Tom, I thought Dave said that the 21 MHz spurious signal tracked his
fundamental and held a 3F/2 relationship with it all the way across the
20 meter band. I don't see how a the 14 MHz fundamental beating with
a fixed frequency oscillation could do this (Dave was the spur tracking
really exactly 3*F/2 WRT to the 14 MHz signal??).
Can a free running oscillator injection-lock to a pump signal near its
2nd or 3rd harmonic? If so, perhaps that would explain it? Another
possibility would be some poorly shielded RF device with a frequency
divider that is capturing on Dave's nearby TX signal (or one of its
harmonics). The frequency divider could produce the F/2 component
which in turn could beat with the 14 MHz signal and to produce the
3F/2 component. The fact that the spurious signal is bidirectional
in its response to Dave's antenna suggests to me that its due to a
harmonic of his signal that is created either in or before the 20
meter antenna (I would expect a Yagi to look bidirectional at its
harmonics, whereas it would be unidirectional at its operating
frequency).
Interesting problem.
73 de Mike, W4EF...........................
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "'Amps'" <amps@contesting.com>; "David Robbins" <k1ttt@arrl.net>
Sent: Friday, May 17, 2002 6:45 PM
Subject: RE: [Amps] al-1500 parasitic?? or some other problem?
>
>
> > Well, I can now say for sure that it is not the amp. I have found
> > that by feeding only the top 6 ele 20m beam and pointing it either due
> > east or west I can generate the f/2 and 3f/2 products with as little
> > as 45 watts. The beam heading is not what I was expecting as it puts
> > both the 40m and 15m towers off the ends of the 20m elements. The low
> > power needed does really narrow it down to something related to that
> > top antenna or something very close to it... especially since I can
> > not generate them with 1500w to a 4 ele 20m beam 45' below it.
> >
> > I can also say that its not the guy wires as the 17 year old rusty
> > ones were replaced yesterday.
>
> Hi Dave,
>
> I'm positive you are wasting time looking for non-linear joints
> producing a F/2 or 3F/2 product. Sub-harmonics are impossible to
> produce by virtue of a non-linear system.
> .
> Look for a mixing product with another local oscillator or signal of
> some sort, or a spurious oscillation in a device with gain.
> 73, Tom W8JI
> W8JI@contesting.com
>
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