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I have recently finished the build of ?a QMX+ with ?RWST transformer for 12V operation.

I have gone very cautiously with testing via PUTTY, starting at 9V and always with a 50 ohm dummy load.

I’m mostly encouraged apart from 160m, but could do with advice on how much I should be worrying about the following points and where to look for any problems.

1)????? Connected to PUTTY and running hardware tests.

2)????? Audio filter sweep ok on all bands.

3)????? RF filter sweep most bands acceptable, some not so great , particularly 160m. Sweeps from -16 to -12 dB. I’ve checked the turns on L401 and soldering and capacitor values C401. C440.

4)????? Image sweep ok all bands except 160m where image is -4.1 dB

5)????? SWR sweep on dummy load all 1.1 ish

6)????? Low pass sweep OK-ish, some 4 or 5 dB down on band centre frequency.

7)????? ADC I/Q ?test all bands ok ,except 160m where Q is half the amplitude of I and? in-phase instead of 90 deg.

8)????? From diagnostics screen, output power at Vin +9V / 12V supply :

160m=3.8W / 6.1W

?80m=2.4W /4.3W

60m=1.5w /2.5W

40m=1.6W /2.7W

30m=1.8W /3.0W

20m=1.6W /2.6W

17m=2.1W /3.0W

15m=1.7w/2.8W

12m=1.7w /3.2W

10m=1.7W/3.2W

6m=0.3W /0.4W

9)? So image and ADC I/Q tests on 160m look wrong consequently the? receiver doesn’t seem to work on this band. I’ve read about PCM1804 problems but as all other bands are ok on image and ADC I/Q, it doesn’t seem likely that is the cause? Any ideas ?

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Thanks for the response Alan,

I was under the impression that was the QMX not QMX +, but if that's so I can rest easy? and wait for a firmware upgrade.

73 Hugh

Hugh, the QMX plus does work on 160M. ?I think you have a poor solder joint on the band pass filter L401. ?It is tapped, for 160M and 80/60M. ?Your output is good on 160, so the LPF is fine. The receive filter sweep relies on clock 2 getting all the way from the output, back through the filters. ?If you have a problem with the 160M section of L401 there won’t be enough signal to give meaningful test results on the diagnostics. I recommend checking L401 continuity on the toroid side of the board on the solder pads. If C401 isn’t soldered correctly you will have the same fault. Anyway usual caveat that I might be wrong but this is the most likely explanation. 73 Nick G0OQK

The image and i/q response is due to a firmware issue.? It can be ignored for now (yes on the qmx and qmx+, they both use the same firmware).

Your power out on 6m is very low.? If that band is important to you, you can likely adjust the LPF or the T501 windings to improve it .

Thanks for the feedback Nick, I'm pretty sure I've done those continuity checks but I will look again around L401/C401 tomorrow.

73 Hugh GM8FXD

Nick, I thought 160m receive wouldn't yet work correctly? TX should work, but IIRC the image sweeps will NOT be correct.?
See: /g/QRPLabs/topic/107754303

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-Nate?

N8BTR

Ok Stan thats useful to know, save me banging my head on the bench !!

Yes the low pass response on 6m is well down.

73 Hugh GM8FXD

I was able to go from 0.6 watts on 6 meters to 2.6 watts by removing turns from L520, the toroid closer to the antenna.? I ended up removing 4 turns, but you will want to do this one turn at a time, checking power out and the LPF curve as you go.

Hi Dan,thanks for the suggestion, I will indeed try that next.

Hans diagnostic tools are great help with this sort of problem.

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While waiting for firmware to fix 160m problem is the bandpass filter response below typical ?

I will be doing Nicks suggestion around L401,C401.

73 Hugh GM8FXD

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On Thu, Jan 9, 2025 at 03:18 AM, Hugh-Gm8fxd wrote:

lem is the bandpass filter response below typical ?

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Thanks Nate,

Yes filter shape is not too far off, just noted the overall signal level seemed low.

Probably ok for these low frequencies, just curious if it was typical.

73 Hugh GM8FXD

Excellent advice Dan !

I took 1 turn off L520 and redistributed the turns evenly and measured 2.5W at 9V supply.

I can also now hear our local 6m beacon, so I will leave it at that.

Many thanks.

73 Hugh GM8FXD