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Roger, it would help to isolate this if you could use an SDR program to capture screenshots of the I/Q mode output in each of your 3 modes (OK, Noisy, Quiet).? This would isolate whether it is a PCM1804 problem or a problem later in the audio generation circuitry (D/A and amplifier).? If the IQ data into an SDR program looks normal, the problem is in the audio path.? If the IQ data reflects the problem, then it is likely the PCM1804 chip.
?
Since all of the data you can give us right now is very subjective, this would also be objective measured data.? To do this, download a simple (free) SDR program like sdrpp or NaP3.? I have both of these, they are pretty easy to set up.? NaP3 may be a bit more intuitive.? Then you just need to set the data input source to be the QMX device, after the QMX USB is attached and QMX powered on.? (You can skip the rig control CAT stuff for now, all we really care about is the SDR panadapter/waterfall screen).? If you tune the QMX to one of the FT8 frequencies like 14.074, in a 'good' operating mode, you should see the large FT8 signal stack somewhere on the SDR display - it may not be centered, due to the 12kHz IF and 48kHz sampling rate.? You will also see other signals and tone spurs across the display.? Now if you can get the QMX into a 'bad' mode, if the SDR display still looks the same, you need to look for the problem in the audio circuitry.?? If, on the other hand, the SDR display looks like a big wide blob of energy, it is almost certainly the PCM1804 chip putting out digital garbage instead of a clean I/Q signal.? Or if the display goes quiet, it may also be the PCM1804, maybe not initialized correctly.?? There is, of course, a possibility that the problem is an intermittent solder connection in the RF path somewhere leading up to the PCM1804, so before replacing that chip, I would touch up all the RF solder joints, starting with the BPFs (L401), the trifilar transformer (T401), and the circuitry of the mux and mixer chips and the dual-op-amp chips.
?
Good luck in finding this.? Or maybe just ignore it since it is so easy to get back into a good mode.
?
Stan KC7XE
 

Can't resist - even on such a serious topic.
Subject:? ? Q
? ? ? ? To:? ? Roger
?
Would that be Roger Moore?
Sounds like a Bond thing!
-------
Robert Giuliano
KB8RCO
 

Stan --

I guess you're not confirming, because if you had heard "very noisy" on a QMX+ you would not suggest simply ignoring it.

I just ran trials on all bands and every band produced at least one noisy start.? Overall score was R/N/Q 106 / 12 / 4.

A bad RF connection still makes sense, I thought I had fixed it when I found a loose collar on a SMA-BNC adapter.

Na3P appears to be Windows only, sdrpp wouldn't install 3 versions of its binaries for Ubuntu, the fourth binary installed but came up with no audio on Ubuntu 24.04 LTS, upgrading to Ubuntu 24.10 found an audio library but no spectrum, and my life is looking too short to waste more time on this.? Maybe I'll adapt Quisk or write my own.

Thanks for your thoughts.? You're right that "very noisy" and "very quiet" are a little subjective,?

-- 73 -- rec -- ad5dz --


On Thu, Jan 23, 2025 at 6:04?PM Stan Dye via <standye=[email protected]> wrote:
Roger, it would help to isolate this if you could use an SDR program to capture screenshots of the I/Q mode output in each of your 3 modes (OK, Noisy, Quiet).? This would isolate whether it is a PCM1804 problem or a problem later in the audio generation circuitry (D/A and amplifier).? If the IQ data into an SDR program looks normal, the problem is in the audio path.? If the IQ data reflects the problem, then it is likely the PCM1804 chip.
?
Since all of the data you can give us right now is very subjective, this would also be objective measured data.? To do this, download a simple (free) SDR program like sdrpp or NaP3.? I have both of these, they are pretty easy to set up.? NaP3 may be a bit more intuitive.? Then you just need to set the data input source to be the QMX device, after the QMX USB is attached and QMX powered on.? (You can skip the rig control CAT stuff for now, all we really care about is the SDR panadapter/waterfall screen).? If you tune the QMX to one of the FT8 frequencies like 14.074, in a 'good' operating mode, you should see the large FT8 signal stack somewhere on the SDR display - it may not be centered, due to the 12kHz IF and 48kHz sampling rate.? You will also see other signals and tone spurs across the display.? Now if you can get the QMX into a 'bad' mode, if the SDR display still looks the same, you need to look for the problem in the audio circuitry.?? If, on the other hand, the SDR display looks like a big wide blob of energy, it is almost certainly the PCM1804 chip putting out digital garbage instead of a clean I/Q signal.? Or if the display goes quiet, it may also be the PCM1804, maybe not initialized correctly.?? There is, of course, a possibility that the problem is an intermittent solder connection in the RF path somewhere leading up to the PCM1804, so before replacing that chip, I would touch up all the RF solder joints, starting with the BPFs (L401), the trifilar transformer (T401), and the circuitry of the mux and mixer chips and the dual-op-amp chips.
?
Good luck in finding this.? Or maybe just ignore it since it is so easy to get back into a good mode.
?
Stan KC7XE
 

On Fri, Jan 24, 2025 at 10:46 AM, Roger E Critchlow Jr wrote:
f you had heard "very noisy" on a QMX+ you would not suggest simply ignoring it.
I have indeed heard "very noisy" on my QMX, and it was caused by digital garbage coming out of the PCM1804, which I replaced to fix it.? And I certainly could not ignore it.? I did verify that it was the PCM1804 using the method I suggested to you.? The only reason I suggested a possibility of ignoring it in your case is because a) it seems to start directly at power-on, and b) a simple power-cycle cures it about 90% of the time (per your numbers).? If that were an acceptable operational scenario for you, you wouldn't need to fix it (until/unless it got worse).? I wasn't suggesting to ignore the noise.? And if it was me, I would indeed search it out and fix it.
Stan KC7XE
 

I wonder if it's from the pressure at the encoder. Every time you press the PCB is bend a little bit. Could it be a colder solder joint is changing the parameters. Or could it be an unwanted solder connection does the same?
?
73 Ludwig
 

That's a possibility.? I suppose I could pop off the front panel and use a jumper in the appropriate pin socket.? That could eliminate both button pressure and vibrations.? But all roads lead to cold solder joints, and I just got a nice new chisel tip yesterday.

-- 73 -- rec -- ad5dz --

On Fri, Jan 24, 2025 at 3:24?PM <DH8WN@...> wrote:
I wonder if it's from the pressure at the encoder. Every time you press the PCB is bend a little bit. Could it be a colder solder joint is changing the parameters. Or could it be an unwanted solder connection does the same?
?
73 Ludwig

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