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I’ve boxed up my Specan into a chassis and carefully shielded the LPF, BPF, Crystal filters, Log Amp Detector as well as the Arduino on a copper ground plane in a steel metal chassis. ? I am getting a -65 dBm noise floor, whereas I seem to recall getting -88 dBm when it was all spread out on a plywood breadboard, (albeit with a copper ground plane also). ?I see here you had a -92 dBm noise floor. ?Any guidance? ?When I de-power the 2nd Oscillator, the noise floor drops down appropriately. ?I have checked all the decoupling capacitors and added a filter onto incoming +12 VDc.

Ashar, I have tried experimenting with the grounding of the smaller modules, to see if it impacts.? I re-oriented the 12 VDC power lines, and seem to get some improvement to now get -75 dBm ish noise floor levels.? ?If I disconnect the power to the 100 Mhz 2nd oscillator, then the 0 power level measured on the Log Amp drops about 10 dBm.? ? I may add an Inductor on the Log Amp power to try filter more.? ?I tried to replicate your design, and note that you had attached the power lines close to the ground plane with small copper wire loops; and recommend running these wires perpendicular to any (imagined) RF fields.? ?Also, I note that you had two Youtube Videos issued, and Take 1 showed your noise floor at about -75 dBm; then Take 2 video (doing two-tone testing demonstration with new software) resulted in a -88 dBm noise floor level.? ?Do you recall (many years now) if you had made some changes between those 2 videos, that resulted in such lower improved noise floor?? ?Its been a fun journey for me, and I may just accept the -75 dBm level, but am interested in finding how to optimize a bit more.? Cheers, Va3nma Nigel

I shielded the 100 MHz oscillator and this reduced all noise issues. ?The oscillator is as spraying into the power lines.