[HBR] Birdies

[Brian Burns]

Hello Ian,

~ Sometimes it can be very difficult to tell which signals are causing the
interference. High harmonics of the BFO can mix with lower harmonics of some
other oscillator, for example. You can sometimes get a clue by observing how
fast a birdie moves relative to the tuning control - a fast-moving birdie
indicates a multiple of your variable oscillator is involved.

~ There are programs that will calculate mixing terms that fall within a
given window, but in a typical superhet there are too many such windows, and
the number of potential interferers is just too large to manage (in my
limited and frustrated experience, anyway!).

Right, the little buggers multiply like rabbits! I figure that a combination
of shielding and by-passing would be the place to start. For the BFO and
second LO, that will hold still at least, might it be possible to use a
simple band-pass filter to at least quiet down their harmonics?

Pity the poor HB-XX guys with 4 oscillators running at the same time!

Cheers,

Brian




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