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Re: question about rain, and telemetry from AO-40


I can only address the RF side of the question:
Have you listened on the freq. when AO-40 is not in view?  I wonder if
there might be a low level signal such as a birdie that might be corrupting
the signal [i.e. QRM]?  I have a big "fat" birdie on 145.901 which is
overwhelmed by the much larger beacon signal.

Another possibility is intermod from off freq. affecting your preamp gain
stability.  The way you test for that is by measuring signal threshold with
and without the antenna connected.  It requires connecting a signal
generator thru a directional coupler into your antenna feedline and
reducing signal level to minimum detection level.  If things degrade
significantly with the antenna connected then you have IM.  Some times a
band pass filter placed after the preamp can reduce IM getting into your
Rx.  Common sources of out-of -band IM are from FM broadcast, TV, and
paging transmitters.

Of course rain is a source of RF noise, too.  But that would degrade your
SNR which isn't what you appear to be telling us.

But it may be something non-RF that I am not knowledgeable about.


Mark L. Hammond wrote:
>Hello all,
>By now, I've had pretty good opportunity to print lots of AO-40 telemetry.
>What I've observed at my station is troubling me...when the weather is 
>clear/dry, I can print AO-40 with a signal where there is no S meter 
>reading at all.  When it's raining/wet outside, I can't print the thing 
>worth beans at even S7!  We've had three days of rain since the launch, and 
>on each rainy day it prints horribly.  There is clearly a pattern.  I can 
>get a few good L, K, or M blocks, but hardly any A blocks come through to 
>514 bytes.  Rather, they all appear to be short, about 450 or so.
>I do believe it's a local problem, not the bird.
>Does anybody have an suggestions as to WHY I might observe this?  The high 
>S meter/audio level with little or no good A blocks really has me 
>stumped.  I don't seem to hear any higher static levels, any new birdies, 
>etc.  If it were just a "wet antenna" trouble, I would have expected really 
>poor S meter indication.
>I'm open to suggestions :-)
>Thanks and 73,
>Mark L. Hammond  [N8MH]
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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