I acquired? a damaged QCX-mini from an sk estate.? The volume knob and and pot shaft are missing.? Looks like the shaft of the potentiometer broke below the case, possibly it was dropped and hit the knob.? The unit powers up at 12volts and appears to work just fine.? The remaining shaft is operable by placing a splunger on the remaining shaft and ,with difficulty , I can adjust the AF gain.? At power up it says it is a? 2020 version 1.07a, which I would guess is the firmware.? Does anyone know what the part # or part description might be?? Possibly even the digikey part #, as they are in my back yard.? Seems like it would be straight forward to pull it out of its case and replace the pot and knob with original parts.? It is a 30 meter model if that matters.

Thanks in advance,

AD?SN

All right.? Continuing to explore the subtleties of my new QMX+.

Starting my QMX+ in CW mode sometimes comes up very noisy, sometimes very quiet, but usually just right.??

Starting in DIGI mode always comes up just right.

That suggests that it's the AGC that's making things very noisy and very quiet.? (I'm doing all of this with the default AGC parameters.)

Well, can I get very noisy just by switching between CW and DIGI?? No.? I tuned 7074kHz and switched between CW and DIGI until I got tired, and I never got the radio to switch into very noisy or very quiet.??

What happens?if I start noisy/quiet on?CW and switch to DIGI?? The?noisy/quiet persists and I get noisy/quiet on?DIGI.? And it stays noisy/quiet if I switch back to CW again.

That seems to let the AGC off the hook.??

Is anyone else seeing this?? Here are the scores for three trials I just did on 20m.? I'm recording the number of starts that were right (R), noisy (N), quiet (Q), or other (O).??I set the audio gain to a comfortable level before I start.? Noisy is too loud to listen to, quiet is too soft to hear well.? The AGC is using the default parameters.? I thought that FT8 made a good source of noise, but apparently dead air may work even better.? Use a speaker if you aren't sure how noisy it gets.

R / N / Q / O

10 / 2 / 2 / 0 20m 14074

19 / 1 / 2 / 0 20m 14074

15 / 5 / 2 / 1 20m 14084 quiet (O was an intermediate noisy R and N)

Thanks for reading,

-- 73 -- rec -- ad5dz --

On Tue, Jan 21, 2025 at 3:36?PM Chuck Harris via <cfharris=[email protected]> wrote:

There is no AGC on DIGI, see page 62 of the operating manual:

"AGC: ON/OFF parameter which enables the entire AGC system.? The AGC
system is only operational in CW mode.

-Chuck Harris, WA3UQV


On Tue, 21 Jan 2025 15:05:59 -0700 "Roger E Critchlow Jr" <rec@...>
wrote:
> Thanks, Dick, that was worth exploring.
>
> I put my QMX+ on a dummy load, started it, and sprayed the PCM1804
> with a can of Dust Off compressed air with a director tube on it.
>
> The compressed air would induce a chuckling noise that got louder and
> lasted longer the longer the chip was sprayed.? The noise quickly
> decayed when the spray was removed.? When turning the radio off and
> on, there was a vestige of the chuckling noise each time the audio
> powered up, but the chuckling quickly decayed.
>
> None of these experiments produced either the loud noise or the
> quieted receiver that I originally reported.? The chuckling was easy
> to listen to at the audio gain level that I last used, the painfully
> loud noise is a full throated hiss that forces you to remove an ear
> bud.
>
> The maximum temperature rating for the PCM1804 is -70C to 125C, the
> recommended temperature rating is -10C to 70C.? When I pulled out my
> IR thermometer gun, it read the PCM1804 temperature at 15C, and the
> longest spurt of compressed air I tried only lowered the temperature
> to 13C. Turning the receiver on I was only able to raise the PCM1804
> temperature to 17C.? I think I need a different thermometer, or maybe
> the effect I'm hearing is actually the result of temperature gradient
> stress.
>
> However, when I put the receiver back on the magloop antenna, tuned
> it to 14074, and turned it on in CW mode, I got the painfully loud
> noise twice in about 20 trials and normal reception on the other
> trials, no quieted receiver.? Repeating the experiment in DIGI mode,
> no painfully loud noise or quieted receiver in 20 trials.
>
> Is it possible that the AGC works differently in CW and DIGI?? ?And
> maybe this painfully loud noise is an AGC artefact?? The loud noise
> is similar to the effect of turning the audio gain up until the audio
> goes into distortion, though I can't make myself push the gain too
> far.
>
> An interesting hour, thanks for the suggestion,
>
> -- 73 -- rec -- ad5dz --
>
> On Tue, Jan 21, 2025 at 6:36?AM Richard Hattaway via
> <rhattaway= [email protected]> wrote:
>
> > My HB QMX is painfully noisy when I start it. This issue is
> > temperature sensitive in my case. I can put the radio near a room
> > heat vent and the time it takes to settle down is significantly
> > shorter. My shack is ~ 60 F in the winter. If I allow the radio to
> > sit away from the vent overnight it takes a minute plus to calm
> > down and not be painfully noisy. I am sure this is an 1804 issue
> > and it will be addressed when all the things needed to change it
> > get here.
> >
> > If your radio finally calms down it might be the same issue ?
> >
> > 73
> > Dick
> > W4PID
> >
> >
> >
>
>
>
>
>