[amsat-bb] Observations on 'strange observation on AO-40 S2 beacon'

["Gould Smith" <gouldsmi@xxxxxxxxxxxxx>]

Hello All,

I was recording the Doppler shift of the AO-40 beacon Easter afternoon to
make a graph for the Analog guide  (No jokes about whether I have a life or
not).

I noticed some strange behavior.  As the satellite was approaching I
expected the Doppler to increase in freq, and it did for a couple of
measurements ( I was recording the time and frequency every 2 MA units).
Then I noticed a decrease in the frequency and the waterfall (AO40Rcv)
display indeed slanted to the left rather than the right.
I scratched my head awhile, checked my relationship to the satellite again,
wondered whether I had misread the dial.  Then the frequency increased
again, then a slow increase, then a decrease.  Measured the time it took for
a horizontal waterfall reading to scroll to the bottom of the screen (about
40 secs) to see what kind of resolution I could expect from the slope of the
signal on the waterfall display.
This went on for an hour confusing me more and more.  I started recording
the time, freq and increase or decrease, more often, changed the audio
cable, turned off everything else.  Nothing changed.
Then I noticed that the Doppler shifted at the same time it got darker out.
It was a very sunny day with spotty, large, thick cumulus clouds.  When one
of these clouds moved in front of the sun and I saw the Doppler change I
knew I was on to something.  As Stacey suggests it is a downconverter
problem, there would be a rapid temperature change and it would be reflected
in the downconverter.  Then when the cloud moved and the sun heated the
converter I would see a pronounced shift in the waterfall slope.  Then it
would level out as the temperature stabilized.  I watched this for about 20
minutes longer, confirmed this a couple of more times and
realized I would not get any valid data to graph.

But, I did identify one more environments factor that influences the AO-40
receive signal.

Gould,  WA4SXM

----- Original Message -----
From: "Stacey E. Mills" <w4sm@cstone.net>
To: <amsat-bb@AMSAT.Org>
Sent: Monday, April 28, 2003 1:24 PM
Subject: [amsat-bb] Re: my strange observation on AO-40 S2 beacon


>
> >Hi all
> >
> >      Today(Apr-28-2003), I observed some strange on AO-40 S2 beacon
> >requency. Before 01z, everything is quite normal. But after on 01z until
> >06z(LOS of today at my location), the beacon frequency was abruptly
> >jumped up
> >a few kHz many times.
>
> [snip]
>
>
> >73, Kazu  JJ1WTK
> Kazu,
>
> I believe that you have a downconverter problem.  Either the voltage is
not
> steady or there is another oscillator stability problem with the
> converter.  Others have experienced problems of this type from time to
> time, and have traced them to downconverter problems.
>
> I have been monitoring the telemetry all day with no difficulty.  A good
> test is to note the exact time of the jumps, then when the telemetry
> archive has been updated for that orbit, download that day's telemetry and
> check to see if there is a discontinuity in telemetry blocks related to
the
> jump that you observed.  A few KHz is a HUGE jump and would unlock
> virtually every telemetry gathering station for a protracted period of
> time.   If the telemetry continues unaffected through the time that you
> observed the "jump" it's a sure bet that it's a local problem.
>
>
>
>
> --
>   ________________________________________________________________________
>   Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
>     Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
>   ________________________________________________________________________
>
> ----
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