I have had two instances over the past few years of similar noise Mike.
Both cases turned out to be small switching power supplies...one for a
Dell laptop, the other for an LCD monitor. Both supplies were very
quiet under normal circumstances, but were laying on the floor along
with lots of coax including the feedlines for the low-noise receiving
antennas. When my feet would move things around under the op table,
sometimes one of those two supplies would wind up on top of or next to a
low-level coax. The coupling was magnetic, not RF. Switching power
supplies radiate a magnetic field and coax is not "shielded cable" WRT
to a magnetic field. A magnetic field will produce unequal current in
the shield and center-conductor of coax. Moving the little switchers
off the floor solved the problem. SteppIRs and other new gear often
come with their own switching power supplies. The 33 V StepIR supply is
A LOT noisier than the standard 24V one BTW.
73 Hal N4GG
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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