"Yes the harmonic DOES have a growl to it!"
Hi Martin,
You've described a classic symptom of an intermod problem, which
I refer to more specifically as "RF flooding." No amount of filtering
of your transmitted or received RF signals will fix it. In most cases
the intermod originates in your own ham shack, in your home or in
nearby homes or buildings.
It results from a very strong RF signal entering an electrical or
electronic device with little or no protection from a very strong RF
signal. When the RF enters the device it mixes with AC power or
digital signals and re-radiates both the fundamental and harmonics
of the very strong RF signal onto the AC power wiring which serves
as an antenna, but the reradiated signal is modulated by 50 or 60 Hz
AC power and its harmonics or by digital signals (these are the
sources of the "growl" you reported).
The RFI hunting process is nearly identical to hunting any other
RFI problem. Turn your transmitting antenna to the direction
that causes the most "growl." Then turn your receiving antenna
or RFI hunting antenna to maximize the "growl." Then hunt the
RFI the same way you do for AC power line RFI.
Start by turning off all AC power in your home except for your
transmitter and receiver. All other equipment in your shack and
your home -- especially all UPSs and wall warts -- must be turned
off and all wall warts unplugged.
Good luck!
73
Frank
W3LPL
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