[AMRadio] Collins 32V1 diagram needed...

[Vince Werber]

Hi all,

I have had a problem with my 32v1... it has a parasitic that
takes off with certain tunings and loads...  This 'simulcasting'
situation could be a combo of the vfo and the final oscillating
maybe????

Comments????

73
Vince
ka1iic
-.--.

On Mon, 8 Apr 2002, Larry Szendrei wrote:

> 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.
> remainder of original message snipped....
>
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