Walford Electronics Ltd.

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 Aerial RF amplifier Tuning Detector Audio Amp Phones Regen Rockwell V2 RX Page 1

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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 9

Parts list for the Rockwell V2 Resistors 5% 4 330R OR,OR,BN,GLD R3B,5, 11,12 Capacitors 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 10

Rockwell V2 RX Page 11

Rockwell V2 RX Page 12