Rockwell V2 RX Page 1

Walford Electronics Ltd. Upton Bridge Farm, Long Sutton

Langport, Somerset TA10 9PZ Tel 01458 241224

E mail electronics@walfords.net Designers & suppliers of kits for radio enthusiasts

Proprietor Tim Walford BSc MIET CEng G3PCJ

The Rockwell V2 RX

Introduction

This is a simple project that is suitable for people new to building electronic projects that can

also be used as an introduction to amateur radio – most probably in a Radio Club. Its has two bands –

usually it would be built initially for the Medium Wave (MW) broadcast band first where there are

strong broadcast stations that are easy to hear. These use the Amplitude Modulation (AM) technique

for which the Regen TRF RX is excellent. Later the parts can be added for listening with general

coverage to short wave broadcast stations that also use AM; and then adapted for amateur Morse or

possibly voice transmissions, on either of their 40 or 80m bands. The amateur 160m band is also good

for demonstrating amateur radio techniques with across playing field type contacts. The kit uses just

four transistors without any integrated circuits so it is easy to follow how it works! The kit includes all

parts to build the receiver but you will also need a pair of modern stereo 32 Ohm headphones and a

PP3 9 volt battery. You will need a small 18 or 20 Watt soldering iron with flux cored solder - 60:40

tin:lead solder is easier to use than lead free types but is not always easy to obtain! Do NOT use

plumbers solder! For other tools you will need a small screwdriver, wire cutters and general purpose

multi-meter. A length of wire is included for an initial ‘throw-out’ aerial!

It has its own holder for a 9 volt PP3 battery (not supplied) but can also be used with an

external DC supply, typically that might be the nominal 12 v supply of any associated transmitter.

Please read right through these instructions before starting on its assembly.

Brief Explanation

The block diagram is shown in Fig. 1 below. Very weak signals from the aerial enter the

receiver and are first amplified by the un-tuned radio frequency (RF) amplifier; the next stage (tuning)

decides which signal you will actually listen to. The Regen stage is associated with the tuning and

improves the selectivity when it is near the point of oscillation. The detector stage recovers the audio

signal from the incoming RF signal. The very weak audio is then passed to the audio amplifier which

makes them strong enough to drive your phones. Four transistors are used. The full circuit is given in

Fig. 2. The technical description is in Appendix 1.

Fig. 1 - Block Diagram of the Rockwell V2

RF

amplifier

Detector Audio

Amp

Phones

Aerial

Tuning

Regen

Rockwell V2 RX Page 2

General Construction Advice – Single sided PCBs Not all of the points below maybe applicable to your particular kit but in general you should

sort the parts into different types and check against the parts list to make sure all are present and can

be identified. Resistors use a standard 4 band colour code where the first three indicate the value as

two decimal places followed by a decimal multiplier - details can be looked up on the web; this code

is also used for some inductors that look like wire ended beads – so take care to sort them apart! If

necessary, use a magnifying glass to read the value of small parts or, if possible, measure them. The

number printed on small capacitors (two decimals plus decimal multiplier like resistors) is the value in

picoFarads. Comparing the actual number of each size with the parts list can also help. The smaller

the capacitance value, the smaller will be the physical size - examine them very carefully because

small changes in size will help identify them. If there is any doubt about the value of parts (their

markings are included in the tables when first encountered), check their value with a meter. When

resistors are mounted on end, put them into the board as shown in the layout diagram since the top

end maybe used as a test point. There are also pads for additional test points into which you can solder

10mm off cuts of stiff wire or Vero-pins.

The PCB is etched only on one side, so that all connections – including the 0 volt line – are

etched as copper tracks on the underside of the board. The PCB has been lacquered to resist oxidation;

the lacquer is specially designed to be soldered through so do not attempt to remove it! Only insert

parts with the power off. Follow the layout diagram very carefully and it is a good habit to compare

the circuit with the track pattern as you insert parts so as to check for correct part location and to help

understanding of the circuit. If you have difficulty finding a particular part on the layout diagram, use

the circuit to identify its ‘role’ and hence to find its general position on the PCB. As you insert parts,

tick them off in the tables.

If you have only limited soldering experience, I suggest practice on some scrap printed circuit

board material first. Soldered joints should be smooth, bright and have concave curvature between

component lead and copper track. Grey or pitted blobs are no good! Modern parts can withstand

extended soldering iron heat so the danger comes from simultaneous excessive heat and mechanical

disturbance, which can lift the tracks. When remaking a poor joint, always use a little more solder so

there is fresh flux to help the job! When satisfied with the joint, clip off any excess lead wire with

your wire cutters.

Fit the parts in the order suggested in each construction stage. Earth/0 volt tracks are usually

slightly wider and sometimes shown with ‘hairs’ similar to those of a chassis symbol. Use an 18 Watt

iron with 60:40 tin/lead resin cored solder if you can obtain it. Modern lead free solder needs a

slightly higher temperature. Some transistors and integrated circuits are static sensitive, so it is

desirable to use a proprietary personal earthing strap - especially if your shack is dry and has a

synthetic carpet! Keep the semiconductors in the anti-static conducting bag until needed. Make sure

your iron is ‘mains earthed’ and, if using a mains PSU, connecting its 0 volt terminal to mains earth

through a 1M resistor is sensible. The layout diagram shows the position of individual parts as viewed

from on top of the component side; the transistors are drawn as though you could see all of their leads

to help get their orientation correct, in reality part of their leads will be obscured by the transistor's

body. Take particular care with the orientation of transistors, integrated circuits and electrolytic

capacitors that can easily be put in the wrong way round. Transistors may need their central lead

(referred to as CL in the building tables) to be bent forwards or backwards from their flat face -

possibly in the opposite way to that already done by the manufacturer. All parts should be on the top

or plain (no copper) side of the PCB. Load the PCB in the order suggested and do test each stage as

you go. This is important! If a test is ‘failed’ do not proceed further as you may compound whatever

is causing the difficulty – investigate and cure it before going on! This general approach much

increases the chances of it working properly right from the start! Do not build the whole thing and

hope it will work! Spares for all parts are normally available from Walford Electronics. For those

needing a bit of extra help, if you let me know, I can usually supply any photo in a kit’s instructions

by e mail.

Rockwell V2 RX Page 3

Assembling the RX

You start assembling the Rockwell as a plain Tuned Radio Frequency (TRF) receiver, so it is

ideal for hearing the powerful broadcasting stations of the Medium Wave (MW) band. Later you can

add the parts for amateur band reception and even those associated with a transmitter. The parts layout

is shown in Fig. 2 and Photo 1 later is of a completed Rockwell V2. Because the PCB may not be

marked or screen printed with individual part numbers, you will need to locate the correct holes and

check the track pattern carefully as you progress. When inserting parts, consider the role of that part in

the circuit and hence what it should be connected to on the PCB – if in any doubt, cross check the

track connections with the circuit. Tick each part off in the lists as you insert them, in the last box of

each line.

Stage 1. Start with the parts that it should only be possible to fit in one location; also see the notes

after the table below:-

PP3 holder with wire strap LK 1 – see below Two screw antenna connector – lead holes facing to right 3. stereo phones socket – see below Four rubber feet underside in corners – see below Wire link earth LK2 between PP3 holder and antenna terminals R2 RFG preset 1K + short 6 mm shaft + knob R6 Regen preset 1K + short 6 mm shaft + knob C4 PolyVaricon capacitor with strap – see below

The PP3 battery holder is secured in place by its terminals and a wire strap LK1 placed tightly

around its other end. This anchor wire should be cut to roughly the correct length; the insulation

stripped off all of it, and then inserted into the two holes just outside the end of the PP3 holder. Solder

one end first, and then form to roughly the correct shape and pull the wire tight around the end of the

holder before soldering the free end of this wire – Photo 2. Push the wire tight against the holder so

that it does not get in the way of the battery!

The phones socket is mounted without any connection to the central sleeve contact of the

socket – make certain this does not accidentally connect to the earth track that runs down the side of

the PCB! (If you later decide to mount the Rockwell in a metal box, the sleeve contact MUST be

isolated from the metalwork otherwise you will short the supply and or damage your phones!)

The rubber feet, at all four corners, need to be placed carefully right in the corners so that they

do not rest on top of, or cover up, other soldered joints in that corner, otherwise they might not stick

so well! If necessary, carefully trim off any excess beyond the edge of the PCB with a sharp knife.

The extra wire earth link LK2 is adjacent to the terminal end of the PP3 holder and has arrows

heads on the PCB (Is 4 PCB onwards). Check that you are not shorting out the supply! See Photo 4.

The preset R2 acts as an RF gain control potentiometer (or ‘pot’) with small plastic shaft

pushed into the preset’s slots. The 6 mm knob is fitted for 8 and 4 ‘o’clock’ limits and finally pushed

quite hard onto the shaft. The Regen preset R6 & knob are similar but turned around on the PCB.

Before fitting the PolyVaricon C4, adjust both the trimmers on its rear face for least

capacitance, or least overlap of the two sets of trimmer plates. It is mounted on its back, with its

central earth lead through the PCB and soldered directly to the earth tracks between points G and H.

The PolyVaricon body is secured to the PCB by a another strap of stripped wire pulled tight across its

body – as before secure one end, bend to approximate shape, and then tighten and solder the free end -

see Photo 3. If necessary, put a small kink in it to make the wire tight. Carefully adjust the shaft fully

anti-clockwise and then push the knob on with its pointer showing just above 9 o’clock. You may

have to push it quite hard for it to stay there! If it goes on too far and rubs on the body, ease it back up

the shaft a little with a screwdriver. Now insert another single strand stiff bare wire link LK3, formed

into a hoop, between points H and J (left arrow Photo 5). The left hand 65 pF lead of the PolyVaricon

adjacent to point H should be soldered initially to this hoop for maximum effect from C4 alterations –

but you may decide to change it later like right hand arrow of Photo 5! The other right hand lead of

the PolyVaricon (for its 150 pF section) should be soldered to a separate short lead installed into the

pad marked as point G. Make certain these two nearby wires do not touch each other! See photo 3.

Rockwell V2 RX Page 4

Stage 2. Next install the audio output stage:-

C12 100 /uF 25v electro ? Polarity R12 330R – OR,OR,BN,GLD R11 330R R10 100K – BN,BK,YL,GLD TR4 BS170 - CL Back ? Orientation Solder two short test lead wire off cuts (10 mm long) in the points labelled L and M. It is

worth checking that your phones are actually 32 Ohm for each earpiece – first check they are switched

to stereo if they have a switch and then measure the resistance with your multi-meter from the tip

contact to the sleeve of their plug, and then from the ring to sleeve for the second earpiece. This

should make them show about 64 Ohms between tip and ring contacts. If they are wrong low

impedance sort, typically 8R, then all signals will be much weaker. Do not use the old style high

impedance phones either! Then plug in your phones which must be switched to stereo if they have a

switch. Next insert your 9v PP3 battery. Measure the voltage on point M with respect to 0 volts/E – it

should be about 7 volts with a 9 volt battery. Temporally grounding point L (with a lead to the E

terminal), should make the voltage on point M should go to 0 volts, and is likely to cause loud clicks

in the phones! Remember to remove the battery before doing any more soldering.

Stage 3. Fit the audio amplifier first stage:-

C11 470 pF disc - 471 R8 100K C10 150 pF ceramic plate – 151 Small yellowish rectangular caps! D3 1N4148 ? Orientation – black band to left C8 150 pF disc D2 1N4148 ? Orientation – black band to left R9 2K2 - RD,RD,RD,GLD To right side of PolyVaricon C2 100 /uF 25v electro ? Polarity TR3 BS170 – CL Back ? Orientation Solder another short off cut test lead (10 mm) into the point labelled F. When you now insert

the battery with the phones plugged in, the voltage on point M should now be about 3 volts when

point L is NOT grounded. You may hear it click in the phones as you switch on. You can now do the

‘screwdriver finger hum’ test! Put your finger on the shaft of a metallic screwdriver and gingerly

apply it to point F, when there should be some sort of click or hum as your body picks up the 50 Hz

signal from any adjacent mains wiring. There might even be audio from some un-tuneable powerful

broadcast station but it is likely to be faint! Remove the battery.

Stage 4. Fit the tuning parts – see notes below:-

C3 100 /uF 25v electro ? Polarity – by the antenna terminal block C6 150 pF disc C5B 150 pF disc S1 Slide switch Carefully bend the tabs down to prevent

them fouling the PP3 holder.

L1 & L2 100 /uH – beads marked like resistors with bands coloured

BN,BK,BN,SLV for 101 – see below

L1 and L2 are connected in series in the slanted position for the initial Medium Wave

broadcast band. Set the slide switch S1 towards the front for the LF band.

You may be able to receive your first proper signals now (with phones and battery installed),

by temporally connecting your aerial wire (draped around room) to the junction of L1 and L2. The

signals should be tuneable but are likely to be a bit weak. If there are not any signals, apart from a

faint hiss, it does not necessarily mean there is something wrong – just check the part locations and

proceed to the next stage after removing the battery etc. Remove the aerial lead.

Rockwell V2 RX Page 5

Stage 5. Fit the RF amp stage:-

R1 100K C1 470 pF disc – 471 TR1 BS170 - CL Fwd ? Orientation Fit a short test wire (10 mm) in point B. Change the aerial connection to the A terminal of the

two screw connector. Set the RF gain preset R2 to about halfway and plug in phones and battery. The

voltage on point B should be about 0.5 volts with respect to ground/0 volts. Now the signals should be

somewhat louder and the tuning a bit sharper! You may well find that you need to decrease the RFG

R2 to avoid distortion and overloading of the output stage, especially at night.

Stage 6. Next add the parts to make it regenerative:- R7 2K2 R5 330R C9 100 /uF 25v electro ? Polarity R3A 100K D1 1N4148 – black band towards front ?Orientation R4 1K – BN,BK,RD,GLD C7 150 pF disc R3B 330R TR2 BS170 – CL Back – wide leads ? Orientation

Insert a short test wire (10 mm) into point D. Remove the aerial connection; turn the

Regen preset R6 fully anti-clockwise and prepare to measure the voltage on point D when the

battery has been installed. Point D should rise from about 1.75 volts to about 2.5 volts, and

that on point F from 0 volts to about 0.3 volts, when the Regen preset R6 is fully advanced.

Return the Regen R6 to fully anti-clockwise. Now listen carefully as you swiftly advance the

Regen preset again – there is likely to be a ‘plop’ as the regen stage breaks into oscillation at

about half way round; there is often also a change in the background hiss in the phones.

Return the Regen control to right back and re-connect the aerial to terminal A. Now advance

the Regen preset to near the point where it ‘plopped’ before and then tune around. Any

broadcast stations should be both much stronger and the tuning should be much sharper. With

the Regen control R6 advanced even further, the regen stage will begin to oscillate, so that as

you tune across the wanted station, you will hear all sorts of nasty whistles - this is normal

and correct! For these broadcast stations (or any amateur) using Amplitude Modulation

(AM), the optimum setting for the Regen control R6 is just below the point where these

whistles begin. There is only one correct tuning point. Because the sensitivity has increased, you

will now need to reduce the RFG pot R2 so that the output audio is undistorted. With

practice, you will find that it is now possible to hear many more stations, and that they can

now be better separated from each other. The coverage will now be about 700 KHz to 1.3

MHz. You may be able to hear Radio 5 Live on 909 KHz, Talk Sport on 1089, and Absolute

Radio on 1215 KHz.

Rockwell V2 RX Page 6

Stage 7. Adding the HF band

The parts for the second band (HF) can be installed for either a higher frequency

section that includes the 40m amateur band, or for a lower section that covers the 80m

amateur band. The choice is made by series or parallel connection of the ready wound 10 /uH

inductors (marked BN, BK, BK, SLV). The slide switch must be towards the rear for either

of these HF bands! Without the optional extra trimmer capacitor C5A, and the change in

connection of C4B mentioned later, the scheme will be more suitable for general coverage of

the ‘short waves’ and overseas AM broadcasting stations; this is because the frequency range

is large & hence is ‘tender’ to adjust. The tuning technique is the same as MW AM.

For the higher band including 40m – install the 10 /uH inductor beads L3 and L4 in their

parallel electrically and physical positions. The coverage will be about 6.1 to 8.1 MHz.

For the lower band including 80m – install the 10 /uH inductor beads L3 and L4 in series in

their slanted positions. The coverage will be about 3 to 4 MHz.

Listening to amateur signals

Radio amateurs mostly use Morse (known as CW) or Single sideband (SSB) phone

signals; to copy these, the regen stage does need to be actually oscillating so the Regen

control R6 needs to be above the critical point of oscillation. Maximum sensitivity and

selectivity is just above the point where oscillation starts – as before small changes in R6 will

make quite a difference! For CW, there will be two tuning points at which a suitable beat note is

heard; either can be used depending on which has least interference from unwanted signals. For SSB

(or double sideband) there will only be one tuning point at which the voices of incoming stations

sound correct. For both these modes, the tuning is more critical than for AM, so you will find it quite

hard to adjust the tuning with C4 for easy listening – CW is a little easier than SSB/DSB but the

solution is restrict the tuning range with C4 to just the amateur band or a portion of it. Fitting a larger

knob to C4 will help & reduce hand effects! Use just enough RF gain R2 to hear the wanted signal.

To restrict the tuning range of C4, alter the connection of the left hand C4B 65 pF section of

the PolyVaricon from the link LK3 between points H and J, to point F – this might need a slightly

longer lead in point F (Photo 5)! To bring the centre of the tuning back to the amateur band, you

MUST also add the 65 pF yellow trimmer C5A and connect it to the switched end of the inductors for

L3/4. (The Issue 4 PCB has a track for this connection, but Is 3 has an extra wire added to the holes

for C5A.) Having made these alterations, fully advance the Regen R6 so that it is oscillating strongly;

this will enable you to hear it on a nearby general coverage RX, or to drive a frequency counter

attached via a divide by 10 probe to point F, so that you can adjust the trimmer C5A to bring the

frequency to the centre of your desired tuning range. If neither of these items is available, listen for

the amateur Morse signals. When set for the 40m amateur band close to 7.05 MHz with C5A, the

tuning range will be about 120 KHz and CW will be much easier to copy - also SSB with care! If you

want an intermediate tuning range, you can try connecting C4B to the spare hole on the track between

R3B and C6.When set for the lower frequency HF band these alterations will also make it much easier

to copy signals on the 80m amateur band. (If you are using a counter to measure the frequency, be

aware that it will go up slightly when you remove the probe, due to the loss of its capacitance.)

To use the Rockwell on the 160m amateur band (say for across playing field type

demonstration contacts), normally the inductors L1/2 would be changed to their parallel

position (physically and electrically) instead of being set for the MW. The coverage will be

about 1.4 to 2.4 MHz. As for the higher frequency bands, AM will be relatively easy to tune

but for CW and SSB/DSB you might wish to consider reducing the effective value of C4A by

adding a small capacitor in series with its connection to point G, and connecting an extra

trimmer direct to point G, to bring the tuning back to near 1.9 MHz.

Frequency stability will be much improved by changing the 10 /uH bead inductors

L3/4 for T50-2 toroids; 40m needs a single 5 /uH (31 turns of 24 gauge enamelled wire) & for

80m 15 /uH (45 turns) is enough. For the 20 or 30m bands, try a T50-2 toroid with 14 or 20

turns respectively. All toroids will need the trimmer C5A added & C4B altered to point F.

Rockwell V2 RX Page 7

Alterations for use with a transmitter

For use with Rimpton AM or Isle CW TXs, there are two aspects to be considered:-

Protecting of the front end Assuming that there is no transmit/receive (T/R) relay provided

with the transmitter which could disconnect the aerial input at point A from the

aerial/transmitter output, then the easiest approach is to turn off the RF amplifier TR1. This is

done by arranging the TR circuits of the transmitter to effectively disconnect point C of the

Rockwell from ground when transmitting. See Fig. 3. A resistor of about 10K needs to be

added to make the source of TR1 rise to the supply voltage when point C is not grounded,

this will protect TR1 and subsequent stages from up to about 5W of transmitter RF! To

enable point C to be controlled, the track linking it to the RX 0 Volt tracks needs to be cut

where there is a small cross across the earth track and point C must be connected to a suitable

output of the transmitter control circuits. It would be normal for the aerial input A to be left

permanently connected to the transmitter side of aerial/matching unit.

Muting the RX The simple method of disconnecting the audio output (by a TR

relay disconnecting the phones) will work because it would turn the whole RX off! Instead,

the easiest solution is to shut the audio amp down by AC grounding the point L when

transmitting. See Fig 4. You will need to add an electrolytic coupling capacitor of 100 /uF

25v, taking care to connect its positive side to point L, and its negative side to an extra 1M

resistor (BN,BK,GN,GLD) to ground. The junction of this 1M and 100 /uF is then connected

to the muting output of the transmitter. This arrangement should prevent nasty TR thumps in

the phones but it does take a few seconds to settle after switch on.

Linking to the Rimpton AM TX This transmitter has a TR changeover relay whose

normally closed R output can be directly connected to the Rockwell’ A terminal. It should not

be necessary to turn off the Rockwell’s RF amp. It also has a muting output at point Q which

should be connected to the junction of the extra 1M and 100 /uF capacitor as described above.

The instructions of the Rimpton described the links for the Redlynch but they are very similar

for the Rockwell.

Using the Rockwell Experiment with different aerials, or locations for it, and get used to the controls! Get the

aerial wire up as high as you can without doubling it back on itself. You may find that adding an RF

earth connection from the E terminal of the aerial block to some nearby large metallic item may help

– water pipes or the case of a mains powered piece of equipment. The sound quality will generally be

best if the RF gain control R2 is advanced no more than is necessary for comfortable headphone

listening. At night it is usually possible to hear more stations because the weak RF signals from

distant transmitters are not attenuated so much. If you find that the powerful Medium Wave broadcast

stations are always very weak, it maybe that the building that you are inside (typically of reinforced

concrete construction), is acting as a Faraday cage which prevents the weak radio signals from getting

through the walls to your aerial; then try moving to outside and throwing the aerial over some nearby

fence etc! Unplugging the phones will effectively turn the receiver off, with negligible consumption,

even though most parts are still ‘live’. Remember to disconnect the battery if doing any mods!

Output to an external power amplifier

The easiest arrangement is to add a 100R resistor across the phones socket and feed

the audio out from the drain of TR4 via 470 nF capacitor to the external amplifier. The RX

will then always be turned on, so you might wish to add a power on/off switch.

That’s enough from me – as ever I shall be delighted to hear how you have got on. My thanks

to Chris Whatmough, and David Perry, for their helpful comments.

© Tim Walford G3PCJ Updated Oct 31st 2016

Rockwell V2 RX Page 8

Photo 1 - The Rockwell with parts fitted for MW and 40m narrow band.

Photo 2 – Securing the PP3 battery holder Photo 3 – Mounting the PolyVaricon C4

Rockwell V2 RX Page 9

Appendix 1 - Tech Description

Supply aspects The RX normally runs off the PCB mounted PP3 battery and is switched on

by insertion of phones. The circuits are live but not working, with negligible consumption, when the

phones are unplugged! The supply can be up to 15 volts as might be used for a transmitter.

Audio amplifier The amplifier has two stages; the first part (TR3) provides the high voltage

gain. The second (TR4) provides a little more gain and operates at a higher current suitable for the

low impedance stereo connected phones that are the drain load. Both TR3 and 4 are BS170 MOSFET

transistors that require a small positive bias voltage (about 2 volts) on their gate relative to the source

in order to turn them on. The bandwidth of the amplifier (about 3 KHz) is primarily determined by the

time constant of R10 and C11. Both transistors are working in the common source mode, the gate bias

for TR3 being provided via R8 and the detector diodes D2/3 from the output stage TR4. This ensures

that point M is normally at about +3 volts – as determined by the 2 volts to just turn on TR3 plus the

two diode drops of about half a volt each. R12 sets the current through the phones and LED. The

standard arrangement of the phones socket will not work with a mono plug because it requires the two

32R earpieces to be connected in series between the tip and ring contacts of the stereo plug.

Detector This stage is a full wave detector performed by 1N4148 silicon diodes D2

and D3. To overcome their high conduction threshold voltage (about 0.5 volts at low current) they

have a small standing current provided from R8/9, with direct connection to the gate of TR3. This

type of detector requires a time constant long compared to the period of the RF carrier frequency (say

1 MHz) but short compared to the upper modulation frequency of about 3 KHz – this is provided by

the combination of R8 and C10. To avoid the detector loading the tuned circuit unnecessarily, and so

making the selectivity poor, the detector is fed from the low output impedance of the regen stage TR2

acting in effect as a buffer; this applies irrespective of whether it is actually oscillating or not. The

detector also works for CW and SSB reception when the Regen stage TR2 has to be oscillating.

Tuning The switch S1 selects either of the pair of 100 /uH inductors L1/2 for MW/160m (LF)

work, or the 10 /uH ones L3/4 for HF bands 40 and 80m; the 65 pF section C4B of the PolyVaricon is

normally connected across both pairs of inductors but the 150 pF section is only added for the LF

bands across L1/2. The series value of capacitors C5B/6/7 are also always across the inductors. Both

pairs of inductors can be connected in either series or in parallel depending on the band desired. The

trimmer C5A can be added, and C4B changed to point F, to reduce the HF tuning range. The

inductors are connected to the supply rail which is heavily decoupled by C3, so that any signal

developed across them is fed directly to the detector D2/3 by the regen stage TR2 and C8. If desired

T50-2 toroids can be used instead of the ready wound bead inductors to improve stability and would

have to be used for the 20 or 30m bands.

Regen stage Another BS170 MOSFET TR2, connected as a Colpitts oscillator, is connected to the

tuned circuits with C4/5/6 so that as its bias is increased by raising the voltage on the slider of the

Regen preset R6, the stage gets near the point at which oscillation begins. This is the critical point for

optimum reception of all types of signals so a stable voltage is required; this is derived form the

nearly constant voltage at the source of the output stage, with suitable filtering to prevent instability.

The arrangement also turns the regen stage off when the phones are removed! The diode D1 ensures

smooth level control once oscillation starts. The values for R6/7 are chosen for ‘spread out & smooth’

operation of the Regen control either side of the critical point at which oscillation starts. The inclusion

of R3B helps to make the transition from not oscillating to actual oscillation, rather smoother.

RF amplifier This is an un-tuned or broadband RF amplifier that will pass ‘all’ RF signals

that come from the aerial! It adds gain from a low impedance aerial, and makes it easier to interface

the aerial to the tuning inductors. It uses another BS170 MOSFET, with a suitable gate bias derived

from the feedback via R9 from the source of TR4, so that it is also turned off when the phones are

removed. R2 sets the operating current of TR1 at about 1 mA and because the gate is heavily

decoupled by C2, it operates in the grounded gate mode. It is important to avoid overloading of the

detector and subsequent stages, so it is convenient to make R2 an RF gain control so that any

incoming large signal can be adjusted down to suit. By connecting the aerial input to the slider,

instead of the more usual arrangement for a pot, it allows the DC current through R2 to be unaffected

by its setting. TR1 is susceptible to static on the aerial so R1 has been added to discharge any static

that might build up on the aerial wire.

Rockwell V2 RX Page 10

Parts list for the Rockwell V2

Resistors – 5% Capacitors 4 330R – OR,OR,BN,GLD R3B,5,

11,12 5 150 pF ceramic plate – 151 C5B,6,7,8,

10 1 1K – BN,BK,RD,GLD R4 2 470 pF disc - 471 C1,11

2 2K2 – RD,RD,RD,GLD R7,9 4 100 /uF 25v electro C2,3,9,12

4 100K – BN,BK,YL,GLD R1,3A, 8,10

1 65 pF yellow trimmer C5A 2 1K - 15mm shafted preset

+ shaft R2,6 1 65/150 pF PolyVaricon C4

Inductors – they are like beads Miscellaneous 2 10 /uH – BN,BK,BK,SLV L3,4 4 Rubber feet 2 100 /uH – BN,BK,BN,SLV L1, 2 1 Two screw aerial connector block

1 Single pole slide switch S1

1 3.5mm small PCB stereo skt

Semiconductors – in anti-static bag 1 PP3 battery holder 3 1N4148 D1,2,3 3 Small 6mm knobs For R2/6, C4 4 BS170 TR1,2,3,4 5 m Stiff single core wire Aerial, C4, PP3 TRN Walford G3PCJ Oct 25th 2016 1 Rockwell V2 etched PCB - Is 3 or 4

Photo 4 - Earth wire link at the end of the PP3 holder nearest the antenna connector

Photo 5 – Connection of C4B to

point F for reduced tuning range

Rockwell V2 RX Page 11

Rockwell V2 RX Page 12