In the picture you can see the SMA connectors of the Wavelab unit, underneath the PA0HME board. Underneath the Wavelab unit is a heatsink. To the right and also on the heatsink is a Leo Bodnar “reference clock” (LB). This was set to 586,537,100 Hz. The Output 1 BNC socket is placed close to the “Rx In” SMA socket of the Wavelab unit. I inserted a small piece of wire in the Rx In SMA socket of the Wavelab unit to act as a receiving antenna.
To the Tx Out socket, I attached a 10 dB attenuator feeding the power meter. The blue+green wire pair is for measuring the current across JP5.
586,537,100 Hz x 41 = 24,048.021,1 MHz. With the 24 GHz transverter band selected on the K3 and the K3 dial tuned to 24,048.021,1 MHz, I found the IF output pretty well spot on frequency when the K3’s transverter offset was set to -0.32. (-111 dB level on the P3 display). The carrier was remarkably steady, so all the frequency locking seemed to be working.
This was my first reception ever on the 24 GHz band.
I added the PTT short for transmit. With 6.4V across the DC In pins, 1.3 A flowed across JP5.
With 2.5 W drive on 2m from the K3, JP5’s current increased to 1.4A. The RF Out from the Wavelab unit measured 30 dBm, so 1 Watt. The heatsink got quite hot.
Then the output became erratic and then I got no output. I was very puzzled. 24 GHz reception still worked fine.
More U5 RF Amp Troubles
I checked around U5 with the TSAU probe and found that the U5 RF amp (TQP369182) had stopped working. I had already replaced this chip; see last post.
I removed the zero ohm resistor from JP3 where I soldered another pair of wires and added a 1.5 ohm resistor across the pair. Across that I added an analogue 100 uA meter is series with a 1 Kohm pot (variable resistor). So in effect I had a milliameter across JP3. This showed erratic, low or no current.
I re-fluxed U5 and resoldered the ground pin and tab. The resulting soldered tab did not look so pretty, but I then got a steady 45 mA across JP3 and 1 W out at 24 GHz. Transmit was working again!
Pin1 on J2 showed -1.56 V. J5 drew 1.5 A (1.3 A with no drive). The “%” scale on the “Modulation” meter effectively shows 44 mA across JP3. With the 22 ohm R10 plus the milliameter, there is probably 24 ohm in the DC feed to U5.
An analogue meter is great for monitoring fluctuating currents.
U6 amp problems
I left the Wavelab receiving the LB harmonic. When I came back after several hours, reception had stopped. Suspecting the U6 amp (another TQP369182, like U5), I pressed down on each of its pins in turn. This made no difference. However when I pressed down on the U6 package, reception restarted, only to stop again when I released the pressure. I suspected a dry joint as I had had with U5, but re-soldering did not help. Jumpering the tab or pin2 to ground did not help either.
Reluctantly I took the heat gun to the package and removed it. I soldered in my last remaining amp chip into place. That worked fine! So both transmit and receive were working.
I wonder whether I have damaged the amps by heat when I have struggled to solder them to the board? Perhaps an internal connection has broken and pressure distorting the package fixes it temporarily. Soldering heat does sink away well for these chips. A hot plate might help.
I hope U1 doesn’t fail; I don’t have any spares left and the manufacturer seems to have stopped making them!
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 whenI 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.
Jim KM5PO kindly let me add my order to the North Texas Microwave Society’s order list. In a surprisingly short space of time the mostly-populated board arrived and I set about familiarising myself with the board. Jim’s slides were a great help. Jim also sent me an ATTiny chip, pre-programmed to get me on 24,048 MHz with a 144 MHz IF. I ordered the BoM from Mouser UK for the remaining components.
R1, R10 and R20.
On 3-July-2023 Mike K6ML noted: “Like others, I subbed TQP369182 for U1, U5 and U6. So, I changed R1, R10 and R20 to 22 ohms to set the bias current to the data sheet value. Saves a few mA and the MMICs run cooler; probably no big deal”.
Chips running cooler sounded good, so I set about taking off R10, R1 and R20 in that order. I stuck some protective Kapton tape to the board in order to mask off other components. Others will be familiar with these techniques, but this was my first try. Mostly, I avoid SMDs (Surface Mount Devices) where possible!
I set the PA0MHE board on a wooden base. (A plastic one might melt and stick to the PCB).
I tried removing R10 first. I used the heat gun, blowing away from the other nearby components and viewing my work under a magnifying lamp. After some seconds heating I was able to ease R10 from its pads using a small-tipped screwdriver.
I added more tape for R1 and R20 (the latter just labeled “20” on the board, below C19/C14).
Below shows after heat-gunning, with R1, R10 and R20 removed. My tape did shrivel, so I am guessing it is not the top quality stuff. Anyway, the other components remained attached to the board, so the tape probably helped.
Basically I followed Jim’s slides and started at the top of my Mouser BoM list of components and worked down. Page 25 of Jim’s slides mentioned U3 the 2.45 GHz filter and the inductors L2, L5, L6, so I started with these and the new 22 ohm resistors for R10, R20 and R1.
U3 2.45 GHz filter.
If I soldered U3 again, I think I would prefer using the fine-tipped soldering iron and tiny snips of solder, but for my first component I decided to use solder paste and a hot-air gun. I decided to fit U3 first as it didn’t have many other components close by: just C9 and C10.
I tried measuring the series resistance of the filter with a multimeter. I could tell no difference between the filter and a dead short with my meter (to 0.1 ohm accuracy), so measuring the resistance of the filter when on the board would not help with knowing whether the board had taken it properly.
With a scalpel tip I scraped away a little board insulation from the copper pads above (towards the top of the board) and below the filter position (towards the bottom of the board), so as to improve the chances of good connections at the ends of the filter. I added a little liquid flux to the contact pads on the board.
I set the filter in position, then using the same fine-tipped scalpel blade, I transferred a small amount of solder paste to the left and right edges of the filter. (I decided not to try the top and bottom ends soldering at the same time). I cleaned the scalpel & held the filter against the board with the scalpel tip. (Earlier, I had tried a cocktail stick as a tool to hold down the component, but the cocktail stick had burst into flame!) I applied the heat gun (450C), angling away from the other components. Through the magnifying lamp lens, I could see the solder paste go liquid & wet the side contacts. As far as I could tell, the solder had not run anywhere else.
I used the scalpel blade to apply minuscule amounts of solder paste to the top and bottom end contacts across to the board pads. Once again, I used the cleaned scalpel tip to press the filter to the board. The solder ends appeared to melt & wet the end contacts nicely.
With the multimeter I checked the continuity between the top ( as seen on the board) of C9 and the bottom of C10. It looked like a dead short, so either the filter was fitted correctly or… there was a dead short.
Looking with a magnifier, it looked as though no solder had run where it should not have done. There were no visible solder bridges between ends and sides. I had created a lot of very fine solder balls which I would clean off later when I cleaned the whole board.
One component fitted!
I remembered that as a member of the UK Microwave Group, that I had access to the Chip Bank. I ordered some 22 ohm 0806 SMD resistors.
Soldering components to the board
Mostly, I have not used the heat gun as I did above for the filter. Mostly, I have applied liquid flux to the boards contact pads, cut a short length of fine reel solder (maybe only 1mm long – a solderette!) then with the component stuck down with Koptan tape, or pinned down with a wooden skewer or both, I placed the solderette beside the component pin and on the board’s copper contact pad, then applied a very fine-copper-tipped soldering iron to melt the solder and make the joint.
L5 33 nH and R10 22 ohm
When the 22 ohm resistors arrived, I decided to attempt adding L5 (33 nH) and R10 22 ohm (near to U5, near the top of the board). The inductors may be damaged by too much heat, so I decided to use a very fine-tipped soldering iron.
L5 first: I checked the continuity of the inductor. OK. I wetted the contacts on the board with liquid flux. Then I cut a solderette and placed it against one end of the inductor held on the board by the tip of a wooden skewer and applied the fine-tipped soldering iron to melt the solder. The solder wet the contact nicely & ran up against the inductor contact. A bit of blue plastic casing came away from the inductor, dislodged by the skewer, but the inductor’s continuity was still OK.
I cut another solderette for the other end. It soldered well. L5 installed!
R10: I added the new 22 ohm resistor in the same way. Then I checked the resistance from the right of C16 to the top of JP3. About 22 ohm (the value of R10), so looking good.
L6 33 nH and R20 22 ohm
I repeated the procedure, for L6 and R20, applying the gentlest of pressure on the inductor to hold it in place whilst soldering. I checked resistance from right of JP4 to bottom of C14: about 22 ohm.
L2 33nH and R1 22 ohm
I repeated the procedure again for R1 and L2 and checked the resistance from the right of JP1 to the left of C6: about 22 ohm again.
L53, L54 3.9 nH inductors
These were the next item on the Mouser delivery sheet. Soldering with the iron and solderettes had been going well, so I used this method for these inductors. L53 goes to the left of U53 and C73. L53’s resistance measured as 0.1 ohm on the board.
L54 goes to the right of U54 and C74/84.
Q31, Q32 NPN bipolar transistor pair (5 pin)
Sticking with the soldering iron approach, I attached Q32 to the right of U32 and R40 in the bottom, left-hand corner of the board. At first, I did not find a place for Q31. See later.
U32, U33 LDO Voltage regulators (29302AWU)
I scraped the underside of the devices’ contacts clean, including the tab.
Holding the U32 device in position with the wooden skewer, I soldered the left-most pin with a solderette and then the right-most likewise. Then I re-used the bigger solder-station soldering iron on each pin & ran a little more solder in from the reel in order to make sure of good contact. With the device secure, I soldered the other three pins. Then I used the hot air gun to get the tab hot and the ran solder under the tab. Same again for U33.
U1, U5, U6 RF amplifier DC-6GHz NF 3.9 dB
I tried U5 at the top of the board first. I soldered the left pin with the fine-tipped soldering iron, then the right & then the centre. I used a longer snippet of solder for the tab. A fair bit of solder ended up on top of the tab, so I tried the heat gun in an attempt to run the solder in underneath more, but that did not work, so I left it as it was. The tab looked electrically soldered to the board pad, so I guess it will heat sink OK.
I added U1 and U6 similarly.
U36 Voltage regulator 5V -ve output
This was rather close to U31, but soldered in fine with solderettes and the fine-tipped soldering iron.
D36 zener diode
I used Kapton tape to secure the diode and then soldered it to the board with the fine-tipped iron.
U51 ATTiny
Again Kapton tape to hold the device to the board, the pin-1 dot to the LH top corner (C51 connects to pin-8). I soldered pins 1 and 5 (opposite diagonal corners) to secure the device and then soldered the rest of the pins.
Q31 NPN bipolar transistor pair (5 pin)
I did not find a label on the board for this device, but working back from the schematic, I figured out where it went: just above R37, near J32, the PTT connector at he bottom right of the board.
RV1 100 ohm trimmer resistor
I soldered this in with the fine-tipped iron. Max resistance was with the pot fully anti-clockwise, showing as 34.5 ohm on the test meter, with the trimmer on the board.
I added headers for DC supply, PTT and Bias-T followed by SMA sockets for 10 MHz ref and IF.
Note the jumper (looped underneath the board) in J2 across pins 9 and 10 for -5V sense.
DC Power supply lead
I connected a connector block with a 7.5V 5W zener diode, a DVM and a fuse holder. I didn’t find an “idiot diode” on the board, so I added the zener both as over-voltage protection and reverse-polarity protection. In the event of reverse-polarity, the zener should forward conduct, showing less than 1V (reversed) to the board and blowing the fuse. MOSFET reverse-polarity protection would be better really.
So that was most of the assembly, excepting the pin strip headers.
g3yjr 