Re: [IRCA] 1100 Wobbler bizarre!

["Bob Foxworth" <rfoxwor1@xxxxxxxxxxxxxxx>]

> The Wobbler on 1100 is truly bizarre!
>
> It looks like the variation is caused by incipient oscillator failure.
As the
> frequency varies, it shifts the tuning and loading on the power amps.
> That varies the voltage applied to the oscillator. A feedback
condition.


This would imply that this is a design issue with the type of
transmitter in
use. I believe many of the Cuban xmtrs are old and of Eastern European,
probably Czech mfg. A way to corroborate this would be to identify the
make of every xmtr that is doing this. I think this a very reasonable
candidate explanation, as nothing else I've heard (including mine)
makes much sense at all.


> Note that some extremes of frequency variation, the frequency has
> rapid variations on it...as though the bass component of the
modulation
> frequency is FMing the signal briefly.


We would need to do a better job of correlating modulation type
with exhibited wobble behavior. I have, in my limited experience,
herard wobbles when the underlying signal was not audible,
and I think I have heard wobbles when the underlying signal
was voice. But I am not the guy to ask about that, given my
limited hearing of them. One of my spectacular receptions was
on Musical-590 last year when the strong wobble replaced
the modulation, briefly,  which was nowhere near timed in
rhythm or beat.

If an oscillator was drifting into instability, the wobble would
I think tend to slowly appear and fade. I have heard them start and
stop abruptly as if a switch was thrown on and off.

Another problem is when the wobble appears strong and the
underlying signal has faded out. I have heard this on 1100, 1120
RCH. If the freq and site are the same, wouldn;t the fades be
similar?

> I don't think that external power variations have a thing to do with
it.
> A grid that unstable would constantly be losing sychronization among
> generators on the high-voltage tielines. That would trip breakers and
> cause very frequent blackouts.

I don't think power is an issue here either, but one problem I have is
that I believe this condition (incipient failure) would tend to get
worse
over time. The wobbles last sometimes for days which implies there
are no armies of techs standing by to retune these failing rigs when
the wobble begins, but they eventually all seem to cure themselves,
even if for a finite time.

Wouldn't entropy suggest that by now, every Cuban xmtr would be
"all wobble all the time"?


> 73 de Charles
>         -----
>
> Charles A Taylor, WD4INP
> Greenville, North Carolina


- Bob               0816 est


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