Locking to the 10 MHz external reference
I noticed that D52 was lighting less brightly than D51.
With the PPT pins not closed (so Rx, receive mode) I sniffed around with my TinySA Ultra (TSAU). There were various frequency peaks. A bit messy really. Touching the chip packages resulted in the peaks moving, so it all seemed rather unstable.
On the groups.io chat, Zack W9SZ had noted that he had to increase the level of the 10 MHz reference input to 15dBm to get both DDS chips to lock properly. I didn’t want to increase the input, so I opted to adapt the 10 MHz reference onboard attenuator: resistors R51, R52 and R53.
I took a heat gun to R52 (the top of the pi attenuator) and removed it. I cleared a bit of board insulation close to the bottoms of R51 and R52 and fluxed and tinned the enlarged solder pads using a fine-tipped iron. Using the same iron, I then I replaced R52 with an SMD trim-pot of 270 ohm (“330 ohm” from the UK uW Group’s chip bank).
With some tweaking of the pot, down to about 50 ohm, I got both LEDs to light brightly when I applied power, D52 lighting first, then D51 half a second later.
Sniffing with the SA again showed two clear peaks at 1807 and 2220 MHz. Everything looked stable and touching the chips did not shift the frequencies, so it looked like both DDS chips were locking to the 10 MHz reference input.
144 MHz IF (Intermediate Frequency) input
(1807 x 12) + 2220 + 144 = 24,048 MHz for UK operation. You may be using 432 MHz instead of 144 MHz as the IF, so your frequencies will be different.
In the menu settings on the K3, I set up a transverter band for 24,048 MHz to produce output at 144 MHz. Checking the K3’s 144 MHz output on the power meter, I found that the minimum power out that I could achieve was about 2.5W.
Looking at the IF input attenuator, the four input resistors (R2 to R5) might dissipate 2W and the other resistors in the attenuator might dissipate another 0.5W, so it might just work, so long as I don’t accidentally put more than 2.5W in.
I could use a different exciter (like an FT-290), but the K3 and the internal 2m transverter are both frequency locked to the 10 MHz reference, so I prefer to use the K3.
Playing safe, initially I added a 10dB attenuator to the IF input and fed the K3 output via that, so I had about 250 mW into the IF input. Sniffing with the SA showed a peak at 2364 MHz (2220+144) and another at 2156 (2220-144), so mixing was working.
I tweaked RV1 CW (clockwise) from full CCW (counter clockwise) position. This reduced the sniffed 2364 MHz signal by 10 dB. Then I removed the outboard 10dB attenuator and tried IF 2.5W input. The adjustment to RV1 seemed to have given an extra 10dB attenuation, countering the 10dB increase of 144 MHz IF input. The onboard IF attenuator resistors ran rather hot, but probably OK. A heatsink and/or fan might not go amiss.
I added a ground pin to the board, close to the J52 solder pads, so that I could earth a probe for power measurements. The pin connected the top and bottom copper surfaces, so acted as another via.
With a power meter looking at the C8 input to the U2 mixer (the probe’s outer earthed to the new ground pin) I turned RV1 CCW. When I stopped at full CCW the 144 MHz into C8 was 4.4 dBm. This seemed a reasonable test signal. Jim suggests 5 dBm.
U3 “2.45 GHz” filter function
The U3 filter appeared to attenuate the unwanted 2076 MHz mixer image by an extra 15 dB or so.
U5 RF amplifier failure & replacement
When I measured the current into U5 at JP3, I got erratic readings: 35 mA, 11mA, 0 mA. In case there was a dry joint, I tried re-heating with the heat gun, to no avail. I shorted JP3 with a 0 ohm chip resistor and the looked at the power levels in and out. Rather than gain, I got a loss of about 10 dB for U5.
I removed U5 with the heat gun. The solder had taken well to the solder pads on the board. I replaced it & re-soldered, but no joy. U5 appeared to have failed. I don’t understand how or why. On the 24 GHz groups.io chat, a couple of people had reported failures of the U5 chip.
Adrian G4UVZ, had a couple of TQP369182 chips spare after a similar experience. He sent them to me. Thank you Adrian!
I selected a new chip and tacked the side pins to the board using the fine-tipped soldering iron. I added a bit more solder to the tab & then heat-gunned the chip.
I re-tested the current at JP3: 45 mA. Fine.
With about -40 dB (read on the TSAU via -10 dB) feeding C13, -20 dB appeared at J3, pins 3&4, so an apparent gain from U5 of about 20 dB. The datasheet quotes 20.5 dB gain at 2600 MHz, so good agreement. The replacement chip appeared to be working.
Test in receive mode (RX)
I removed the “-5V sense” short from pins 9&10 on J2 (J2 on LHS of the board).
I removed the PTT short. This put the board in receive mode (RX).
D31 on, D34 off, D32 on, D35 on.
I measured the current to the board as 307 mA (JP4 open, 6.1 V supplied).
JP4 voltage (for U6) is 4.9V. This gave a current of 39 mA across JP4. A bit less than I had expected, but probably OK. I soldered a 0 ohm chip resistor across JP4.
Jim suggests: “inject -20 dBm 2364 MHz into C20“. On Portsdown 4 (PD4) I selected the Signal Generator function and selected the Lime Mini (LM) as output. I selected calibration of the LM, then an output level of -9.9 dBm (Lime Gain=73). With the 10 dB attenuation on the PD4 output, this should apply -20 dBm to C20.
With the K3’s 24 GHz transverter offset=0.28, I found the K3’s dial reading accurate to within 5 Hz. With the PD4 sig-gen set to 2364.021,453 the K3’s dial read this as 24,048.021,004 MHz, so the PD4 was generating a carrier about 450 Hz low at about 2.4 GHz.
After “inject -20 dBm 2364 MHz into C20“, Jim suggests “Rx 144 MHz output -28 dBm“. After amplification, filtering, mixing and attenuation, this is an effective “loss” of 8dB. On the TSAU I measured -37.8 (2364 MHz input) and -46.5 (144 MHz output), a “loss” of 8 dB, so very good agreement. With U6 drawing 39 mA, the receive chain seemed to be working.
In Rx mode, I measured the current to the board as 340 mA (JP4 closed).
In Tx mode, I measured the current to the board as 356 mA.
Soldering the Pin Strip Headers on
Maartin’s checklist says: “Finally I mount the pinstrips and mate with the RF module”.
I started with J3, top left. Pins 19/20 are LHS, Pins 1/2 are RHS. I soldered pins 3/4 and made sure there was continuity to left of R15 and no continuity to ground. I checked that the header was seated well against the back of the board.
I soldered pins 17/18 and made sure there was continuity to the top of JP8 and no continuity to pins 15/16 and no continuity to ground.
I soldered pins 15/16 and made sure there was continuity to the bottom of C45 and no continuity to pins 17/18 or to ground.
I soldered the ten pins 5 to 14 and made sure there was continuity to ground and not to the other pins.
J4 next. This is on the RHS edge of the board, with pins 19/20 at the top and pins 1/2 at the bottom. I soldered pins 13/14 and checked the continuity to C20. On checking the header was well seated, I found it was slightly out. I re-heated the solder with pressure on the header. It seated properly.
I soldered pins 3/4 and made sure there was continuity to right of JP9 and none to ground.
I soldered pins 5/6 and made sure there was continuity to ground and not to pins 3/4.
I soldered pins 15/16 and made sure there was continuity to ground and not to pins 13/14.
I soldered pins 9/10/11/12 and checked continuity to ground and no continuity to 13/14.
For structural stability I soldered pins 1/2 and also 19/20, though these are electrically unconnected.
I left pins 7/8 and 17/18 unsoldered.
Finally, J2. This is on the LHS edge of the board with pins 1/2 at the top and pins 19/20 at the bottom.
I soldered pins 3/4. I checked no continuity with pins 1/2 and 4/5.
I soldered pins 19/20 and checked continuity to ground.
I soldered pins 17/18 and checked no continuity to pins 19/20.
I soldered pins 15/16 and checked continuity to ground and no continuity to 17/18.
I soldered pins 13/14 and checked continuity to ground and no continuity to 15/16.
I soldered pins 11/12 and checked continuity to left of JP7 and no continuity to 17/18.
I soldered pins 9/10 and checked no continuity to pins 11/12.
I soldered pins 7/8 and checked continuity to left of JP6 and no continuity to pins 9/10.
I soldered pins 5/6 and checked no continuity to pins 7/8 and pins 3/4.
I soldered pins 1/2 as they will provide a monitor output ( varies from -0.5 to -3.5V).
Jumper currents
In Rx mode:
measured; Jim’s example currents
JP6 375 mA, 443-453 mA
JP7 236 mA; 236-239 mA
JP9 265 mA; 246-264 mA
I connected an ammeter across JP5.
In Tx mode:
JP5 1.3 A; 1.2 A TX idle, 1.7 A with drive
JP8 1.3 A; 1.2 A TX idle, 1.7 A with drive
All looked OK, so I soldered 0 ohm resistors across JP6, JP7 and JP9.
I removed my added ground pin so that the board would not be pushed proud of the Wavelab unit by the back of the pin.
I mated the PA0HME board to the Wavelab transciever and rested the assembly on a heatsink.
g3yjr 