Hi all,
Some of you who are experiencing QRM from medium wave broadcast stations
may find this story interesting, and it may even help you to help them
(the broadcaster) solve their problem.
I used to operate 160 meters at a club station about two miles away from
a MWBC site that had two transmitters duplexed into one antenna. There
were several mixes that could be heard. Some of them were generated in
nonlinear devices that were not part of the broadcasters equipment. The
mixes that were generated by the broadcasters equipment seemed to be
mostly within the legal limits. The one component that was clearly above
the limits was the second harmonic of KVEC 920 kHz, on 1840 kHz. The
transmitter they were using was bought used from a station that had been
on 1050 kHz (or something like that) and the second harmonic trap was
still tuned to 2100 kHz, instead of 1840 kHz. Tuning the trap to the
right frequency helped a lot. The trap consisted of a fixed capacitor
and a roller inductor that was pretty corroded. So it was somewhat
intermittant. I offered to build them a trap that would work
consistantly, they declined and eventually bought a new transmitter
instead. Sadly none of the cooperative effort to solve their problem was
initiated until after I notified the FCC they were out of compliance.
Previous to that they just said it was my problem and not theirs.
Ken N6KB
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