[Elecraft] Hum coupling?

[Stuart Rohre]

Actually, Tom switching supplies may have a worse coupling effect since they
have an oscillator going at higher frequency than the power line, in
addition to power line 60 Hz.

And, even coupling of RF between Tuner and Radio can happen.  At a Field Day
one time, a tuner was placed on a Yaesu transceiver, and did not tune a
dipole well at all.  After some frustration, we discovered there was
magnetic coupling right thru the aluminum case of the tuner from its coil to
the radio's tuned circuits causing an RF feedback.

Moving the tuner from the top of the radio cured all problems.
-Stuart
K5KVH