John, N9JG wrote:
I am using an Orion to drive my Drake L-4B, and I operate mostly on 40
meters. My antenna is a 110 feet long dipole, center-fed with open-wire feed
line, and elevated about 30 feet with the support for one end attached to
the house chimney. My shack is in a 2nd floor bedroom, and the circuit
breaker panel is located in the basement at the opposite end of the house.
The house has a brick exterior, and one end of the antenna is only a few
feet from the shack.

When I operate high power on 40 meters, a GFCI equipped circuit breaker,
which is located in the house circuit breaker panel, moves to the open
position. None of my station equipment is attached to this breaker; this
particular breaker powers four outlets in the garage and two outlets on the
house exterior. None of these outlets are normally in use.

The most likely explanation is that you have large RF currents in the
power wiring of the house, due to some combination of common-mode
currents on the feedline, and/or direct coupling from the hot end of the
doublet into the house wiring in the roof.

Those RF currents will then flow to ground through the power wiring. At
the same time they will couple into the live and neutral wires, and then
flow through your GFCI in common-mode (roughly equal currents, in phase
on both wires). Since most GFCIs have poor common-mode rejection at
frequencies much higher than 60Hz, a substantial RF voltage can be
coupled through to the inputs of the IC amplifier inside the GFCI - so
it trips.

That is my best guess. To find out what's really happening, you need a
clamp-on RF current meter such as the MFJ-854 (not the MFJ-853 - it's
rubbish) or build your own from the information he
http://www.ifwtech.co.uk/g3sek/clip-on/clip-on.htm
http://www.w8ji.com/building_a_current_meter.htm

IMO this meter is the ONLY way to see and understand where the RF
currents are flowing. Then you can take steps to minimize them.

(By the way, you can almost certainly forget about an "RF ground". From
a 2nd-floor shack it's almost impossible to provide a ground path that
has a low enough impedance to shunt significant fraction of the RF
current away from the mains wiring.)


Is it possible
(or even desirable) to install one or more bypass capacitors inside the
breaker panel, and immediately adjacent to, the ground-fault circuit
interrupter? If so, what type of capacitor is recommended?

Capacitors on the power wiring are the wrong answer anyway. Almost
certainly, you need series chokes. K9YC's article about ferrite chokes
and RFI is essential reading, and an article by W1HIS (although way
over-the-top for most people) is full of practical ideas:

http://audiosystemsgroup.com/RFI-Ham.pdf

http://www.yccc.org/Articles/W1HIS/C...S2006Apr06.pdf
(or http://tinyurl.com/qnzs3 )


Use the RF current meter to track down the power conductors that are
carrying the largest RF currents, and then see what some ferrite chokes
will do. Obviously the first place to try the meter will be on the
various wires coming into the breaker panel, and that should give you a
good clues about where the RF is getting in.

But almost certainly you should start applying chokes in the 2nd-floor
wiring, and especially in the shack. Keep repeating the current
measurements at the breaker panel to monitor your progress, but try to
avoid making modifications there.

As W1HIS found, another reward for cleaning up RF currents on the house
wiring is likely to be greatly reduced noise on receive.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek