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Just completed my Rev 3 Hi band QMX. Rx sensitivity is okay and Tx power out is very good on all bands. Probably all needs a bit of tweaking, but pretty good so far.

However, there is noise present on receive on all bands, CW or digital, with antenna or dummy load, battery or power supply. It varies with volume setting. Lo band QMX with same attachments has no noise.

Attached is a recording of it on 20m FT8 frequencies. This is representative of all bands, all modes, DL or antenna. I am wondering where to start for troubleshooting. Any suggestions?

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73, Dan? NM3A
There are moments when everything turns out right .... Don't let them alarm you; they pass.

-Jules Renard

Follow up:
Observing waterfall in WSJT-X shows noise as well. Picture shows 20m, 18m, 15m, 12m, & 10m from bottom to top. One picture is with rig attached to dummy load and cycling through from 20m thru 10m. The other picture is on the antenna again cycling through from 20m through 10m. Each band has two cycles of FT8 data.?

I believe this would point to the noise coming before the D/A and audio amplifier sections. Although I don't think the CPU is the culprit, I don't think it can be ruled out. IC405 and IC406 are unlikely, as there would have to be a similar fault in both chips.?

I swapped both SMPS from my lo band QMX, but no change in noise. So I doubt power bus issues. Bad capacitor somewhere?

That leaves the RF sections or the PCM1804. I think, anyway. Any further suggestions to check?
--
73, Dan? NM3A

Any ideas anyone?
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73, Dan ?NM3A