2112

91

92£12.50 each. P&P £2.50

IKEGAMI MONITOR20" Black & White

45 B & K FREQUENCY RESPONSE TRACER type 4707B & K LEVEL RECORDER type 2305. 50d13 Potentiometer. Brand new with accesso-46

9394

ries..- - ..................................................47 TEXAS SILENT 100 PRINTER Model KSR733 - 30048

9596

97

ADVANCE SIGNAL GENERATOR type E2 100KHZ-100MHZ £45PYE SCALAMP 40KV RMS Max ELECTROSTATIC VOLTMETERPYE SCALAMP 20KV RMS Max ELECTROSTATIC VOLTMETER _________

Solid state. Video in, int. ext. Sync.£65 each

TELETYPE PRINTERSKSR 33 - ASCII Keyboard £50

ASR 33 - as above with 8 -bit Punch and

49 MOSELEY WAVEFORM TRANSLATOR type............................................£5050 HOUSTON INSTRUMENTS LOG VOLTMETER -CONVERTOR Model HLVC150...._.....£75

51 POLARAD FIELD STRENGTH METER type FIM-B2 with RF Tuning Unit FIM-X2 7360-

98

99100

SINE & SQUARE WAVE AUDIO GENERATOR type TE-22 20HZ 200KHZ... .....£35BLACK & WHITE 20" MONITOR by IKEGAMI type PM2OITS. Solid State E65

1 D,ODOMHZ._POLARAD MICROWAVE REOEIVER MODE! R with RF Tuning tinas covering 400-52 PLEASE CHECK AVAILABILITY BEFORE ORDERING Reader £752050MHZ and 7400-22.000MHZ ............ . . ...£150 COMPONENT LIST AVAILABLE S.A.E. OR PHONE PDP 8 in Oft RACK CABINET £100

BARCLAYCARD (VISA) and ACCESS taken. Official orders welcomeCALLERS VERY WELCOME STRICTLY BETWEEN 9am-1pm and 2-5pm Monday to Saturday inc.

1111 I 11:11r EA. LTNORWOOD ROAD, READING TELEPHONE NO. READING 669656

(2nd turning left east Reading Technical College in King's Road then first right - look on right for door with "S oked Wheel")

All units £6 carriage. Plus V.A.T. on total

D.I.L. MINIATUREON -OFF

SWITCHESGold.plated contactsSealed base ideal for pro-gramming 6 -position atless than halfmanufacturers price

ONLY75p

Will fit Into 14 -pin MIsocket. Ten at 65p ea per10055p ea

HONEYWELL PROXIMITYDETECTOR integralamplifier, 8v 0 C 13.50 eaPHOTO CONDUCTIVECELL, £1.25. High -powerCds cell, 600MW, forcontrol circuits.Resistance 800 ohm to 4KMax volts 240 Size 11/2 x1/2in

RIBBON MICROPHONEwith pre-arnp on chassis.E1.75.

MULLARD MODULESLP1171 LP1179IF. Strip AM, FM

Front endPair 0'5.75

Complete with DataLP1186

LP1157varicap Med. & Long£5.00 Tuner E2.50

CRYSTALS COLOUR TV

4 433619 inc,'s 11.25Miniature type sealed

ULTRA SONICTRANSDUCERS KIKCI.Complete on BinScreened cable. E1.75

each; pairs £2.95.ULTRA SONICTRANSMITTER. Completeunit luncesed requires1.5V1, E3.25.FOSTER DYNAMICMICROPHONES. 200 ohmimpedance. Moving coil.Complete on chassis 11.75oair

U.H.F. MODULATORSLatest type, adjustable,ideal for computers

with data circuitSize 3x 21/2x 1 inch

Only £3.50

In screened case

MINIATURE EDGEINDICATOR METER

With illuminated dial scale0-10. F.S.O. 100 microamp.Size 11/2 x 11/2 x 1/2 deep.Only £1.65.

LM380 Amplifier ..........05pLM318N Hi -Slew Op. Amp

£150LM323K, 6v. 3 -amp, reg.

LM310N Volt, Follower

LM311H High Pert Volt,Comparator............11.00

LM384N, 5 -watt Amp 11.20LM393N Dual Corn__ 60p7905 Reg. -5v

MINIATURE HIGH-OUALITY FANS

"Whisper Model" by Ra-ton. Low -power consump-tion (less than 10 watts)Silent running 115v Itwoin series for 230v.150/60Hz. Sae 41/2 x 41/2 x

taro. ONLY £6.50 EACHincl. V A T.

BRAND NEW50% less than manufactur-

er's price

STEREO CASSETTEMechanisms 6 or 12 volt.Complete with Heads +Erase and Solenoid. Brand

TV CENDERGENCE POTS(URI

50 ohm100 All

SOP

5K

MONSANTO

Half -inch1 Display

High Intensityft each

set of 4 13 50Common anode

la Pin Oil Package

BRIDGE RECTIFIERBOO PIV 35 amps

11/2x 11/2x1/2in. 13.50

STEREO CASSETTE TAPEHEADS. Qualityreplacement for mostrecorders with mountingplate. Record/Replay 2.80

MARRIOTT TAPE HEADSQuarter track.TeXRypPS1 8 Record/Replay

XR PS3 6 Record/Replay

XES11 Erase leach) .11.00

HEWLETT-PACKARDDISPLAYS

-765°HIGHEFFICIENCY

AND VERY BRIGHTOnly 01.00 each

Set of 6 for ESHalf -inch red commonanode will replace

DL70/14-pin Dil.

EX -MOTOROLA5 + 5 -WATT

CARSTEREO

AMPLIFIERSComplete and tested units.Medium and Long Wave.Supplied as two built units15 x 2 x 2in.l with circuitand data. Only £5 pair.Includes pre -amp.

NATIONALP 8080A8216. .11.75104148 DIODESFull spec. but no polarityband. Per 1,000 £10

MINIATURE MP.C.POTENTIOMETERS. ModelM2 High -quality, 5%tolerance, 2 -watt, with lin.spindles. All values, 47ohms -47k only 60p eachper 10. 50p each per 100;40p each

RECHARGEABLEBATTERIES

VARTA 3.6 volts DEAC,MAN 225 E1.50

DAYFIT 6 -volt, 4.5 amp

XTAL FILTER 10.7 me/s.12.5DB separation,11/2x11/4x1 inch E7.00100KC/S + 1 meg. 3 -pin

.12.103

"CHERRY" ADD-ON KEYPAD

LISTPRICE

£22.00

011R PRICE

ONLY£7.50

Incl. V.A.T

A compact 12 -buttonkeypad suitable for usewith Keyboard toextend 'its functionsplus four extra keys.

Supplied brand new

A 3 x 4 non -encodedsingle mode keyboard

QUANTITY DISCOUNTS on ALL items (unle s stated), 15% per 10, 20% per 50, 25% per100. All items BRAND NEW (unless otherwise stated).DELIVERY from stock - Add post 35p per order.

EXPORT enquiriesinvited

TELEX 262284TransonicsMono 1400 SUPERSEM

Please add V.A.T. to all orders

FAST DELIVERY : TOP QUALITY

Phone 0752 21256

Export enquiries welcome

r SUPERSEMPLYMOUTH 0752 21256

MEMORIES AT UNFORGETTABLE PRICES

1-24 25-99 100+ 1,000+4116 P-3 200ns .90 .85 .80 .75

2114 LP 450ns .90 .87 .85 .802708k 450ns 2.70 2.50 2.30 2.252716k 450ns 12.45 2.30 2.10 2.002732k 450ns 3.85 3.65 3.60 3.258981 P-45 Cmos 2.25 2.15 2.05 1.858725 S 200ns 7.05 6.55 6.05 5.55K4164 200ns 5.00 4.75 4.50 4.258039 8 -bit 3.05 2.90 2.75 2.458080AP CPU 2.15 2.05 1.95 1.758085A CPU 2.80 2.65 2.50 2.208155P + Timer 3.10 2.95 2.80 2.508156P + Timer 3.45 3.25 3.05 2.658212P i/o Port 1.10 1.05 1.00 .858216 Bus Driver 1.05 1.00 .95 .858224P Clock Gen 1.30 1.20 1.15 1.058226P Bus + B/Drives .92 .87 .82 .758228P System Cont 2.25 2.15 2.05 1.858243P i/o Exp 2.00 1.95 1.90 1.808251AP Prog. Int./Face 2.60 2.50 2.40 2.308253P Prog. Int./Time 3.60 3.40 3.20 2.858255AP Peril:I./Inter 2.25 2.15 2.05 1.85

8257P DMA Cont 3.75 3.65 3.35 3.008259 Inter Cont 3.60 3.40 3.20 2.858279P Key Disp 4.60 4.50 4.00 3.504044 P-3 300ns 1.90 1.80 1.70 1.55

3rd FloorBritannic HouseDrake CircusPlymouth PL4 8AQ



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CUNARD HOTEL, LONDON MAYS-7*82Opening Times:10.00 hrs -18.00 hrs(closing 1700 hrs on the last day)

Specially designed forbusinessmen who are

aware of the needto make their

company more efficient!This three day event, running parallel with the majorconference, is designed to show the hardware andsoftware equipment and expertise available in thisarea of Information Technology.

All aspects relating to the practical issues of purchasingand installing, operating and applying VideotexSystems will be covered.

Exhibits wil I range from large "Turnkey" packages to thesmaller, but equally Important peripheral devices -terminals, printers, subscribers and telecommunicationsInterfaces.

This is the 5th in the highly successful series of viewdataand videotex exhibitions sponsored by IPC BusinessPress, the world's largest business publishers. In the pastthese exhibitions have been successfully used inlaunching the latest adaptors and complete systems.These systems are the modern tools of the new era inInformation Technology.

Don't miss out on this opportunityto make your company more eft lerdi

Fill out and return the form below.

Run in parallel with

VIDEOTEX SYSTEMS '82 CONFERENCE

Cunard International Hotel, May 5-7

VI DEOTEXISPlease send tickets for Videotex Systems '82 ExhIbition to:

Nome

Company

Address

L

TELETEXT AND PRESTEL

VIEWDATAUniversal single plug-in board

Combined

TELETEXT

AND

PRESTEL

The Lion Viewdata plug-in board is an inexpensive Teletext, Prestel and Viewdatasingle board designed for use in televisions and microcomputers. A programmableinterface serial and parallel accepts remote controls, keyboards and microcomputerinterfaces. The board is directly exchangeable with our Teletext only board IMullardset), and other teletext boards are simply exchangeable.

An add-on adaptor with full remote control is available with all the features of theboard giving, both Teletext and Prestel for £250 and this can connect to any set. Otheradaptors using the plug-in board are available for Nordmende, Grundig, Ferguson,Lion and certain other sets at £199. These sets then can be made full editing byprovision of our keyboard or with some types of microcomputer. Powerful featuresinclude:

* Full editing or message keyboardoption

* Printout option of Teletext, Prestel orViewdata pages

* Microcomputer interface* Autodial local and remote program-

ming* Teletext, Prestel and Viewdata* Timed Teletext pages

* Re -programmable interface*Cassette recording facility for

recording whole books of information* Local editing and programming* 8 -page storage option* RGB video output* Video games interfacing* Replacement of Teletext boards

LION VIEWDATA TV, 18 Harcourt Terrace, London, S.W.10 - Tel: 01-373 5218


HEED

PARABOLIC DISHES

6ft dia. for use in satellite reception andmicrowave transmissions. Please sendS.A.E. for full details and data sheet.

Harrison Bros.Electronic Distributors

1

22 Milton Road, Westcliff-on-Sea, Essex SSO 7JXTel: Southend (0702) 32338

86



U.K. RETURN OF POST MAIL ORDER SERVICE, ALSO WORLDWIDE EXPORT SERVICEBSR DE LUXE AUTOCHANGER £20Plays 12", 10" or 7" records,Auto or Manual. A highquality unit backed by BSRreliability. Stereo Ceramic _...

Cartridge. AC 200/250V. Size At. pb131/2x 1 1 1/4in. 3 speeds.Above motor board 33/4in. `......-Below motor board 21/zin.Post £2 Board £1 extra

HEAVY METAL PLINTHS Post £2Cut out for most BSR or Garrard decks.Silver grey finish, black trim. Size 16x133/4in. £4DECCA TEAK VENEERED PLINTH. Post £1.50Superior finish with space and panel for £5small amplifier. Board is cut for B.S.R.183/4in.x 141/4in x4in. Black/silver facia trim. Also withboard cut out for Garrard only £3. Plastic cover £6

TINTED PLASTIC COVERS Post £2177/ex131/ex31/4in. £6 181/4x 121/2X3in. £6171/4x93/4x31/2in. £3 143/4x 121/2x27/ein. £5133/4x 12x 21/4in. £5 16%x 13x4in. 5151/4x 131hx4in. £6 141/2x 131/ex 23/4in. £517x127/ex 31/2in. £6 171/4 x 133/4x 41/ein. £6

Callers Only (not suitable for post)

211/2x 141/4x 21/2in. E6 21 x137/6x41/ein. £6233/4x 14x 37/ein. £6 303/4 x 133/e x 31/4i n. £6

BSR SINGLE !0',

PLAYER DECKSBSR P232 BELT DRIVE -,.::. ,-...:::;,.:

QUALITY DECK ...i.

Manual or automatic play.Precision ultra slim arm. ---....-0` £24Cueing device. Bargain price 1,-... '',' Post £2With stereo ceramic cartridgeBSR P204 SINGLE PLAYERS SPECIAL OFFERSTwo speed 33/45 r.p.m. hi-fi decks with stereo car-tridges, cueing device and snake arm.Ceramic - 240VAC £15 or 9V DC £19Magnetic - 240V AC £20 or 12V DC £24GARRARD 6-200 SINGLE PLAYER DECK £22 Post £2Brushed Aluminium Arm with stereo ceramic cartridgeand Diamond Stylus, 3 -speeds. Manual and AutoStop/Start. Large Metal Turntable. Cueing Device.Ready cut mounting board £1 extra.GARRARD 730SP. 240V. £27.50. Magnetic Cartridge

arm, 3 -speed player, p.p. £2-Snake _single

BATTERY ELIMINATOR MAINS to 9 VOLT D.C.Stabilised output, 9 volt 400 m.a. U.K. made in plasticcase with screw terminals. Safety overload cut out. Size5 x 31/4 x 21/2in. Transformer Rectifier Unit. SuitableRadios, Cassettes, models, £4.50. Post 65p.

DE LUXE SWITCHED MODEL STABILISED. £7.50. Post£1. 3-6-71/2-9 volt 400ma DC max. Universal outputplug and lead. Pilot light, mains switch, polarity switch.DRILL SPEED CONTROLLER/LIGHT DIMMER KIT. Easy to build kit.Controls up to 480 watts AC mains, E3. Post 650.DE LUXE MODEL READY -BUILT 800 watts. Front plate fitsstandard box. £5. Post 65p

EMI 131/2 x Sin. LOUDSPEAKERSModel 450, 10 watts R.M.S. withmoving coil tweeter and two-waycrossover; 3 ohm or 8 ohm.£9.50 post £1.50. "Final Clearance".SUITABLE BOOKSHELF CABINET £6.50.18 x 11 x 6in., post f1.50

RELAYS. 6V DC 95p. 12V DC £1.25. 18V £1.25.BLANK ALUMINIUM CHASSIS. 6x4-£1.45; 8x6-£1.80;10x7-£2.30; 12x8 -f2.60; 14x9 -K3; 16x6-£2.90;16x 10-E3.20. All 21/2in. deep. 18 swgANGLE ALI. 6x 3/4 x 3/4i n. 18 swg. 30p.ALUMINIUM PANELS, 18swg. 6x4 -45p; 8x6 -75p;14x3- 75p; 10 x7 --95p; 12 x 8-£1.10; 12x 5- 75p;16x6-£1.10; 14 x 9-E1.45; 12x12-£1.50; 16x 10-E1 .75.PLASTIC AND AU BOXES IN STOCK. MANY SIZESALUMINIUM BOXES. 4x4x11/2 £1. 4x 21/2x 2 £1. 3x2x16x4x2 £1.60. 7x5x3 15.40. 8x6x3 £2.50. 10x7x3 £3.12x 5x 3 £2.75. 12 x8x3 £3.60. All with lids.BRIDGE RECTIFIER 200V PIV 2a £1. 4a £1.50. 8a £2.50.TOGGLE SWITCHES SP 30p. DPST 40p. DPDT 50p.RESISTORS. 1011 to 10M. 1/4W, 1/2W, 1W, 1p: 2W 10p.HIGH STABILITY. 1/2w 2%10 ohms to 1 meg. 8p.Ditto 5%. Preferred values, 10 ohms to 10 meg, 3p.WIRE -WOUND RESISTORS 5 watt, 10 watt, 15 watt 20pPICK-UP CARTRIDGES SONATONE 9TA £2.50. 9TAC £3.80BSR Stereo Ceramic SC7 Medium Output £2. SC12 £3.PHILIPS PLUG-IN HEAD. Stereo Ceramic. AU1020 1G306 -GP310 - GP233 -AG3306 - AG33101 £2.LOCKTITE SEALING KIT DECCA 118. Complete £1.ANTEX SOLDERING IRON 240V 15W £5.25. 25W £5.95.JACK PLUGS Mono Plastic 25p; Metal 30p.JACK PLUGS Stereo Plastic 30p; Metal 35p.JACK SOCKETS Mono Open 20p; Closed 25p.JACK SOCKETS Stereo Open 25p; Closed 30p.FREE SOCKETS - Cable end 30p. Metal 45p.2.5mm and 3.5mm JACK SOCKETS 20p. Plugs 20p.DIN TYPE CONNECTORSSockets 3 -pin, 5 -pin 10p. Free Sockets 3 -pin, 5 -pin 25p.Plugs 3 -pin 20p; 5 -pin 25p; Speaker plugs 20p; Sockets 15pPHONO PLUGS and SOCKETS ea. 15p.Free Socket for cable end 20p. Screened Phono Plugs 25p.300 ohm TWIN RIBBON FEEDER 10p yd.U.H.F. COAXIAL CABLE SUPER LOW LOSS, 25p yd.COAX PLUGS 30p. COAX SOCKETS 20p.NEON PANEL INDICATORS 250V 30p.

i.

...',;:

MINI -MULTI TESTERDeluxe pocket size precision movingcoil instrument. Impedance + Capacity- 2000 o.p.v. Battery included.11 instant ranges measure:DC volts 10, 50, 250, 1000.

:'......

*

AC volts 10, 50, 250, 1000.Co amps 0-100mA.Continuity and resistance to 1 megohms in two ranges.

De Luxe Range Doubler Model,£6.50 Post 65p 50,000 o.p.v. £18.50. 7 x 5 x 2in. Post £1

NEW PANEL501.ta 100p.a,1m a, 5m a,500ma, 1 amp,25 volt, 50 volt,21/4x2x11/4in.

METERS £4.50500µa,

50m a, 100m a, I ,,,,,,T"",,,,,,;',).2 amp D4+..

VU Meter. 'Post 65p

RCS SOUND TO LIGHT CONTROL KITKit of parts to build a 3 channel sound to light £15unit. 1,000 watts per channel. Suitable for homeor disco. Easy to build. Full instructions supplied. post 95pCabinet £4.50 extra. Operates from 200MV to 100W.200 Watt Rear Reflecting White Light Bulbs. Ideal forDisco Lights, Edison Screw. 6 for £4, or 12 for £7.50.Post 65p. Suitable panel mounting holders 85p.

RCS "MINOR" 10 watt AMPLIFIER KIT £14This kit is suitable for record players, guitars, tapeplayback, electronic instruments or small PA systems.Two versions available: Mono, £14; Stereo, £20. Speci-fication lOW per channel; size 91/2 x 3 x 2in. SAEdetails. Full instructions supplied. 240V AC. Post £1.

RCS STEREO PRE -AMP KIT. All parts to build thispre -amp. Inputs for high, medium or low impper channel, with volume control and PC Board £2.95Can be ganged to make multi -way stereo mixers Post 65p

MAINS TRANSFORMERS Post250-0-250V 7OmA, 6.5V, 2A £4.50 E2250-0-250V 80mA, 6.3V 3.5A, 6.3V 1A £5.00 £2350-0-350V 250mA, 6.3V 6A CT £12.00 £2300-0.300V 120mA, 2 x 6.3V 2A C.T.: 5V 2A £12.00 £2220V 45mA, 6.3V 2A E2.50 Et

AUTO 115V to 240V 150W £9. 250W E10. 400W £11. 500W E12. £2.

GENERAL PURPOSE LOW VOLTAGETapped outputs available2 amp. 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 25 arid 30V E6.00 f21 amp. 6, 8, 10, 12, 16, 18, 20, 24. 30, 36, 40. 48, 60 £6.00 E22 amp. 6, 8, 10, 12, 16, 18, 20, 24, 30, 36, 40, 48, 60 £10.50 £23 amp. 6, 8. 10, 12. 16.18, 20, 24, 30, 36, 40, 48, 60 E12.50 £25 amp. 6, 8. 10, 12.16, 18, 20, 24, 30.36, 40, 48, 60 E16.00 E25 8 10-16V. 1/2 amp. E2.50 80p 12-0-12V. 2 amps E3.50 £16V. 1/2 amp. E2.00 El 15-0-15V.2 amps £3.75 El6-0-6V. 1/2 amp. E3.50 El 20V 1 amp E3.00 f19V. 250ma. E1.50 80p 20-0-20V 1 amp ' £3.50 £19V. 3 amp £3.50 El 20-40-60V 1 amp £4.00 E29-0-9V. 50ma E1.50 80p 25.0.25V 2 amps £4.50 £110-0.10V. 2 amps E3.00 El 28V 1 amp Twice £5.00 E210-30-40V. 2 amps £3.50 £1 30V 11,3 amp E3.50 El12V. 100ma £150 80p 30V 5 arnp and12V. 750 ma £2.00 80p 17-0-172a £4.50 £212V 3 amps E3.50 El 35V 2 amps £4.00 ElTOROIDAL 30-0-30V 4a and 20-0- 20V 1/2a . E10 E2CHARGER TRANS Post RECTIFIERS Post6-12 volt 3a £4.00 -E2 6-12 volt 2a £1.10 80p6-12 volt 4a £6.504 E2 6-12 volt 4a £2.00' 80p

OPUS COMPACTSPEAKERS £22_pair Post f2TEAK VENEERED CABINET11x81/2x7in, 15 watts50 to 14,000 cps. 4 ohm or 8 ohm

OPUS TWO 15x 101/2x 73/4in 25 watt2 -way system £39 pair. Post £3.

LOW VOLTAGE ELECTROLYTICS 10p1 mf, 2 mf, 4 mf, 8 mf, 10 mf, 16 mf, 25 mf, 30 mf, 50 mf, 100mf, 250 mf. All 15 volts. 22 mf/6v/10v; 25 mf/6v/10v; 47mf/1 Ov; 50 mf/6v; 68 mf/6v/10v/16v/25v; 100 mf/10v; 150 mf/6v/10v; 200 mf/10v/16v; 220mf/4v/1 Ov/1 6v; 330 mf/ 4v/10v; 500 mf/6v; 680mf/6v/10v/1 6v; 1000 mf/2.5v/4v/10v; 1500 mf/6v/10v/16v; 2200 rnf/6v/10v; 3300 mf/6v; 4700 mf/4v.500m F 12V 15p; 25V 20p; 50V 30p. 1200m F 76V 86p.1000mF 12V 20p; 25V 35p; 50V 50p; 100V 70p.2000m F 6V 25p; 25V 42p; 40V 60p; 1 200m F 76V 80p.2200m F 63V 90p. 2500m F 50V 70p; 3000m F 50V 65p;4500mF 64V £2. 4700mF 63V £1.20. 2700mF/76V £1.HIGH VOLTAGE ELECTROLYTICS8/450V 45p 8+8/450V 75P 32-4-32+16/350V 90p2/500V 45p 8+16/450V 75p 100+100/275V 65p16/350V 45p 8+8/500V £1 150+200/275V 70p32/500V 75p 32+32/350V 50p 220/450V 95p32/350V 50p 32+32/500V £1.80 32+32+32/325V 75p50/450V 95p 50+50/300V 50p 50+50+50/350V 95pCAPACITORS WIRE END High Voltage.001_002_003_005..01_02_03, .05 mfd. 400V 5p.1MF 200V 5p. 400V 10p. 600V 15p. 1000V 25p..22MF 350V 12p. 600V 20p. 1000V 30p. 1750V 50p..47 M F 150V 10p. 400V 20p. 630V 30p. 1000V 60p.

NEW baker Star soundhigh power full rangequality loudspeakersproduced to giveexceptional

discotheques. Theseloudspeakers are

reproduction. Ideal forHi-Fi, music P.A. or

recommended wherehigh power handling isrequired with qualityresults. The high fluxceramic magnet ensures clear response.

MODEL INCHES OHMS WATTS TYPE PRICE POSTMAJOR 12 4-8-16 30 HI -F1 £14 F2

DELUXE MK II 12 8 15 HI -F1 £14 £2

SUPERB 12 8-16 M HI-FI £24 £2

AUDITORIUM 12 8-16 45 HI-FI £22 E2

AUDITORIUM 15 8-16 60 HI -F1 £34 f2GROUP 45 12 44-16 45 PA £14 f2GROUP 75 12 44-16 75 PA £18 f2GROUP 100 12 8-16 100 Guitar £24 E2

DISCO 100 12 8-16 100 Disco EN £2

GROUP 100 15 8-16 100 Guitar £32 f2DISCO 100 15 8-16 100 Disco I:32 £2

BAKER 150 WATT MIXER/POWERAMPLIFIER £89 Post f2

SLAVE VERSION £75For Organs, Discotheque, Vocal, Public Address. Three loud-speaker outlets for 4, 8 or 16 ohms. Four high gain inputs, each 20my, 50K ohm. Individual volume controls "Four channel" mixing.150 watts into 8 ohms R.M.S. Music Power. Distortion less than1%. Slave output 500 M.V. 25K.ohm. Frequency Response 25 Hz- 20kHz ± 3dB. Integral Hi-Fi preamp separate Bass & Treble.Compact - 16" x 8" x 51/2". Lightweight - 14lb: Master volumecontrol. Made in England. 12 months' guarantee. 200/250v A.C.mains or 120V to order. All transistor and solid state devices.100 Volt Line £15 extra.New Stereo Slave Model 150 -i- 150 wan £125. Post £4.BAKER'S NEW PA150 MICROPHONE PA AMPUFIER OB. PP £34 channel 8 inputs, dual impedance, 50K-600 ohm 4 channelmixing, volume, treble, bass. Presence controls, Master volumecontrol, echo/send/return socket. Slave input/output sockets.

BAKER £69 Post £250 WATT 4. 4- .4."4:AMPLIFIERIdeal for PA systems, Discos and Groups. Two inputs,Mixer, Volume, Controls, Master Bass, Treble Gain.

RCS offers MOBILE PA AMPLIFIERS. Outputs 4-8-16 ohms20 -wan RMS 12v DC, AC 240N, 3 inputs. 50K £46 PP £2.40 -wan RMS 12v DC, AC 240v, 4 inputs. 50K 100v Line E75 PP £2Mic 1; Mic 2; Phono; aux, outputs 4 or 8 or 16 and 100r line60 -watt RMS, Mobile 24 volt DC & 240 -volt AC mains. inputs 50K.3 mics + 1 music. Outputs 4-8-16 ohm + 100 volts line 55 PP £2

FAMOUS LOUDSPEAKERS"SPECIAL PRICES"MAKE MODEL SIZE WATTS HMS PRICE POSTSEAS TWEETER 4in 50 £9.50 5GOODMANS TWEETER 31/2in 25 £4.00 ElAUDAX TWEETER 4in 30 5.50 ElSEAS MID -RANGE 4in 50 £7.50 £1SEAS MID -RANGE Sin 80 £12.00 flSEAS MID -RANGE 41/2in 100 £12.50 £1GOODMANS HIFAX 71/4in 100 /8/16 f22 £2AUDAX WOOFER Bin 40 54.00 £2GOODMANS WOOFER Bin 25 /8 £6.50 ElGOODMANS HB 8in 60 £12.50 flRIGONDA GENERAL 10in 15 £2AUDAX WOOFER 10in 50 £16.00 f2GOODMANS PP12 12in 75 8/15 £24.50 £2GOODMANS GR12 12in 90 8/15 £27.50 f2G000MANS HP0 12in 120 115 £29 £2EMI HI-FI 13x8 10 3/8 E9.50 flSPEAKER COVERING MATERIALS. Samples Large S.A.E.B.A.F. LOUDSPEAKER CABINET WADDING 18in wide 34)5.CROSSOVERS. TWO-WAY 3000 c/s 3 or 8 or 15 ohm £1.90. 3 -way950 cps/3000 cps 20 watt rating. £220.3 way 60 watt E6.LOUDSPEAKER BARGAINS3 ohm, 4in, 5in, 1 x 4in, £1.50; 61/2in, 8 x 5in, £3; Bin, £3.50.8 ohm, 24in, 3M, 5in, £1.50; 61/2in, E3; 8in, £4.50; 12in, £6.15 ohm, 31/zin, 5 x 3in, 6 x 4in, £1.50.25 ohm, 3in, 5 x 3in, 1 x 4in, £1.50.120 ohm, 31/4in dia. EL

watts. No crossover required 4-8-16 ohm, 73/4x31/4in. £10.50 1100 waMOTOROLA PIEZO ELECTRIC HORN TWEETER, 33/4in. square 5

THE "INSTANT' BULK TAPE ERASER £9.50 Post 95pSuitable for cassettes and all sizes of tape reels.AC mains 200/250V. Hand held size with switch 44and lead 1120 volt also in stock).Will also demagnetise small tools.Head Demagnetiser only £5.

R.C.S. LOW VOLTAGE STABILISED POWERPOTENTIOMETERS Carbon Track PACK KITS £3.95 Post 65pSkit to 2M11. LOG or LIN. L/S 50p. DP 90p. Stereo L/S All parts and instructions with Zener diode printed circuit,£1.10. DP £1.30. Edge Pot 5K. SP 45p. mains transformer 240V a.c. Output 6 or 71/2 or 9 or 12V d.c.

up to 100mA or less. Please state voltage required.

RADIO COMPONENT SPECIALISTS 337 WHITEHORSE ROAD, CROYDONRadio

9-6. Closed all day Wed. Open 7Radio Books and Components Lists 31p stamps. (Minimum post/packing charge 65p.) Access or Barclaycard Visa. Tel: 01-684 1665 for SAME DAY DESPATCH. Cash prices includeVAT.


VALVE OUTPUT Transformers (small) 90p.TRIMMERS 10pF, 30pF, 50pF, 5p. 100pF, 150pF, 15p.MICRO SWITCH SINGLE POLE CHANGEOVER 30p.TWIN GANG, 1 20pF 50p. 500 plus 200pF £1.GEARED TWIN GANGS 25pF 95p.GEARED 365+365+25+25pF £1.TRANSISTOR TWIN GANG. Japanese Replacement 50p.

HEATING ELEMENTS, WAFER THINSize 11 x 9 x 9ein. Operating voltage 240V, 250W approx.

two sheets of metal or ceramic, etc.ONLY 60p EACH (FOUR FOR £21 ALL POST PAID.

Suitable for Heating Pads, FoodWarmers, ConvectorHeaters, Propagation, etc. Must be clamped between

Mil -I1 :Ei i ;II i'l I 4 : li f-

THANDARQuality British -made Portable Instruments.

_

MULTIMETERS: sms ,,,, MillDM450 £119DC 10p.HV-1200V AC 100# to 750V

emeelmesemmememeeDC 01nA-10A AC InA-10A0.010-20M11 41/2 digit LED -w,h,'

TM351 £99 *IMO DC 100µV -1000V AC 100µV -750VDC 100nA-10A AC 100nA-10A0.111-20M0 3,/2 digit LCD wwwwwwwammeseggeiffee

FUNCTION GENERATOR:TG102 £145Freg. Range: 0.2Hz-2MHz

Carriage for all Thandar

PORTABLE OSCILLOSCOPE:SC110 £139

Orders £1

SABTRONICS* Available in KITS *Making Performance Affordable

HANDHELD DMMs Assm Kit2033 £36.75 2035A £62AC/DC 1000/-1000V AC/DC 1000/-1000VAC/DC 104A -2A AC/DC 0.1µA -2AOhms 112-20Mil Ohm 0.1f1 -20M11

£49

FREQUENCY METERS:

Assm

8 digit LED

Kit 1;308110A 20Hz-100 MHz £678610A 20Hz-600 MHz £82

FREQUENCY METERS:

£49 .

£68 aaill011111M-------

9 digit LEDAssm Kit

8610B 10Hz-600MHz (0.1 Hz Resolution) £998000E110Hz-1000MHz (0.1Hz Resolution) £155

Carriage for all SABTRONICS orders £1

£84-

SAFGAN BRITISH -MADE SCOPES* DUAL TRACE* 5mV/Div Sensitivity* XY Facility* Z Modulation a* Calibration Output* Portable/Lightweight

DT 410 10MHz £179DT 415 15MHz £1DT 420 20MHz £19885 P&P £2XI -REF -X10 probe £11.50

e e

I s g I 10

LEADERWhen Quality Counts

LSG-16 £55A compact solid state RF Signal Genera-tor, most suited for checking the IF cir- g . ... a e 03 1 4icults and tuners in AM, FM and TV sets. ..,,,,..,,,,,

Frequency range up to 100MHz (300MHz on Harmonics).Carriage £1

7-711 .... LCR-740 £149.... el' ....... A highly efficient impedance bridge for

.--measuring resistance, capacitance andits ii ill inductance. The D factor of a capacitorand the 0 sector of a coil can also bemeasured.

Carriage £1Many more instruments available from all these ranges

ADD 15% VAT ON ALL PRICESLIKLNIVIllel All prices correct at 2-2-82 E&OEP.4 Cash with Order or Credit Card `--

CALLERS WELCOMEOPEN MONDAY TO FRIDAY 9am-5.30pm

DAROM SUPPLIES4 SANDY LANESTOCKTON HEATHWARRINGTONCHESHIRE, WA4 2AY(0925) 64764

Catalogueavailablejust sendA4 size22p s.a.e.

Happy MemoriesPart Type 1 off 25-99 100 up4116 200ns .95 .85 .654116 250ns .90 .80 .602114 200ns Low power 1.20 1.10 .952114 450ns Low power 1.10 1.00 .854118 250ns 3.25 2.95 2.656116 150ns CMOS 4.95 4.45 3.652708 450ns 1.95 1.85 1.652716 450ns 5 volt 2.25 2.15 1.952716 450ns three rail 6.40 6.00 4.952732 450ns Intel type 4.25 3.95 3.352532 450ns Texas type 4.25 3.95 3.35

Z80A-CPU £4.75 Z80A-P10 £4.25 Z80A-CTC £4.25

Low profile IC sockets: Pins 8 14 16 18 20 22 24 28 40Pence 9 10 11 14 15 18 19 25 33

Soft -sectored floppy discs per 10 in plastic library case:5 inch SSSD £17.00 5 inch SSDD £19.25 5 inch DSDD £21.008 inch SSSD £19.25 8 inch SSDD £23.65 8 inch DSDD £25.50

74LS series TTL, large stocks at low prices with DIY discountsstarting at a mix of just 25 pieces. Write or telephone for list.

Please add 30p post & packing to ordersunder £15 and VAT to total

Access & Barclaycard welcome24 -hr. service on (054 422) 618

Government & Educational orders welcome, £15 minimumTrade accounts operated : Telephone or write for details

Prices are still tending to dropTelephone for a quote before you buy

Happy Memories (WW)Gladestry, Kington

Herefordshire HR5 3NYTelephone:

(054 422) 618 or 628

Bf

-and compatibility of TV sets with TV games andhome computers for that matter. Problems arisewhen a set doesn't like a non-standard input signal.Television's special feature sets out to solve thisproblem and also features a detailed list of manu-

facturers suggested modifications.

LOPT TESTERLine output transformer failure is a commonenough failure -with some makes more thanothers -but it's not always easy to be sure that thetransformer is defective. This useful, easy -to -construct tester will help to solve the problem and

save you time.Lots more, too.

TELEVISIONGET A COPY TODAY

WW - 075 FOR FURTHER DETAILS88 WIRELESS WORLD MAY 1982

fe.w.rszzegvaesage(Registered in England 1179820

01-747 1 555267 & 270 ACTON LANE, LONDON W4 5DG. Telephone: 01-994 6275Telex 291429

9.30 a.m.-6 p.m.MON.-SAT.

CONTINUOUS

STABILISED POWER SUPPLIESFARNELL A15: 210/240V 1P. Dual Op. 12-17v per rail at 100mA.Remote sensing, current limit protection. (164x130x38mm), withmanual. £12.COUTANT 0A2: Op. amp, psu, 120/240V IP. Dual Op. 12-15v at100mA( 138x80x45n-i m.) £12 ea. or 2 for £22.BRANDENBURG Photomultiplier PSU. 19in. rack mounting.Metered, current limit protection.374 300V-1KV at 5mA 376 660V-1K6V at 10mA375 500V-1K5V at 6mA. All models £40.PIONEER MAGNETICS POWER SUPPLIES . 5V 150 amp, outputinput 115 vac. (Switchmode) Price £120 each.Various other makes of power supplies in stock.

D TO A CONVERTERS15MHz, 8 BIT

By Micro Consultants Ltd. 5052 cable drive op. Linearity 0.25%, max.0.125% typ. Settling time: 2V step 70nS typ. 2MV step 50nS colourtelevision transmission standard. Diff. gain 0.5% diff. phase shift0.5° types rad 802 and MC2208/8. Unused. Ex -maker's pack.

SPECIAL OFFER PRICE: £20NEW IN STOCKA range of high quality transformers SPECIALLY WOUND for us. Bybuying direct we can offer these superb SPLIT PRIMARY &SECONDARY transformers at highly competitive prices.6VA 0-12, 0-12

0-15, 0-15 2.2012VA 0-4V5, 0-4V5

0-6V, 0-6V0-9V, 0-9V0-12V, 0-12V 2.990-15V, 0.15V0-20V, 0-20V

20VA 0-4V5, 0-4V50-6V, 0-6V0-9V, 0-9V

0-12V, 0-12V0-15V, 0-15V0-20V, 0-20V

50VA 0-6V, 0-6V0-9V, 0-9V0-12V, 0-12V0-15V, 0-15V0-20V, 0-20V

120VA 0-30V, 0-30V0-40V, 0-40V

3.80

4.75

8.90

CASED AUTO TRANSFORMERS240V Cable input. American outlet socket.Rating Price 750VA £23.50300VA £13.00 1000VA £27.00500VA £18.00 1500VA £36.00Other Transformers 12VA1.2VA. 6-0-6, 9-0-9, 12-0-12 0-12, 0-12 2.96p

all 1.14 18VA1.5VA 9-0-9 2.64p12V 80p 24VA15V 1.00p 12-0-12 3.36p2.4VA 12V 4.84p12-0-12 1.48p 30VA24V(pcb) 1.00p 15-0-15 3.62p4VA 36VA5-0-5 1.25 9-0-9 4.70p6VA 50VA24V 1.50 0-2-4-6-8-10 6.00p

ALUMINIUM BOXES PLASTIC BOXESAB7 2.75x5.25x1.5in 11.06 75x50x25mm black or white 65pAB8 4x4x1.5in 11.06 180x110x55mm black 1165AB9 4x2.75x1.5in 11.06 80x60x4Omm black 92pAB 10 4x5.25x1.5in 11.23 215x130x85mm black or white £3AB11 4x2.5x2in 11.06 120x100x45mm black 11.15AB12 3x2x1in 77p 100x75x4Omm black 99PAB13 6x4x2in 11.43 150x100x6Omm black 11.35AB14 7x5x2.5in 1190 BLUE REXINE COVEREDAB15 8x6x3inAB16 10x7x3in

nnn.06 ALUMINIUM BOXES

AB17 10x4.5x3in 12.52 RBI 6x4.5x2.5in 12.15AB18 12x5x3in 12.77 RB2 8x5x3in 12.77AB19 12x8x3in 13.34 RB3 9x5x3.5in. 12.99

RB4 11x8x4in. /3.45RB5 11x7.5x4.5in 14.29

MAIL ORDER: Gds. + 15% VAT plus VAT -INCLUSIVE Adm/Pkg./Post:

/.Kg E1.30 2Kg E3.00 6Kg E4.401/zKg £1.70 3Kg E3.45 6-10 15.003/4Kg 1220 4Kg 0.90 Over 10Kg1Kg £2.55 5Kg £4.20 Quote

SPECIAL OFFERS

Headers Blue Mac 16 -pin 50p; 24 -pin 80p. Brand new and boxed.Speakers: 2in. 16 ohm 200mW 60p; 7x4in. dual -cone 8ohm highquality 5W LS £1.60. Brand new and boxedMultiturn Pots. We have large stocks, all makes, multiturn pots, cer-met, etc.Bourns type 3299X 1 K/50K 30p eachBourns type 3386P 5K/trimpot 30p eachSpectrol Sin. 22ohm/100K 30p eachAlso large stocks of cermet presets type 62 by Beckman and AB type81E 30p each

Discounts available on quantity

Full range available of Plessey moulded track presets, screwdriver orknob operation 25p eachCassette Decks: With stereo heads, mechanically complete, but withno electronics. Brand new, smart black modern finish

£7.45 inc. VAT + P&PVU Meters: 40x30x23mm deep. White/red scale on black background.Brand new 60pPolyester Capacitors by Siemens, Mullard and Rifa.2.2p.F at 100/250v radial block 15p each3.3µF at 100v radial block 25p each4.7µF at 100v radial block 30p each10µF at 63v radial block 40p eachMains Filters by Erie/Corcom from 3A to 15A, 250v AC rated....£3 each

SPRAGUE: Series 36D Computer grade electrolytics 3,300 at 40V.Brand new and boxed 35p ea.SIEMENS: Procond Radial Polyester Film Capacitors. 101.1F at 63V.Brand new Only 40p

Quantity available

***********************************. .VIDEO GAME

. .BOARD

.* FIELD GOAL VIDEO GAME, BY TAITO. A top quality board* complete with 6800 CPU system with 2716 eproms with circuit ** diagram, plus all connections for either colour or black and *** white monitors ITV sets). Price £20 + VAT M. P/P £2.55.

* POWER SUPPLY KIT TO SUIT + circuit diagram. *

** Price £15 + VAT £2.25. P/P £3.45.

* 2 x 22 -WAY GOLDPLATED DOUBLE -SIDED 0.156" EDGE ** ** CONNECTORS to suit videoboards. ** Price £1.60 pair + VAT 24p. P/P included. ** ** THE COMPLETE KIT £46 INCLUSIVE. Full details on application. ** *

WE PURCHASESurplus component stocks, redundant materials,obsolete computers; for cash.

We also collect - distance no object. Just call:

C. T. Electronics (Acton) Ltd.267 & 270 Acton Lane, London W4 5DG

Telephone 01-747 1555; 01-994 6275

Telex 291429

This advertisement is mainly of our excess stockholding. We also have excellent stocks of semiconductors, hardware, cables,etc., etc. For further details send for our lists and retail price catalogue, phone or visit our shop. All prices are exclusive of VAT(and P&P). Minimum Mail Order £5 + P&P + VAT. Government departments, schools, colleges, trade and export welcome.

WW - 093 FOR FURTHER DETAILSWIRELESS WORLD MAY 1982 89

NucletudeAmplifiers

Over 65 Models AvailableClass A wide band Linear R.F. Amplifiers or VCO's in

the range D.C. to 4 GHz; with power output up to 100Wand gains to 60 dB; you can't do better than Nucletude.Modular D.C. powered and mains operated bench units

available. Get full details from Telonic Berkeley U.K.

A 2 Castle Hill Terrace Maidenhead, Berks SL6 4JRTelephone: Maidenhead 10628) 73933 Telex: 849131 (Telber Gl

TELONIC/BERKELEy U.K


TIME WRONG?MSF CLOCK is ALWAYS CORRECT - never gains or loses,

SELF SETTING at switch -on, 8 digits show Date, Hours,Minutes and Seconds, auto GMT/BST and leap year, canexpand to Years, Months, Weekdays and Milliseconds,also parallel BCD output for computer or alarm, etc.,STOPCLOCK and audio to record and show time onplayback, receives Rugby 60KHz atomic time signals, built-in antenna, 1000Km range, GET the TIME RIGHT, only£62.80.

60KHZ RUGBY RECEIVER, as in MSF Clock, serial data outputfor computer, etc., decoding details, £17.90.

Each fun -to -build kit (ready made to order) includes all parts,printed circuit, case, postage etc., instructions, money -backassurance so GET yours NOW.

CAMBRIDGE KITS45 (WEI, Old School Lane, Milton, Cambridge. Tel: 860150

Distortionbelow .002%10Hz/100 Khz£41.60(Model 1491

+ TAXP.P. £2.25

AUDIO SIGNAL GENERATORFIRST-CLASS PERFORMANCE

AT VERY LOW COST

1v RMSOutput. AttenuatedSine/Square Wave

(Kit C35.65)(Model 1461

'----Also available with frequency readout. Send for lists on func-

tion gen, THD meters, millivoltmeters, etc.Based on a Linsley Hood design

TELERADIO ELECTRONICS, 325 FORE STREET, LONDON N9 OPETelephone 01.807 3719 Closed Thursdays

INIRCLAWMIDINg.

==PM COMPONENTS LTD

VALVE & COMPONENTS SPECIALISTS

INTEGRATED CIRCUITSAN124 2.50AN2140 2.50AN240P 2.80AN612 3.25AN7150 2.95BA521 3.358RC1330 076BTT822 2.10ETT6016 1.75HA1151P 2.50HA1366W 2.95LA3350 2.50LA4031P 2.70LA4032P 2.50LA4400 4.15LC7120 350LC7130 3.50LC7131 5.50LC7137 5.50M51513L 2.30M51515L 2.95MB3712 2.00MC1307P 1.00MC1310P 1.50MC1327 0.95MC1330P 0.76MC1349P 1.20MC1350P 0.76MC1351P 1.50MC1352P 1.00MC1357 2.35MC1495 3.00MC14011BCP

0.32ML231B 1.75ML2328 1.75ML237B 1.95ML238B 4.20ML23913 2.10ML920 4.12ML922 3.29ML928 1.65

MSM5807 6.75PLLO2A 6.75SAA1020 8.95SAA1021 7.50SAA1024 4.50SAA1025 7.25SAA5000A 3.05SAA5010 6.35SAS560S 1.60SAS570S 1.60SAS580 2.85SAS590 2.85SAS660 1.85SAS670 1 85SL490 1.96SL9018 4.85SL917B 6.65SL918A 6.00SL1310 1.80SL1327 1.10SL13270 1.10SL1431 1.37SL3046 0.95SL76544 2.05S5760035 1.65S5760135 1.65S5760235 1.65SN76033N 1.65SN76110N 0.89SN76115N 1.25SN76131N 1.30S57622605 1.55SN76227N 1.05SN76532N 1.40SN76533N 1.305576544N 1.30SN76650N 1.05S5765705 1.00S5766205 0.95SN76650N 0.95SN76651N 1.50SN76660N 0.80

SN76666N 0.70SW153 2.74TA7061AP 3.95TA7063P 0.80TA7073AP 1.80TA7108P 1.00TA7120P 1.85TA7130P 1.50TA7171P 1.85TA7172P 1.85TA7176AP 2.50TA7203 2.95TA7204P 2.15TA7205AP 1.95TA7222AP 1.80TA7310P 1.80TA7313 2.95TA7313AP 2.95TAA310A 215TAA320A 2.00TAA370A 2.50TAA470 3.50TAA550 0.25TAA570 1.80TAA621AX1 3.00TAA630S 3.15TAA661B 1.20TAA700 1.70TBA120A 0.70TBA120AS 0.70TBA120B 0.70TE3A120S 0.70TBA120SB 0.70TBA120S0 0.70TBA1207 0.70TBA120U 1.00TBA395 1.50TBA396 0.75TBA4405 2.55TBA4800 1.25T8A510 1.65TBA5100 1.65TBA520 1.10TBA5200 1.10TBA530 1.10

TBA5300 1.10TBA540 1.25T8A5400 1.35TBA550 1.45TBA550C1 1.45TBA560C 1.45TBA560C13 1.45T8A570 1.00TBA641Al2

2.50TBA641B11

3.00TBA641-13113.00TBA651 1.75TBA673 2.45TBA7000 1.80TBA720A 2.45TBA720AQ 2.45TBA750 1.85TBA800 0.89TBA810AS 1.35TBA810S 1.35TBA820 1.45TBA890 2.50TBA920 1.65TBA9200 1.65TBA950/2X 2.35TBA990 1.49TBA9900 1.49TBA1441 2.15TCA270 1.10TCA270S 1.10TCA270S0 1.10TCA640 2.50TCA650 2.50TCA800 2.15TCA8305 1.40TCA940 1.85TCEP100 1.95TDA440 2.20TDA1002 1.25TDA1004A 2.20TDA1006A 2.50TDA1010 2.15TDA1054 0.90

TDA1170 1.95TDA1170S 1.95TDA1190 2.15TDA12700 3.95TDA1327 1.70TDA13270 1.70TDA1352B 1.43TDA1412 0.85TDA2002 1.95TDA2020 2.45TDA2030 2.80TDA2140 3.76TDA2522 1.95TDA2523 1.95TDA2524 1.95TDA2530 1.54TDA2532 1.95TDA2540 2.15TDA2541 2.15TDA2560 2.15TDA2581 1,15TDA2590 2.95TDA2591 2.95TDA2593 2.95TDA2600 295TDA2611A 1.95TDA2640 2.60TDA2650 2.15TDA2653 215TDA2680 2.15TDA2690 1.35TDA9503 3.95UPC1185H 3.95UPC566H3 2.95UPC575C2 2.95UPC1001H 2.50UPC1025H 2.50UPC1156H 2.95UPC1182H 2.95UPC1350C 2.95UPC2002H 1.95555 0.35741 0.35

SEMICONDUCTORSAC126 0.22AC127 0.20AC128 0.20AC128K 0.32AC141K 0.34AC142K 0.30AC176 0.22AC176K 0.31AC187 0.25AC187K 0.28AC188 0.22AC188K 0.37AD142 0.90AD143 0.82AD149 0.70AD161 0.39AD162 0.39AD161/2 0.90AF124 0.34AF125 0.32AF126 0.32AF127 0.32AF139 0.42AF150 0.42AF239 0.42AU106 2.06AU107 1.75AU110 2.00AU113 1.48BC107 0.10BC107A 0.10BC107B 0.10BC108 0.10BC108A 0.10BC10813 0.10BC109 0.10BC109B 0.10BC114 0.11BC116A 0.128C117 0.19BC119 0.24BC125 0.12BC140 0.31BC141 0.25BC142 0.21BC143 0.24BC147 0.09BC148A 0.09BC1488 0.09BC149 0.09BC157 0,10

BC158 0.09BC159 0.09BC160 0.28BC161 0.28BC170B 0,10BC171 0.08BC171B 0.10BC1728 0.10BC173B 0.10BC174 0.09BC182 0.09BC182LB 010BC183 0.12BC183L 0.09BC184LB 0.09BC204 0.10BC208B 0.138C212 0.09BC212L 0.09BC213 0.09BC213L 0.09BC237 0.09BC238 0.09BC251a 0.12BC252A 0.15BC258A 0.39BC300 030BC301 0.30BC303 0.26BC307 0.09BC327 0.108C337 0.10BC338 0.09BC461 0.30BC478 0.20BC547 0.10BC548 010BC549A 0.08BC550 0.07BC557 0.07BC55713 0.07BC558 0.07BD115 0.30BD116 0.52BD131 0.32BD132 0.35BD133 0.40BD135 0.3080136 0.30BD137 0.2800138 0.30

BD139 0.32BD140 0.30BD159 0.65BD166 0.4680179 0.72BD182 0.70BD201 09380202 0.6580203 0.7880204 0.70BD222 0.46BD223 0.48BD225 0.4680233 0.35BD234 0.35BD236 0.45BD237 03050238 0.33BD410 0.55813434 0.55BD437 05080517 0.8080520 0.65BDX32 1.50BF115 0.35BF127 0.24BF158 0.18BF160 0.27BF167 0.24BF173 0.22BF177 0.38BF178 0.26BF179 0.34BF180 0.29BF181 0.29BF182 0.29BF183 0.29BF184 028BF185 0.28BF194 0.118F195 0.11BF196 0.11BF197 0.11BF198 0.10BF199 0.14BF200 0.30BF241 0.15BF256 0.28BF256/LC 0288F257 3.288F258 0.25B F259 0.268F271 0.268F273 0.13

BF336 0.34B F337 0.29BF338 0.328F355 0.37BF362 0.38BF363 0.31BF371 0.20BF394 0.19BF457 0.23BF458 0.23B F459 0.36B F595 0.23BF597 0.25BFR39 0.2313FR41 028BFT42 0.28BFW92 0.85BFX29 0.30BFX84 0.28BFX85 0.28BFX86 0.30B FX88 0.25BFY50 021BFY51 0.21BFY52 0.25BFY90 0.77BR100 0.19BR101 0.30BRC4443 0.85BT106 1.00BT108 1.22BT116 1.20BU105 1.22BU108 1.69BU124 1.00BU126 1.22BU204 1.55BU205 1.30BU208 1.39BU208A 152BU208/02 1.89BU326A 1.42BU407 1.24BU500 1.75MJ3000 1.98MJE340 0.40MJE520 0.48MRF450A 11.50MRF453 13.50

MRF477 10.00MRF475 2.50620068 1.70R20108 1.70R2322 0.58

R2323 0.8682540 2.48RCA16334 0.90RCA16335 0.80TIP29 0.40TIP29C 0.42TIP30C 0.43TIP31C 0.42TIP32C 0.42TIP33B 0.75TIP41C 0.45TIP42C 0.47

0.85TIP120 0.80TIP122 0.79TIP161 2.95TIP2955 0.84TIP3055 0.66TIS91 0.20TV106/2 1.50252219 0.28252905 0.402N3054 0.592N3055 0.522N3702 0.122N3703 0.12253704 0.12253705 0.12253706 0.122N3708 0.122N5294 0.38255296 0.482N5298 0.52255496 0.662SA715 0.952SC495 0.802SC496 0.802SC1096 0.802SC1172Y 2.202SC1173 1.152SC1306 1.252SC1307 1.852SC1449 0.802SC1678 1.252SC1945 2.102SC1953 0.952SC1957 0.802SC1969 1.952SC2028 1.152SC2029 1.802SC2078 1.452SC2091 0.852SC2314 0.8035211 1.50

DIODESAA119BA102BA1158A145BA148BA154BA155BA156BAX13BAX16881058

0.080.170.130160.170.060.130.150.040,060.30

80126 0.10B0127 0.11BY133 0.15130164 0.45BY176 1.2080179 0.6380206 0.14130208-800 0.3380210-800 0.33BY223 0.90BY298-400 0.22BY299-800 0.22BYX10 0.20

80036-15060.20

BYX38-600R0.80

BYX55-600 0.30130071-600 0.600A47 0.090890 0.050A91 0.060895 6060A202 0.101560 0.0615914 0.04

N4001 0.04N4002 0.0454003 0.0454004 0.0554005 0.0554006 0.0554007 0.0854148 0.02N4448 0.10N5401 0.12N5402 014N5403 0.12N5404 0.12

N5405 01355406 0.1355407 0.1655408 0.16TT44 0.04TT827 0.48TT921 0.09TT923 0.15TT2002 0.11

SPECIAL TUBEM17.151 GV/R

198.00

WIREWOUNDRESISTORS

BASESETC.

ZENER DIODES

PREFERRED VALUES4 Watt 4R7 -1K8 0.13

2K2 -6K8 0.1610K 0.22

7 Watt R47 -4K7 0.145K6 -12K 0.1515K -22K 0.18

11 Watt 1R-100 0.1815K 0.21

17 Watt 1R -10K 0.2415K -22K 025

87G 0.15B7G Skirted

0.30B8G 0.7089A 020BOA Skirted

0.30B1OB 0.168138 0.508 Pin DIL 0.1014 Pin DIL 0.1214 Pin DIL/0

0.3016 Pin DIL 0.15OCTAL 0.35CANS 0.27

BZX61 0.156V2 7V5 8V2 9V1 10y 11V 12V 13V15V 16V 18y 20V 22V 24V 27V 30V33V 36V 39V 47V

BZY88 0.072V7 3V 3V3 3V6 3V9 4V3 4V7 5V15V6 6V2 6V8 7V5 8V2 9V1 10V 11V12V 13V 15V 18V 24V 27V

THERMISTORS BATTERIES

VA1040 0.23VA1056S 0.23VA1104 0.70VA8650 0.45

7V Power Mikebatteries

TR175 E1.40 eaother prices on

request


----

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HENRy5iv COD IVISMPIONUTER

KIT TANGERINE COMPUTEREN

,12:R-sPA,LONDON & HOME COUNTIES STOCKISTS 'NE

AND gEk4AMEATIONs 404 EDGWARE RD. LONDON, W2 1ED TEL: 01-402 6822

TANGERINE* TANGERINE TANGERINE *TANGERINE TANGERINE

MICROTAN 65 TANEX, BASIC, X BUGFULL MANUALS: MICROTAN,

All ER eachAll £43.00Microtan 65 is the most advanced,powerful, expandable microcomputer available italso hatfbens to be themost cast effective'

Electronic TodayInternational held a

mammoth survey of kits.The result Microtan 65

WINS COMPUTER CLASS!

MICROTAN 65 CONTENTS

High quality, plated thin hole printed circuit board. solder resist and silkscreened component identification. 6502 microprocessor 16 monitorTANBUG Now with 'V' Bug 1K RAM for user programme, stack anddisplay memory VDU alphanumeric display of 16 rows by 32 charactersMICROTAN 65 system file border 136 page, bound, users hardware'software manual with constructional details and sample programmesLogic and discrete components to fully expand MICROTAN 65

KIT FORM £69.00 + VAT,MICROTAN 65 assembled and tested,Specification as above, but assembled and fully bench tested by ourselves

£79.00 + £11 85 V A T total /90 85

TANBUG V2.3 Kit £21.85 incl.

TANRAMAVAILABLE NOW TANRAM 40K Bytes on

one board, Single hoard of hulk memoryuttering 76 Static RAM 121141, and 326Dynamiti, RAM 141161 Onboard refresh istotally transparent to CPU operation and isunaffected by normal DMA's TANRAM fullyexpands the available address space of the6502 microprocessor MICROTAN, TANEX and TANRAM togetherprovide IHK RAM 48K RAM. and 1K I/O - that's a lot of memoryand a lot of 1/0, Built and tested TANRAM ASSEMBLED

40K RAM CARD with 16K DYNAMIC RAM £76 .VATCONTENTS High quality plated thru hole printed circuit board, solderresist and silk screened component identification Full complement ofI C sockets for maximum expansion 64 way DIN edge connectorIK RAM 121141 Data bus buffering TANRAM users manual

EXTRA RAM:IK STATIC 121141 12.95 each 166 DYNAMIC 141161 11 50 each

Minimum

Config Kit

CONTENTS + V A T £6 45, total 149 45

High quality plated thru hole printed circuit board, solder resist and silkscreened component identification I C sockets for maximum expansion64 Way DIN edge connector 16 RAM. cassette interface. 16 parallel

r

I/O lines, a T T.L.serial I/O port, two 16 bit counter timers, data busbuffering. memory mapping, logic and discrete components formaximum expansion TANEX users manual

POWER SUPPLIESInput 240V AC. Output 5 Volts at 3 Amps Regulated.Will power both MICROTAN and TANEX fully expanded. Built onthe same site printed circuit board as MICROTAN etc Aral lahle as afully built and tested unit

£23.00 = VAT 1345, total £26.45.X MPSZ +5V 6A, +126. -5 and I 2V switch mode system PSU

£69.13 + V A T

MEMORIES EXPAND YOURDiscounts 10% for 4, 15% for 8. 20%

2102 16 x I Static RAM 8Op

2708 f 3 502716 16.50MK 4116 16K x 1 Dynamic RAM

(1,50 All includi

SYSTEM WITH OUR TANGERINE

for 16 APPROVED CHIPS

IM 6402 UART 14.5021141Kx 4 Static RAM £2.95

4118 1K x 8 Static RAM 17.50

no VAT

MONITORS (PROFESSIONAL)RECONDITIONED AND NEW FROM £35.00 to £129.95

71 KEY ASCII KEYBOARD £56.34+ V A TNO EXTRAS NEEDED

Uses gold crosspoint keys. Includes numeric keypad and ribbon table,

Available as fully assembled and tested

SUPER METAL CABINET IN TANGERINE/BLACK

£20.00 + V A T 13 00 total f23 00

NEW PRODUCTS loll V.A.T. incL)SYSTEM MOTHERBOARD 14 CONNECTOR)SYSTEM MOTHERBOARD 112 CONNECTOR).. 112.55

SYSTEM RACK FRONT PANEL _E15.64

SERIAL I/O BOARD MIN. 12 PORTS). 186.70

SEND FORFREE BROCHURE

CENTRONICS Ideal for Tangerine

PRINTERSSHEIKOSHA £199 + VAT

Model 730 £350 + V A T

Model 737 £395 + V A T

NEW MICROTANTEL [

POST OFFICE APPROVED i :

PRESTEL - VIEWDATA FULL COLOURGRAPHICS MICROTANOWNERS CAN COMMUNICATE WITH EACHOTHER CAN STORE PRESTEL CAN BEUSED AS AN EDITING TERMINAL CAN BEINTERFACED WITH PET. APPLE ANDNASCOMJust connect to the aerial socket of any colour or black and whitedomestic T V receiver and to your Post Office installed lack socket andyou are into the exciting world of PRESTEL Via simple push button useyou are able to view 170.000 pages of up to the minute information onmany services. order goods horn companies all this withoutt leavingyour armchair,

TANEX (Minimum conligurattoM Assembled

£53.00 +VAT £7 95. total MO 95

TANEX EXPANSIONExpanded. TANEX offers 7K RAM,locations for 4K EPROM (27161.locations for 10K extendedMICROSOFT BASIC, 32 parallel I/Olines, two Ili seriall/D ports, athud serial I/O port withRS232/20mA loop, full modemcontrol and 16 programmable baudrates, four 16 bit counter rioters.cassette interface, data busbuffering, and memory mapping

EXPANDED TANEX KIT (Excludes ROM, XBUG and BASIC(

£89.70 + V A T /13 46. total /103 16EXPANDED TANEX ASSEMBLED

£99.70 +V A T 114 96. total 1114 66

OPTIONS TO FULLY EXPANDED TANEX

IOK Extended MICROSOFT BASIC in EPROM with manual)(49.00 +V.A T 17 35, total 156 35

Extra RAM 1K 12 x 2114115.20+VT 78p, total 15 98

SERIAL I/O KIT f10.26 +V AT 11 60. total Ell 806522 VIA £8.00 +VAT C1 20. total 19 20XBUG 117 35 +V. A T 12 60, total /19 95

± 12v KIT £9.20 incl.

ADD-ONKEYPAD

A compact 12 button keypadsuitable for use withkeyboard to extend its functionsplus tour extra keys. Suppliedbrand new with with data. A3 x 4 non -encoded single modekeyboard in sloped format

LIST PRICE£2200

OUR PRICE

£7.95 VAT

PROFESSIONAL ASCII KEYBOARDSIdeal forTangerine£29.95 VAT

52 key 7 bit ASCII codedPositive strobe .56-12VFull ASCII charactersParallel output with strobe

Power light on controlChip by General Instrument(G I I TTL output

Superbly made Size13.55 x15 ins Black keys with white ledgens Escape shift return &

reset keysControl repeat & bellComplete with DATA

TANGERINE TANGERINE TANGERINE TANGERINE *TANGERINE TANGERINE TANGERINE *TANGERINEAll orders pre -paid and official advertised here to beforwarded DIRECTLY toCOMPUTER DEPT., 11/12 PADDINGTON GREEN, LONDON W2

FULLY GUARANTEED ' BUY WITH CONFIDENCE.

BRITISH DESIGN & MANUFACTURE AND ON DEMONSTRATIONIN OUR COMPUTER DEPT.

FOTO LA KPOSITIVE LIGHT SENSITIVE AEROSOL LACQUER

Enables YOU to produce perfect printed circuits in minutes!Method Spray cleaned board with lacquer. When dry, place positive master ofrequired circuit on now sensitized surface. Expose to daylight, develop and etch.Any number of exact copies can of course be made from one master. Widelyused in industry for prototype work.

FOTO LAK £2.25Developer 35pFerric Chloride 55p

Pre -coated 1 / 16 Fibre -glass board204mm x 114mm £1 .50204mm x 228mm £3.00408mm x 228mm £600467mm x 305mm £8.00

Plain Copper -clad Fibre -glass. Single -sided 'Double -sided,

Approx. 1.00mm thick ft. sq . £2.00 £1.75Clear Acetate Sheet for making master, 260mm x 260mm 15p

Postage and packing 60p per order. VAT 15% on total

G. F. MILLWARD ELECTRONIC COMPONENTS LIMITEDP.O. Box 19, Praa Sands, Penzance, Cornwall TR20 9TF

Telephone GERMOE (073-676) 2329TRADE ENQUIRIES INVITED

100R 1k 10k

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ONLY 3p EACH Special9 Offer: 5 PCS of EACH (445 REGIS -106 9k1 91k 1M

Minimum order E10 TORSI ONLY £11.50.Minimum 5 pcs per value High Quality High Stability, Huge

89 Values (124) Strength.VAT inclusive. Add £1.00 p&p all areas.

ORION SCIENTIFIC PRODUCTS LTD.4 Golden Square, London, W.1

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4kfizAPG.A.S. ELECTRONICS16, ST. ALF EGE PASSAGE, LONDON SE10

TELEPHONE: 01-853 5295TELEX: 923393 LASER G



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POWER UNITSNow available with

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OUTPUT 2. 0-70v, 10A AC

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VALRADIO LIMITED, BROWELLS LANE, FELTHAMMIDDLESEX TW1 3 7EN

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Staffs. B78 1AB. (NOTE New Address) ..

IN VIEW OF THE EXTREMELY RAPID CHANGE TAKING

PLACE IN THE ELECTRONICS INDUSTRY, LARGE QUANTI-

TIES OF COMPONENTS BECOME REDUNDANT. WE ARE

CASH PURCHASERS OF SUCH MATERIALS AND WOULD

APPRECIATE A TELEPHONE CALL OR A LIST IF AVAILABLE.

WE PAY TOP PRICES AND COLLECT.

BROADFIELDS & MAYCO DISPOSALS21 Lodge Lane, N. Finchley, London, N.12. 5 mins. from Tally Ho corner

Telephone 445 2713/0749 194611


`This book is excellent.'- Jim Strasma

Ùnquestionably the most accurateand comprehensive reference I have seen to date.'

- Jim Butterfield

Bestseller - comprehensiveteaching and reference book onall software aspects ofCommodores 2000, 3000,4000 and 8000microcomputers andperipherals.

Many programs, charts and diagrams.17 chapters, appendices, and index.iv + 504 pages. 19 x 26 x 2'/:cm.Paperback. ISBN 0 9507650 0 7.Price in UK and Europe E14.90 each(incl. post and heavy-duty packing).LEVEL LTD., PO Box 438, Hampstead,London NW3 1BH. Tel: 01-794 9848.

Cut out or copy coupon, or write to:LEVEL LTD., PO Box 438, Hampstead, London NW3 1BH.

Send copy/iesof Programming the PET/CBM at £14.90 (post free)

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WIRELESS WORLDwhy not take advantage of our reprint service.Reprints can be secured at reasonable cost toyour own specifications providing an attractiveand valuable addition to your promotionalmaterial. (Minimum order 250.)For further details contactMichael Rogers, IPC Electrical -Electronic PressLtd. Phone 01-661 3036 or simply complete andreturn the form below.

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COMPUTER WAREHOUSBULKBUYSPECIALS

RAM SCOOP4116 200 NS 8 for £12.954164 200 NS £8.50 each2102-650 NS 8 for £5.50

INC VAT

TELETYPE ASR33I/O TERMINALS

OOPore

From £195 ARC.+ VATFully fledged industry standard ASR33 data ter-minal. Many features including: ASCII keyboardand printer for data I /0, auto data detect circuitry,RS232 serial interface, 110 baud. 8 bit paper tapepunch and reader for off line data preparation andridiculously cheap and reliable data storage. Sup-plied in good condition and in working orderOptions: Floor stand £12.50 -i- VAT

KSR33 With 2Orna loop interface £1 25.00 -i- VAT.

Sound proof enclosure £25.00 + VAT

DIABLO S30 DISK DRIVES44' %IP

O

25 WAY "D"CONNECTORS

50+25p 1.70 1.10

25S 1.90 1.20

ALL + VAT

100+0.951.00

"OLIVETTI TE300"PRINTER/TERMINALS

E NOW OPENMONDAY -SATURDAY

9.30-5.30

WIRE WRAP SKTS.24 Pin Vero 28p14 Pin Gold 22p16 Pin Gold 24p100 PCS Mill Ord.

C10DATA CASSETTES

10 for £5.75Inc VAT

MPUEXPERIMENTORSt 5v. 1 2v -1 2v.24v

POWER SUPPLY

A complete I/O terminal with integral 8 holepaper tape punch and reader, full ASCIIkeyboard, 120 column printer, and controlunit. The printer is capable of 150 baud with aserial TTL or balanced input-output sold ingood overall condition but untested. Completewith circuit unguaranteed. Connect direct toyour micro at ONLY £99.00 +£1 1.50 carr +vat.

Once again we are very pleased to offer this superb Power

Supply Unil and hope to satisfy most of our previouscustomers wit were disappointed when we sold out due to

demand last time they were advertised"! These units may lust

have well been made for your lab they consist of a semi-

enclosed chassis measuring 160rom x 120mm x 350mm

containing all silicon eleclionics to give the follovnrig fully

regulated and short cacie proof outputs of

+ 5v A 2 amps (IC + 12x A 800 ma DC

-12v 9, BOO ma DC + 24v A 350 ma DCand d that s not enough a fully floating 5v output is 50 ma DC

which may be sensed to give a host of other voltages Al

outputs are brought out to the front panel via miniature jack

sockets and are also duplicated at the rear on shod flying

leads. Units accept standard 240v mains input They are

ex GPO and may have minor scratches on the from panels,

they are sold untested but in good internal condition

16.50 each + £2.50 p+p complete with circuitand component list Transformer guaranteed HURRYWHILE STOCKS LAST!!

Another shipment allows us to offer youeven greater savings on this superb 2.5 MB(f or matted) hard disk drive. Two types areavailable both fully refurbished andelectronically identical, the only differenceis the convenience of changing the diskpacks.S30 front loader, pack change via frontdoor £550 + vatS30 fixed, pack change via removal of topcover £295 + vat+& - 15v PSU for 2 drives £125 + vatCarriage Et insurance -on drives £15.00 + vat fullyDEC RK05, NOVA, TEXAS compatable further info oncontrollers etc on request.

MAINS FILTERSProfessional type mains filters as used by "Main FrameManufacturers ideal for curing those unnerving hang upsand data glitches. fit one now and cure your problems,Suppression Devices SD5 Al 0 5 amp £6.95Corcom Inc F190030 amp Et 3.95 + pp 11.00

THE PRINTER SCOOP OF THE YEARTHE LOGABAX Z80 MICROPROCESSOR CONTROLLED

LX180L MATRIX PRINTERA massive bulk purchase enables us to offer you this

superb professional printer at a fraction of its recentcost of over £2000. Utilising the very latest in

microprocessor technology, it features a host offacilities with all electronics on one plug in P.C.B. Juststudy the specification and you will instantly realise itmeets all the requirements of the most exacting

professional or hobbyist user.STANDARD FUNCTIONS * Full ASCII character set * Standard

ink ribbon * RS232A124 serial interface -7 xtal controlled baud rates upto 9600 *194 characters per line * Parallel interface * Handshakes on serial and parallel

ports *4 Type fonts, italic script, double width, italic large, standard * Internal buffer* Internal self test * 170 CPS * Variable paper tractor up to 17.5" wide * Solid steelconstruction * All software in 2708 eproms easily reconfigured for custom fonts etc.

All this and more, not refurbished but BRAND NEW At Only £525 +VAT

OPTIONAL EXTRAS* lowercase opt ionE25.00 16 k bufferE30.00 Second tractor forsimultaeous dual forms £85.00 Floor stand £45.00 specialist carriage £19.00 Allitems plus VAT data sheet on request

DC SYSTEM SUPPLY 8" FLOPPY DISK DRIVESProfessional fully cased fan cooled system supply.Standard 240 Vac input with the following DC outputs5 V@ 1 1 amps +1 5-1 7v @ amps, -1 5-1 7v @ 8 ampsand +24v @ 4 amps, All outputs are fully crowbar

' protected and the 5 volt output is fully regulated. Soldtested and in a new or little used condition completewith circurt£55.00 + can E8 50 + vat DIM 1 5 5" x9" x

NATIONAL MA1012 LEDCLOCK MODULE

*12 HOUR* ALARM* 50/60 HZThe same module as used in most ALARM/CLOCKradios today, the only difference is our price! Allelectronics are mounted on a PCB measuring only3" n 11" and by addition of a few switches and 5/16volts AC you have a multi function alarm clock at afraction of cost. Other features include snoozetimer, am pm, alarm set, power fail indicator, flash-ing seconds cursor, modulated alarm output etc.Supplied brand new with full data onlySuitable transformer £1.75. £5.25

Ali 3 2"

F LE CTRONICCOMPONE NTSg, EQUIPMENT 66%

DISCOUNTDue to our massive bulk purchasing programmewhich enables us to bring you the best possiblebargains, we have thousands of I .0 s, Transistors,Relays, Cap's., P.C. B.' s, Sub -assemblies, Switches,etc. etc. surplus to our requirements. Because wedon't have sufficient stocks of any one item toinclude in our ads., we are packing all these itemsinto the "BARGAIN PARCEL OF A LIFETIME"Thousands of components at giveaway prices!Guaranteed to be worth at least 3 times what youpay plus we always include something from our adsfor unbeatable value' 1 Sold by weight

2.5kis f 4.75+pp £1.25 5ids f 6.75+pp f1.8010k1s f11.75+pp £2.25 20Icis E19.99+ pp £4.75

Unbelievable value the DRE 7100 Er 7200 8" diskdrives utilise the finest technology to give you 100%bus compatablIttywah most drivesavailable today, theonly drfference being our PRICE and the superbmanufacturing quality The 7100 single sided Er7200 double sided drove accepthardor soft sectoring.IBM or ANSI standard giving a massive 0.8 MB(7100) Et 1.6 MB 172001 of storage. AbsolutelySHUGART, BASF. SIEMENS etc compatable.Supplied BRAND NEW with user manual and 90 day warranty7100 single sided £225.00 * 9.50 carr vat7200 double sided (295.00 + 9.50 carr + vatfull technical manual £20.00 alone f 9.00 with drive, refund of difference on purchase of drive.Data sheet on requestSPECIAL new, KODE PSU, drives 2 DRE drives E39.99 + carr + vat8" single sided, single or double density diskettes Et 80 each Et 5.00 for 10 Inc. lib case + vat.

COOLING FAN SPECIALKeep your equipment cool and reliablb with our range of professional fans.ETRI 99XU01 Miniature equipment fan 2 40 v ac working DIM 92 x 92 x 25 mm BRAND NEW.complete with finger guard. Makers price Et 6 our price f1 0.25BUHLER 69.11.22 micro miniature 8-16 v DC reversible fan. Measures only 62 x 62 x 22 mm.'Uses a brushless DC serve motor. almost silent running ideal portable equipment, life in excess of10.000 hours. BRAND NEW manufacturers price £32.00 our price £13.95 illMUFFIN/CENTAUR cooling fans tested ex equipment 240v £6.50. 1 1 5v £5.50 +£1.90KOOL TRONICS Powerful snail type blower gives massive air movement with centrifugal rotorDIM as a cube 8- x8- x6" air aperture 2.5- x2.5" with flange fixing. BRAND NEW 1 10v 50 Hzac worlungONLYE9.95 + £1.90 p&p. .

. ELECTRONICS

1- Dept. W.W. , 64-66 Melfort Rd., Thornton Heath, MAIL ORDERCroydon, Surrey. Tel: 01-689 7702 or 01-689 6800 INFORMATIONUnless otherwise stated all prices inclusive of V.A.T. Cash with order. Minimumorder value £2.00 Prices and Postage quoted for UK only Where post andpacking not indicated please add 60p per order. Bona Fida account ordersminimum £20.00. Export and trade enquiries welcome. Orders despatchedsame day where possible. 3% surcharge on Access and Barclaycard orders.

RE CONNECTORS50 22 BNC PLG 50p75 22 BNC PLG 50pP1259 PLG 40pS0239 SKT 35p100 PCS MIN ORD.

HIGH SPEEDDATA MODEMS

A superb pece of er peeving made by SE labs ltd. to a

"no cost spared" spec lot the GPO. the Modem 12 4 asynchronous Modern for use on DATE( 2412 services. or

other data inks. Many features iodide swechable V26

modulabon, 2400 baud hi duplex 600/1200 standby.

auto answer, 4 wire or 2 was operahon. See test

status inclicabon. CMOS technology. modular construchon.

onginal cost over £700 each Believed brand new,

suppled compete wrth PSU et

£185.00 + £9.50 ,arreoe+ VAT Perm an may he mound for correction to PO Ines

DISTEL 0"Dial our Database!"Get information on 1000's of stockitems and order via your computer. 300baud on 01-689 680018.30 to 0900 6 days a week and allday Sundays ITS FREE!

SOFTY 1 £t2EPROM BLOWER

Software development system invaluable tool for designers,hobbyists. etc. Enables open heart surgery on 2716. 2708 etc.Blows, copies, reads EPROMS or emulates EPROM/ROM/RAMin situ whilst displaying contents on domestic TV receiver. Manyother features. ET 1 5 + carr. + VAT. Optional 2716, 2716

Function Card £40 + VAT. PSU £20 + £1.50 carr. +VAT.Softy 2 for 2716/2732 Et 69 -I -VAT

Write of phone for more details.

9" VIDEOMONITORS

Ex -equipment 9" Motorola Video Monitors 7511 compositeinput, tested but unguaranted. £39.99 +£7.50 carriage+ VAT. Complete with circuit.

SEMICONDUCTOR'GRAB BAGS'

Alined Semis amazing value contents include transistors, digital, linear, I.0 s.

Macs. diodes, bridge recs, etc. etc. AN devices guaranteed brand new full specoath manufacturer's markings, fully guaranteed. 50. bag £2.95 100. bag E5.15TTL 14 SeriesA gigantic purchase of an "across the board" range of 74 -Fri. series I.C.'senables us to offer 100. mixed "mostly TTL" grab bags at a price which two othree chips in the bag would normally cost to buy.

1Fully guaranteed al I.C.'s full spec. 100, £6.90 200,02.30 300. E19.50

RC/1FULLY CASED

ASCII CODED

KEYBOARDSIULAL -TANGERINE,OHIO ETC,

Straight from the U.S.A. made by the world famous R.C.A. Co., theVP600 Series of cased freestanding keyboards meet all require-ments of the most exacting user, right down to the price!Utilising the latest in switch technology Guaranteed in excess of5 million operations. The keyboard has a host of other featuresincluding full ASCII 126 character set, user definable keys,upper/lower case, rollover protection. single 5V rail, keyboardimpervious to liquids and dust, TTL or CMOS outputs. even anon -board tone generator for keypress feedback, and a 1 year fullR.C.A. backed guarantee.

VP601 7 bit fully coded output with delayedstrobe, etc.VP611 Same as VP601 with numeric pad.VP606 Serial. RS232 20MA and TTL output, with

,electable Baud Rates.VP616 Same as VP606, with numeric pad,Plug and cable for VP601, VP611 £2.25

Plug for VP606, VP616 £2.10

Post, Packing and Insurance.ORDER NOW OR SEND FOR DETAILS.

£43.95£54.95

£64.26£84.34

£1.95

5v D.C. POWER SUPPLIESFollowing the recent "SELL OUT' demand for our 5v3 amp P. S. U. we have managed to secure a large quan-tity of ex -computer systems P.S.U.'s with the followingspec.; 240 or 110v A.C. input. Outputs of 5v @ 3-4amps, 7.2v @ 3 amps and 6.5v @ 1 amp. The 5v and7.2v outputs are fully regulated and adjustable withvariable current limiting on the 5v supply. Unit is selfcontained on a P.C.B. measuring only 12" x 5 n 3'.The 7.2v output is ideal for feeding -on board- regu-lators or a further 3 amp LM323K regulator to give aneffective 5v @ 7 amp supply.Supplied complete with circuit at only £10.95 +£1.75pp.Believed working but untested, unguaranteed.

WIRELESS WORLD MAY 1982 WW - 089 FOR FURTHER DETAILS 95

PRICE ON APPLICATION?

We also manufacture servo amplifiers, and can adapt our proven contact -less sensing system to new applications.

FLIGHT LINK CONTROL LTD.UNIT 12, THE MALTINGS

TURK STREET, ALTON, HANTS GU34 1DLPhone: 0420 87241 (24 hours). Telex: 858623 TELBUR G

Being engineers, and believing that "an engineer is anyone who canmake for £1 what any fool can make for £5," we usually give prices in ouradvertisements. Recently, however, several customers using our joystickcontrols with complete success have admitted that they did not send fordetails as soon as they might have done because they thought the pricestoo low!

Don't make that mistake - please send for full details, judge thejoysticks on their merit, and only then give yourself a pleasant surprise byreading the prices.

By specialisation, volume production and controlled overheads we areable to offer well -engineered, innovative and reliable joystick controlsranging from £1.50 each for TV games units in quantity to £2,000 for aone-off triple axis force -feedback system, including torque -motor ampli-fiers. Our current ranges cover most combinations of:

* 1, 2 or 3 axes, or up to 6 degrees of freedom.* Potentiometer, wafer switch, microswitch and contactless sensing.* Sprung, friction or detent positioning, or force feedback systems.* Press button switches in handles or handgrips.* Miniature TV game units up to very heavy duty for mobile and heavy

engineering environments, including a triple axis contactless unit 14"high.

* Interfaces for VDU, TV game, microcomputer and hydraulic valveapplications.

* In addition we can design and build prototypes or one -offs within 2/3weeks, and build special requirements into standard units within days.

DISTRIBUTORS:Australia: Tecnico Electronics, Lane Cove, Sydney, N.S.W., Australia.Sydney 427 3444.USA/Canada: P.Q. Controls Inc., 71 Dolphin Road, Bristol, Connecticut06010 USA. (203) 583 6994.Sweden: Svensk Telindustri, Box 5024, S162 05 Vallingby, Sweden 8380/320.Singapore: Innovative Design Systems PTE Ltd., 50 Orchard Road, Singa-pore 0923 3382922.Holland: Howell International b.v., Postbus 126 2170 AC Sassenheim,Holland 02522-1 15 09.


INSTANT ROM TMl

ROM/EPROM Emulators

A NEW MICROSYSTEM PROGRAMMING AID* Plug-in replacement for all popular ROMs and EPROMs* Instantly programmed at normal system speed* No erasure required before re -programming* Contains CMOS RAM with battery back-up* Retains data for up to 10 years* No limit to number of programming cycles* 24 -pin ROMEPROM pin -out - fits into standard socket* Available as 2K 8, 4K 8, and 8K , 8 modules* Removable - easily copied in an EPROM Copier'Instant Rom' ROM/EPROM EMULATORS are new programming aids forMicrocomputer development. They contain CMOS RAM, which has a low -current'standby' mode of operation. A lithium cell retains the data for up to 10 years.No recharging is required.Data or programs are written to INSTANT ROM (using an additional 'Write'signal) at full system speed in your Development System. You use it like RAM.When the 'Write' signal is removed, the device becomes effectively a ROM.When the power is switched off, data is retained.INSTANT ROM can save you a lot of time.Bugs can be corrected immediately. There is no need to erase and re -programEPROMs. INSTANT ROM can be used for long periods; when the program isfinally 'bug -free', an EPROM can be programmed.INSTANT ROM is available as a replacement for 2516/2716 (2K devices),2532/2732 (4K devices), and 2364/68764 (8K devices).

INSTANT ROM is a Trade Mark of the Manufacturers:

GREENWICH INSTRUMENTS LIMITED, 22 BARDSLEY LANE,GREENWICH, LONDON SE10 9RF, UK.

Tel: 01-853 0868. Telex: 896691 TLXIR Attn. GIL.

:sex Tinwsic Listem

* RS232 Interface * Powerful Tiny * Autostart Operation48 I/O Lines Basic Processor with Watchdog Timer

* Up to 16K Byte EPROM *Accommodates InstantEPROM Programmer ROM Modules

The Essex Tiny Basic Computer is an ideal choicefor data acquisition and process control systems. Itscrystal controlled timer and interrupts provideaccurate timing and fast response to critical events,while the watchdog timer ensures reliable operation.Programs can be entered and tested from an RS232terminal, and then be copied into EPROM. Alter-natively, Instant ROM modules may be used bothduring development and for program storage.'INSTANT ROM is the trademark of Greenwich Instruments

PRICE EXCLUDING VAT: £185 - CARRIAGE WITHIN THE UK £2- PLEASE SEND FOR FULL INFORMATION

C3EEssex Electronics CentreUniversity of Essex, Colchester, C04 3S0.Telephone: Colchester (0206) 865089

96


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Scopex Instruments now offer you an unrivalled choice of oscilloscopes at under £300.The straightforward and successful 14D10 with asensitivity of 2mV/cm at 10MHz on bothchannels at £240 + VAT. The new 14D15 15MHzdual trace 5mV/cm with active TV syncseparator at £250 + VAT and the sophisticated14D10 10MHz dual trace 2mV/cm active TV sync.separator and line selector at £290 4-- VAT.All these above prices include two probes,mains plug and carriage U.K. mainland.10cm x 8cm display, add and invert facility,probe compensation, pushbutton x -y and tracerotate are all standard features of this 14D range.

You the customer decide the extras youneed to fulfil your specific requirement.An Independent British Company

1/41-COPEXCredit Cards and Orders Pixmore House

Pixmore Avenue, Letchworth,contact our Sales department at: Herts SG6 1JJ Tel: (04626) 72771.

Please send me full details of the 14D10 range.

Name

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OrderVALVES VATVALVES Minimum£1 IS INCLUDED

A1065 1.40 EL821 6.20 SP61 1.80 6804 3.40 12AV6 0.95 61468 5.20A2293 8.80 EL822 9.95 1121 23.00 6AQ5 1.00 12AX7 0.65 6360 2.85A2900 13.75 5M80 0.85 1122 18.50 6AQ5W 1.80 128A6 0.90 6550 6.60AR8 0.75 EM87 1.30 U25 1.15 6856 1.15 128E6 1.25 6870 14.00ARP3 0.70 E151 0.95 U26 1.15 6876 0.90 12847 1.95 8552 8.20ATP4 0.60 E181 0.65 U27 1.15 5AU6 0.60 128Y7A 2.30 7199 2.858124 3.90 E186/87 0.60 U191 0.85 6AV6 0.85 12C8 0.65 38P1 11.00CY31 1.40 EV88 0.65 U281 0.70 6AX4GT 1.30 12E1 18.95 5FP7 18.00DAF96 0.70 EZ80 0.70 0301 0.65 6AX5GT 1.30 12J5GT 0.55 4EP1 32.00DET22 28.95 EZ81 0.70 U600 11.50 6886 0.55 12K7GT 0.70 88J 14.00DF96 0.70 GM4 5.90 U801 0.90 68E6 0.60 12K8GT 0.80 88L 14.000476 0.75 G1501 1.30 U BC41 1.20 6806G 1.60 1207GT 0.60 CV1526 16.0001.92 0.60 GZ32 1.05 UABC80 0.75 66J6 1.30 125C7 0.65 007-32 3480D186/87 0.65 GZ33 4.20 UAF42 1.20 6807A 0.85 12547 0.65 DG7-36 36.00D1802 0.70 GZ34 2.75 UBF80 0.70 6867 4.80 125J7 0.70 DPM9.11 38.40E55L 14.90 GZ37 3.95 U8F89 0.70 6BW6 6.20 12S07 1.45 013-33GME88CC 1.60 KT66 6.30 UBL21 1.75 6BW7 090 12SQ7GT 0.85 4160E88CC/01 3.10 9.20 UCC84 0.85 6C4 0.50 12Y4 0.70 spec aE92CC 2.80 KT88 8.95 UCC85 0.70 6C6 0.55 1303 0.70El 80CC 4.20 13.80. UCF80 1.30 6C46 8.20 1305 0.90E180F 7.70 MH4 2.50 UCH42 1.65 6CL6 2.75 1306 0.80E182CC 6.26 ML6 2.50 UCH81 0.75 6CX8 3.80 14S7 1.15 PLUMBICONEA76 2.25 MX10/01 21.50 UCL82 0.95 6C15 1.15 19A05 0.85 P800 3LFEA8C80 0.80 N78 9.90 U F41 1.35 606 0.70 1903 11.50E891 0.60 082 0.70 UF80 0.95

oP0820, ,106

6F6 1.60 19G6 8.50 ' "" '"EBC33 1.15 082 0.80 UF85 0.95E8C90 0.90 PABC80 0.60 UL84 0.95

6F6G8 1.10 1945 39.55 X0102086F7 2.80 2001 0.80 X01020B

EBF80 0.60 PC85 0.75 UM80 0.90 6F8G 0.85 20F2 0.85EBF83 0.60 PC86 0.95 UM84 0.70 6F12 1.50 20E1 1.30EBF89 0.80 PC88 0.95 UY82 0.70EC52 0.65 PC 97 1.50 UY85 0.85

6F14 1.15 20P1 0.656F15 1.30 20P3 0.75 SPECIAL V

EC91 4.40 PC900 1.15 V8105/30 1.25 6F17 3.20 20P4 1.25SCE 10008

EC92 0.85 PCC84 0.50 VR150/30 1.35 6F23 0.75 20P5 1.354CX 50008

ECC81 0.65 PCC89 0.85 25L1.75 25L6GT 0.95ECC82 0.60 PCC189 1.05 X61M 1.70

EB3M

6F33 10.50 25Z4G 0.75 W153, ECC83 0.65 PCF80 0.80 XR1-6400A 6F48 4.20 30C15 0.50 DM 25LB

ECC84 0.60 PCF82 0.70 82.90 6GA8 1.95 30C17 0.50IL 1420

ECC85 0.60 PCF84 0.75 2759 19.00 6GH8A 0.95 30018 2.45IL 1430

ECC86 1.70 PCF86 1.50 2749 0.75PCF87 0.50

646 IL 14401.60 30F5 1.15 GXU6ECC88 0.80 28000 3.45PCF200 1.60

6J4 1.35 30FL2 1.40 081597ECC189 0.95 2801U 3.75 6J4WA 2.00 30FL12 1.25 CV2116ECC804 0.90 PCF201 1.65 2803U 16.00 6J5 2.30 30FL14 2.15 BR 189ECF80 0.85 PC5800 0.50 Z900T 2.45 6J5GT 0.90 30L15 1.10 BR 179ECF82 0.65 PCF801 1.75 183 0.85ECF801 1.05 PCF802 0.85 1L4 0.50

6J6 0.65 30L17 1.10 0861316J6W 0.90 30P12 1.15EC434 2.25 PCF805 2.45 165 0.60 6JE6C 2.95 30PL13 1.25

GMU 2

ECH35 1.70 PCF806 1.20 1S4 0.45 6JS6C 2.95 30PL14 2.45TY4-500

2.10 PCF808 2.75 1S5 0.45 6K7 0.80 35L6GT 1.40BK485/5552A

ECH42 1.20 PCH200 1.35 174 0.45 61(06 3.35 35W4 0.80MIL 5948/1754,

ECH81 0.70 PCL81 0.75 1U4 0.80 6L6M 2.80 3524G1 0.80ECH84 0.80 PCL82 0.95 1X28 1.40 6L6G 2.50 5005 1.15ECL80 0.70 PCL84 0.90 2021 1.10 6L6GC 2.10 50CD6G 1.35 ICECL82 0,75 PCL86 1.05 1.85* 6L6GT 1.25 7581 1.25 SN5402N 0.28ECL83 1.40 PCL805/85 1.25 21(25 16.95 6L7G 0.85 75C1 1.70 SN541OF 0.32ECL85 0.80 P0500/5104.30 24.50* 6L18 0.70 76 0.95 SN5470F 0.48ECL86 0.90 PFL200 1.10 2X2 1.15 6LQ6 2.95 78 0.95 SN54196J 1.20EF37A 2.15 2.80 384 0.70 6LD20 0.70 80 1.70 SN7407N 0.29EF39 1.25 PL36 1.25 3872 2.40 6KG6A 2.70 8582 1.40 SN7408N 0.18EF80 0.65 PL81 0.85 306 0.50 607G 1.30 2.55 SN7445P 0.85EF83 1.75 PL82 0.70 3022 23.00 6587 1.00 807 1.25 SN74453P 1.10EF85 0.60 PL83 0.60 3E29 19.00 6SG7 1.15 1.90 SN7453N 0.18EF86 0.75 PL84 0.95 3S4 0.60 65J7 1.05 813 19.32 SN74L73N 0.38EF89 1.05 PL504 1.45 4832 18.25 6SK7 0.95 6850* SN7474N 0.30EF91 1.50 PL508 2.40 56/254M 16.90 6SL7GT 0.85 8298 14.00 SN7485N 0.95EF92 2.90 PL509 5.60 58/255M 14.50 6SN7GT 0.80 832A 8.90 SN74L85N 1.10EF95 0.65 PL519 6.10 5B/258M 12.50 6SR7 1.10 866A 3.80 SN7491AN 0.32EF96 0.60 PL802 3.95 5C22 29.90 6507 0.95 866E 6.25 SN74123N 0.42EF183 0.80 P133 0.70 5R4G1 1.80 6V6G 1.50 931A 13.80 DM74123N 0.38EF184 080 P180 0.70 5U4G 0.75 6V6GT 0.95 954 0.60 SN15836N 0.26EF812 0.75 P181/800 0.85 5V4G 0.75 6X4 0.95 955 1.20 cX4 0.95EFL200 1.85 PY82 0.65 5Y3GT 0.95 6X4WA 2.10 956 0.60 SN76013N 1.80E490 055 P183 0.80 5Z3 1.50 6X5GT 0.65 957 1.05 5476003N 1.60EL32 1.10 PY88 0.85 524G 0.75 6Y6G 0.90 1625 1.80 04760334 1.35EL34 1.80 PI500A 2.10 5Z4GT 1.05 6Z4 0.70 1629 1.95 MC6800P 5.80

2.90. PY809 6.45 6/30L2 0.90 787 1.75 2051 2.90 MC68800PEL81 2.46 01801 0.80 6AB7 0.70 8BN8 2.95 5763 4.20 6.40EL82 0.70 00V03/10 7.50 6AC7 1.15 902 0.70 5842 750 MC1451188EL84 0.80 00V03 -20A 6AG5 0.60 906 2.90 5881 340 2.20EL86 0.95 21.50 6A1-16 1.15 10C2 0.85 5933 6.90 81702AL 3.30EL90 1.90 00V03 -25A 6AK5 0.65 10F18 0.70 6057 2.20 MM6300-IJEL91 4.20 36.50 6AK8 0.60 10P13 1.50 6060 1.95 3.80EL95 0.80 00V06/40A 6AL5 0.60 11E2 19.50 6064 2.30 MCM6810APEL504 1.70 16.10 6AL5W 0.85 12A6 0.70 6065 3.20 3.40EL803 5.90 0W03-12 4.20 6AM5 4.20 12876 0.70 6067 2.30 6340-1J 3.60EL509 355 SC1/400 4.50 6AM6 1.50 12AT7 0.65 6080 530 M1C945-5D 0.28EL802 1.70 SC1/600 4.50 6AN8A 2.60 12AU7 0.60 6146 495 M1C936-5D 0.22

VALVES AND TRANSISTORSTelephone enquiries for valves, transistors, etc:

FIELD TELEPHONES TYPE "J".Tropical, in metal cases.

retail 749 3934, trade and export 743 0899. 10 -line MAGNETO SWITCH -"D10" CABLE HELD TELEPHONES BOARD. Can work with every

Geiger Muller Tubes GM4, MX12/01 and others.type of magneto telephones.TEST SET FT2 FOR TESTING Transceivers A40,A41, A42 and CPRC26. PRICES MAY VARYHARNESS "A" & "B" CONTROL UNITS "A" "R"

"J2."POSTAGE: £1-E3 45p; f3 -f5 55p;

Misetcrophetc.ones No 5, 6, 7 connectors,1"mes, carfra carrier s, £5-£10 60p; £10-£15 80p; £15-

DRUM CABLE continuous connection YC 00433. £20 1 00p.

Signal Generators MARCONI TF 144H/4.5; TF14411/65 10 kHz-72MHsPrices on application

COLOMOR Tel. 01-743 0899 or 01-749 3934

(ELECTRONICS LTD.) Open Monday to Friday

170 Goldhawk Rd., London W.12 9 a.m.-5.30 p.m.

PROGRAMME & DEVIATION CHART RECORDERS

Single and twochannelversions chartaudio toIEC/BS PPMstandards andtrue peakdeviation.

1'43,eiyeS

Broadcast Monitor Receiver 150kHz-30MHz * Stereo Disc Amplifier 2 and 3 *Moving Coil Preamplifier * 10 Outlet Distribution Amplifier 3* Stabilizer * FixedShift Circuit Boards * Illuminated PPM Boxes * PPM2 and PPM3 Drive Circuitsand Ernest Turner Movements.

Surrey Electronics Ltd.The Forge, Lucks Green, Cranleigh, Surrey GU6 7BG. Tel. 04866 5997

EV88 -A low-cost evaluation system forthe 8088 microprocessor

EV88 is a single board microcomputer that is ideal forevaluating the 8088 8-bit/16-bit microprocessor. EV88 canalso be used as a powerful controller, and, with a suitablecross -assembler running on a standard microcomputer, andan EPROM programmer, for low-cost development of 8088 -based systems.

EV88 is supplied fully assembled and tested, with compre-hensive documentation, and a copy of The 8086 Book, byRector and Alexy. All you need is a 5V 1A power supply and aterminal or a suitable microcomputer.

* 8088 microprocessor in minimum mode (software compa-tible with the 8086 16 -bit microprocessor).

* Comprehensive monitor in 2K EPROM.* 2K CMOS RAM.* Cassette interface.* 24 lines of I/O.* Eight levels of interrupt.* RS -232 compatible serial interface (300 baud to 9600

baud).* Three -channel counter/timer.* Buffered data, address and control lines.* Double Eurocard.* On -board expansion to 16K EPROM/RAM (sockets pro-

vided).* Breadboarding area.* All bus signals available on 64 -way DIN 41612 connector.* Single 5V supply.* Price £300 plus VAT. Includes delivery.8088/8086 design service available (software and hardware).

LFH Associates Ltd.40A High StreetStony StratfordMilton Keynes(0908) 566660


CHILTERN ELECTRONICSB.C.M., Box 8085, London WC1N 3XX. Tel: 0494 714483

THIS MONTH SPECIAL OFFERBRAND NEW SURPLUS-DRI32 5 Megabyte DISKS. A top quality exchangeablecartridge disk drive, that will easily interface to a mini/micro. Fully guaranteed - withfull manual.

Usual price over £3,000. Our price only £420l 1+ VAT/carriage)Controller for S100 bus £400. Controllers for PDP11/LSI-11 available.

DATAPRODUCTS 2230 LINE PRINTERS. These beautiful 300 line/min printers have astandard Centronics parallel input and usually cost over £7,500. They are ideal forreally heavy volume printing. Ours have been in use for around a year, and are fullyrefurbished with 6 months' warranty.

Our price £950 (+ VAT/carriage)

MAIL ORDER BARGAINSAll prices below include VAT and delivery. Same day despatch.

GOULD SWITCH -MODE POWER SUPPLIES, 5v 20 amps. (BRAND NEW). These littlepocket size modules weigh less than 4lbs. but deliver full 20 amps at 5v. Add a pot tomake variable 0-6v, or connect in series for higher voltages. 0.1% Regulation and fullover V/I protection.

List £250 +. Our price £34.50

PROTOTYPE PC CARDS. Over 200 Common IC's (most 7400 series) in wire wrapsockets on useful wire -wrap cards. IC's/Sockets easily removed -no unsoldering.

Only £11.50

VIDEO MONITORS 9 -INCH. Standard Composite Video in. 240v PSU. Excellent defini-tion -ideal for micro. Complete with service manual and ready to plug in £34.50ASCII KEYBOARDS. Top quality 84 Key ASCII with all U/L Case and Control codes incase £34.50POWER SUPPLIES 5v 3 amp. Standard Mains Input - out 5v 3a fully regulated andprotected. £11.50EPROMS-TMS 2516. Brand new - these usually cost around f3 to £5 each.

Our price £13.80 for 10.MODEM PROTECTION BOXES RS232. Completely isolate your valuable system fromover voltage - consists of 2 RS232 Cannon Connectors, one on long lead, and neataluminium box with 16 Zener diodes and fuses. If you are using external lines,connect this between your system and it could save you thousands of pounds. £11.50FLOPPY DISK CONTROLLERS. Contain NEC Floppy control IC, 8080 Micro and com-plete controller for single density 8 -inch floppy into 8 -bit parallel port. New withmanual £34.60

WE STOCK COMPLETE RANGE OF DEC SYSTEMSFROM PDP8E TO PDP11 /70 AND VAX

FOR MORE DETAILS TELEPHONE NIGEL DUNN ON 0494 714483, ANY TIME

For regular copies of our catalogue please send postcard with address.

WW -065 FOR FURTHER DETAILS


Superior Quality Precision Made

NEW POWER RHEOSTATSNew ceramic construction, heavy duty brush assembly, continuously rated.25 WATT 10/25 50 100/150/250/500/1101 1.5k11E3.10 + 305 P&P. 1E3.91 inc. VAT).50 WATT 25011 E5.50 + 50p P&P. 1E6.90 inc. VAT).100 WATT 1/5/10/25/50/100/250/300/ 500/11d1/1.51,11/2.5kil/

,5k11/3.51d1E7.25 + 75p P&P.129.20 inc. VAT).Bleck Silver Skirted Knob calibrated in Nos. 1-9, 11/2in dia. brassbush. Ideal for above Rheostats 24p ea. *VAT.

SOLID STATE E.H.T. UNITInput 230V A.C. Fully isolated. Aprox. 15KV. Built-in 10 sec. Timer.Easily modified for 20 sec. 30 sec. to continuous operation. Size155x85x5Omm. Price 0 75p P&P. (Total inc. VAT E6.61).

MINIATURE SOLENOID FLUID VALVE12v DC 15ohm coil normally closed. Stainlesssteel body with vocable flow adjuster 1/8".B.S.T. inlet and outlet. Size: 58x27x25mm.Weight: 130gr. Price: E2.60 + 35p P&P (Totalinc. VAT E3.39)

240v A.C. SOLENOID VALVEDesigned for Air/Gas at 0-7. Water 0-5 psi. Inlet/outlet 343". Forgedbrass body. Manuf. Dewraswitch Asco.Price: E5.50 + 75p P&P. (E7.10 incl. VAT). n.rit.,

METERS (New) - 90mm DIAMETERAC Amp. Type 62T2: 0, 1A, 0-5A, 0-10A.AC Vok. 0-150V, 0-300V.DC Amp. Type 6505 0-5A, 0-10A, 0-50A. DC Volt 15V, 30V.All types 0.60 ea + P&P 75p (65.00 inc. VAT) except 0-50A DC, 0-100A DC. Price 6.00 plus 75p P&P (66.61 inc. VAT).Ex

ULTRA VIOLET BLACK LIGHTFLUORESCENT TUBES4ft 40 watts E8.70 inc. VAT E10 (callers only).2ft 20 watts E6.20. Post £1.25 1E8.57 inc. VAT & Pl.(For use in standard bi pin fittings).12in 8 watt £3.00 + 30p P&P (E3.97 inc. VAT).9in 6 watt Q.50 + 45p P&P (0.39 inc. VAT).6in 4 watt E2.50 + 45p P&P (0.39 inc. VAT).Complete ballast unit for either 6V, 9V or 12V tube 230V AC op.E5.50 Post 55p (E6.96 inc. VAT & P). Also available for 12V DC E5.50Post 55p 1E6.96 inc. VAT & Pl.400W UV LAMP AND BALLAST complete E38.00 Post E3.50 (247.73inc. VAT & P). 400W UV LAMP only E14.00. Post E2.00 1E18.40 inc.VAT &

BLACK LIGHTSelf -ballasted Mercury U.V. 175W Bulbs. Available for either B.C.or E.S. fitting. Price incl. p&p & VAT E11.50.Black Light U.V. Tubes front bin to 45 from stock. Foolscap s.a.e.for details.

All Mail Orders - CallersAmple parking space

Showroom openMonday -Friday

VARIABLE VOLTAGE TRANSFORMERS

INPUT 230/240V a.c. 50/60 OUTPUT 0-260V200W 1 amp inc. a.c. voltage £15.00as KVA (21/2 amp MAXI E19.001 KVA (5 amp MAX) E25.002 KVA (10 amp MAX) E41.003 KVA (15 amp MAX) E49.005 KVA (25 amp MAX) E79.0010 KVA 150 amp MAX) E174.0015 KVA (75 amp MAX) 6270.00

3 -PHASE VARIABLE VOLTAGE TRANSFORMERSDuel input 200 -240V or 380-415V. Star connected3 KVA 5 amp per phase max 008006 KVA 10 amp per phase max E162.00 Carriage, packing10 KVA 16 amp per phase max 029.00 & VAT extra

LT TRANSFORMERS13.0 13V at 1 amp 6.80 P&P 75p 1E4.08 inc VAT).0.15V at 12 amp. 0.30V at 12 amp 620.40 P&P E2. 31E26.11 inc VAT&P).0.6V/12V at 20 amp 618.20 P&P £2.00 (inc VAT E20.93).0 12V at 20 amp or 0.24V at 10 amp E14.90 P&P E2.00 1E19.43 incVAT & P).0.6V/12V at 10 amp E9.10 P&P E2.00 (inc VAT E12.76).0.6V/12V/17V/18V/20V at 20 amp E20.90 P&P £2.001£26.68 inc VAT& P).0.10V/17V/18V at 10 amp (11.55 P&P £2.00 inc P&P 1E15.58 incVAT).

SNIP OF THE MONTH! 220-240V. Prim-ary, 0.24V. Secondary at 4 amp. Fullyshrouded. New Price f41-£1 P&P. (Totalinc. VAT £5.75). N.M.S.Other types in stock, phone for en-quiries or send SAE for leaflet.

FROM STOCK AT PRICESTHAT DEFY COMPETITION!AC GEARED MOTORS C.F. BLOWERSDC MOTORS AC CAPACITORSMICROSWITCHES STROBE KITSRELAYS FLASHTUBESREED SWITCHES CONTACTORSSOLENOIDS SYNCHRONOUSPROGRAMME TIMERS MOTORS

Phone in your enquiries

'SERVICE TRADING CO

EPROM ERASURE KITWhy waste money! Build your own EPROM ERASURE for a frac-tion of the price of a made-up Unit. Complete Kit of parts less Case,to include 12" 8 watt 2537 Angst Tube. Ballast Unit, pair of bi-pinleads, Neon Indicator, safety Microswitch, on/off Switch, Circuit.LESS CASE. Price: E13.60 75p P&P. (Total incl. VAT. E16.50).Warning: Tube used in this circuit is highly dangerous to the eyes.Unit MUST be fitted in suitable Case.REVERSIBLE MOTOR. 42 RPM 110V A.C. 10db In. Will operate on230V A.C. Speed remains at 42 rpm but torque reduces by 50%.Price E16.50 + E2.50 P&P (Total incl. VAT EV .28).5 rpm or 15 rpm ./pole non -reversible Motor. Either type E5.50each E1 P&P. (Total incl. VAT E7.48). N.M.S.BRAND NEW CASSETTE TYPE MOTORS. Three types. 6V. 71/2V.12V. Price, any three, for f2 + 50p. P&P (incl. VAT 62.881 N.M.S.Geared Motor 120 r.p.m. 1/10 h.p. approx. 151b in. 230V AC. Cont.Rating. Non.reversible. Size 150mm by 90mm by 85mm. Spindleatom dia. 30mm long. Complete with capacitor and relay for max.load starting. Offered at mere fraction of mfrs. price. E11.50 incl.P&P and VAT.

ROTARY CARBON VANE VACUUM & COMPRESSORDirect coupled to 1/3 h.p. 110/115V AC Motor 4.2 amp. 1380 rpm.Motor manuf. by A.E.I. Pump by Williams. Max. Vac. 2566 H.G.Max. pressure cont. 10 p.ei. int. 15 p.s.i. Max. airflow 3 c.f.m. at66066 H.G. Price E30 + P&P 0109.10 Inc VAT). N.M.S.Suitable transformer 240V op. E10 P&P E2 (E13.80 incl. VAT).N.M.S.WATER PUMPMfg. by S.P.A. Astaisi of Italy. 220/240v AC 50 hz. 2800 R.P.M.approx. 1/350. Centrifugal pump with 11/2" inlet/outlet. Deliveryapprox. 40 gals per min. at 10Ibs head. (Non -self -priming). PriceE16.50. P&P E2.50 (61.85 inc. VAT). N.M.S.HY-LYGHT STROBE KIT Mk IVApprox. 4 joules. Adjustable speed. Price E27 + E2 P&P. (Total inc.at 03.36). Case and reflector price Ell + E2 P&P (Total inc. VAT0496). Foolscap s.a.e. for further details inc. Super Hi-Lyght.INSULATION TESTERS NEW500 VOLTS 500 megohms E49.00 P&P E2.001E58.65 inc. VAT & PI 1000 VOLTS 100011 E55.00P&P E2.00 (E65.55 inc. VAT & P). SAE for leaflet.TIME SWITCH VENNER TYPE ERDTime switch 200-250V a.c. 30 amp contact 2 on/2 offevery 24 hrs. at any manually pre-set time 36 hourspread reserve and day omitting device. Built tohighest Electricity Board Specification. Price E11.50P&P Et 50.(E14.95 inc. VAT). R&T.SANGAMO WESTON TIME SWITCHType 5251 200/250 AC 2 on/2 off every 24 hours. 20 amps contactswith override switch. Diameter 4" x 3", price 0.50 P&P Et (E12.08inc. VAT). Also available with solar dia. R&T.Also available Sangamo Weston 60 amp and AEG 80 amp. Phonefor details.Type 52881 on, or 1 timed c/o every 24 hours, day omitting device.Price Ell + El P&P. 1E13.80 incl. VAT). N.M.S.Type 5388. As above, plus 36 hours spring reserve. Less perspexcover. Price: E13 61 P&P (E18.10 incl. VAT). N.M.S.

AEG 80 AMP TIME SWITCHE15.50 E1.50 P&P (E19.55 inc. VAT).

N.M.S. - New Manufacturers' Surplus.R&T - Reconditioned and Tested.

57 BRIDGMAN ROAD, CHISWICK, LONDON W4 5BB, 01-995 1560ACCOUNT CUSTOMERS MIN. ORDER £10,

Personal callers only. Open Saturdays

9 Little Newport StreetLondon WC2H 7JJTel: 01-437 0576


MARKETING Ltd.

Z-733/e.

SERIES 600The D&R SERIES 600range of professionalmixing consoles has foundits way into hundreds of(hospital) broadcast studios,discotheques, clubs, entertain-ment and outdoor Public Addresssystems and recording studios.Available in 6, 12, 18 or 24 channelconfiguration with, as standard, separatebalanced mic. and line inputs, insertion points,gain, three band tone controls, two auxiliar lines,pan -pot and linear fader, plus pre -fade -listening and overload LEDper channel. The output section includes four master faders, echoreturn and phones controls and two large V.U. meters.Optional XLR-3 connectors, 48 volt phantom powering, stereochannels with R.I.A.A. correction, talkback, fader controlled startswitches, balanced outputs and 24 volt D.C. mains powering areavailable.

SERIES 600/12CONSOLE

Visit our stand at Communications 82 - National Exhibition\ Centre, Birmingham - 20th, 21st, 22nd, 23rd April 1982.

D.S.N. MARKETING LTD, Westmorland Road, London NW9 9RJ A.

`Telephone: 01-204 7246. Telex: 895 4243. VISATrade, Wholesale, O.E.M. & Export enquiries welcome.

D&R Electronica was founded over 10years ago with the aim of developing andmanufacturing high quality mixingconsoles for the studio and entertainmentindustry with a special emphasis on valuefor money design engineering. The resultis a range of five basic models with alarge number of channel configurationsand options. All models are highly flexiblein use and give the best quality possibleat todays state of technology.SERIES 200 -A small mixer speciallydesigned for four track recording.SERIES 600 -A range of mixers for liveamplification, broadcast studios and twotrack recording.SERIES 400 - 'In -Line' mixing consoles forbudget 4, 8 or 16 track recording.SERIES 1000 -A range of comprehensive'In -Line' consoles for professionalrecording studios.SERIES 8000 - Top of the range 'In -Line'consoles with integral patch bay for toprecording studios. A large number ofancilliary signal processing unitscomplement the D&R programme.

Please complete this coupon for futherdetails:-

D&R Series 200 AD&R Series 600D&R Series 400 "IlD&R Series 1000D&R Series 8000 1 D&R Ancilliary

EquipmentBULLET loudspeaker componentsVITAVOX loudspeaker equipmentHELIOS mirror balls

NAME

ADDRESS

DI 48/WW - 066 FOR FURTHER DETAILS


CAMBRIDGE LEARNINGSELF -INSTRUCTION COURSES

A PRACTICAL DIGITALELECTRONIC KIT FOR* LESS THAN £20 *

SUITABLE FORBEGINNERSSUPERKIT)

'24.IE

Digital Electronic Nit

suitable for beginners

NO SOLDERING!

Learn the wonders of digitalelectronics and see how quicklyyou are designing your owncircuits. The kit contains:seven LS TTL integrated circuits,breadboard, LEDs, and all the

DIL switches, resistors, capacitors, and other components tobuild interesting digital circuits; plus a very clear andthoroughly tested instruction manual (also available sepa-rately). All this comes in a pocket size plastic wallet foronly £19-90p inc VAT and p&p. This course is for truebeginners:- needs no soldering iron.- asks plenty of questions, but never leaves you stuck and

helpless.teaches you about fault-finding, improvisation, andsubsystem checking.

- the only extra you need is a 4,1V battery (Ever Ready.1289, or similar), or a stabilised 5V power supply.

Using the same breadboard you may construct literallymillions of different circuits.This course teaches boolean logic, gating, R -S and J -Kflipflops, shift registers, ripple counters, and half -adders.Look out for our supplementary kits which will demonstrateadvanced arithmetic circuits, opto-electronics, 7 -segmentdisplays etc.It is supported by our theory courseDIGITAL COMPUTER LOGIC AND ELECTRONICS E. £6.00for beginners, and our latest, more advanced text,DIGITAL DESIGN £7.00

Please send for full details (see coupon below).

GUARANTEE No risk to you. If you are not completelysatisfied, your money will he refunded upon return of theitem in good condition within' 28 days of receipt.CAMBRIDGE LEARNING LIMITED, Unit35, RI VERMILL SITE,FREEPOST, ST IVES, CAMBS, PE17 4BR, ENGLAND.TELEPHONE: ST IVES (0480) 67446. VAT No 313026022

All prices include worldwide postage (airmail is extra -please ask for prepayment invoice). Giro A/c No 2789159.Please allow 28 days for delivery in UK

Please send me:SUPERKIT(S) @ £19.90Free details of your other self -instruction courses.

I enclose a *cheque/PO payable to Cambridge Learning Ltdfor £ (*delete where applicable)Please charge my:*Access / American Express / Barclaycard / Diners Club

Eurocard / Visa / Mastercharge / TrustcardExpiry Date Credit Card No

Signature

Telephone orders from card holders accepted on 0480 67446Overseas customers (including Eire) should send a bank draftin' sterling drawn on a London bank, or quote credit cardnumber.

Name

Address

Cambridge Learning Limited, Unit35. Rivermill Site, FREEPOST,St Ives, Huntingdon, Cambs, PE17 4BR, England. ( Registeredin England No 1328762).


J

TECHNOMATIC TECHNOMATIC TECHNOMATIC

* SPECIAL OFFER *1.24 25-99

2114L - 200ns 95p 90p2114L - 450ns 90p 85p2716 (+5V) 210p 200p2732 425p 400p2532 400p 375p6116P-3 550p 500p

UNIVERSAL INTERFACE FOR PETSSelf-contained all-purpose interface unit for new orold PETs providing a range of parallel input/outputports, 16 -bit timers, ultrafast multi -channel Anal-ogue to Digital Converters, Digital to AnalogueConverters and Programmable Sound Generators.Internal Motherboard System allows easy upgrad-ing. Built-in PSU.

£149+ £2.50 P&PSEND FOR DETAILS

A ATOMmy _ _ _ _

ftalliaN5Basic 8K + 2K Kit £120 Built

Fully Expanded 12K + 12K £185(P&P £2.50/Unit)

F.P. ROM £20 1K RAM (2 x 21140 £2

Full range of Hardware and Software available.Send for the Atom List

ATOM SOUND BOARD AND ATOM VISION KITSNOW AVAILABLE

BBC Microcomputer Memories, Expansion Sockets and Connectors nowavailable.

TELETEXT DECODER(As described in Elektor Oct./Nov./Dec., '81)

Kit for complete decoding board and keyboard £85 + £1 P&PReprint of articles £1.25

SOFTY IIAn ideal software development tool. Aprogram can be developed, debugged andverified and then can either be corn

- umsi et t:I Int oa

hostEPR

OcoMmopruttheer reSOFTY into its EPROM socket.See the review in Sept. '81 PE for the

. various facilities provided on SOFTY.SOFTY complete with PSU, ROMULATOR

& TV leads

£169 + £2 P&P

New Z80 Development System. Plugs into TV and cas-sette recorder. 40 -key direct ASSEMBLER/EDITOR, 24

41111

MENTA

bits of I/O. Ideal for study, microcontrol and robotics.Power supply and TV lead incl.

£115 + £1.50 P&P

Xeltron Diskettes:Floppy Disc Drive Mechanism. S.S.D.D. £23 for 10 Discs + Library Case.Teac FD50A 51/4", £150 + £2.50 P&P. D.S.D.D. £27 for 10 Discs + Library Case.Olivetti FD501AF 51/4", £150 + £2.50 P&P. 12" BMC Green Screen Monitor, £140.

UV ERASERSUV1B E42 UV140 E61.50 UV141 £78

Up to Up to As UV140 but ._.,......,-...

6 EPROMS 14 EPROMS with timerAll above ERASERS fitted with the safety interlocks to avoid accidental exposureto UV rays.

TECHNOMATIC TECHNOMATIC TECHNOMATIC


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hi! perrormance hi! competitive hi!

OSCILLOSCOPESwith

PERFORMANCE,

QUALITY& RELIABILITY

at the

RIGHT PRICE

1577A - 35 MHz - Dual Trace -2 mV/div1566A - 20 MHz - Dual Trace -5 mV/div1560A11-15 MHz - Dual Trace -10 mV/div1562A - 10 MHz - Dual Trace -10 mV/div

Features include

Large Bright Rectangular CRT- GraticuleIllumination

Sweep Times from 0.1 kts/div plus x 5 MAG Auto Trigger -Single Sweep -Hold Off -Delay

Line Excellent Video Sync - Line and Frame Single, Dual ADD, SUB, ALT, CHOP and X -Y

aft *modes

TTL Intensity Mod - UNCAL. LED indicators Front panel control of Trace Rotation, Astig and

DC Balance of Vert AmpsFREE 2 YEAR Guarantee (inc pick up and9return)

Prices from just over £200IMO 4)

Also AVAILABLE a range of more than 20 Oscilloscopes from 1 to 100 MHzReal Time, Digital Storage, Battery Portable, X -Y and Programmable -DMMs - Frequency Meters - Electronic Voltmeters - Power and DIPmeters - Variable Power Supplies - Noise meters - Signal Sources, AF,RF, Function, Sweep, TV Pattern and Stereo - Wow and Flutter etc etc.Ask for FREE Data and Prices.

House of InstrumentsClifton Chambers, 62 High StreetSaffron Walden, EsSex CB10 1EETel: (0799124922 Telex: 818750

ExtendedCREDITavailableCIARAto

VISA .fhi! competitive hi! House of Instruments Ltd.


MINI -DISK DRIVETEST BOX

A simple aid to test and alignment ofdrives without tying up valuablesystem time.Neatly presented in handy case withleads and connectors for 2 drives.Needs +12V and +5V through stan-dard drive connectors (provided).Circle number for further details.

Price £135 + carriage and VAT

MELKUIST LTD.35A Guildford Street, Luton LU1 2NQ

Tel: 0582/416028Telex: 825828 MELKST G


UNIVERSAL BENCH POWER SUPPLY

01.110V1

-05-

.111,1114 C-OL PISU

Electtom sal 1.41.

Output is fused and mains isolated.

2 ranges:0-125v 4 4amps0-250v @ 2amps

AC or DCContinuously

variable.

£198.00Exc. carriage

and VAT.

1.71:1Vei-Sal Lid. 32 Portland Road, Luton, Bedfordshire LU4 8AXTelephone: Luton (0582154309


FAST FOURIER TRANSFORMfor the PET and Apple microcomputers

Machine code subroutine permitting high -resolutionfrequency analysis at an unprecedentedly low cost.Suitable for research and O.E.M. use.

* Interfaces to BASIC and Pascal* Compact fixed-point data storage* 80dB dynamic range* Transforms 256 points in 4 seconds

£125 4K points in 100 seconds

Further details from:Structured Software

23 Redcar DriveEastham, Wirral

Merseyside L62 8HEPlease specify PET, Apple Pascal or Apple BASIC



B. BAMBER ELECTRONICSAirmec Millivolt Meter Type 301A £50Pye UHF Signal Generator Type SG1U £150Marconi AM/FM Signal Generator Type TF1066 8/6

£300Marconi 20 mHz Sweep Generator Type TF1099 £25Motors suitable for driving cam switches 120volt AC 1RPM £1 eachAdvance Signal Generator Type C2 £25Servomex AC Voltage Stabiliser 240v.a.c. 9 amp £25Cathode Ray Tubes Type M38-100LG & M28-233GHnew & boxed £5 eachVery Large Capacitors 8 mfd 7-10 KV D.C. Wkg. £25Modern Telephones 746 style two tone grey, used butgood condition £8 eachScottish Instruments Microfiche Reader Model M20 E25Antique Cambridge Portable Electrocardiograph £50Mains Isolating Transformer 500 VA 240volt input,240volt C.T. output housed in metal box but less lid

£15 eachVolstat Constant Voltage Transformer 190-260 volt in-put, 240 volt RMS output 250 watt £45Gould 25 watt miniature switching power supplies 5volt 5 amp £25Marconi AM/FM Signal Generator Type TF995A/5 £250Bells Power Unit Type TSS 156 0-30 volt 0-15 amp. Var.

£40Avo Valve Characteristic Meter MK IV £55Marconi Carrier Deviation Meter Type TF791D £185Airmec Modulation Meter Type 210 £75Schomandl Frequency Meter Type FD1 30-900 mHz £50EEL Street Lighting Photometer Type 106/2 £40Marconi HF Spectrum Analyser Type OA 1094A/S £100Meguro Signal Generator Type MG6-230E 16kHz-50mHz £185Rhode & Schwarte Polyskop SWOB 1 Type BN4244/2/75

£250Sinclair Digital Multimeter Type DM450 £95Telequipment Scope Type S51B £95Hewlett Packard Spectrum Analyser Type 8518.... £1200PYE WESTMINSTER W15 AMD mid -band multichannelsets only. No mikes, speakers, cradles or leads. £45

PYE WESTMINSTER W15 AMD mid -band crystalledand converted to 129.9 MHz, 130.1 MHz and 130.4 MHz.Very Good Condition. £140PYE WESTMINSTER W30 AM Low band sets only. Nocontrol gear. Sets complete and in good condition. £45PYE VANGUARD AM 25T High band, complete withleads, control box, etc. £25PYE VANGUARD AM 25B Low band, sets only. £10PYE BASE STATION F27. High band. £100PYE RTC Controller units for remotely controlling VHFand UHF fixed station radio telephones over land lines.£20PYE PC1 Radiotelephone controller, good condition, 2only at £50 eachPYE CAMBRIDGE AM1OD dash mount sets completeand in good condition but untested. £40PYE CAMBRIDGE AM1OB Boot mount sets, high bandsets only, no control gear, good condition. £25PYE REPORTER MF6 AM High band sets, complete butless cradles. Few only at £150PYE EUROPA MF5 FM Low band sets, complete but lessmike and cradle. £90PYE EUROPA MF5 UHF Mobile sets complete but lessmike and cradle. £90PYE R412 UHF Base station receiver. £120PYE F460 UHF Base station complete and in good con-dition. £150PYE F9U UHF Base station. £50PYE F401 Base station, High band AM. £400DYE BC10A Battery chargers for PF2, with battery adap-tor. £25PYE POCKETFONES PF1. Suitable for 70cm, suppliedwith service manual. E25PYE BC5 (New) Chargers for PF1 Pocketfones. £25PYE PF2 High Band, Pocketfones. £8024 VOLT to 12 volt Converters to Westminster, etc. £15

PLEASE NOTE all sets are sold less crystals unlessotherwise stated. Carriage on RT equipment - MobilesE2 each. Base stations V5 each. Red Star available atcost.

IC TEST CLUPS, clip over IC while still soldered to pcbor in socket. Gold plated pins, ideal for experimentersor service engineers 28 pin DIL £1.75. 40 pin OIL £2.00.Or save by buying one of each for £3.50.10.7 MHz SSB XTAL FILTERS (2.4kHz Bandwidth). Lowimp. type. Carrier and unwanted sideband rejection min-40dB (needs 10.69835 and 10.70165 xtals forUSB/LSB not supplied). Size aprox 2" x 1" x 1".£10.00 each.LOW PASS FILTERS ILow imp. type). 2.9MHz smallmetal encapsulation. Size 11/2" x $" x 3'4".75p each.VIDICON SCAN COILS (Transistor type, but no data)complete with vidicon base £3.50 each. Brand new.ISEP SLOTTED HORIZONTAL RAIL available in 9ftlengths. £4.00 each.ERSIN MULTICORE SOLDER 3 core solder wound on aplastic reel, 20 swg. Alloy 60/40 tin lead. Available in500gm reels. £5.75 each.BNC RIGHT ANGLED PLUGS 75 ohm type GE 37502 C1250p each or 12 for £5.00.SCREWS. Pack of nuts, bolts, washers, tags, self tapsetc. Mixed BA and metric. Sold by weight. £2.00 perKilo.FERRANTI MICROSPOT CATHODE RAY TUBES Type3H/1010. Suitable for Photographic Multi -Channel Re-corder Systems. Fitted with a mounting collar andprism cemented to the faceplate, screen aluminisedPhosphor P. The tubes are also fitted with mountingunits type MU1053 and deflection coil type SC48A. Fewonly at £55.00 each.

We are open all day Saturday. Hundreds ofbargains for callers. Stockist of Switches,Relays, Caps, Resistors, etc. Pleaseremember to add 15% VAT to all MailOrders.

GOOD SECONDHAND EQUIPMENTALWAYS WANTED FOR CASH

ALL PRICES QUOTED EXCLUDE P/PAND VAT UNLESS OTHERWISE STATED

SAIKUVICA110 5 STATION ROAD, LIMEPORT, CAMBS CB6 1 QEPHONE: ELY (0353) 860185

INDUSTRIAL MUSCLEAT A REALISTIC PRICE

* POWER BANDWIDTH DC to 100KHZ + 1db

* OUTPUT POWER IN EXCESS OF 500 WATTS PERCHANNEL INTO 2 OHMSOR IN EXCESS OF 1KW SINGLE CHANNEL INBRIDGE MODE INTO 6 OHMS

* HARMONIC DISTORTION LESS THAN 0.01% DCTO 100KHZ AT 1KW INTO 6 OHMS

* INTERFACE BOARDS CAN BE CUSTOM DESIGNEDAND BUILT TO CATER FOR A WIDE RANGE OFSPECIALISED USES

* OUTPUT MATCHING TRANSFORMERS AVAILABLETO MATCH VIRTUALLY ANY LOAD

* UNCONDITIONALLY STABLE INTO ANY LOAD* BASIC PRICE INCLUDING BRIDGE MODE

SWITCHING AND HANDLES £455

S & R AMPLIFICATION6 Tanners Hill, London S.E.8

Telephone: 01-692 2009

Toroidalnsformers

THE COTSWOLD"BUDGET RANGE" OFFERS

BUILT-IN QUALITY COUPLEDTO A RELIABLE

DELIVERY SERVICEMOST TYPESFROM STOCK

IEC 65VDE 0550

BS 415TO ORDER

PHONETELEX, WRITE

FOR DATA SHEETAND PRICE LIST

Cotswold Electronics LTD.Unit T1, Kingsville Road, Kingsditch Trading Estate, Cheltenham GL51 9NX

Tel: 0242-41313 Telex: 897106



103

RHODE & SCHWARZSelective UHF Vi Meter. Bands 4 & 5. USVFSelectomat Voltmeter USWV £450.UHF Sig. Gen. type SDR 0.3 -1 GHzUHF Signal Generator SCH £175.XUD Decade Synthesizer & Exciter.POLYSKOPS SWOB I and II.Modulator / Demodulator BN 1 7 9 50/ 2.

P. F. RALFE ELECTRONICS10 CHAPEL STREET,

TEL: 01-723LONDON, NW 18753

DC POWER SUPPLIES*APT 10459/8, 12-14V @ 5 Amps £25 (£2 p.p.)*APT 10459/8,24V @ 5 Amps f.25 (£2 p.p.)*We

can supply the above power supply at anyfixed voltage between 5V and 36V at 5A £25.*Mullard Dual supplies. Brand new withhandbook. Pos & Neg 12V at 1A and 0.4A respecti-vely. Dimensions 9x4x5ins. £10 + (£1 p.p.)*FARNELL Current limited. Dimensions 7x5x4ins.Following types available: 13-17 Volts @ 2A £15.27-32 Volts @ 1A 5V £15.5V @ 3A £15. (pp £1.501.

iti a .I..

Meter.(FSD)-300V.

853

sweep

5121BKF6

TEKTRONIX

ILAMBDA& 248A.with control equipment

generator £150£90

model£75£85

£125.

MARCONITF99 58/2 AM/FM Signal Generator.TF2500 Audio power meterTF1 101 RC oscillators £65.6551 SAUNDERS. 1400-1 700MHz FM.TF106 613/1TF 1 1 1 . Power meter. 25W. 500M Hz£50.TF1 3 70A RC Oscillator £1 35.TF7 91D Carrier Deviation Meter.

SPECIAL PURCHASE

POWER SUPPLIESi

.-.. -.-.... .

RANK KALEE 1742 Wow & FlutterAIRMEC 314A Voltmeter. 300mVAIRMEC Wave Analysers typesDERRITRON 1KW Power Amplifierfor vibration testing, etc.TELONIC type 1204 0-500MHzTELONIC type 121 Display scopesTELONIC type 101 Display scopesWAYNE KERR AF signal generatorRADIOMETER Distortion Meter

SPECIAL PURCHASE OF

Excellent LXS Series DC power units at less than atenth of new price. The snag? - they're all 110V ACInput. Prices as follows:

Carriage5V at 24A. LXS D5 OV R. £25. (List £350).__each.5V at 14A. LXS CC 5 OV. £20. (£258).

£2.50 extra

Special note: The 5V power supplies may beoperated (both primary from 230V) and DC output

1

to give a maximum output voltage of 12.5DC whenconnected in series. Deduct 10% from price for twooff or more, i.e., 12V DC at 24A for £45 + Tax! Verycheap!

BECKMAN TURNS COUNTER DIALSMiniature type (22mm diem.). Counting upto 15 turn "Helipots". Brand new withmounting instructions. Only £2.50 each.

VARIABLE VOLTAGE BENCH SUPPLIES- al

Variable voltage DC power supplies for workshopuse. Constant voltage, variable 0-30V output at 1A.Cased, free standing, volt -metered output. Shortcircuit proof. Size 4 x 5x 7". Only £30 -each (pp£1.50).

* VIDEO EQUIPMENT SALE * ,

CONTENTS OF COMPLETEMONOCHROME STUDIO,_r-MARCONI Video/Audio mixing desks.Monochrome Video cameras corn-plete with on -board monitors.Video monitors types CONRAC II (9"tube) PROWEST 13".To be sold in first-class working condi-tion.Offers invited for complete lot.

454 PORTABLE OSCILLOSCOPES

ektronix 0 -1 I f z .ual-beamoscilloscopes in stock now. 5mV/cm Y -am-plifier (1mV cascaded). 2.4ns risetime.Calibrated sweep delay. We can offerthese units in first-class operational condi-tion complete with three months' guar-antee, for a once only price of £85Q. ,

A

COMMUNICATIONS TEST EQUIPMENT 4 -re

MARCONI TF1066B/1. AM/FM Signal Genera- *. tor. 10-470MHz. 0.2uV-200mV output. FM De- .4..., viations up to ±100KHz from 30Hz-15KHz £550-7 MARCONI TF995A/5 AM/FM Signal generator, In* Narrow deviation model 995 covering 1.5- ** 220mHz £450 *4 MARCONI TF106413/5 FM signal generator .1.- covering in three ranges 68-108, 118-185 and

4( 450-470MHz. Modulation FM fixed deviations -0.* of 3.5 and 10KHz. AM fixed 30% £225 11K4( MARCONI TF7910 FM Deviation meter £1851 lIC

SPECIAL OFFER FOR MIS MOWN REDUCED TO £11.50.00\sgewoossomma.,

* OSCILLOSCOPES *TEKTRONIX 500 SERIES SCOPES AT

BARGAIN PRICES:All in good working order. Available to callers only

TYPE 543B with 'CA' plug-in 25MHz DB SOLD OUTTYPE 545B with 'CA' plug-in 25MHz DB SOLD OUT-TYPE 585A with '82' unit. 80MHz. Few left -£250: Reduced to £200

* ROTRON INSTRUMENT* COOLING FANS 4(

* Supplied in excellent condition, fully '01* tested: *1 1 5V, 4.5 x 4.5 x 1.5" £4.50. 230V 4,* £5. 1 1 5V, 3 x 3 x 1.5" £4 + postage* ea. 3 5P.

-

SEALED LEAD ACID BATTERIESi

Gould GELYTE type P8660. 6V. 6A.H. Measures33/4x2 3/4x23/4 inches. Excellent condition. £4.50.(75p post). PLEASE NOTE. All the pre=owned equipment shown has been

carefully tested in our workshop and reconditioned where neces-sary. it is sold in first-class operational condition and most items.carry a three months guarantee. For our mail order customers wehave a money -back scheme. Repairs and servicing to all equipmentat very reasonable rates. PLEASE ADD 15% VAT TO ALL PRICES.

... .... .

100V DC ELECTROLYTICCAPACITORS

Sprague 'Powerlytic' type 36D. 10,000uF. 100V.Brand new at surplus price! Only £4 ea. PP 50p.

20 -WAY JACK SOCKET STRIPS. 3 pole type £2.50each (-i- 25p p.p.). Type 316 three -pole plugs forabove -20p ea. (p.p. free).

/ 48PAGES

0/2"x I i"

.ORDER YOUR FAVOURITEo'N' AUDIO ACCESSORIES BY MAIL

GiC) SEND FOR YOUR FREE COPYOF OUR 1982 CATALOG

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We Ship the fastest & most convenient way Tor youl Moot Shipments From Stock

SESCOM, INC.RETAIL SALES DIVISION UO2)384-09931 1 1 1 Las Vegas Blvd. North 1800)634-345)Las Vegas, NV 89101-1197 U.S.A. TWO (alo)3e/ -6996


P.&R. COMPUTER SHOPIBM GOLFBALL PRINTER 3982, £70

EPSON MX -80 80.GPs 3982 IBM I/O PRINTERS DOTMATRIX PRINTER WITH SPECIAL INTERFACES.VDUs, ASCII KEYBOARDS, ASR, KSR, TELETYPES,PAPERTAPE READERS, PAPERTAPE PUNCHES,SCOPES, TYPEWRITERS, FANS 4" 5" 6". POWERSUPPLIES, STORE CORES, TEST EQUIPMENT ANDMISCELLANEOUS COMPUTER EQUIPMENT.OPEN: MONDAY TO FRIDAY 9 a.m.-5 p.m.,SATURDAY TILL 1 p.m.

COME AND LOOK AROUNDSALCOTT MILL, GOLDHANGER ROAD

HEYBRIDGE, ESSEXPHONE MALDON (0621) 57440


HYDRAULIC DRIVEUSING SELF- AO -CONTAINEDHYDRAULIC POWER PACK

FEEDBACKCLOSED LOOP CONTROL SYSTEM

,,11rt8f1111 r e.IrMallIMMEGNIMINSOM1111

ROBOTS FROM POWERTRANMICROPROCESSOR CONTROLLED

USING DEDICATED SYSTEM OR EXTERNALCOMPUTER VIA ON -BOARD RS232C INTERFACE

UP TO SIX PROGRAMMABLE AXESREADY -BUILT OR KITS FROM £355

CURRENTLY BEING PUBLISHED IN

PRACTICAL ELECTRONICSFor further details please contact:

POWERTRAN CYBERNETICSPORTWAY INDUSTRIAL ESTATE

ANDOVER, HANTS SP10 3MMTel. Andover (0264) 64455


BRITAIN'S BETTERBARGAIN STILL IN

WORLD-WIDE DEMANDWIRELESS WORLD CIRCARDS at 1976 prices 10% discount for 10 sets!Most sets are still available even though the companion volumesCIRCUIT DESIGNS 1, 2 and 3 are out of print. (CIRCARDS SETS 1 to 30).

wireless world circard Set 14: Digital counters -1

Basic piing caudal

Cisme egret.T. bstahle circutt is a TmgeMimeop- in which the outputc. o. . stair for a

hePing Volution at themgcreeinput If the base -drivecurrent is arranged so that Tr.is in saturahon. s collectorvoltage will . allow 0.10.This is too low to forward -basMe haamemater junction ofTr,. about 01V. end hence Tr,will . °II Thswans its

irEEE.E.E.Single testableVir -12V

o Tr TI.. BC1011R, 1.311.10",

C,, C, 8009013,. D.: PSIOE

1005Hr 15Pwell5nigger inPut 1 gvTrigger input width it: Ins

collectoremitter voltage is high.depending on R. and Rs, andthe hese-drive current for Tr,Rows through 111 and R.Hence t. terminals idclulkJlardlninly) as Q and Q are

a, 11, is forwardbased T.anode of 13, s apProcatiatelrat let..., and biome IIIcathode is connected to a highpotential Ha ft, it ts remesetbased. Therefore Tr, collectorcurrent is reduced. causingH. sn [011.1! cottage,11-111.18 ...dnie current to

This einem Tr, collecmrsTri

oltage to drop and Tr, M.fuT'nt decreases causing arther Incr.. NI Tr, collector

collage. The prams ddnItr11.1until the other stable Haw. Tr.conductmg and Tr, MT, issustained T. next negative.gotng trigger putse resets thecircuit to Ils previour state ItProduces one ouipid pulse foreery two trigger pulses

low and hmh respechm1YI0 an4 10, 011.10 0041111.

The interconnect.. of Ow. Increased frequency ofInstable circuits to give Immo, operation rEEE,EE. ,EEEEEE

"'"" Ilse nigger Input is high,-rrEc counter damn. 11.1 E. additionconnectedthe circuit is in a stable cute11'1". the Mem tnput ndrocennear ...Ind ntgetow-goIng

1111

Putse.edge as steered to Tr, .se

Q output of a prey aus flu-flopisconnected to Me trigger

or T -1 input of the twoThn gm" a natural

count of 2' where is thenumber of Hare and 2. Is theumber of states throughhtch nM1e counter progresses

Circuit modikelimRange of 51.. ft.. e.]1 to CHOmi.., variation 150 to

01.HrRange of rt. Ce 110 to 110090I requency Heim. 140 to001.HrIncrease turn -on speed withcapacito. across resistors R.4. R. 4T...1y 5 to 11, of

Fill gaps in your circuitfiles with these sets of

127 x 204 mm cardsin plastic wallets.

These unique circuitcards normally

contain descriptionsand performancedata of 10 testedcircuits, together

with ideas formodifying them

to suit specialneeds.

1 Basic Active filters 2 Switching Circuits, comparators and Schmitts (But these gaps cannot be filled)6 Constant current circuits 7 Power amplifiers 8 Astable circuits 9 Optoelectronics 10 Micro power circuits 11 Basic logicgates 12 Wideband amplifiers 13 Alarm circuits 14 Digital Counters 15 Pulse modulators 16 Current differencingamplifiers - signal processing 17 Current differencing amplifiers - signal generation 18 Current differencingamplifiers-measurement and detection 19 Monostable circuits 20 Transistor pairs 21 Voltage -to -frequency converters22 Amplitude modulation and detection 23 Reference circuits 24 Voltage regulators 25 RC oscillators - 1 26 RCoscillators -2 27 Linear cmos - 1 28 Linear cmos -2 29 Analogue multipliers 30 Rms/log/power laws 31 Digitalmultipliers 32 Transistor arrays 33 Differential and bridge amplifiers 34 Analogue gate applications - 1 35 Analogue gateapplications - 2.

To IPC Electrical - Electronics Press Ltd.General Sales Department,Room 205,Quadrant House,Sutton,Surrey SM2 5AS

Company registration in EnglandQuadrant House, The Quadrant,Sutton, Surrey SM2 5ASReg. No 677128

Please send me the following sets ofCircards: £2 each,£18 for 10 post free.Remittance enclosed payableto IPC BUSINESS PRESS LTD.

Name (Please print)

Address (Please print)


MICRO TIMES19 Mill Street, BidefordNorth Devon EX39 2JR, EnglandTelephone Bideford (023 72) 79798VAT NO. 321 1198 01

MEMORIES2114 300ns £1.202114 45Ons 95pTC5514P 450ns

6.504K Cmos RAM(1K x4)4116 15Ons e1.254116 200ns £1.00HM6116-3 E7.95(2K. x 8)

EPROMS2708 450ns E2.302716 450ns £2.452732 Intel type £3.86

VOLTAGEREGIAATONS1A7805 5v 39p7812 12v 39p79055v 55p791212v 55p100mA78L05 5v 29p78L12 12v

29p79M05 5v 60p79M12 12v

80p723 31p

INTERSILICL7660 E2.25Volt. Converter

UNEAR ICsNE555NE556RC4136LM301ANLM311PLM3113LM324NLM339NLM348NLM358PLM3B0LM3302LM3900NLM3914LM3915LM13600LM1871LM1872SN76477NUA709UA733UA741UA747UA748TL074CNTL081CPTL082CPTL084CNTL490MC1488MC14898T2687288795

16p45p65p25p80p

£1.4540p40p64p60p65p85p449

E2.00E2.00£1.20E1.90£1.90£1.69

28p68p14p58p26p

E1.0038p55p95p

£1.1059p59p

£1.30E1.30£1.30

652065226532681068216845685068528212821682288255280 CTC280 PIO280ACTC280APIOZ80 DMA280ADMA280 S10/0280AS10/0280 S10/1ZEIOAS10/1280510/22130AS10/2

SUPPORT DEVICESE3.10E5.00£7.70£1.35E1.70

£10.50E1.70E2.45£1.50£1.50E3.80E3.80£4.00£4.00£4.00£4.50

£11.50£14.00£13.50£14.50E13.50£14.50E13.50£14.50

SUPER STEREO DRUM KrT

*6 Rhythms, each with 3 sub -rhythm options

*5 Instruments: Snare, Hi -Hat,Tom -Tom, Cymbal, BassDrum

* Board 4" x 5" packed withcomponents

*Kit includes rhythm selectionswitch and tempo control

Price: Kit E23.96Assembled and tested (excl.

case) E30

LOW NOISE EQUALISER MOD-ULE KITBoard size 1.3" x 1.1"Treble and bass ± 15 dB at 10kHz and 50 Hz.

Prices: £4.95 for KitAssembled and tested Ell

FLOPPY DISCCONTROLLERS

F0177113-01 E17.95FD1791-2 E32.00WD1691D £11.70WD2143-01 £5.00

FD1791-2WD1691D

WD2143-01Sold as completepackage £48.00Data available £3.00

(Plus 50I/ p&p)

8809 SINGLE BOARDCOMPUTER KITIEEE 5.100 STANDARDComplete Kit E17515% VAT plus £2 P&PPlease allow 21 days deliveryBare Board £48Uses 6809, 6850, 6821.ADSMON (2716) E2SDATA AVAILABLE ON 6809SBC S.A.E. please

LOW PROFILEDIL SOCKETS

8 pin 8p14 pin 10p16 pin llp18 pin 15p22 pin 20p24 pin 22p28 pin 26p40 pin 29p

CPUs65026504680268098080A8085A280280A

£4.95£6.20E5.70

£15.00£3.50£5.50£4.00E4.80

COMBO CHIP 12801MK3886 21/2 meg

E15.50

THYRISTORS01060 28p

SN76477N £1.69Sound EffectsGeneratorData available 75p.Lge. 281/2p. S.A.E.

ANTEX SOLDERINGIRONSModel CX 17W

£4.80Kit SK1 15W £6.50Incl. Base, stand,solderKit SK3 17W E6.50Kit SK4 25W £8.50MLX Repair Kit

6.30Spare Bits, each 60p

5-100 KLUGE CARDSimplify your project with aprototype breadboard withextras]Bare Board & Manual E33Delivery: 21 days

CMOS AND 7 ILSSERIES AVAILABLEUPON REQUEST

VEROBLOC SOLDERLESSBREADBOARD360 reliable contacts. Will ac-commodate any size IC. Canbe fully interlocked one withanother. £3.85VEROS100 Prototyping Boards:Microboerd pattern 06-2175L

£17.95Sq. Pad. Universal Patt. £17.95Prototyping Board for Appre-ITT 2020 6015Other Vero Products availableon request.

AY -3-8910 E5.95G.I. SOUND COMPUTER CHIPData Et (Large S.a.e. please151/2o)

ELECTROWAREWs are distributors for allElsotrowsrs ProductsTools, kits, boards, etc.Catalogue available.Please send 30p P&P

TlLsTIL32 45pTIL209 red 10pTIL212 yellow 16p111.216 red 180TIL220 red 12pTIL224 yellow 18p11L228 red 20pTIL232 green 18pTIL311 E5.25TIL 312-3 E1.00TIL321-A £1.15TIL 330A E1.15

ORDERING INFORMATIONPlease add 50p P&P pluS 15%VAT to all orders.EXPORT ORDERS WELCOMEAdd 15% P&P VAT not applica-bleACCESS/BARCLAYCARDorders welcomeSchools, Univ., OfficialOrders welcome.All items brand new,full spec.Excellent delivery service

BARCLAYCARD


POWER SUPPLIESHIGH QUALITY COMBINATION SWITCH MODE AND STATIC

POWER SUPPLIES

Model No.AV81 5v 8A £28AV82D 12v 5A. + 5v 1A. Disc Drive supply £29

Teac FD 50 SeriesAV83 + 5v 8A. +12v 800mA. -12v 50mA. -5v 10mA

+25v 30mA £33AV84 +5v 8A. ±12v 50mA. +25v 30mA £33AV86 Transformer, Rectifier, Mounting Plate and Fuse £18AV87 Power fail detect board 15mS £7.50

Price

Please add £1.20 p.&p. to order. All units are supplied on a satis-faction or money back basis and carry a full guarantee.

Send cheque/P.O. to:AVALON ELECTRONICS72 Ship Lane, Farnborough, Hants

Tel. 0252 511098Trade and other enquiries welcome


Multi Direct DriveCassette Mechanism

4 Xt

3 Motor Direct Drive High Reliability Wide Speed Range,1.2-19cm/s Designed for Full Remote ControlDual Capstan: 0.16% Wideband Wow/Flutter

0.07% DIN Pk Wtd.Wow/FlutterMotion Sensors and Tachogenerator: Intelligent Control of

UnitApplications: Studio Quality Recording Equipment

Compact Transportable Equipment Industrial Recordingand Monitoring

C'N r? %.1 9 R fiFPAPSTPAPST MOTOR3 LIMITED, PARNELL COURT, EAST PORTWAY INDUSTRIAL ESTATE,

ANDOVER, HAMPSHIRE. TEL. ANDOVER (0264)53655 TELEX 477512


EDMUND SCIENTIFIC

1AN

opcO\ ILLUSTRATED CATALOGUE,r0 At last this famous range of

products is now available in theU.K. and Ireland from RHEINBERGS

SCIENCES LIMITED. Over 2000 productsfor industry, education and the enthusiast.

Microscopic AccessoriesMagnifiers 8 MicroscopesLightFibre OpticsMotors 8 PumpsInfrared ProductsPolarizing MaterialToolsOEM

Solar EnergyOpticsMagnetsLaboratory EquipmentLasersPhotographyEducational KitsDiffractiun GratingsHolography

RHEINBERGS SCIENCES LIMITED, Dept. WW1Sovereign Way. Tonbridge. Kent TN9 1 RN Tel 0732 357779


Decade ResistanceBox 8000 £85

0.1% ACCURACY 112 TO 1 00MQ COLOUR CODED

DIGITS

Decade CapacitanceBox 1071 1115 1% ACCURACY 10 pF-100µF COLOUR CODED

DIGITSA compact 7 decade capacitance box. Coloureddigits give nF in white, pF in yellow and i.rF in red.All contacts are gold plated.

0 0 I. 0 5 t 0 0

Low Ohm ResistanceBox 1051 198

0.01Q TO 100K IN LINE READ-OUT 1 WATT POWER

RATING

Microcal 1030 £84

VOLTAGE/CURRENTRANGES

BATTERY OPERATION O. 1% ACCURACYA compact low cost voltage andcurrent source for general use.

Outputs are 10 /A/ to 1 V and 10 p Ato 100 mA.

Decade Resistance BoxesType 106111062

IN LINE READ-OUT PRECISE MECHANICALLY

ANDELECTRICALLYROBUST

148

STABLE -(METALFILM RESISTORS)FULLY SCREENED

2 VERSIONS: 112 to1.2M12 (106111 OR to 12N111 (10621

The 1061/1062 Decade Resistance boxes aredesigned to meet the standard required in botheducational and industrial applications.

Also available through our UK distributors:ELECTROPLAN, ORCHARD RD, ROYSTON, HERTS.TEL: 0763 45145. TELEX 81337 EC PLAN.

TIME ELECTRONICS LTD, Botany Industrial Est., Tonbridge, Kent, England TN9 1 RS. Tel: 107321 355993. Telex: 95481 rf106 WIRELESS WORLD MAY 1982

RECHARGEABLEBATTERIES

PRIVATE & TRADE ENQUIRIES WELCOMEFull range available to replace 1.5 volt dry cells and 9 voltPP type batteries, SAE for lists and prices. £1.45 forbooklet, "Nickel Cadmium Power," plus catalogue.

* New sealed lead range now available *Write or call at:

SANDWELL PLANT LTD.2 Union Drive, Boldmere

Sutton Coldfield, West Midlands, 021 -354 9764After Hours 0977 84093


EPROM PROGRAMMER2716 HEX KEY PAD

POWERFUL EDITOR2711 TVRIMOL/NAOADISPLAY

2532 CASSETTE BACK-UP ROMULATOR

SOFTY STANDS ALONE£169# VAT, EX STOCK, BY RETURNDATAMAN DESIGNS, LOMBARD HOUSE,

DORCHESTER, DORSET DTI IRX. (0305168066


PRINTED CIRCUITSFOR WIRELESS WORLD PROJECTS

Audio compressor/limiter-Dec. 1 9 7 5-1 s.s. (stereo) £4.25Cassette recorder -May 1976-1 s.s. £5.00Audio compander -July 197 6 -1 S s £4.25Audio preamplifier -November 1 9 7 6 -2 s.s. £8.50Additional circuits -October 1 9 7 7 -1 s.s. £4.00Stereo coder -April 1 9 7 7-1 d.s. 2 s.s. £8.50Low distortion disc amplifier (stereo)- September 197 7 - 1 s.s. £2.00Low distortion audio oscillator -September 1977-1 s.s. £3.50Synthesized f .m. transceiver -November 197 7- 2 d.s. 1 s.s. E1 2.00Morsemaker-June 1 9 7 8-1 d.s. £4.50Metal detector -July 1 9 78- 1 d.s. £3.75Oscilloscope waveform store -October 1978-4 d.s. £18.00Regulator for car alternator -August 1978-1 s.s. £2.00Wideband noise reducer -November 1 978-1 d.s. £5.00Versatile noise generator -January 1 9 79- 1 s.s. £5.00200MHz frequency meter -January 1 9 79-1 d.s. £7.00High performance preamplifier -February 197 9- 1 s £5.50Distortion meter and oscillator -July 1 9 7 9 -2 s.s. £5.50Moving coil preamplifier -August 1 9 7 9- 1 s.s. £3.50Multi -mode transceiver -October 1 9 7 9- 10 d.s. £35.00Amplification system -Oct. 1979-3 preamp 1 poweramp £4 20 eachDigital capacitance meter -April 1980-2 s.s. £7.50Colour graphics system -April 1 980-1 d.s. £18.50Audio spectrum analyser -May 1 980-3 s s £10.50Multi -section equalizer -June 1 9 80-2 s.s. £8.00Floating -bridge power amp- Oct. 1980 - 1 s.s. (1 2V or 40V) . . £4.00,Nanocomp 6802 or 6809 - Jan., July, 1981 - 1 d.s. 1 s.s E9.00Cassette interface - July, 1981 - 1 s.s. £1.50Eprom programmer - Jan., 1982 - 1 d.s £4.50Logic probe - Feb., 1981 -2 d.s . £6.00Modular frequency counters - March, 1981 - 8 s.s £20.00Opto electronic contact breaker (Delco) - April, 1981 -2 8.5 £4.00CB synthesiser - Sept. - 1 d.s. £6.00Electronic ignition - March, 1982 - 1 s.s £4.00

Boards and glassfibre roller -tinned and drilled. Prices includeVAT and UK postage. Airmail add 30%, Europe add 10%. In-surance 10%. Remittance with order to:

M. R. SA6IN, NANCARRAS MILL, THE LEVELCONSTANTINE, FALMOUTH, CORNWALL

a TRANSFORMERS 4CONTINUOUS RATINGSMAINS ISOLATORS (screened) 12 or 24 -VOLT RANGEPri 0-120; 0-100-120V (120, 220. 240V) Sec 60 Separate 12V windings Pri 220-240V55-0-55 60 twice to give 55, 60, 110, 115. 120. Ref. 12v Amps 24v P&P125, 175, 180, 220, 225, 230, 235, 240V. 111 0.5Ref. VA (Watts) E P&P 213 1.007* 20 4.84 1.50 71 2.0149 60 8.37 1.60150 100 9.38 1.84151 200 13.69 2.12152 250 16.31 2.64

154 500 25.02 2.9018.07 2.12153 350

155 750 35.91 OA156 11500000 4.5.89

60.OA157OA

158 2000 72.43 OA159 3000 101.12 OA161 6000 203.65 OA*115 or 240v sec only. State volts required.Pri 0.220-240V.

50 VOLT RANGESec. Volts available .5, 7, 8, 10, 13, 15, 17, 20,25, 30, 33, 40 or 20V -0-20V or 25V -0-25V

AmpsRef. 50v 25v102 5 1

103 1 2104 2 4105 3 6106 4 8107 6 12118 8 16119 10 20109 12 24

4.135.038.69

10.3614.1016.3724.5230.2338.18

£ P&P1.401.401.841.902.121.842.70OAOA

8570

10872

11617

115187226

5.06.08.0

10.012.016.020.030.060.0

0.250.51.02.02.53.04.05.06.08.0

10.015.030.0

2.663.194.254.916.787.698.989.82

10.8912.9717.4621.6944.45

1.201.201.201.601.501.401.641.801.902.122.442.64OA

30 VOLT RANGE (Split Sec)Sec. Volts available 3,4, 5, 6, 8, 9, 10, 12,

15, 18. 20, 24, 30V or 12V -0-12V or 15V -0-15V

AmpsRef. 30v 15v E P&P112 0.5 1 3.19 1.20

79 1 2 4.32 1.403 2 4 6.99 1.60

20 3 6 8.10 1.8521 4 8 9.67 1.9051 5 10 11.95 2.00

117 6 12 13.52 2.0288 8 16 18.10 2.2689 10 20 20.88 2.2490 12 24 23.20 OA91 15 30 26.60 3.0092 20 40 35.64 4.83

60 VOLT RANGEPs 220-240V IS plit Sec)

Voltages availe:,le 6, 8, 10, 12, 16,18, 20, 24, 30, 36, 40, 48, 60V, or24V -0-24V or 30V -0-30V

AmpsRef. 60v 30v124 5126 1

127 2125 3123 4

40 568

1012

120121122189

1

2

468

1012162024

4.707.159.20

13.3115.1519.1621.8630.7235.7641.22

P&P1.501.501.902.022.262.242.64OAOAOA

400/440V ISOLATORS400/440 to 200/240

VA Ref. £ P&P60 243 8.11 1.50

250 246 16.07 OA350 247 19.88 OA500 248 24.77 OA

1000 250 50.53 OA2000 252 74.79 OA3000 253 104.86 OA6000 254 207.92 OA

CASED AUTOS240V cable input USA 115V outletsVA Pries P&P Ref

20 E7.21 1.25 56W75 E9.35 1.50 64W

150 E12.10 1.84 4W200 E12.02 1.44 65W250 E14.73 1.60 69W500 E22.14 2.24 67W

1000 E33.74 2.80 64W2000 E60.47 OA 95W

0-15 V CT (7.5-0-7.5V)Ref. Amp Price P&P171 500MA 2.53 .90172 1A 3.59 1.20173 2A 4.35 1.20174 3A 4.54 1.20175 4A 6.93 1.40

SCREENED MINIATURES Pri 240VSec Volts £ P&P3-0-3 3.11 .900-6, 0-6 3.45 1.209-0-9 2.59 .800-9, 0-9 2.41 .900-8-9, 0-8-9 3.36 1.200-8-9, 0-8-9 4.27 1.400-15, 0-15 2.4112-0-12 3.110-20, 0-20 3.3920-12-0-12-20 4.130-15-20, 0-15-20 5.600-15-27,0-15-27 4.830-15-27, 0-15-27 7.30

Ref. mA238 200212 1A, 1A

13 100235 330, 330207 500, 500208 1A,1A236 200,200239 50MA214 300,300221 700 (DC)206 1A, 1A203 500, 500204 1A,1A

.90

.901.201.201.601.501.60

AUTO TRANSFORMERSVoltages available 105, 115, 190, 200, 210, 220,230, 240. For step up or step down.Ref. VA (Watts) TAPS £ P&P113. 15 0-10-115-210-240V 2.39 1.2064 80 0-10-115-210-240V 4.85 1.40

4 150 0-10-115-200-220-240V 6.48 1.6067 500 0-10-115-200-220-240V 13.30 2.2484 1000 0-10-115-200-220-240V 22.70 2.8093 1500 0-10-115-200-220-240V 28.17 OA95 2000 0-10-115-200-220-240V 42.14 OA73 3000 0-10-115-200-220-240V 71.64 OA

80s 4000 0-10-115-200-220-240V 93.01 OA57s 5000 0-10-115-200-220-240V 108.30 OACONSTANT VOLTAGE

TRANSFORMERSFor 'clean' mains tocomputers, peripherals.250VA £127.36500VA +

VAT1kVA +1kVA £203.12

SPECIALISTTRANSFORMERWINDINGSERVICE

TOROIDALS NOWAVAILABLESend stamp for list

PLEASE ADO 15% VAT AFTER P&POverseas post extra

4 OTHER PRODUCTSAVO TEST METERS

8 Mk. 5 Latest Model £122.1071 (Electronics & £45.8073 TV Service) £63.90MM5 Minor £40.50DA211 LCD Digital £58.50DA212 LCD Digital £81.90DA116 LCD Digital £121.70Megger 70143 500v £97.20Megger Battery BM7 £65.30Avo Cases and Accessories

P&P £1.32 + VAT 15%

4MAINS BATTERY ELIMINATORS

No wiring, ready to plug into 13A socket. 6, 9,12V DC 300mA £5.10 + VAT

ANTEX SOLDERING IRONS 15W. CCN240 or C£4.5Safety stand £1.75 25W X25 £4.12V 25W car soldering kit £5.3

P&P 50p + VAT

BRIDGE RECTIFIERS200v 2A 45p400v 2A 55p100v 25A,- £2.10100v 50A £2.60200v 4A 65p400v 4A 85p400v 6A £1.40500v 12A £2.85

P&P 20p. VAT 15%

PANEL METERS £6.70 ea + 76p P/P + VAT43 x 43mm or 82 x 18mm V.U. Indicator50µA, 500uA, lmA, 30V d.c. £1.95+30p P&P,VAT

Educational Meter 10A8 30V E4.50+WIT

Precision De -Solder Pumps - Spring loadedquick action button release for one handworking. Large £5.86 P&P 35p -VAT. Small £5.17P&P 30p+ VAT. Replacement tips: Small65p VAT. Large 86p - VAT.

ANTEX SOLDERING IRONS 15W CCN240 or C£4.50 25W X25 £4.80. 12V 25W car solder kit£5.30. Safety stand £1.75. P&P 55p + VAT

gg;t2==31,

METAL OXIDE RESISTORS E1/100Special Offer TR4 5% Electrosil 1100s only). Use in placeof c.film. 471/ - 751? - 1801/ - 36011 - 39011 - 430i/ - 47011 -51011 - 56011 -82011. 1K - 1K2 - 1K3 - 1K6- 1K8 - 2K - 2K4 -3K - 16K - 20K - 22K - 24K - 27K - 47K - 82K - 100K - 110K -120K - 130K- 180K- 220K- 270K- 300K. P&P 30p VAT

Barrie Electronics Ltd.3,THE MINORIES, LONDON EC 3N 1BJ

TELEPHONE: 01-488 3316/8NEAREST TUBE STATIONS: ALDGATE & LIVERPOOL ST


WIRELESS WORLD MAY 1982WW - 063 FOR FURTHER DETAILS

107

Advertisementsaccepted up 12 noonTuesday, May 4, for Juneissue, subject to spacebeing available.

DISPLAYED APPOINTMENTS VACANT: £13.50 per single col. centimetre (min. 3cm).LINE advertisements (run on): £2.50 per line, minimum 5 lines. (Prepayable.)BOX NUMBERS: £1.50 extra. (Replies should be addressed to the Box Number in theadvertisement, c/o Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS.)PHONE: IAN FAUX, 01-661 3033 (DIRECT LINE)

Cheques and Postal Orders payable to IPC Business Press Ltd.

Engineers &Scientists

£8,589

Communications R & D......the leading edge

At HM Government Communications Centre,we're applying the very latest ideas on electronics andother technologies to the problems of sophisticatedcommunications systems, designed to enable and protectthe flow of essential information.

The work is of the highest technical challenge,offering full and worthwhile careers to men and women ofhigh ability, on projects covering the following areas ofinterest: -

RADIO - from HF to microwave, including.advanced modulation systems, propagationstudies, applications of Microcircuitry.ACOUSTICS SIGNAL ANALYSISMAGNETICS SYSTEMS ENGINEERINGApplicants, under 30 years of age, should have a

good honours degree or equivalent qualification in arelevant subject, but candidates about to graduate mayalso apply.

Appointments are as Higher Scientific Officer(£6,530-£8,589) or Scientific Officer (£5,176-£6,964)according to qualifications and experience. Promotionprospects.

For an application form, please write to theRecruitment Officer (Dept. WW 5), HM Government

Communications Centre, Hanslope Park,Milton Keynes, MK19 7BH.

(1589)

ELECTRONIC ENGINEERRESEARCH & DEVELOPMENT

We are a medium-sized company employing approximately200 in the Cambridge Electronic Industries group of com-panies, specialising in producting television distributionequipment and associated electronic products. An enthusias-tic Electronic Engineer is sought to join our existing de-velopment team. He/she will work in a modern, well-equipped laboratory and will be responsible for seeing pro-jects through from initial conception to final production. Weenvisage that the successful candidate will be 23-35 years ofage, with a degree in electronics and at least two years'experience in a research and development environment.Applicants should have detailed experience, or a keen in-terest, in one or more of the following areas:* Digital and analogue circuit design from D.C. to 1GHz.* Television signal processing.* Cable distribution of television signals.* R.F. communications.The company offers good working conditions, a 37 -hourweek, 25 days' annual holiday and a contributory pensionscheme. Assistance with relocation will be considered whereappropriate.

Please send full C. V. to:Mr C. G. HoughtonPersonnel ManagerLabgear LimitedAbbey Walk, Cambridge (1581)

SeniorElectronics Engineer

A Senior Electronics Engineer is required to join a small butexpanding team working on a variety of projects in the fieldsof Robotics, Image Processing, Real time data collection andtelemetry.The successful applicant will be qualified to degree level andwill have relevant experience in analogue and digital designtechniques.A thorough knowledge of at least one current microprocessoris required, and a high level of enthusiasm and selfmotivation is essential.The company is situated in a pleasant part of Avon, a fewminutes drive from Junction 21 of the M5.Working conditions are excellent and salary is negotiableaccording to qualifications and experience.

Contact G.S. Chewins, Senior Personnel Officer,(Recruitment)BAJ Vickers Limited, Banwell, Avon, BS24 8PD.

BAJ VickersA Vickers company 1586


Appointments

SENIOR MAINTENANCE ENGINEERSCommencing salary from £12,877 p.a. (under review)

Independent Television News Ltd. has vacancies for Senior Engineers in the followingMaintenance Sections at ITN House, London W1.

VTR & Telecine Maintenance(Ref 000009)Responsible for the maintenace of VTR and telecine equipment, including ACR25B, VPR2B,VR1200C, BVU200/800, standard U-Matics and Rank Cintel Mk Ills and associated editing andcontrol systems.

ENG/OB Maintenance(Ref 000010)Responsible for the maintenace of all the ENG and OB transportable equipment includingBVP330 cameras, BVU50 and 110 recorders, VPR2 and VPR20 C -format machines, TBCs andediting systems.

Radio Links Maintenance(Ref 000011)Responsible for the maintenance of our radio link equipment and extensive radio telephonenetwork. Equipment includes frequency agile 2.5GHz video links and numerous UHF andVHF FM R/T systems, both static and mobile.

Sound Maintenance(Ref 000012)Responsible for the maintenance of a varied range of audio equipment, including soundmixing desks and associated studio sound equipment, film and video sound dubbing suitesand a wide variety of audio recorders including r ack machines.

Central Maintenance(Ref 000013)Responsible for the maintenance of not only all our studio equipment, including Marconi Mk9 cameras, CD480 mixers, Quantel DPE5001, Aston Character generators and the usualancillaries but also such equipments as DICE and ACE digital converters, Oracle and graph-ics computer systems.The above vacancies offer a challenge to experienced engineers wishing to join an ex-tremely active company expanding to meet its Channel 4 commitments.Applicants should have qualifications to HNC level or equivalent and be experienced inmaintaining the relevant broadcast TV equipment.It would be of considerable advantage to have some practical experience of computer ormicroprocessor systems.Good prospects exist in all the above posts for promotion, with experience, to SupervisoryEngineer.Generous pension scheme, free life assurance.

Applications should be made in writing giving qualifications and experience to:

THE MANAGER, ENGINEERING MAINTENANCEINDEPENDENT TELEVISION NEWS LTDITN HOUSE48 WELLS STREETLONDON W1P 4DE

11591


Appointments

(15311

11111

TRAINEERADIO OFFICERS

First-class, secure career opportunities.

A number of vacancies will be available in 1982/83 forsuitable qualified candidates to be appointed asTrainee Radio Officers.

If your trade or training involves Radio Operating, youqualify to be considered fpr a Radio Officer post withthe Composite Signals Organisation.

Candidates must have had at least 2 years' radiooperating experience or hold a PMG, MPT or MRGCcertificate, or expect to obtain this shortly.

On successful completion of between 36 and 42 weeksspecialist training, promotion will occur to the RadioOfficer grade.

Registered disabled people may be considered.

SALARY & PROSPECTSTRAINEE RADIO OFFICER: £4159 at 19 to £4897 at 25and over. On promotion to RADIO OFFICER: £5698 at19 to £6884 at 25 and over. Then by 4 annualincrements to £10,034 inclusive of shift working andSaturday and Sunday elements. Salaries reviewedannually.

For full details please contact our Recruitment Officeron Cheltenham (0242) 21491 Ext. 2269 or write to herat:Recruitment Officer, Government CommunicationsHeadquarters, Oakley, Priors Road, Cheltenham,GloucestershireGL52 5AJ

1to°1 144'

tgl I1 ..07- j

IN III Ns NI° "

Television InternationalTelevision International is a large television facilities company

serving the broadcast industry. It supplies both staff and equipmentin the fields of Video Tape, Telecine, Television Studios and TelevisionOutside Broadcasts.

It is at present expanding these facilities and has vacanciesfor substantive engineers in the following departments:

VIDEO TAPE OPERATIONS

Engineers are required with a wide knowledge of broadcastvideo tape work and who are capable of undertaking simple editingand front-line machine maintenance.

TELECINE OPERATIONS

Engineers here should be experienced in the operation andfront-line maintenance of Cintel Mk III Telecine machines and havea thorough knowledge of auxiliary units such as TOPSY andDigiscan.

VISION CONTROL AND MAINTENANCE

Engineers are required with experience of the maintenanceand alignment of electronic equipment. They must be prepared tooperate as a Vision Control Engineer in both studio and outsidebroadcast locations.

Salaries and conditions for the above will be in accordancewith the ACTT grade plus local supplements. The Company benefitsfrom an attractive contributory Group Pension Scheme, whichincludes free Life Assurance. Training will be provided to keep staffabreast of current developments within the industry.

Written applications, together with CV should be sent to:Mr. Alan Edwards, Director of Operations,Television International Operations Ltd.,9-11 Windmill Street,London W1P 1HETel: 01-637 2477

X4A member of the RANK PHICOM VIDEO GROUP 410 (1576)

WISSMSIISSSIWSIIMMBNMIEWHNEVAWSSNEMVISIIKPNMNNINAENOZWVVAVA

Electronics TechnicianAn experienced Electronics Technician is required to work within the MicroprocessorSection of Computer Science, as a broad -based support and service engineer.

The Section is responsible for providing micro -based equipment throughout the researchorganisation in laboratory environments.Candidates should be qualified to Ordinary/Higher TEC level in Electronics, or possessC&G full certificates for Electronics Technicians and should be capable of working on theirown initiative.Previous professional knowledge of microprocessor -based equipment is essential.Candidates must be able to read and interpret modern digital circuit diagrams for both faultfinding and the layout of prototype printed circuit boards and be able to generate suchdocumentation.As much of the work of the Section is involved with computer peripherals a knowledge ofinterface standards and techniques would be useful. Candidates must hold a currentdriving licence.A competitive salary will be paid commensurate with qualifications and experience and willinclude London Allowance and quarterly and annual bonuses. There is a non-contributorypension scheme and flexible working hours are in operation. Consideration will also begiven to relocation expenses in appropriate cases.

Please write or telephone for an application form to: Miss E. M. Butler, Glaxo GroupResearch Limited, Greenford Road, Greenford, Middlesex UB6 ONE. Tel: 01-422 3434, ext.2707. Please quote reference number ZH/424.

Glaxo Group Research Ltd. (1580)

IMMINNIONI versessionstoostagammenorwsami

110WIRELESS WORLD MAY 1982

Appointments

Electronics DesignEngineers

Take your career a stepin the right directionHaving introduced an extended new product range, manyof which are microprocessor based, Marconi Instrumentshas once again confirmed itself as Europe's leadingmanufacturer of test equipment and measurementsystems. Our products are selling throughout the world toall leading users in the Telecommunications and Aero-space industries and we are naturally developing furtherinnovative designs. That is why we are now looking formore Design Engineers with experience in any of thefollowing areas:

RF, Microwave, Analogue, Digital, Software, ATE,Microprocessor Applications.

Whatever your level of experience we would like to hearfrom you. We offer excellent salaries plus a wide range oflarge company benefits including relocation expenseswhere appropriate.

r

marconiinstruments

MEI Mi NMI !MI MN NM MINAME

ADDRESS

AGE

TEL. NO. WORK HOME

YEARS OF EXPERIENCE: 0-1 1-3 3-6 OVER 6

PRESENT SALARY: £5,500 £8,000 £10,000 OVERto to to

£8,000 £10,000 £12,000 £12.000

QUALIFICATIONS: HNC DEGREE OTHERS

PRESENT JOB:

--------So take a positive step in the right direction and

join us in developing tomorrow's technologytoday. Cut the coupon and send it toJohn Prodger, Recruitment Manager,

Marconi Instruments Limited,FREEPOST, St. Albans,

Herts AL4 OBR.Tel: St. Albans

(0727) 59292.

(1234

O

DOLBY SYSTEM

Dolby Laboratories Inc.

Quality ControlEngineer

c. £9000We manufacture a wide range of professional audionoise reduction systems which are used throughoutthe world in the broadcasting, recording and film in-dustries. The quality and reliability of our products isof prime importanceAn engineer is required who will be responsible to theQA Manager for all aspects of quality control in ourmanufacturing and test areas and for the de-velopment of the quality control function.The successful applicant will probably be a graduatewith experience of quality control in the electronicsindustry. A background in audio engineering wouldbe an advantage.The attractive salary is supplemented by competitivebenefits including a non-contributory pension schemeand relocation assistance if needed.

For more informationcontact:Kevin CrossDolby Laboratories Inc.346 Clapham RoadLondon SW9 9APTel: 01-720 1111

and an application form

(1585

Rediffusion Consumer Manufacturing LimitedGroup Leader Test Equipment

Rediffusion Consumer Manufacturing produce a range of advanced colourtelevision receivers at modern factories situated near Bishop Auckland, Co.Durham, and Billing ham, Cleveland. Highly effective product testing is anessential part of manufacturing policy and we wish to appoint an exper-ienced engineer of proven ability, to be responsible to the EngineeringManager for all aspects of a sophisticated range of test console and signalgeneration equipment.The successful candidate will control a team of engineers and techniciansresponsible for the effective and efficient operation of this equipment in amass production environment. Both analogue and digital techniques areinvolved with the main test consoles based on the Motorola 6800 micropro-cessor. Although some test equipment is designed and constructed locallythe main design team is based in Surrey and close liaison with this team isnecessary in order to keep abreast of new developments and influence thedesign of new equipment in the light of production experience.The appointment is based at the Engineering Laboratory of the Bishop Auck-land factory, which is within easy reach of attractive countryside and hasexcellent road, rail and air connections. A wide range of good quality housingat low cost is available and assistance with relocation will be given asappropriate.An attractive salary will be offered with 23 days' holiday per year and after aqualifying period, free life assurance and the benefit of a big companypension scheme.Applicants should be qualified to HNC or equivalent level and previousmicroprocessor experience would be an advantage, although training will beprovided if necessary.If you are interested in this challenging position and would like more details,please write or telephone in complete confidence to:Mr D. AbbottEngineering Product ManagerRediffusion Consumer Manufacturing Ltd.Fullers Way SouthChessingtonSurrey la9 1HJTelephone: 01-397 5411

REDIFFUSION11571)


Appointments

ELECTRONIC TECHNICIANSAND ENGINEERS

Marconi Communication Systems Limited are involved in the installation,commissioning. of communication equipment. worldwide. If you have formalqualifications in an electronic engineering discipline or H.M. Forces equi-valent. with at least seven years experience in installation testing,commissioning and maintaining electronic equipments and hold a currentU.K. driving licence. you could be one of the people we are looking for to fillone of the following vacancies: -

MaintenanceMiddle East - Fixed Term

Successful applicants would have a minimum of three years experienceworking on Tropospheric Scatter, Radio Relay. Line of Sight or LineCommunication Systems and be offered a two year contract with an attractivesalary and excellent allowances.

Installation andCommissioning

Worldwide - PermanentSuccessful applicants would have a minimum of three years practicalexperience working on Satellite Earth Stations. Salaries will be based onprevious experience and qualifications. Excellent allowances.

Send a full C.V. or telephone for application form to Mandy Amos, MarconiCommunication Systems Limited, New Street, Chelmsford, Essex.Telephone: Chelmsford (0245) 353221 Ext. 592.

MarconiCommunication Systems

TEST ENGINEERSmicroprocessor controlled business systems,

optical fibre and microwave transmission systemsMajor advances in the telecommunications field have yielded exceptional growth andcreated additional opportunities for engineers in this expanding technology.As a test engineer you will be locating and rectifying faults, to component level, on arange of digital equipments. So you will need qualifications to at least third yearCity and Guilds in industrial electronics or telecommunications.Salaries will be in the range £5.6-8k according to experience, with overtime and shiftwork available. We can arrange accommodation and offer a generous relocationpackage, where appropriate.

I IN omi mum Nom no gm im im

I Name

I To: Z.K.Mr Flizak, GEC Telecommunications Ltd.,PO Box 53, COVENTRY CV3 1 HJ.

Address_Age

QualificationsPresent EmployerExperience

WW (15931

SdeTelecommunications

CAMBRIDGESHIRECOLLEGE OF ARTSAND TECHNOLOGY

Lecturer II inRadio Communications

EngineeringRequired for September 1982 to teachradio communications engineering,electronics and mathematics on TECCertificate and Higher Certificatecourses.Candidates should have a degree orequivalent qualifications and pre-ferably corporate membership of IEEor IERE. Industrial experience in theradio communications engineeringindustry is essential, and teachingexperience would be an advantage.

Lecturer I inElectronics Practice

Required from January 1983 to teachelectronics practice and servicing onCCLI 224 and TEC Certificate/Diplomacourses in Electronics.Applicants should hold ElectronicsCertificate 222/224 Part III and pre-ferably HNC or HTC in Electronic Engi-neering. Industrial experience with anelectronics servicing department isessential and teaching experiencewould be an advantage.

Temporary Lecturer Iin Electronics

Required for one year from Sep-tember 1982 to teach Electronics andMathematics to TEC Certificate/Diploma Courses in Electronics andTelecommunications.Candidates should have industrial ex-perience in the electronics/telecom-munications industry and preferablyshould have a degree or equivalentqualifications and teaching exper-ience.

Salary scales: L I £5,034-£8,658, L II£6,462-£10,431, starting pointsdepending on qualifications andexperience.

Further details and forms from Headof Department of Engineering, CCAT,Cambridge CB1 2AJ (Tel. Cambridge(0223) 63271 ext. 132) to whom formsshould be returned by 30th April.115961

THE ROYAL FREE HOSPITAL ANDTHE ROYAL FREE HOSPITAL

SCHOOL OF MEDICINE

MEDICAL PHYSICS TECHNICIANII (ELECTRONICS)

Salary on scale: f7600 -E9248inclusive

An experienced engineer is requiredby the Medical ElectronicsDepartment to assist with thedevelopment and maintenance ofelectronic circuits and systems.The successful applicant will beseconded to the Royal Free HospitalSchool of Medicine, Hunter Street,WC1, until about the end of 1982before moving to theinterdepartmental workshop atHampstead, London NW3.Considerable experience in thedesign of electronic circuits andsystems using state-of-the-arttechniques is essential.Applicants should preferably hold aHigher National Certificate inappropriate subjects or anequivalent, or higher, qualification.Application form and jobdescription available from thePersonnel Department, Royal FreeHospital, Pond Street, Hampstead,London NW3 20G. Tel: 01-794 0500ext. 4286. Please quote ref. 0770.Camden & Islington Area HealthAuthority (TI

(1572)


Appointments

Electronic Engineersfor Q.A. Department

Wembley Middlesex.Racal BCC are members of the

highly successful Racal ElectronicsGroup and are world leaders in thedesign and manufacture of tacticalradio -communications equipment.

We require two experiencedelectronic engineers to fill positionsat Intermediate grade within theQuality Assurance department.Preference will be given to engineerswho are familiar with therequirements of Def - Stan 05-21 andwho have experience in a number ofQ.A. functions including defectanalysis, quality costs, and the

monitoring and control of Companysystems.

Applicants aged 26-50 must beeducated to HNC/HTC level orabove in electronics. A workingknowledge of communicationsequipment would be a distinctadvantage.

We offer excellent conditions ofservice including a good basic salaryand Group Productivity Scheme, 27

days annual holiday, a contributorypension scheme and a free lifeassurance.

Racal -BCC

World leaders in electronics

Please apply in writing statingqualifications, experience andcurrent salary to the:Personnel Officer, RACAL -BCC,South Way, Exhibition Grounds,Wembley, Middlesex.

(1573

AQA

Radio Operator Techniciansfor British Antarctic Survey

The British Antarctic Survey requires Radio Operator Techni-cians to man single handed wireless stations at their permanentAntarctic bases. The appointments will cover two consecutiveAntarctic winters which involves an absence from the UnitedKingdom of about 32 months.Applicants must be able to maintain SSB transmitting and re-ceiving equipment as well as aerial arrays. Communication be-tween the Antarctic Stations and the United Kingdom is by radioteleprinter through a cable and wireless station. Teleprinter,morse and voice communication is also maintained betweenforeign Antarctic stations, ships and aircraft.Qualifications: MRGC or better and a capability of sending andreceiving morse at a minimum of 20 wpm.Experience in maintaining communication equipment is essen-tial. A knowledge of teleprinters and touch typing an advantage.Applications from amateur and armed service trained personnelwill be considered provided that the necessary expertise can bedemonstrated.Applicants to work overseas should be single, aged between 22-35, physically fit and male.Salary: From £5,410 per annum plus a pay addition and gratuity.Clothing, messing and canteen are provided free on the stationand free messing aboard ship. Free accommodation whilst over-seas. Low income tax.

Application forms may be obtained from: The EstablishmentOfficer, British Antarctic Survey, High Cross, Madingly Road,Cambridge CB3 OET.Please quote Ref: BAS 57.Closing date: 27 April, 1982

Natural Environment Research Council

HAMMERSMITH AND FULHAM HEALTHAUTHORITY

CHARING CROSS HOSPITAL

MEDICAL PHYSICSTECHNICIAN GRADE 1

Salary scale: £8968-£10319 per annum inclusive

An Electronics Technician with considerable experienceof maintenance of electronic and biomedical equipmentis required to supervise the day-to-day work of ninetechnicians engaged in the repair, calibration and safetychecking of a wide range of medical and laboratory equip-ment.

Applicants should have previous experience of personnelsupervision and an extensive knowledge of the electricalsafety aspects of medical equipment.

Opportunities will exist for the development of electronicinstrumentation and a knowledge of microprocessorswould be desirable. The successful candidate will be ex-pected to participate in the activities of the medicalelectronics section of the department of medical physics.

Ideally, the successful candidate will have an HNC or HNDin electronic engineering.

For an application form and job description, pleasecontact Mrs J. Cordery, District Personnel Department,Charing Cross Hospital, Fulham Palace Road, London W6.Telephone 01-748 2040 ext. 2992.

(1595)


(1809)

113

Appointments

Technical TrainingOfficer

Marconi Avionics are one of the world's leading companies in theresearch, development, design and manufacture of advanced avionicssystems.

We are now seeking a Training Officer to take responsibility foridentifying the changing skill needs throughout our Borehamwoodlocation through close and continuing liaison with development, test andproduction management, followed by the planning and development ofsuitable practical courses. This will be particularly important in the areasof test equipment application and wiring and soldering skills.

Applicants should have a good training background, supported by anHNC and practical experience of electronic circuit construction, testing,and fault diagnosis of analogue/digital equipment. On a personal level,tact, diplomacy, and an ability to communicate effectively at all levels areessentials.

This is an excellent opportunity for a man or woman to make ameaningful contribution to the training needs of a world leader. Salarywill be competitive and accompanied by first class benefits.

For further information, please write or telephone: Tony Elliott,Marconi Avionics Limited, Elstree Way, Borehamwood, Herts,WD6 1RX. Tel: 01-953 2030.

MARCONIAMOK N trSA GEC -Marconi Electronics Company

Kingdom of Lesotho

TransmitterEngineerUp to £11,500 p.a. plus benefitsA challenging post in this beautiful andmountainous kingdom in southern Africa.Applicants must possess an engineering degree andhave at least five years experience in transmitterengineering and maintenance.Duties will include operation and maintenance oftwo 100kw shortwave transmitters, identifyingoperational needs, and staff supervision and training.Appointment will be on contract for two years.Salary includes a substantial tax-free allowance paidunder Britain's overseas aid programme.Benefits include:* Free passages* Generous paid leave* Children's holiday visit passages and education

allowances* Subsidised housing* Appointment grant and interest -free car loanFor full details and application form write quotingYC/202/WW or telephone 01-222 7730 Ext 3639.

Crown AgentsThe Crown Agents for Oversea Governments

& Administrations, Recruitment Division,4 Millbank, London SW1P 3JD. (1575)

(1569)

Leeds WesternHealth Authority

THE GENERALINFIRMARY AT LEEDS

SENIORELECTRONICSTECHNICIAN

(Grade MPT III)

Applications are invited frompersons experienced in electronicmaintenance, preferably withimaging and counting equipment,to work in our well-equippedNuclear Medicine Department.Knowledge of computer systemsparticularly 8080A microprocessorswould be an additional (oralternative) recommendation. Thework is interesting, responsible andincludes design and development ofspecialised electronic units. A lessexperienced person may beconsidered on the MPT IV Grade.Minimum qualifications are HNC inelectronics or equivalent and NHSexperience is desirable.Salary Scale (Whitley conditionsapply).MPT III - £5536 - £7155MPT IV - £4668 - £6137For further information includingJob Description contact: The SectorPersonnel Officer, The GeneralInfirmary at Leeds, Great GeorgeStreet, LEEDS LS1 3EX. Telephone(0532) 32799 Ext 355.Closing Date: 14th May 1982.

11588)

ELECTRONICDEVELOPMENT ENGINEER

We are seeking to expand our development team by recruiting ayoung Graduate with two to three years' experience of de-signing analogue and digital circuitry.Our range of products includes Modulation Meters, SSBTransmitter Drive Units and Spectrum Analysers. Experiencein any of these fields would be an advantage but is not strictlyessential.We are offering an excellent working environment plus a reallyattractive salary to the successful applicant.Please contact H. M. Evans - M.D. by letter or phone.

SAYROSA ELECTRONICS LTD.Anstey Mill Lane, Alton Hants GU34 2QQ

Tel: (0420) 84500 (16041

U.S.A.British -run company near New York seeks ElectronicEngineer (B.Sc. or equivalent) for design of medicaland Industrie: instruments. Could probably representus later in UK. Starting salary $15,000 (£8,000). Pleasesend résumé of training and experience to BaileyInstruments Inc., Saddle Brook, NJ 07662.

1578

SALES REPRESENTATIVEPUBLIC ADDRESS AND AUDIO EQUIPMENT

We are the newly -formed marketing arm of a manufacturing company, now estab-lished for over 50 years.We are looking for someone with, preferably, an electro-mechanical background andprevious selling experience.We are offering a salary commensurate with age and experience, as well as commis-sion, four weeks' paid holiday and a company car.Apply, in first instance, to:

The Managing DirectorD.S.N. MARKETING LTD.

West Morland Road, London NW9 9RJTel: 01-204 7246

114

116051


Appointments

Leading Loudspeaker Company in West Germany is seeking for a

SOLE DISTRIBUTORfor U.K.

Our range of products covers loudspeakers and accessories for Hi-Fi, Musicianand Car Stereo.

The applicant should have good connections to the electronic shops and manu-facturers of cabinets, to whom our products should be offered with priority.

We are seeking a serious experienced Sales Representative with proven record ofsuccess.

Please apply in writingenclosing career details to:

VISATON®11001101100011

000410

VISATON-LAUTSPRECHERPeter SchukatPfalzstr. 5-7P.O. Box 16525657 Haan 1West Germany

iv -amENGINEERING AND

OPERATIONS DEPARTMENTTV -AM, the breakfast television

contractor, requires staff to performengineering and operational duties

at all grades, both within the BreakfastTelevision Centre and on outsidebroadcast including ENG type

operations. Previous experience intelevision broadcasting would be

an advantage.Applications in writing with

curriculum vitae to:THE PERSONNEL ADMINISTRATOR,

BREAKFAST TELEVISION CENTRE,HAWLEY CRESCENT, LONDON NW1 8EF.

SALESENGINEERS

For 1. West Midlands 2. South

East 3. West of England

Required by Townsend -Coates, aleading franchised distributor ofelectronic components.

The successful applicants will have com-ponent knowledge, be already selling toindustry or have sales flair.

We offer competitive salaries plusbonus, company car, non-contributorypension and private health schemes.

Please sent C.V. to:Managing DirectorTownsend -Coates Ltd.Lunsford RoadLeicester LE5 OHH

(1590)


(1594)

115

AppointmentsGARDLINE SURVEYS

ELECTRONICS ENGINEERSDue to continued expansion, we need personnel to operate and maintain the followingtypes of equipment aboard our survey vessels:

DFS IIIN QUANTUM DAS 1A SHALLOW DIGITAL SEISMIC

SIDE SCAN, MAGNETOMETER, SB PROFILERBOOMER/SPARKER

ANALOGUE EQUIPMENTGood salary, sea -going allowances, leave arrangements and company pension schemebenefits. Promotion prospects excellent.This is an opportunity to join a dynamic, fast-growing company involved in all aspects ofshallow marine geophysical surveys.Please write, quoting VVW106, to:

THE MANAGING DIRECTORGARDLINE SURVEYS

ADMIRALTY ROAD, GREAT YARMOUTHOR TELEPHONE: 0493 50723, EXT. 200, MRS. GOFF

DATACOMMUNICATION

NETWORKTECHNICIAN

Up to £8,850BAGS is a wholly owned associated Company of the major ClearingBanks. The main activity of the Company is to provide an electronic fundstransfer service to the banks and their customers.To complement the current services and assist with the plannedexpansion of new telecommunications facilities, the Company is seekingpersonnel who have had previous experience of data communicationsand can demonstrate a working knowledge of:-

* Network operations* Circuit installation and acceptance (P.W. and P.S.T.N.)* Modem and circuit diagnostic routines* CCITT V24 interface specifications* B.S.C. protocol* Data communications test equipment

in order to support our communication networks. Applicantsmust be prepared for shift working in due course.

Excellent benefits are offered in addition to a competitivesalary, which will include, Profit Sharing, over 4 weeks' annualholiday, non-contributory pension and life assurance scheme,subsidised staff restaurant, Sports & Social Club, relocationassistance if necessary.

For further details and an applicationform please telephone Mrs. R. Sidderson 01-952 2333 or write to her at: -

Bankers. Automated ClearingServices Limited,De Havilland Road,Edgware HA8 5QA,Middlesex.

SCOTTISH OFFICEDIRECTORATE OF TELECOMMUNICATIONS

WIRELESS TECHNICIANS (£5,300-£7,060)Applications are invited for at least three posts of Wireless Techni-cian in the central services department of the Scottish Office. Theposts are expected to be based in Edinburgh, East Kilbride andMontreathmont (near Forfar). Candidates must hold an ordinarynational certificate in Electronic or Electrical Engineering or a Cityand Guilds of London Institute certificate in an appropriate subjector a qualification of a higher or equivalent standard and havethree years' appropriate experience. Some assistance may begiven with relocation expenses.A valid UK driving licence and ability to drive private and commer-cial vehicles are essential.Application forms and further information are obtainable fromScottish Office Personnel Division, Room 110, 16 Waterloo Place,Edinburgh EH1 3DN. Tel. 031-556 8400 ext. 4317 or 5028. (QuoteRef. PM (PTS).Closing date for receipt of completed application forms is 14 May,1982. 11607)

UNIVERSITY OF ESSEX

M.Sc.(European

Joint Scheme)This is a new two-year degree schemesupported by the E.E.C., whichinvolves one year in each of the twoco-operating institutions, the Universi-tat Fridericiana Karlsruhe in West Ger-many and the Ecole Superieure d'Ing-en i eu rs en Electrotechnique etElectronique in Paris. The first yearcomprises specialist courses and thesecond year is a project year. A limitednumber of places are available forhighly qualified students. Applicantsshould hold a first or second classhonours degree in Electrical Engi-neering and have a workingknowledge of French and German.The scheme is recognised by S.E.R.C.for tenure of advanced course stu-dentships for the two-year period.Please write to: Dr. B. G. Evans, De-partment of Electrical EngineeringScience, University of Essex, Colches-ter C04 3SQ. Phone: Colchester 102061862286 ext. 2269 Telex: 98440 (UNILIBG)

11599)

Zehntel LtdAUTOMATIC TEST EQUIPMENT

Having experienced rapid expansion since coming hereto the UK, Zehntel are now looking for additional

APPLICATION ENGINEERSZehntel are world leaders in in -circuit test technology,and we need good quality APPLICATION ENGINEERS toassist with our further expansion plans.

If you would like to join a young progressive team ofpeople at our Milton Keynes office, write with your CV to:

PAUL SMITHZehntel Ltd62 Tanners DriveBlakelandsMilton KeynesMK14 5BP

(1583)

WANTEDTELECOMMUNICATION

SALES/SERVICE ENGINEERFor United Arab Emirates

Salary Circa £11,000 Tax FreeMust be able to work independently to promote the com-pany products. We are main distributors for Storno UKand need first-class engineer to push sales and attendcustomers' enquiries. Bachelors only or married nochildren.

Send CV plus photo to:Mr George Fee, General Manager

AL MARIAN UNITED CO.BOX 206

ABU DHABI U.A.E.Telex 22323

Phone 32601711612)

microMicro Processor DesignOur team of experts offer the completeservice from

Design to Manufacture

Artwork Prototype Development Testing Board Manufacture Assembly Packaging

control systems ftr more information contact Micro Control, 1 Cherrywood Drive, Aspley,None, NGB INN, Telephone 0602 298281 (24 hour service). 115971


SITUATIONS VACANT

Classified

SALARY RISES DISAPPOINTING?Our client Companies tend to be more realistic!

AMBITIOUS CIRCUIT DESIGNER26+ for new generation of data recording and display products based onMotorola, family of mpu. Technological and product snobbery appreciated.To £15,000. South Coast.

CONSULTANT PROGRAMMERSFor SW house with contracts in real-time process control. Experience mustinclude one or more of Nova, PDP1 1, X16, 8080, 8086, Z80. To £16,000.London and Manchester.

HW & SW ENGINEERSFor TV and video products including digital standards convertors and real-time picture manipulators. Products based on PDP1 1 and several bit -micros.Assembler Pascal & Fortran. C.£10,500. Berks.

YOUNG DESIGN/DEVELOPMENT ENGINEERSFor communications network control systems based on C.A. mini and 8085mpus. C.£7,000. Beds.

Whatever your experience, please send your c.v. to:

Charles Airey AssociatesTempo House, 15 Falcon Road, Battersea

London SW11 2PJTel: 01-223 7662 or 228 6294

CAPITALAPPOINTMENTS LTD.

CAPITAL HOUSE29-30 WINDMILLSTREETLONDON W1 P 1 HGTEL: 01-637 5 551

THE UK's No. 1 ELECTRONICS AGENCYDesign, Development and Test to £14,000

Ask for Brian Cornwell

SALES to £15,000 plus carAsk for Maurice Wayne

FIELD SERVICE to £12,000 plus carAsk for Paul Wallis

We have vacancies in ALL AREAS of the U.K.

Ask for a Free Jobs List

Telephone: 01-637 5551 (3 lines) 1291i

DIGITAL EXPERIENCE?FIELD SUPPORT

R & D AND SALESVACANCIES IN COMPUTERS

NC, COMMS., MEDICALVIDEO, ETC.

For free registration ring0453 88326401-290 0267

L XELECTRONICS RECRUITMENT SERVICE

LOGEX HOUSE, BURLEIGH, STROUDGLOUCESTERSHIRE GL5 2PWTEL 0453 883264, 01-290 0267

13211

TELEVISIONSERVICE

ENGINEERWe are an expanding TelevisionRental and Retail company with avacancy for an additional Televi-sion Service Engineer.

Suitable applicant will pre-ferably hold an R.T.E.B. certificateor be training towards this qualifi-cation.

The post is directly responsibleto the Service Manager.

A clean driving licence is essen-tial.

A spacious flat is available if re-quired.Hydes of Chertsey Ltd., 56/60Guildford Street, Chertsey, Sur-rey. KT16 913E. Chertsey 63243.

114341

INNER LONDON EDUCATION AUTHORITYLEARNING RESOURCES BRANCH

Television Centre, Thackeray Road, SW8 3TB

The Television Centre produces a range of educational programmesdistributed in the form of videocassettes, sound cassettes and 16mmfilm. It has a colour studio equipped to professional broadcastingstandards (Link 110 cameras, Neve sound mixer, Ampex VPR2s, etc.)a mobile unit and a battery portable camera.

TELEVISION CAMERA OPERATOR (ST1 /2)SALARY RANGE £4,842 - £7,557 plus £1,104 London WeightingAllowanceA vacancy exists for a Television Camera Operator to work principallyin the studio but also to assist if required in a monochrome trainingstudio, in location video recording, and in the mobile unit. When notrequired to work with cameras, the operator would be expected to beattached to other technical sections so a general interest in the techni-cal side of television is highly desirable. Applicants should have hadsome formal training together with practical experience, though con-sideration will be given to those who lack the latter.

FILM SOUND RECORDIST (ST2)SALARY RANGE £6,663 - £7,557 plus £1,104 London WeightingAllowanceThe work is largely film recording using the Nagra, but with periods ofstudio duty (rigging, boom operation, tape and grams, etcl, and filmtransfer work. Working hours are based on a 35 -hour week, thoughovertime is often necessary, particularly where travel to locations isinvolved. Occasional overnight stops are required. Although applica-nts should have thorough knowledge of sound techniques in a filmtelevision environment, consideration will be given to those who arewilling to learn, have appropriate technical qualifications, and exper-ience elsewhere in the sound recording field.

MAINTENANCE ENGINEER (ST3)SALARY RANGE £7,857 - £8,514 plus £1,104 London WeightingAllowanceThe maintenance section has four members and is responsible for allthe equipment at the studio centre, both vision and sound. Applicantsmust have relevant technical qualifications (a knowledge of digitaltechniques would be an advantage), and should have good exper-ience in the field, though consideration would be given to experiencein allied fields. Limitied "on the job" training is available, and theAuthority will pay for attendance at specialised manufacturers'courses, where these are considered necessary.

Further information and application forms are available from theEducation Officer (EO/Estab 1B) Room 365, County Hall, London, SEl.Please enclose an SAE. Completed forms should be returned 14 daysfrom appearance of advertisement.

(1577)

uLtiaair mu nu v Ln 1 larduzin I JUse this Form for your Sales and Wants

PLEASE INSERT THE ADVERTISEMENT INDICATED ON FORM BELOW

To "Wireless World" Classified Advertisement Dept., Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS

Rate £2.50 PER LINE. Average six words per NAMEline. Minimum £12.50 (prepayable).

Name and address to be included in charge if ADDRESSused in advertisement.

Box No. Allow two words plus IT Cheques, etc., payable to "IPC BusinessPress Ltd." and cross "& Co."

REMITTANCE VALUE . ENCLOSED

PLEASE WRITE IN BLOCK LETTERS. CLASSIFICATION NUMBER OF INSERTIONS


ClassifiedSITUATIONS VACANT

IFYOUSEEK

a

DESIGNSOFTWARE

TESTPROJECT

FIELD SERVICESYSTEMS

APPLICATIONSSALES

Or

COMMISSIONING

APPOINTMENTto work with

MICROPROCESSORMEDICAL

INSTRUMENTHF/UHFNHFLOCAL AREANETWORK

SONARMICROWAVE

SATCOMMINI COMPUTER

PROCESS CONTROLMAINFRAMESIMULATION

IMAGE PROCESSINGDATACOMMS

VIDEOWEAPON SYSTEMS

AUDIOor AUTOMATIC TEST

EQUIPMENTand EARN

£7000420000then CONTACT

ELECTRONIC COMPUTER

MANAGEMENTAPPOINTMENTS148/150 High StreetBarkway, Royston

Herts076-384 676/7/8

(till 8pm most evenings)

R & D OPPORTUNITIES. Senior level vacan-cies for Communications Hardware and SoftwareEngineers, based in West Sussex. Competitivesalaries offered. Please ring David Bird at Redif-fusion Radio Systems on 01-874 7281. (1162

BOURNEMOUTH: an opportunity exists for aperson with a sales/management background.Write with c.v. to Box No. 1602.

ARTICLES FOR SALEPRINT SYSTEM for screen printing frontpanels, plastic boxes from easily prepared mas-ters. Ideal small electronics company or BASLSfor self-employment. Ready to use. Willing totrain operator. Photo available. J. Waller, LincolnHouse, Ampthill 0525 402279 evenings. £225 ornearest offer. (1574)

WIRRAL HEALTH AUTHORITYAREA WORKS DEPARTMENT

CHIEF ELECTRONICSTECHNICIAN(M.P.T.II GRADE)

Required to carry out servicing, repair andtesting of medical electronic equipment.The successful applicant will be required toorganise and execute a planned mainten-ance system for electro-medical equip-ment, and to assist in the development ofE.B.M.E. servicing units for hospitals withinWirral Health Authority.Applicants shall be qualified to H.N.C. orequivalent standard and shall have at leasttwo years' experience in the M.P.T.II Grade.Salary scale: E6668 - E8316 per annum.

SENIOR ELECTRONICSTECHNICIAN(m.e.T.111 GRADE)

Required to carry out servicing, repair andtesting of medical electronic equipment un-der the direction of a Chief ElectronicsTechnician.The successful applicant will be expected towork at various hospitals within WirralHealth Authority, and the possession of acar would be an advantage.Applicants should be qualified to O.N.C. orequivalent standard and have at least threeyears' experience in a similar position ofresponsibility.Salary scale: £5536 - £7155 per annum.These posts are the first two for what willbe a developing servicing department.Application forms and job descriptions ob-tainable from the Area Personnel Depart-ment Wirral Health Authority, St James'Hospital, Tollemache Road, Birkenhead,Merseyside. L43 7SF. Telephone: 051-6538133, extension 348.Closing date: May 7, 1982.

11584)

APPOINTMENTSIN

ELECTRONICSto £15,000MESSAGE SWITCH

DATA COMMS-TELEMETRY

TELEGRAPHY-RF COMMS

Interesting and varied op-portunities, U.K. and over-seas. For immediate actionon salary and careeradvancement, contact.

Technomark11, Westbourne Grove

London W2.01-229 9239 11296)

ARTICLES FOR SALEMARCONI Marine Atlanta receivers from £65,collected or carriage at cost. Other marine radioequipment in stock. Eddystone receivers andsome R/T. Marine loudspeakers re-entrant horn6in. mouth 9in long, 15ohm, new and boxed,£12.50 P.&P. Also outdoor hammer finish shal-low re-entrant type with bulkhead mount £6.50P.&P. 3-8ohm or line. Aerial amplifiers 40 to 860megs with output splitter, two models, i.e. bat-tery or a.c. mains, new condition, boxed £12.50P.&P. Ex -Navy brass parallel rules suitablepaperweights, etc, £15 P.&P. Thermographs £40P.&P. Plessey high voltage ceramic capacitors,50kv test 10 amps 0.0027 MFD. Low and p.bandWestminsters in stock, RIT equipment wanted.Low band 6 -channel and single -channel mid -bandCambridges £15 P.&P. Ex -Navy brass clocks withlarge outer second hand and small inner dials forhours and minutes £85 P.&P. Ex -Govt. watchesand Navy deck watches for callers. G.W.M.Radio Ltd., 40-42 Portland Road, Worthing, Sus-sex. Tel: 0903 34897. (1606)

EQUIPMENT FOR coils, transformers, compo-nents, degassing silicone rubber, resin, epoxy.Lost wax casting for brass, bronze, silver, etc.Impregnating coils, transformers, components.Vacuum equipment low cost, used and new. Alsofor CRT regunning metallising. Research & De-velopment. Barratts, Mayo P.z.ad, Croydon CR02QP. 01-684 9917. (9678

PRE -PACKED screws, nuts, washers, soldertags, studding. Send for price list. Al Sales(WW), PO Box 402, London SW6 6LU. (1253

ARTICLES FOR SALE

QUARTZ CRYSTALS HIGH STABILITY GOLD COLD WELD UNITS GUARANTEED 7 -DAY

SERVICE AVAILABLE ANY FREQUENCY

1MHz-70MHz

HYTHE (0703) 848961TELEX: 47506 - CRYSTL G

ELECTRODES

ALSO200KHZ-70MHZ

CLOCK CRYSTALOSCILLATORS TTL

COMPATIBLE DIP PACKAGE

McKNIGHT CRYSTAL CO. LTD.HARDLEY INDUSTRIAL ESTATE

HYTHE, SOUTHAMPTON SO4 6ZY(14071

TO MANUFACTURERS, WHOLESALERSBULK BUYERS, ETC.

LARGE QUANTITIES OF RADIO. TV ANDELECTRONIC COMPONENTS FOR DISPOSALSEMICONDUCTORS, all types, INTEGRATED CIRCUITS, TRANSISTORS,DIODES, RECTIFIERS, THYRISTORS, etc. RESISTORS, C/F, M/F, W/W, etcCAPACITORS, SILVER MICA, POLYSTYRENE, C280, C296, DISC CERA-

MICS, PLATE CERAMICS, etc.ELECTROLYTIC CONDENSERS, SPEAKERS, CONNECTING WIRE,CABLES, SCREENED WIRE, SCREWS, NUTS, CHOKES, TRANSFOR-

MERS, etc.ALL AT KNOCKOUT PRICES - Come and pay us a visit ALADDIN'S CAVE

TELEPHONE: 445 0749/445 2713BROADFIELDS & MAYCO DISPOSALS

21 Lodge Lane, North Finchley, London, N.12(5 minutes from Tally Ho Corner) 194511

CrystalACCURATE

RELIABLE4/

Private enquiries, send .13p in stamps for brochure

THE QUARTZ CRYSTAL CO. LTD.Q.C.C. WORKS, WELLINGTON CRESCENT

NEW MALDEN. SURREY 01-942 0334 Sr 2988

(84931

PRINTED CIRCUITS. Make your own simply,cheaply and quickly. Golden Fotolak Light Sensi-tive Laquer - now greatly improved and verymuch faster. Aerosol cans with full instructions,£2.25. Developer 35p. Ferric Chloride 55p. ClearAcetate sheet for master 14p. Copper -clad Fibre-glass Board approx. 1mm thick L1.75 sq. ft. Post/Packing 60p. White House Electronics, CastleDrive, Praa Sands, Penzance, Cornwall. (714

BRIDGES, Waveform/transistor analysers, Cali-brators. Standards, Millivoltmeters, Oscillo-scopes. Recorders. Signal Generators. 040-376236. (8250

"WORLD Radio TV Handbook" by return,£10.99. "Broadcasts to Europe", quarterly fre-quency guide, £4.50 yearly (sample copy £1.30).Access/Visa welcome. Pointsea, 25 Westgate,North Berwick, East Lothian. (1600)

WORKBENCHES, secondhand. Ex -ITT TVfactory. Open or cubicle style. Need space. De-tails: 042 486 3464.

(1608)

FARNELL transmitter test set TTS 520 RF sig-nal generator with 100 watt loading, rack mount-ing kit, extras, etc. New and unused, cost £6,000.Offers. Sharp M2 80K with printer, 4 floppy discsand interfaces. Also ancillary software. Offers.Newbury (0635) 48809 or 43228 (evenings).

(1611)

ATTENTION television tube rebuilders 2,000type CME:2CH3 ABI:120 monochrome TV tubessuitable for rebuilding. All m good strong cleancartons. Enquiries please to Teletronic (North-East Ltd) "See -Vu" works, Strangford Road,Seaham, Co. Durham. Phone (0783) 812142.

(15941

MAGAZINE BACK NUMBERS: WW, ETI,PW, PE, Elecktor, Everyday Elect., R & E Con-structor, Comp Age, Comp Today, PCW, PractComp, Television, Hobby Elect., etc. SendS.A.E. + 50p PO for list. Mr Gordon (Box No.1579). (1579)

PARAMETRON 477 Spectrum Analyser Freq. 200KHz-50MHz.. nisHEWLETT-PACKARD 3500 Attenuator DC-1MHz 600 Ohm

.noMARCONI 868B Universal Bridge 1% 1KHz & 10KHz CIOWAYNE KERR 8901/S261/R261 Admittance Bridge 50-250MHz nzaMARCONI TF.2424 VHF/UHF Freq. Meter 4 Digit DC-512MHzGAUMONT KALEE Flutter Meter..MARCONI TF.893 Power Meter. .115MARCONI TF.2600 Sens. Valve Voltmeter 10V.300V f.s.d.

1%.... .195WAVETEK 740 Phase meter 10Hz-2MHzTEKTRONIX 564 Storage Scope DC-I0MHz 3A6 &383 Plug -Ins ..ADVANCE 50.628 Signal Generator 150KHz-220MHzA.M. to 30% _ENADVANCE HIE Signal Generator 15Hz-50KHz Sine/Sq.0/P. _noADVANCE SG65A Oscillator 10Hz-100KHz Sine/Sq. 0/P,068 .196MARCONI TF.2950 Mobile Radio TestMARCONI TF.10668 AM/FM Signal Generator 106111,-470MHz.MARCONI TF.1101 R -C Oscillator 20Hz-200KHz .160PHILIPS PM.8455 Stereo Generator ..11MPROSSER 8100/8340 Wave Finn GeneratorTAYLOR SG.62A AM/FM Signal Generator ....................0136TEKTRONIX LO9 Pulse Generator ..........................From 11211KORTING 82515 Colour TV Service Generator .............12N

ULV 2518 Ultra Sonic Cleaner, 3 Compartments,Filtration, Cunt distillation... OFFERS OVER ErAOBPL CZ.457/4 Component Comparator and CZU 457/4 3Channel Automaton..........._....PDSFERROGRAPH RTS.2 Recorder Test Set 1225

Send SAE for hat to:

MARTIN ASSOCIATES'MURIA% BECKHAMPTON

NEAR MARLBOROUGH, Wills.TEL AVEBURY (117-23) 219 (1384)

OVENS, FURNACES, temperature recorders,XY co-ordinate table, be detectors, heavy dutycastors, oscilloscopes, VHF tuners CH21-68, cab-inets cardex, and cabinets 19 inch, test equip-ment, Tektronix 434 storage scope, £2,000, 567sampling scope with plug -ins and digital unit£250, 575 transistor curve tracer £160. 524 TVscope £100, TEK plug -ins 1A4 £60, 82 £45, CA£45 and also mainframe 500 series calibrators.Gestetner duplicator recently reconditioned bymakers 460S £400, Coutant 0-30 volt at 10 ampspower supply £80. Send S.A.E. for lists or phone"Q" services, 29 Lawford Crescent, Yateley,Camberley, Surrey. Tel. 871048 (0252). Ask forMr Q. (1570)

PRINTED CIRCUIT DESIGN, artwork,photography, prototypes, low volume production(non p.t.h.), screen printing, self -adhesives.Contact - G. N. Slee, 78 Derry Grove,Thurnscoe, Rotherham, South Yorkshire S63OTP. Tel: (0709) 895265. (1593)

TELETEXT (Ceefax/Oracle) or Viewdata (Pres-tel) add-on adaptors for your existing television ormicrocomputer. Discount prices. Mail order.Trade enquiries welcome. Avon Office Services,FREEPOST, Bristol BSIO 6BR. Tel: (0272)502008 any time. (1587)

118 WIRELESS WORLD MAY 198?

ARTICLES FOR SALE

ClassifiedSERVICES

IONISER KIT OPERATED)

This negative ion generator gives you the power to saturate your home or officewith millions of refreshing ions. Without fans or moving parts it puts out apleasant breeze. A pure flow of ions pours out like water from a fountain, fillingyour room. The result? Your air feels fresh, pure, crisp and wonderfully refresh-ing.All parts, PCB and full instructionsA suitable case includng front panel, neon switch, etHOURS:Monday to Friday 9 am -5 pm.Saturday 9 am -4.30 pm.

Wide range of Japanese integrated circuits and transistors stockedT. POWELL

Advance Works, P.E., 44 Wallace Road, London NI 1PQTel. 01-226 1489 Please allow 14 days for delivery

£12.50c. £6.50

Price includes post & VATBarclay/Access Welcome

RACAL COMMUNICATIONSRECEIVERS

500 Kc/s - 3OMc/s 1Mhz wide. RA17L - £175.RA117E - £225. A few sets available as new at£75 extra. All receivers are air tested and cali-brated in our workshop, supplied with fullmanual, dust cover, in fair used condition. Newblack metal louvred cases for above sets £25each. RASED - ISB - SSB - £75. RA218 -SSB - ISB and fine tune for RA117 - £50,TRANSMITTER DRIVE UNIT RA79. 1.5mc/s -30mc/s SSB ISB DSB FSM CW£150. AERIAL TUNING UNIT and protection unitMA197E1 - £25 to £50. DECADE FREQUENCYGENERATOR MA35013 Solid state synthesiserfor IAA79 or RA117 - RA217 - RA1217 - f150to £200. MA250 - 1.6mc/s to 31.6mc/s - £150Mewl. MA2596 - precision frequency stan-dard - 5mc/s Imc/s 100khz - £100 to £250.RACAL MA152 - Standing wave ratio indica-tor. FX2mc/s - 25mc/s Power up to 1000wans- 50 ohms - Auto trip switch - Transistormains 100 - 250AC, new and boxed - £40.RACAL COUNTER 836 (9036) 32mc/s TTI circuitdesign - tested with manual - £50 to E75.OSCILLOSCOPES COSSOR COU150 - 35mc/s -Twin Beam - Solid State - £175 with manual.TEXTRONIC OSCILLOSCOPE 647 and 647A SolidState - 50mc/s and 100mc/s bandwidth - £250and £350. Tested, circuit and instructions.AERIAL MASTS - we have three masts ap-prox. 130ft high, complete with all fittings. Base- insulators, etc., Mast steel tube 8" all partsgalvanised, supplied brand new, all itemsboxed - £1000 - or each complete mast -£400.

All items are bought direct from H.M. Govern-ment, being surplus equipment. Price is en -works. SAE for all enquiries. Phone for appoint-ment for demonstration of any item. John'sRadio, Whitehall Works, 84 Whitehall RoadEast, Birkenshaw, Bradford BD11 2ER. Tel.(02741684007. V.A.T. and Carriage extra.

INVERTERSHigh quality DC -AC. Also "nobreak" (2ms) static switch,19" rack. Auto Charger.

COMPUTER POWER SYSTEMS

Interport Mains -Store Ltd.POB 51. London W11 38ZTel: 01-727 7042 or 0225 310916

(9101

THE SCIENTIFICWIRE COMPANY

SWG

8 to 29Otto 3435 la 4041 lo 4341

48 to 49

P.o. Box 30, London, E.4

ENAMELLED COPPER WIRE

Ilb 8oz. 4oz.

2.76 1.50 .803.20 1.80 .903.40 2.00 1.104.75 2.60 2.008.37 5.32 3.19

15.96 9.58 6.38

2oz

60.70.80

1.422.503.69

SILVER PLATED COPPER WIRE14 to 30 6.50 3.75 2.20 1.40

TINNED COPPER WIRE

14 to 30 3.38 2.36 1.34Press include P&P. VAT and Wire DataSAE for list. Dealer enquiries welcome.Reg Othce: 22 Coningsby Gardens.

.90

.19063)

ARTICLES WANTED

WANTEDSurplus Stock and Offers

All kinds of Electronic Components, Kits and finished products.We are a leading electronics mail order house in Germany. Pleasecontact us at:130hler-Elektronik, PO Box 32D-75 70 Baden-BadenTelephone 7221/3486 Telex 781210 belekd.

11582)

WANTED!

Receiving Valves, Antiquetypes but unused and boxed.

VAN DATA SYSTEM CO., LTD.1-12-8, Kyomachibori, Nishi-ku Osaka 550, JAPAN.

(1487)

WANTED: Electronic components and equip-ment in quantity. Competitive prices paid. Speed,courtesy and cash on collection. Linway Electron-ics, 843 Uxbridge Road, Hayes End, Middx. UB48HZ. Tel: 01-573 3677. (1558)

WANTEDTest equipment, receivers, valves, transmit-ters. components, cable and electronicscrap, any quantity. Prompt service andcash. Member of A I3 Ft A

M & B RADIO86 Bishopsgate Street

Leeds LS1 4B60532-35649

CIRCOLECTHE COMPLETE ELECTRONIC SERVICE

Artwork, Circuit Design, PCB Assembly, Test & Repair Service, Q.A. Consultancy,Prototypes, Final Assembly.Quality workmanship by professionals at economic prices.Please telephone 01-767 1233 for advice or further details.

1 FRANCISCAN ROADTOOTING, LONDON SW17

113911

FACILITIES AVAILABLE*Circuit Design & DevelopmentDigital and Analogue* Artwork LayoutFree prototype bd. (non PTHISupplied with orders over E100.* Board ManufacturePrototype to semi -production.*Wiring & AssemblyPCB assembly, wiring and cable forming.* TestFull test facilities available.* Copper Clad BoardD/S fibreglass 1000 Sq inches of assorteduseful sizes. E6.00 inc. post.

One or all services avail.able, no order too small.Please telephone Chelms-ford 357935 or write toH.C.K. 1 Bankside, off NewStreet, Chelmsford, Essex.

(1169)

° Dayville Servicesty Limited

A complete P.C.B. service offered. Wewill work from your circuit diagram andproduce the finished board.Any type of board manufactured includ-ing double -sided and P.T.H. Legend andsolder resist available if required.Our rates are very competitive and weoffer 4 FREE collection and delivery ser-vice on orders above £200. Turnaroundcan be as little as three days.Telephone Colchester (0206)71000/869514 with your P.C.B. require-ments and we will be happy to oblige.40 Military Road, Colchester CO1 2AN.

114901

30,000 SERVICE SHEETS IN STOCKCOLOUR MANUALS ALSO AVAILABLE

TV Monos £2, Transistor Radios £2,Tuners £2, Tape Recorders, RecordPlayers and Stereograms £2. Stampedaddressed envelopes with all quota-tions. Also colours available. Car Radios£3 + stamped addressed envelope. Allvalve radios £2. Stamped addressed en-velope please. Quote advert. no. withorder. C. CARANNA

71 Beaufort Park, London NW11 6BX01-458 4882 (Mail Order) 113251

DESIGN SERVICES. Electronic design de-velopment and production service available fordigital and analogue instruments. RF Transmit -ten and receivers, telemetery and controlsystems. 20 years' experience. R.C.S. Electronics,Wolsey Road, Ashford, Middlesex. Phone MrFalkner 53661. (8341

DESIGN AND DEVELOPMENT. ANAL-OGUE, DIGITAL, RF AND MICROWAVECIRCUIT AND SYSTEM DESIGN. Also PCBdesign, mechanical design and prototype/smallbatch production. - Adenmore Limited, Unit103 Liscombe, Bracknell, Berks. Tel: Bracknell52023. (656

Design Engineers

DIGI-TELELECTRONICS

Video character & imagegeneration systems

Microprocessor -controlledvideo systems

Prototype & small batchproduction capacity

20 Trenches Road,Crowborough, Sussex.Tel. (089 26 ) 5069

Buyers and DisposalOfficers(please note)

COOKE INTERNATIONAL SERVICES areWholesalers and Factors of Surplus TestEquipment and Components. Buying or

selling contact:

COOKE INTERNATIONALSERVICESRamalla House

Ancton Lane, Middleton -on -SeaBognor Regis, Sussex P022 6NJ

Telephone: 024-369 2849

BOARDRAVEN LTD.

PRINTED CIRCUIT BOARDS

Manufactured to your specifications. Single/double sided. Very speedy deliveries on prototypesand quantity. Master layouts if required.Contact:J. K. Harrison, Carnaby Industrial Estate, Brid-lington, North Humberside V015 30Y. Tel.(0262178788.

(1168)

SMALL BATCH PCBs produced from your art-work. Also DIALS, PANELS, LABELS. Cam-era work undertaken. FAST TURN-AROUND. - Details: Winston Promotions, 3Hatton Place, London ECIN 9RV. Tel: 01-4054127/0960. (9794

SHEET METAL WORK, fine or general frontpanels chassis, covers, boxes, prototypes, 1 off orbatch work, fast turnround. - 01-449 2695. M.Gear Ltd., 179A Victoria Road, New Barnet,Herts. (812

PRINTED CIRCUIT MANUFACTURE. Veryfast, reliable service. Lowest prices. Prototypeswelcome. Inhouse photography. Phen 0674-573for instant quote or write to AKTRONICS Ltd.,42/44 Ford Street, Moretonhampstead, Devon.

CAPACITY AVAILABLE

ELECTRONIC DESIGN SERVICE. Immedi-ate capacity available for circuit design and de-velopment work, PC artwork, etc. Small batchand prototype production welcome. - E.P.D.S.Ltd., I A Eva Road, Gillingham, Kent. Tel: Med-way (0634)577854. (9667

BATCH PRODUCTION wiring and assemblyto sample or drawings. Mclleane Electricals Ltd,19b Station Parade, Ealing Common, LondonW5. Tel: 01-992 8976. (169

PHONE YOURCLASSIFIEDS TO

IAN FAUXON 01-661 3033

NV ELECTRONICS LTD.THE PCB ASSEMBLERS

More and more companies are investi-gating the advantages of using a profes-sional subcontractor. Such an undertak-ing requires certain assurances.TW are able to satisfy all of them -quality, competitive pricing, firm de-livery, and close co-operation with thecustomer.Assembled boards are 100% inspectedbefore flow soldering and reinspectedafter automatic cropping and cleaning.Every batch of completed boards isissued with a signed certificate ofconformity and quality - our finalassurance.

For further details, contact us at our newworks:

Blenheim Industrial ParkBury St. EdmundsSuffolk IP33 3UTTel: 0284 3931 (1466)


CROTECH OSCILLOSCOPES NATIONWIDE AVAILABILITY LOCAL TO YOU.

(1)141))

KENTWOODELECTRONICSReadingTel: 0734 698040

NORTHERNINSTRUMENTSLeedsTel: 0532 791054

MA RSHIONELECTRONICSI pswichTel: 0473 75476

AUDIOELECTRONICSLondon W2Tel: 01-724 3565

CARSTONELECTRONICSLondon NW1Tel: 01-267 5311

GLEVUMINSTRUMENTSGloucesterTel: 0452 31620

RT & IELECTRONICSLondon El 1Tel: 01-539 4986

BURDONINSTRUMENTSStoke-on-TrentTel: 0782 616631

DARWENELECTRONICSDarwen, Lancs.Tel: 0254 711497

PI LLondon SE15Tel: 01-639 4461

Crotech insturriEnis limited 5 Nimrod Way Elgar Road Reading Berkshire RG2 OEBTelephone: (0734) 866945 Telex: 847073 POWLIN G


INDEX TO ADVERTISERS MAYAppointments Vacant Advertisements appear on pages 108-119

PAGE PAGE

Acoustical Mfg. Co. Ltd. 55 Faircrest EngineeringAdcola Products Ltd. 5 Farrell Instruments Ltd. cover ii, 27, Reader Card

24 Flight Link Control Ltd 968 Fylde Electronic Laboratories Ltd 227

Antex (Electronics) Ltd cover iiiAspen Electronics Ltd 6 Galatrek International Ltd 14

Audio Electronics 23 GAS Electronics 93Avalon Electronics 106 Global Specialities Corp. (UK) Ltd 15

Avel Lindberg (Cotswold) 103 GP Industrial Electronics Ltd 56Greenwich Instruments 96Griftronic Emission Ltd 12

Ambit InternationalAnalogue AssociatesAnglia Components

Bamber, B. Electronics 103107 Hall Electric Ltd. 26

17 Happy Memories 8894 Harris Electronics (London) 7

Harrison Brothers Electronic Distributors 86Hart Electronic Kits Ltd 16Henry's Radio 8, 84, 92House of Instruments 102

Barrie Electronics Ltd.Black Star Ltd.

Broadfield & Mayco Disposals

Cambridge Kits 90Cambridge Learning 100Carston Electronics Ltd. 20, 21Chiltern Electronics 98Chiltmead Ltd 84CIL Microsystems Ltd. 6Circuit Services 14Clark Masts Ltd 9Clef Products (Electronics) Ltd 18

Colomor Electronics Ltd. 98Computing Today 18

Crotech Instruments Ltd. 120CT Electronics (Acton) Ltd. 89

Danavox (Gt Britain) Ltd. 2Darom Supplies 88Dataman Designs 107Display Electronics 95DSN Marketing Ltd. 99

Electronic Brokers Ltd. 3, 5, 7, 9Electrovalue Ltd. 25Electroversal Ltd. 102Essex Electronics 96

ILP Electronics Ltd 19, 22Interface Quartz Devices Ltd. 4Intergrex Ltd. 24Irvine Business Systems Ltd. 27

Kelsey Acoustics Ltd. 12KEF Electronics Ltd 25, 27

Langrex Supplies 85Level Ltd 94LFH Associates Ltd 98Lightning Electronic Components 94Lion Viewdata 86

Melkuist Ltd 102Memotech 13Micro Times 106Midwich Computer Co. Ltd 17Millward, G. F., Electronic Components Ltd 92Modem Book Co., The 16Monolith Electronics Co. Ltd., The 18

Northern Electronics 8

PAGE

16 Olson Electronics Ltd. 4Olympic Transformers Ltd 14Orion Scientific Products Ltd 92

Papst Motors 106PM Components 90, 91Powertran Cybernetics 104P. & R. Computershop 104

Radio Components Specialities 87Ralfe, P. F., Electronics 104Reprints 94Rheinbergs Sciences Ltd 106RST Valves 85

Safgan Electronics 17Sagin, M. R. 107Sandwell Plant Ltd. 107Scopex Instruments 97Service Trading Co. 99Sescom Inc. 104Shure Electronics Ltd. 28Sinclair Research Ltd. 10, 11South Midlands Communication Ltd. 8Sowter, E. A., Ltd. 6Special Products (Distributors) Ltd. 22S. & R. Amplification 103Structured Software 102Supersem 84Surrey Electronics 98

Technomatic Ltd. 100, 101Tektronix UK Ltd. cover ivTelemet (Alpha Bridge) Ltd 25Teleradio Electronics 90Television Magazine 88Telonic - Berkeley UK 90Tempus 83Thurlby Electronics 18Time Electronics Ltd. 12, 106

Valradio Ltd. 94Videotex '82 86

West Hyde Development 12

Wilmslow Audio 4Wireless World Circards 105

OVERSEAS ADVERTISEMENTAGENTS:France & Belgium: Norbert Heflin, 50 Rue de CheminVeat, F-9100, Boulogne, Paris.

Hungary: Mrs Edit, Bajusz, Hungexpo AdvertisingAgency, Budapest XIV, Varosliget.Telephone: 225 008 - Telex: Budapest 22-4525INTFOIRE

Italy: Sig C. Epis, Etas-Kompass, S.p.a. - Servizio Estero,Via Mantegna 6, 20154 Milan.Telephone: 347051 - Telex: 37342 Kompass.

Japan: Mr. Inatsuki. Trade Media - IBPA (Japan), B.212.Azabu Heights, 1-5-10 Roppongi, Minato-ku, Tokyo 106.Telephone: (031 585 0581.

United States of America: Ray Barnes, IPC BusinessPress, 205 East 42nd Street, New York. NY 10017 - Tele-phone: (212) 867-2080. Telex: 238327.Mr Jack Farley Jnr., The Farley Co., Suite 1584, 35 EastWalker Drive, Chicago, Illinois 60601 - Telephone: (312163074.Mr Victor A. Jauch, Elmatex International, P.O. Box 34607,Los Angeles, Calif. 90034, USA - Telephone 1213) 821-8581 - Telex: 18-1059.

Mr Jack Mentel, The Farley Co., Suite 650, Ranna Build-ing, Cleveland, Ohio 4415 - Telephone: 12161621 1919.Mr Ray Rickles, Ray Rickles & Co., P.O. Box 2028, MiamiBeach, Florida 33140 - Telephone (305) 532 7301.Mr Tim Parks, Ray Rickles & Co., 3116 Maple Drive N.E.,Atlanta, Georgia 30305. Telephone: 14041 237 7432.Mike Loughlin, IPC Business Press, 15055, Memorial Ste119, Houston, Texas 77079 - Telephone 1713) 783 8673.

Canada: Mr Colin H. MacCulloch, International Advertis-ing Consultants Ltd., 915 Carlton Tower, 2 Carlton Street,Toronto 2 - Telephone (416) 364 2269.* Also subscription agents.

Printed in Great Britain by QB Ltd., Sheepen Place, Colchester, and Published by the Proprietors IPC ELECTRICAL -ELECTRONIC PRESS LTD., Quadrant House, The Quadrant, Sutton, SurreySM2 5AS, telephone 01-661 3500. Wireless World can be obtained abroad from the following: AUSTRALIA and NEW ZEALAND: Gordon & Gotch Ltd. INDIA: A. H. Wheeler & Co, CANADA:The Wm. Dawson Subscription Service Ltd, Gordon & Gotch Ltd. SOUTH AFRICA: Central News Agency Ltd: William Dawson & Sons (S.A.) Ltd. UNITED STATES: Eastern NewsDistribution Inc., 14th floor, 1 1 1 Eighth Avenue, New York, N.Y. 10011.

120WIRELESS WORLD MAY 1982

Wireless World, May 1982

p ug irifor Fingertip C ol!

A,7

\\4Vtake the heat out of a delicate situation.

Ready to use Antex new model XS -BP soldering iron comes with afitted plug, ready to switch on.

The new handle in extra -tough material features a detachablefinger -guide for precise control in operation and a hexagonalmoulding to prevent the iron rolling on the work bench.

We have retained our well -proven heating element. Efficiency ofheat transfer and ease of fitting slide -on, slide -off bits make this theprofessional's choice of soldering instrument. The iron is alsoavailable for 115, 50, 24 or 1 2 volt.

* fitted with the NEW safety plug.

sendnowt ANTEX (ELECTRONICS) LIMITED00110

RSP Model XS-BP (25 Watts £5.30 + VAT)Model CS-BP (17 Watts £5.30 + VAT)

MAYFLOWER HOUSE, ARMADA WAY, PLYMOUTH, DEVON TELEPHONE 0752 667377 TELEX 45296

Please send the ANTEX New Range full colour brochure to: NAME

ADDRESS _ WW5WW -002 FOR FURTHER DETAILS

C3

Wireless World, May 1982

TEK MULTI -PURPOSEOSCILLOSCOPES

SO ADVANCEDTHEY COST YOU LESS

The Tektronix 2200 Series.Simply great.

Tektronix traditions of excellence indesigning and manufacturing oscillo-scopes are recognised all over theworld. But rather than rest on pastlaurels, we have veered dramaticallyfrom the well established design pathswe ourselves have laid down.

With the 2213 priced at £670* and the2215 at £850*, these 60 MHz dualtrace oscilloscopes are an entirelynew form of instrument.

Their most remarkable characteristicis the way in which major designadvances have provided full -rangecapabilities at prices significantlybelow what you would expect to pay.How has this been accomplished? Tobegin with, we have reduced thenumber of mechanical parts by morethan half. This not only saves manu-facturing time, it lowers costs andimproves reliability.

Ttkt ronix 2215

Board construction has been greatlysimplified and the number of boardsreduced. Board connectors have alsobeen reduced substantially andcabling cut by an amazing 90%.

The p213 and 2215 have a high effi-ciency regulated power supply whichdoes away with the need for a heavypower transformer. There are no line -voltage adjustments. Just plug theinstrument into a power socket supply-ing anything from 90 to 250 volts,48-62 HZ, switch on and you areready to measure. Power savingcircuitry has eliminated the coolingfan, resulting in further economies insize and weight.

These scopes have it all. Dual trace.Delayed sweep for fast, accuratetiming measurements. Single timebase in the 2213, dual time bases inthe 2215. An advanced triggering

system, automatic focus and intensity.Beam finder - and much more.

Interested? Then why not telephoneyour nearest Tektronix office or circlethe enquiry number for furtherinformation.

Performance SpecificationsBandwidthTwo channels, DC -60 MHz to 20mV/div, 50 MHz to 2 mV/div.Light Weight611 kg (131/2 Ibs). 6.8 kg (15,0 Ibs) withcover and pouch.Sweep SpeedsSweeps from 0,5s to 0.05 Lis (to 5ns/div with x10 magnification).SensitivityScale factors from 100 V/div (10xprobe) to 2 mV/div (1 x probe).Accurate to ± 3%. AC or DC coupling.

Also available from Electroplan. Prices subject to change without notice.

Tektronix UK LimitedPO Box 69, Harpenden, Herts. AL5 4UPTel: Harpenden 63141 Telex: 25559

Regional Telephone Numbers: Maidenhead0628 73211, Manchester 061 428 0799,Livingston 32766, Dublin 850685/850796

PT 206

ThIctronbcoCOMMITTED TO EXCELLENCE


Documents

worldradiohistory.com · Test solid state devices in, or out of, circuit Fast location of shorted, open and leaky components Test diodes, transistors, LEDs, electrolytics, FETs, MOS