[AMRadio] Collins 32V1 diagram needed...

[Larry Szendrei]

Hi Todd & list, 

"Simulcasting" as described suggests a parasitic oscillation in the
modulator and/or speech amp. I had this problem when I added inverse
feedback to the modulator section of a DX-100. The cause is due to phase
shifts in the driver/modulator iron: what was negative feedback at low
frequencies then becomes positive feedback at high (supersonic)
frequencies. I rolled off the freqeuncy response of the feedback loop,
and eliminated the problem. What happens is you get sidebands at the
oscillation frequency ("subcarriers," if you will) that are also
modulated with your audio. Any oscillation in the modulator/speech amp
section will have the same efect - not just the special cause I ran into
with the DX-100 modification.

I'm not sure if the 32V series used negative feedback around the
modulators or not, but if it does, you can't reverse phase simply by
switching the plate leads, because only one configuration will give (the
desired) negative feedback - the other way will induce positive feedback
(which also might explain the "simulcasting").

A 3rd explanation of the simulcasting phenomenon, although not
applicable to the case in point with a 32V series rig, is the case of a
PDM transmitter with an inadequate PDM filter. Here, the modulated
sidebands would be displaced from the (desired) carrier frequency by
multiples of the pulse (fundametal) frequency. Just ask Steve WA1QIX or
Tom K1JJ about this!

73,
-Larry/NE1S

Todd Bigelow - PS wrote:
> 
>  Never had any complains about TVI with mine either, Vince - haven't used it
> in a few years now because it was 'simulcasting' above and below the primary
> frequency, quite strong too. Haven't had a chance to dig into it and find out
> why, but I did have a gentleman call me from White Plains, NY the last time I
> used it to inform me that I was wiping out their MARS net, so I shut down. I
> was on 3.880 or so, they were around 4.020 or 4.2, can't recall. Mid 90's was
> the last time I was on with it, maybe 96-97. Talked with Tim, Gary, Tom and
> many of the old crew regularly with it. Only 'mod' I recall making was to
> flip the plate caps on the modulators to change the phase.
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