Radio Board

The new ISS 10.2 Just delivered - 7 April 2026 - kitted up ready for construction.

The new ISS 10.2 Built up and ready for testing. Build time ~ 3 hours - 7 April 2026

Radio Board features:

This is the most complicated board with over 600 components. Most of them are surface mounted.

• VFO – The Variable Frequency Oscillator operates from a few kHz above the LO frequency to 160MHZ, that covers all bands from 2200-meters  to 2-meters. The Si5351 device has been used. Against some criticism it has proved to be an excellent stable  device. Two of these Si5351 devices are used, one exclusively for the VFO and the other for BFO / CIO / TXO.  Temperature compensated crystal oscillators (TCXO) are fitted as standard.

• Double-balanced mixer (DBM). Either the SMD ADE-1 or an older SBL-1 can be used.

• Front-end Diplexer filter. This is both a bandpass and notch filter in one. It is located after the Mixer and before the first IF.

• IF stages. There are 4 Intermediate Frequency stages. One before the crystal ladder filters and the others after.

• SSB and CW Crystal Filters. Individual crystal filters are 2.3kHz wide for SSB and 500Hz wide for CQ (At -6dB). These filters are not too easy to set up and construct, therefore they have been designated to a small sub-pcb and will be supplied constructed and tested. Bare PCBs can be supplies as well

• Noise Blanker (NB). This is mounted on a small sub-pcb that plugs into the main Radio Board. It filters out such as Woodpecker, static-crashes, electric fence and other burst noise.

• Variable IF. The IF frequency is normally within a few kHz od 8MHz, and  dependency is on the centre frequency of the SSB and CW Crystal Filters. Once the IF frequency is know, it is set for both SSB and CW the firmware, changeable from the front panel and stored in EEPROM.  Different IF Frequencies can be also be used if the experimenter wishes, again, set in firmware.All Crystals can be purchased already matched from hampiradio.com.

• Audio Notch filter. To filter out any interfering heterodyne (single tone) within the audio spectrum.

• Four stage Audio filter.  This audio filter has 3 SSB stages and 1 CW stage). This filter cleans up audio hiss very well and narrows the audio bandwidth. This might seem like an over kill having  both crystal filters and Audio filtering, but under harshest conditions ti is useful to have both at hand.

• Audio amplifier that can be selected for 4 or 8 Ohm speaker marching.

• Automatic Gain Control AGC.

• Full break-in CW RX/TX switching and muting.

• CW Keyer. A stereo 3.5mm stereo jack socket is fitted for a straight key or paddle to be fitted. (Various keyers options are in the firmware) 

• TX microphone compression, Audio filtering, Balanced Modulator, filtering and amplification are int he transmit circuitry.

• Various other ancillary functions

Radio Board – Hand fitted parts list

Below is a parts list of the hand mounted parts for this board: (Use sliders in the tables to view any hidden text)

Construction

• Carefully inspect the board for damage and note any missing parts. Some parts are not fitted due to cost and it is much cheaper to hand fit them, other parts are intentionally fitted (nf on the circuit diagram).

• It is not necessary to fit pins in the Test Points, but this can be done as a preference. A oscilloscope fits in the PCB test point holes conveniently (1mm). 

• Choose and fit the mixer. This can either be a surface mount (SMD)  ADE-1 or SBL-1 (Through hole). Either perform equally well.  Be careful to observe the orientation, look for where Pin 1 must go.

• Solder all of the MYLAR Capacitors which are associated with the Receive Audio Filter and the Transmit Audio Filter. The values are all marked on the PCB in silk screen. The values begin with an ‘M’ indicating these tall green Mylar capacitors. Examples are M10n for 10nF or on these capacitors marked 103. In the RX Audio Filter section will be found these values: M27n for 27nF marked 273, M12n for 12nF marked 123, M15n for 15nF marked 153, M2n2 for 2.2nF marked 222, M22n for 22nF marked 223, M18n for 18nF marked 183, M1n5 for 1.5nF marked 152, M10 for 10nF marked 103. In the TX Audio Filter section will be found M27n for 27nF marked 273, M12n for 12nF marked 123, M6n8 for 6.8nf marked 682, and M2n2 or 2.2nF marked 222. The lead widths, space between the wires coming out of the bottom of these Mylar capacitors varies, and the PCB footprints cater for this. Choose one of the three holes and the one hole at the other end of the footprint to suit the lead width.

• Solder the 26 pin IDC Plug observing the orientation. Pin 1 is to the top right and the cut out groove goes towards the top of the board.

• Solder in these parts:  White pin headers (1 x 4 pin J6, 1 x 3 pin J23, 4 x 2 pin J1, 13, 15, 26, ), and Pin-Headers

• Continue reading below for construction and mounting of the inductors and transformers and the rest of the parts.

• Finally and lastly fit the two sub-pcb boards. These are a SSB / CW Crystal Filter board, and a Noise Blanker board. These both employ 1.4mm OD socket receptacles (look like pins one end with a hole the other. The easiest way to ensure these sockets are soldered in straight is to push them onto the sub-board pins, and then offer up the sub-board to the main board putting the sockets all the way into the main board holes. Turn the boards over and solder from the bottom.

Inductors and ferrite transformers

The ferrite transformers need to be carefully constructed using the instructions following. It is worth taking time and patience to do this as fault finding incorrectly transformers or shorted turns (due to scratching of the enamel wire causing short circuits) is a nightmare. Enjoy the process…

Diplexer Filter (Bridged Tee)

A diplexer is both a notch and a bandpass filter combined.  The diplexer design described here is for the standard HamPiRadio, and is centred on 8MHz

If you are an experimenter and intend to have a different IF frequency then the diplexer will need to be adjusted in frequency accordingly. The Diplexer needs to be designed / tuned to the centre of the IF Frequency.  An article can be found here: https://www.qsl.net/g3oou/mixerterminations.html and a calculator here: https://www.changpuak.ch/electronics/calc_16a.php
To calculate: B = Bandwidth in Hz, Fs = Centre frequency in Hz, R = Impedance in Ohms (50R).

L3 = R / (2π x B)
L6 = (B x R) / (2π x Fs2)
C8 = B / (2π x Fs2 x R)
C41 / C44 = 1 / (2π x B x R)

Diplexer coils L3 and L6 on the Radio Board.  (Note the capacitors are already fitted).

Notes:
– If you have an an inductance meter measure the inductance of these coils and squeeze or spread out the turns to get the correct measurement.
– There is provision on the PCB to tie down these coils with a length of non conductive thread / Cable Lacing etc.
– When winding coils on ferrite be careful to not scratch off the enamel coating. The ferrite can have sharp edge. While it does not matter if the ferrite is in contact with the actual copper wire as ferrite is an insulator, it does matter a lot if the windings are shorted together. Shorted-turns will effect performance negatively, and are very hard to find.

Ferrite Transformer Information

There are now only 6 transformers to be wound and fitted on the Radio Board.

Winding details:

T2 & T3 (Noise Blanker). These are similar in construction but T3 has more turns and is reversed. This description is for T2. From the sketches above:

1. Cut the length of enamelled copper wire for the Primary and wind onto the core. There are 12 turns. One turn is the wire passed through one hole AND back again through the other hole. Keep the turns somewhat tight and be careful to not scratch the wire on the ferrite.

2. (Note: on this sketch the primary is not shown). Cut the two pieces of wire for the secondary. Scratch off 5mm of enamel on one end of each wire, and twist together and solder. See the red and green wired in the diagram. Next pass the two free wire ends through the core at the opposite end from the Primary turns.

3. (Note: on this sketch the primary is not shown). Now pass the wires back through the core. This forms the 2 turns – Centre Tapped (CT). The only difference with T3 is it has 4 turns Centre Tapped, and so the 2 wires have to be passed through the ferrite core AND back again one more time. Things can get a little tight, but it is not too difficult with care. Use tweezers to push the wires through if needed, again being careful not to scratch the enamel. If needed use a small wooden tooth-pick and push it through a hole to gently move the wires aside.

4. Sketch 4 shows the completed T2. Cut the wires back to 15mm long and scratch off the enamel 5mm and tin.

6. The transformers can now be soldered onto the PCB.. Next, have a cuppa and congratulate yourself. This is probably the most fiddly part of the board!

Above: T4 & T5 (SSB and CW Crystal Filter Matching).

These two transformers are identical. The crystal filters are designed to operate with a 300 Ohms matching.  T4, changes the 50 ohms to 200 ohms and T5 changes the 200 ohms to 800 ohms.

1. Cut two pieces of wire 0.3mm or 0.32mm enamelled copper wire to length and twist them together roughly 3 or 4 twists every cm.  If you can find two different colours or shades of enamel, that will be very handy in a while.

2. Wind the twisted pare onto the ferrite core passing it through the centre hole 10 times. (If you count the external turns it will be 9. A turn is counted for every time the wire passes through the home)

3. Separate the 4 ends of the wires.  Cut the wires back to 15mm long and scratch off the enamel 5mm from the ends and tin with colder.

4. If you used different coloured enamel then it is easy. Select one colour end and twist it to the other end of the wires, the different coloured wire and tin with solder.

5. If all wire is the same colour, then use a multimeter on a low Ohms range (often the lowest range is 200 Ohms and this is the one to select) or using a buzzer function. Identify the wires buzz out OK (If they all buzz you have shorted turns due to damages enamel, and will have to start from step one again!). Now, identify two odd the wire ends that so not buzz and are at OPPOSITE ends of the windings. See the sketch, you are selecting one red and one blue wire. Twist together these ends where they were tinned and solder them together.

6. As an extra check, the two free ends not soldered together should buzz as they are connected in series.

7. These transformers can now be soldered onto the PCB.  Ensure that the two wires soldered together are put through the hole marked CT.  The other two ends are then connected to the other two holes, it doesn't matter which wire goes to which hole.

T8 (IF Output to Product Detector input).

1. Stare with the Secondary (S) winding. This must be bifilar wound. This is done in a similar way to the above Tin a very similar way to T4 & T5 above, but but there are only 5 turns and the wire is a lot shorter.  Twist and solder the two centre tapped in the same way also.

2. Add the 10 Primary (P) windings next and strip and tin the ends.

3. This transformer can now be soldered onto the PCB.  Ensure the CT is in the correct hole.

T10 (TX RF).

This is a simple transformer with a Primary and Secondary. Build and fit as per this picture.

The completed construction

The construction should not be completed. Carefully look over the board and check that everything is looking good and complete.  Remember there are just a few surface mount parts that are not populated (NF=Not fitted)

Alignment & Selection of Software Calibration Options

The minimal HamPi Radio components needed to set up the Radio Board are as follows:

1) A CPU Board programmed with the latest firmware. See Firmware page.

2) A Keypad Board

3) A Rotary tuning encoder, 400ppr Rotary Encoder fitted with a tuning knob

4) A Radio Board

3) 26way ribbon cable 30cm long

6) A 4 wire screened cable from the CPU VFO connector to the Radio Board VFO J6 connector. (This is done by using half of the Rotary Control cable which is supplied in sufficient length(1M) to do both jobs. The screen of this cable must be connected to 0V pin 2 of the Radio Board end, J6.

7. A means to power the boards with 13.8V. This is done initially (Until the PA is fitted) by applying 13.8V to the Radio board using the 2-Pin connector J16. Pin 1 is -ve and Pin 2 is +ve. (You can alternatively feed the 13.8V to the CPU board and the Radio board will be fed through the 26 way Ribbon Cable)

Notes:

• All information about the transceiver calibration is stored on E2Prom on the CPU Board, and this means that every time a different CPU board is used the complete calibration procedure needs to be done again, or the settings transferred. The good news is that once a CPU + Radio board pair are calibrated the procedure should not be needed for the lifetime of the transceiver.

• The following procedures must be executed in the order described. If things do not go to plan reset the procedure as follows: Power off and on again. Get to the IF= selection in the CalFeatures, select the Base IF Frequency of 8, 9 ot 10.7MHz and then press the Set Button. The CPU will reset followed by a restart. At this point you can start the procedure described below again. If things are really not going well a Factory Reset can be performed by connecting the Pi Pico directly to n Arduino Ide and using the Serial Monitor to type in FaCtOrY ReSeT. The CPU board has to also be connected to clear the E2Prom. You will need to be familiar with the Arduino IDE to do this however. It should never be necessary.

Connecting up

1. Connect a 26way IDC Ribbon cable from the CPU board to the Radio Board. (These are the only two 26 way IDC connectors in the rig, so you can’t get it wrong). See the CPU board page for the construction of the cables).

2. Connect the 4 way shielded cable from the CPU board connector marked VFO to the similar connector J6 by on the top LHS corner of the Radio Board by the VFO Si5351 (U17). (The spare 4 way screened way cable from the Rotary Encoder used for the main tuning can be used for this purpose. Earth the screen only at the CPU end. Keep the amount of exposed 4 internal wires short, less than 1cm).

3. Plug the Keypad and Main Rotary Encoder into the CPU board where indicated (VFO).

4. Connect power to the PCB. J16. The setup should power up with red (PWR) and green (RX) leds on the Radio Board. The TFT display will fire up. The Tuning and Keypad should also operate, and a green RX led on the Keypad.

5. Remove and reconnect the power to reset things, and don’t change any controls.

Set the Initial IF Frequency

If the SSB / CW Crystal Filter sub-board has been supplied, it will have the frequency for each written on the sub-pcb. These two frequencies are needed during this set up.

1. Radio calibration features are in a normally hidden menu as they will rarely be needed and have a huge effect on the way the HamPiRario operated. When using the Calibration features be very careful. Once calibration is done it should never have to be done again for the lifetime of the radio.

2. Press the FUNC button a few times until ‘Calibration:’ and ‘Off’ is displayed on the bottom line of the TFT display. Press the ‘Set’ button twice and OFF will change to ON.

3. Now when the Func Button is pressed it will select the normally hidden calibration features.

4. Press the Func button until ‘Set IF:” is displayed. Now by turning the main Dial the Base If frequency can be selected. These are 8 MHz. 9 MHz or 10.7 MHz. The normal Base IF frequency for the HamPiRadio is 8 MHz. Select this and press the Set button. After a couple of seconds the radio will do a firmware reset and will be set to IF of 8 MHz. This saves this selection permanent memory. (E2PROM).

 Note: Your Crystal Choice will most likely not be exactly on say 8.000,000MHz. That is fine, just choose the closest IF selection here to the SSB Crystals you intend to use. As an example with the prototypes the actual centre frequency of the 6 stage SSB filters resembles 7.998,650MHz. This actual IF offset will be catered for below in a later calibration step.

Note: If for any reason the Tuning Control is not working check using an oscilloscope there is a 25MHz oscillator signal at the oscillator output and OSC input pin 2 of the Si5351 U17.

Equipment needed: For the following procedures a frequency counter is required. It needs to be able to accurately measure a 10MHz frequency. Allow some time (30 minutes or so) for the Frequency Counter and the Radio Board to fully warm up.

Calibration of the VFO Clock Crystal Frequency

1. This sets in permanent memory the frequency offset of the VFO Oscillator / clock.

2. Use the frequency counter and measure the VFO signal at TP18 (VFO) near J6 on the Radio Board.

3. Follow these instructions carefully and do not press any other radio buttons or the procedure will fail.

4. Enter the ‘Calibration On’ mode again, and press the FUNC (Function) button until ‘VFO Calibration’ is displayed.

5. Press the ‘Set’ button and observe the frequency on the frequency will display close to 10MHz.

6. Now adjust this frequency up or down until the frequency shows exactly 10MHz (10.000,000Hz)

7. Once this is done press the SET button once again. This will save the VFO calibration in E2PROM (permanent memory) so that at power up the calibration is recovered. This procedure should never need to be redone.

Calibration of the BFO Clock Crystal Frequency

1. This procedure is exactly similar as that above for the VFO Calibration.

2. Press the FUNC (Function) button until ‘BFO Calibration’ is displayed. (Re enter the ‘Calibration On’ mode again if necessary).

3. Do the same procedure as above but using measuring the frequency at point TP3 BFO. (If the signal level at TP3 does not work (it is a low level signal) on the ISS 9 Radio Board, then carefully probe for the BFO signal on either side of C146 which os located close to U14 (Si5351). On later issue boards there will be a now test point)

Selection of Crystal Filter Crystals

At this stage of construction the centre frequencies of both SSB and CW filters should be known, and in the following procedures these will be entered in to the radio firmware. (The selection of the Crystal SSB and CW filters has its own page on this website here SSB & CW Filters)

Calibration and programming the SSB IF Frequency

Notes: At this stage you should have already have either a) Already purchased the needed Crystals, or b) selected and tested the needed Crystals for the radio Board. These notes will assume you have got all 13 needed Crystals and they are soldered to the Radio Board. 2 for the first IF/Delay filter, 6 for the SSB/Wide filter and 5 for the CW Narrow filter. For the following procedures a further assumption will be all crystals are 8MHz (or within a few kHz. If you do not already know the Filter centre frequencies go to the SSB & CW Filters page.

1. Press the FUNC (Function) button until ‘SSB IF=’ is displayed. (Re enter the ‘Calibration On’ mode again if necessary).

2. Adjust the main Dial to select the frequency of the SSB Crystal Filter centre frequency. The resolution is 50Hz. An example will be 7998150 on the display.

3. Next, Press the ‘Set’ button. This will save this filter centre frequency.

Calibration the CW IF Frequency

1. Press the FUNC (Function) button until ‘CWIF=’ is displayed. (Re enter the ‘Calibration On’ mode again if necessary).

2. Adjust the main Dial to select the frequency of the CW Crystal Filter centre frequency. The resolution is 50Hz. An example will be 7998650 on the display.

3. Next, Press the ‘Set’ button. This will save this filter centre frequency.

Setting the Calibrated SSB and CW Filter frequencies into Memory

1. Press the FUNC button one more time and ‘Reset CPU? (Set)’ will be displayed.

2. Press Set and the HamPiRadio will do a firmware reset. This will set up all the functionality ready for use.

Congratulations! The Radio and CPU board are not calibrated for each other and ready for the next construction phases. These two boards are now a pair, meaning the calibration settings in permanent memory (E2PROM on the CPU board match those of the crystals and filters on the Radio Board. If ever the Radio or CPU boards are changed, this calibration procedure must be done again from the beginning. If all has been done successfully, it should never need to be done again.

Note: THE IFW and IFN functionality only operates in receive and never in transmit.