Reached a point of diminishing returns on this internal noise issue.
Here’s what is effective:
5v DC-DC converter (Drok) upgraded.
Single board LPF on converter output.
Proper grounding on converter.
RF shielding on 22 pin DPI ribbon
RFI cover over display module
HAT RFI plate on Pi4
These enhancements have attenuated the internally generated RFI.
Especially shielding the DPI cable.
Looked at the receiver chain.
Improper IF level can cause what I’ll call pulse oscillation on the higher bands 20 meters and above. On this unit going above 45-60 just causes increased internal noise. S/N suffers greatly especially in LSB.
On this unit it would pulse when IF level setting was between 30-40. Strange thing it stops when you increase or decrease the level.
Checking the receiver sensitivity. I compromised to maintain decent sensitivity and minimal to almost no internal generated RFI. Forget weak signal work but it will catch 90%. Doesn’t appear to have a significant effect on FT8.
RFI mods are working to a point.
When I received this unit 40 meters had an oscillating noise floor and was unusable. Now FT8 on 40 is no problem.
On this unit the IF level ended up being 15-20.
With 15 being were I left it. Yours will be different.
So the IF gain setting is (of course)sensitive and critical for optimum signal with tolerable receiver noise.
This coupled with the internal shielding
has improved the overall operation of the SBITX V3.
Thanks everyone for your assistance and tolerance.
Kb4yho