I have a Ham IV that when I turn on the brake the receive signal takes on a
60 or 120 hz hum . I though it might be the control box too close to my
Icom 746 PRO. I have a switch box connecting two lowband wire antennas and
a triband beam to the Icom. If I listen to a signal on the wire antennas I
do not get the hum modulation on the incomming signal when I rotate the
beam. Those coax wires are not near the rotator wires. This tends to
eliminate the transfromer of the rotator box from getting into the Icom by
magnetic coupling. If I switch to the beam , then turn the brake on the
rotator box I will get hum modulation. The triband is fed with some Davis
Bury flex (foil and braid shield coax) and the rotator wires are taped to
the coax for a distnce of about 100 feet.

The antenna does not have to ratate, just mashing the brake release button
will make the signal hum modulate on receive.

The Icom is being powered by an Astrom 50 amp supply and the rotator plugs
into the 120 vac outlet.