Experimenting is in order. One thing you could try, with care, is to plug in the fridge with a cheater adapter that isolates the frame from ground to see if that helps. As a next step, ground the frame to something other than the power line 3rd wire. Another thing would be an old school 60Hz isolation transformer, although I have found there tends to be too much capacitance between windings. A transformer with a groundable shield between windings might work. You could try a UPS if you had one large enough, but of course they can be their own source of RFI. Then it is on to the line filter option.

On 1/3/2025 11:47 AM, Paul N1BUG FN55mf wrote:

Since my return I have been plagued by periodic RFI that reduces S/N on
630m by 10 to 15 dB, maybe more at times. It tends to cycle on for one
to three hours, then be off for a few to several hours. Audibly in AM
mode it is a somewhat rough 120 Hz buzz. Noise blankers don't touch it.
I can identify this RFI from below 10 kHz to above 500 kHz, but there
are several broad peaks and valleys across the range. The worst of them
is very broad centered approximately on 450 kHz but remaining almost
flat up to and across 630m. I have not tried to find the upper frequency
limit since I really don't care about anything above 500 kHz.

Early this morning I found it the culprit. It is my refrigerator!
Perhaps a line filter will help, although my luck is rarely that good.

I'm still chasing one, possibly two serious RFI sources affecting 2200m
but won't go into that here.

73,
Paul N1BUG

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