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Re: Drake instability & Dielectric Filter Simulation



Hi Bill and All,

I can confirm that the noise that I (and others) have encountered with
the G0MRF modified Drakes is indeed instability.  My tests have not been
nearly as detailed as yours but I have been focusing on the amplifier
input circuit.  I have two units and one is worse that the other
(naturally it was the one I had put up to test).  Both of the units seem
to be sensitive to input terminations.  As long as I have a good antenna
on the good one it seems to be OK.  I only notice the problem with it
when I use a dipole that I built into a BNC connector on it and I move
things around near the antenna on the bench.  I destroyed the input
hairpin on the bad one during a repair before the modification and I
tried to rebuild it with a small piece of wire.  Since I got it back down
off the mast I have played around with a short loop of wire on the input
and have noticed some improvement although it now has a bout 4 db less
gain than the other one.  I had the test dipole on the bad one yesterday
and it was oscillating like mad unit I put a 6db pad between the antenna
and the converter and then it settled down.

I still have some tests to run but I can't seem to get back to them. 
Thanks for posting your results here.  I'll do the same when I have more
info.

73's de Jess - W4MVB
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