Radio Board

Updated 12 August 2024 MW

Board features:

• VFO – from a few kilohertz above the LO frequency (Sat 8MHz) to 150MHZ. The Si5351 device has been used. Against any criticism is has proved to be an excellent device, stable and quiet in nature. Two of these Si5351 devices are used, one exclusively for the VFO and the other for BFO / CIO / TXO. A TCXO can be fitted is desired.
• Double-balanced mixer. The SMD ADE-1 works very well or an older SBL-1 can be used.
• Front-end diplexer filter
• First Xtal filter / delay and Noise blanker (Woodpecker, static-crash, electric fence etc)
• Variable IF to suit your Crystals! Different IF Frequencies can be chosen using the Function rotary control. The current design works on either 8, 9 or 10.7MHz. These are the base frequencies and a software feature allows the IF to be varied away from any one of these base frequencies. For example, you can buy bags of 10 / 100 XTALS from a supplier and then match 8 of them together in frequency and for minimum loss, and these become the First filter (2) and SSB (6). Next you can select another 5 XTALS on the same frequency, or close by frequency, and these become the CW XTAL filter.
• All Crystals needed can be sourced from hampiradio.com or SSB & CW Crystal filters can be sources from Spectrum Communication who sell them for 9, at a reasonable price and they work well. You can source and select your own (note above).
• Front end and triple Intermediate Frequency variable gain Amplifiers (AGC) using dual gate MOSFETs BF998 devices.
• Notch filter
• Balanced Detector
• Four stage Audio filter (2 SSB and 2 CW stage). This cleans up audio hiss very well and narrows the audio bandwidth.
• Audio amplifier.
• Automatic Gain Control AGC.
• Full break-in CW RX/TX switching and muting.
• CW Keyer (stereo jack and software keying for straight key or paddle)
• TX VOGAD microphone amplifier / compression
• TX Audio filtering
• TX Modulator
• TX amplifier stages & RF TX Output amplifier
• Other ancillary functions
• This board has recently been converted to SMD for the majority of the components as the parts count was approaching 500, which is complex and the chances of construction errors / dry joints etc became too high. This means the project is drastically simplified. See the photo below and note the SMD parts and the as yet on this photo unmounted hand fit parts.

The photos below show part of the Radio board (An earlier prototype).

Component Selection and General Information

• Crystal CW Filter / SSB Filters. IF Frequency choice. Decide on the IF frequency. 8, 9, or 10.7mHz. 8 or 9mHz is recommended. Other base IF frequencies are easily possible with a requested firmware change.
• Crystal CW Filter. The CW filter can be omitted, but if you are a seasoned CW Op you will want it even thought the Audio Filter is adequate.
• Various areas were left unmasked giving provision for screening, but screens were (fortunately) found to not be unnecessary.

Diplexer

Diplexer	8MHz IF	9MHz IF	10.7MHz IF
C1 (C8 on PCB)	33pF	70pF	50pF
L1 0.32mm (L3 on PCB)	9.9uH T50-6(Red) 47turns (16mm/turn 660mm)	4.4uH T50-6(Yellow) 30 Turns (500mm)	4.4uH T50-6(Yellow) 30 Turns (500mm)
C2 (C41+C44 on PCB)	2200pf	1640pF (820pf+820pf)	1262pF (820pf+470pf)
L2 (L6 on PCB)	0.19uH T37-6(Yellow) 7 turns (100mm)	0.19uH T37-6(Yellow) 7 turns (100mm)	0.19uH T37-6(Yellow) 7 turns (100mm)
Resistors (R96 & R101 on PCB)	51R & 51R	51R & 51R	51R & 51R

Ferrite Transformers

Part	Core	Primary turns	Secondary turns	Wire	Length in mm
T1	HP-43 Front End Amp	16	7	0.3 (28SWG)	150 + 75
T2	BN43-2402 Noise Blanker in	12	2ct (1+1)	0.2 (38SWG)	250 primary, 40 + 40 secondary
T3	BN43-2402 Noise Blanker out	4ct (2+2)	12	0.2 (38SWG)	60 + 60 primary 250 secondary
T4, 5	HP-43 SSB Filter in and out	7	7	0.3	80 + 80 twist together by hand then Bifilar wound
T6, 7	HP-43 CW Filter in and out (Optional)	11	11	0.3	115 + 115 twist together by hand then Bifilar wound
T8	HP-43 IF Amp out	8	4+4	0.3	85/50+50
T9	BN43-2402 TX Balanced Modulator	6	3 + 3	0.2	20mm/turn
T10	HP-43 TX Buffer out	11	5	0.3	110/60

Transformer Winding Notes:

• The HP-43 ferrites used for the HamPiRadio. They are 6mm x 2mm with a 3mm aperture (hole). These can be ordered from AliExpress or supplied by me. (The ‘HP43 stands for HamPi 43 material).
• One turn of enamelled copper wire is 8mm and 15mm is allowed for the tail ends.
• These operate at the IF frequencies perfectly well and are much smaller than the traditional FT37-43
• FT37-43 ferrites will also work but are much larger and will be more cumbersome to fit. They are also expensive.
• Take care when winding these inductors not to scratch the enamel from the wire. Since ferrite is non conductive it doesn’t matter if the copper is in contact with the ferrite, but if you get ‘shorted turns’ there will be tears as it can take ages to fault find. By ‘doing it right first time’ a lot of tears will be saved…
• Turns for single hole cores (HP-43) are counted as each time the wire passes through the aperture/Hole, so the turns counted on the outside of the core will be one short. 10 through the hole will count as 9 on the outside. (Remember the Telegraph Poll error?)
• For the BN43-2402 one turn is counted as the wire passing through one hole AND back through the other hole.
• Once wound trim any excess wire off leaving a nice amount to solder in place with, then scratch off about 4mm of the the enamel from the end of the using a sharp blade (scalpel).This is easily done on the edge of the bench etc… Next tin the wire ends with solder.
• The actual wire diameter is not critical so use what you have. Where 0.3mm is called for above, 0.28 or 0.32 can be used.
• It is really handy to use different coloured wire for primary and secondary for obvious reasons (or they will become obvious soon!)

Noise Blanker

• IFT1 / IFT2 At present a TOKO 4520 10mm transformers are used. The available hampiradio.com transformers marked 3245 and are custom manufactured, but the manufacturer put in the needed centre tap! If the TOKO 4520 cannot be sources the HamPi 3245 can be carefully opened rewound to add the needed centre tap.

• The HamPi 3245 needs an external 47pf capacitor which are already mounted on the PCB. If two TOKO 4520 (4.4uH) 10mm transformers are used they have an internal 51pF capacitor fitted and if used the external 47pF capacitors must be removed from the PCB.

• When testing put an oscilloscope on TP8. Apply a -20dBm (or a large) signal on the antenna (or PCB J9 input) and tune the two cores for maximum output. This is a basic two stage narrow band RF amplifier which amplifies the RF input to trigger static crashes and Woodpecker signals etc. The filter cuts out interferences above about -50dBm to trigger the blanker, and must be larger than the desired received signal. Filter F1/F8 is a delay so that the noise blanker is de-activated by Q6 before the noise arrives at the blanker (Q6 is normally on).

Construction

• Carefully inspect the board for damage and note any missing parts. Some parts are not fitted due to cost, it is much cheaper to hand fit them.
• Do any suggested modifications next. It is easiest to do these, if there are any, before adding the other parts.
• Choose and fit the mixer. This can either be an ADE-1 (SMD) or SBL-1 (Through hole)
• Fit U9. This can either be an SL602 or SL612. There is no difference between them. Add a tiny blob of solder to opposite pins, say pin 1 and pin 5. Seat the IC carefully by soldering these two pins first ensuring the device is straight. Pin 1 is tip left when viewing the board with the silk screen text readable. Solder the other pins carefully.
• If not already fitted, mount and solder all capacitors associated with he Crystals. There will be 13 crystals in all. It is best to use COG type parts as they will be temperature stable. An example is: 50V 39pF C0G ±5% 0805 Multilayer Ceramic Capacitors. The footprint for these caps caters for both SMD and THT parts.
• Solder all of the 13 crystals. Note: It is possible to use SMD Crystals if you can find suitable ones. The footprints allow for mounting them on the reverse side of the PCB.
• Solder all of the MYLAR Capacitors which are associated with the Audio Filter and the TX Audio Filter.
• Solder the 26 pin IDC Plug observing the orientation. Pin 1 is to the top right.
• Solder these other parts: White pin headers (1 x 4 pin J6, 1 x 3 pin J23, 4 x 2 pin J1, 13, 15, 26, ),

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 and connected Kapad Board 2) A Radio Board 3) 26way ribbon cable to connect the two. 4) A means to power the boards with 13.8V, done with a 2 wire + connector connected to either board. 5) A 400ppr Rotary Controller fitted with a tuning knob. 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.

Note: 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. 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.

Note: The following procedures must be executed in the order described. If things don’t go to plan resett 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 below again.

1. Connect a 26way Ribbon cable from the CPU board to the Radio Board.
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 VCO Si5351.
3. Connect power to the PCB. This is done by putting 13.8V to EITHER the CPU or Radio board using the 2-Pin connector J16. Pin 1 is -ve and Pin 2 is +ve
4. Press the Function button a few times until CalFeatures is selected and change to ON using the Main Tune/Func control.
5. Continue pressing the Func Button until IF= 8.000,000 (or 9.000,000 or 10.700,000) is displayed.
6. Rotate the Main control until the correct IF is selected for your SSB Crystal Filter choice.
7. Press the SET button. This saves the selection permanently to E2PROM. After a second or two the CPU will reset.
8. 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 have. As an example witht he prototypes the actual centre frequency of the 6 stage SSB filters resembles 7.998,525MHz. This actual IF offset will be catered for in a further calibration setting detailed below.
9. Note: For the above procedure to work correctly is it vital that the IFW (IF Wide) and IFN (IF Narrow) radio features have NT been adjusted away from 0HZ on the display.
10. 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.

1. Calibrate the VFO Frequency

1. This sets in software the actual frequency of the Si5351 VFO Oscillator / clock.
2. Use a frequency counter and measure the VFO signal. This can be done TP10 near J6 on the Radio Board.
3. Ensure the VFO on the display of the CPU is set to 14.200.000MHZ and press the LOCK button.
4. Set IFW to 0 To do this first set to SSB mode. Press the Set button.
5. Set IFN to 0. To do this first set to CW-N mode. Press the Set button.
6. Set MODE is set to USB.
7. Press the Function button a few times until CalVFO is displayed. Now turn the function control one way or the other until the Frequency Counter displays the correct IF frequency. This will be 22.201.500 MHZ for a 8MHZ IF, 23.201.500 MHZ for a 9MHZ IF, and 24.901.500 for a 10.7MHZ IF. When it is spot on, press the SET button. This will save the calibration in E2PROM so that at power up the calibration is remembered permanently. It should never (but could) need to be redone.

2. Calibrate the BFO Frequency

1. This sets in software the actual frequency of the Si5351 BFO Oscillator / clock.
2. CALIBRATE BFO. Use a frequency counter and measure the BFO signal. This can be done Pin 1 of J7. Ensure the MODE is set to USB.
3. Set IFW to 0 To do this first set to SSB mode. Press the Set button.
4. Set IFN to 0. To do this first set to CW-N mode. Press the Set button.
5. Set MODE is set to USB.
6. Press the Function button until CalBFO is displayed. Now turn the function control one way or the other until the Frequency Counter displays the correct BFO frequency. This will be 8.001.500 MHZ for a 8MHZ IF, 9.001.500 MHZ for a 9MHZ IF, and 10.701.500 for a 10.7MHZ IF. When it is spot on, press the SET button. This will save the calibration in E2PROM so that at power up the calibration is remembered permanently. It should never (but could) need to be redone.

3. Selection of Crystal Filter Crystals

The selection of the Crystal SSB and CW filters has its own page on this website here SSB & CW Filters

4. Calibration the SSB IF Frequency

1. Calibrate/set the IF frequency based on the chosen actual SSB Crystal Filter Crystals.
2. All current rigs have used a ‘base’ frequency of 8Mhz, and crystals that are close to this Base. (for example 7.998525MHz for the first IF filter (2 xtals) and the SSB filter (6 xtals).
3. Switch off the radio and on again. This will not loose the above calibration of the VFO and BFO.
4. Inject to the RF into J9 or -73dBm. Connect a loudspeaker to the Headphones Socket.
5. Set the radio to CWW mode. 14.200,000MHZ
6. A 1kHz tone should be heard. If not increase the RF input until necessary up to a maximum of -20dBm. If a tone cannot be heard the reason needs to be found and fixed.
7. Note: (Adjustment of RZv12 AGC Gain and RV14 Smtr Cal 0 will be needed, and is described elsewhere. For not there should be S0 displayed on the S-Meter for zero RF input and S9 for -73dBm. These two settings will not work accurately until the SSB Filter is correctly calibrated).
8. Press the Func button to select IFW. Now adjust the IFW with the Main Control up and down and observe the volume going up and down but the tone staying the same.
9. When the volume it at a mid and maximum volume (You are allowed to use the volume control to not deafen yourself or upset others!) stop and grab a pen.
10. Some explanation is now needed: The SSB filter will have a relatively flat top, or passband and when the IFW is adjusted from side to side of this passband the signal strength on the S-Meter and the volume will steadily fall away. This is the skirt on the sides of the passband of the filter. It is not very important to get over technical here and insist on exactly -6db falloff. What can be done is to adjust the IFW and observe the SAME amount of falloff on each side of the passband.
11. A very workable procedure is to get roughly to the middle of the passband using the IFW and adjust the S-Meter to exactly S9 with an input of -73dBm. Next vary the IFW one way and note down the IFW frequency when the S-Meter shown exactly S8 (which is roughly -6dB). Now go the other way across the passband at S9 until the signal shows S8 at the other end and again note down the IFW frequency.
12. The SSB Filter Centre Frequency can now be calculated and it is half way across the passband. What was noted down? An example will be -2475Hz on one side of the passband at S8 and -375Hz on the other side at S8. Now the maths. 2475HZ – 375HZ = 2100Hz. Next 2100HZ/2 = 1050Hz. Next add this to the lower bandpass so 1050Hz + 375Hx = 1424HZ. Remember the original IFW were negative numbers? So we end up with a 8.000,000HZ Base frequency minus 1425Hz = 7.998575MHz SSB Crystal centre frequency and this will become the HamPi IF Frequency.
13. Next, Press the Set button. Ths will save this precious SSB frequency in memory, but not for long.
14. Note to MW or a volunteer constructor: Produce a video / YouTube clip of this, it will speak volumes!

5. Calibration the CW IF Frequency

1. The CW filter (5 xtals) procedure is similar to that above. The CW filter can be a centred on a different frequency, but does need to be in a similar range as the RX signals still have to pass through the Duplexer that is a tunes circuit and the first IF filter which has a wiser but not limitless passband. (for example 7.999800 is fine).
2. Press the MODE Button once to change to CWN (Narrow). This changes over from the SSB to the CW Crystal Filter.
3. Follow a similar procedure to that above but changing the IFN using the main control.
4. The passband this time will be very narrow, roughly 500Hz. Find and note the side skirts of the passband. Due to the extra attenuation of a CW Filter the maximum signal strength on the S Meter will be about S8, so the -6db points on the skirts will be at 1dB less, so look and note when they are at S7.
5. Now the maths again. 2200Hz – 1800HZ = 400Hz. Next 1400HZ/2 = 200Hz. Next add this to the lower bandpass so 1800Hz + 200Hx = 2000HZ. Remember the original IFN were also negative numbers? So we end up with a 8.000,000HZ Base frequency minus 2000Hz = 7.998000MHz SSB Crystal centre frequency and this will become the HamPi IF Frequency.
6. Next, Press the Set button. This will save this precious CW frequency in memory, but not for long.

6. Setting the Calibrated SSB and CW Filter frequencies into Memory

This is achieved by now by navigating to the IF= selection in the CalFeatures again without changing anything else and simply pressing the Set Button. The IFW and IFN values previously set will be added or subtracted from the initially set Base IF Frequency and then programmed into E2PROM. The IFW and IFN values are returned to 0HZ and the CPU resets itself.

Congratulations! The Radio and CPU board are not calibrated for each other and ready for the next construction phases. If ever this calibration procedure is executed it can be done as a complete HamPi in its case.

Comment: When now using the IFW and IFN features and 0 (0HZ) offset is displayed this is the centre of the passband of the Crystal Filters respectively. The volume and S Meter will start to drop at equil frequencies away from this centre frequency, for example the SSB filter, IFW will drop off at above +1000HZ and below -1000HZ.

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