> 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 _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
