[Elecraft] Re: Help with Birdie (not "tweet tweet!")

[Mike Harris]

G'day,

> Also to give me a birdie at ~28.7 the 4 Mhz oscillator would
> have to be off by approx 100 Hz !!

Errr, not quite.  the 4MHz oscillator would have to be off by 100kHz,
hardly likely.

I also have this birdie but it is low level.  It used to be a feature
in receiver technical reports quoting something like "no internally
generated signals above S1" or similar.  Most, of course, just vanish
under the band noise.

Now in this case the important thing to notice is that it tunes much
faster than the actual tuning rate, that is, even with the normal 10Hz
fine tuning, the signal steps at a much higher rate than 10Hz.  This
gives you a clue to the possible mixing product of the internal
oscillators that is causing it.

A spurious (birdie) signal that tunes at five times tuning rate, for
example is a 5th order product that could be caused by the 3rd
harmonic of one oscillator mixing with the 2nd harmonic of another.
It all becomes quite messy.

There was a chart giving oscillator harmonic relationships and their
spawn in the "Collins SSB Handbook" published about 35 years ago.  I
no longer have my copy.  Maybe there is something similar in other
handbooks, more probably a piece of software now days.  An interesting
puzzle on a winters night.

I don't think I've gone too far adrift with the above.  Any designers
out there with the info?

Regards,

Mike VP8NO