I set up my Icom 735 in my shack, grounded the radio and tuner to a
copper bus salvaged from an old fuse box with #12 wire. The bus is
attached to a ground rod directly outside the window with six feet of
#4 THHN. The antenna is a fan dipole cut for 40 and 20, 38 feet up on
top of the house. Field strength numbers are from a Radio Shack SWR/FS
meter and therefore completely arbitrary.

The GFCI outlet that protects the circuit the rig is on would
sometimes operate fine for hours, and sometimes trip even with the rig
power at the lowest setting. I finally got to taking some readings and
found that I was having the most trouble on 40 meters. I changed my
grounding several times until I finally arrived at the current
configuration. The situation improved somewhat, and the thing rarely,
if ever, trips on other bands. The readings from the FS meter seemed
to be all over the place. Sometimes the GFCI would trip when the meter
was reading 1 and sometimes it would work fine with the needle pegged.

I didn't take enough readings to generate a clear picture of what's
happening, but it would appear that it was sensitive to very small
segments of the 40 meter band. Power output and grounding factors
seemed to have little if anything to do with it. I could have long
QSOs, spin 20kc down the dial and pop the thing off. Another
interesting issue is that since I swapped out the GFCI for a regular
duplex outlet, there's less RF in the shack.

I assume the internal components were either part of, or reacting to,
some ground loop issues. Anyway, I said all that just so I could ask
if anyone else has had a similar experience, or if anyone has a better
understanding of the physics/electrical engineering issues behind the
problem.

Thanks in advance,
73
Jon - KC2PNF