I've been watching this topic with interest. I can't add anything from a
detailed technical perspective to the discussion, but I can say that perhaps
it's not so un-common. During one contest I had major problems with a 7 MHz
transmission generating a large signal at exactly f/2. It was fully locked
to the fundamental, but a bit raspy in nature with wide sidebands. It was
power related in a non-linear fashion, and disappeared at low powers.
I never tracked it down since it had gone away when I next came to use the
station. Gear was a pair of FT1000MPs, pair of ICE switched bandpass
filters, an LK-800A on the 40m station (and a Ten Tec Titan in line on the
80m station). The was however really strong coupling between the 402CD and
the 80m loop hanging beneath it with, prior to the 80m bandpass filter,
severals 10s on W of 40m RF indicated on the Titans meter in Rx. In reality
it was less than that since the SWR was high on the 80m loop on 40, but
substantial levels of coupling anyhow.
73,
Andy, G4PIQ
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