Next I tried putting lots of ferrite on the incoming coax. At first I thought I was getting somewhere, after putting about 20 clamp on ferrites on the coax, the RFI was pretty much eliminated. Unfortunately, so were all signals on this part of the spectrum.
This part, just above, is downright scary; sounds like ALL your pickup is via induction between coax, the BALUN and some wire in the 'loop' (and not exclusively due to a "propagating" RF wave creating/inducing currents flowing only in the loop!)
Obviously, speaking RF ex cathedra
the majority of the signal was not via differential 'signals' (RF energy) appearing at the input to the BALUN from the loop, but rather something much more involved and un-intended (i.e. not per the intended design!)
One or two 'isolation' ferrite transformers in series with the coax cable might have been tried as well, but with probably the same results as the clamp ferrites.
(Of course, I assume we all understand that the 'differential' currents flowing on the inside shield and outside center conductor of the coax (in what is called "TEM", TEM00 for "Transverse ElectroMagnetic" mode) are not in anyway affected by application of ferrites around the outside *shield* of the coax!)
my $1.25 on the subj anyway.