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Re: frequency jumps while listening to AO-40??

I copied AO-40 telemetry yesterday on Orbit 519 from about MA = 80 (14:45 
UTC), until MA = 227 (01:45 UTC Monday).
During almost all of this time, I was in the shack actually listening to 
the beacon and QS0's on a separate receiver.  I never detected any problem 
with signal shifting.  Even during the brief times that I wasn't in the 
shack, my telemetry decoder never lost lock.  It doesn't take much of a 
shift to cause it to fall out of lock so this is good evidence that there 
was no problem at the spacecraft.  I suspect that this is downconverter 
local oscillator instability for whatever reason (temperature, voltage, 
etc).  I HAVE experienced exactly this phenomenon with one of my older 
downconverters.  However, the one that I'm using now has never had this 
problem.  Likewise, the other control stations have not described this as a 
problem that they have encountered.

>Hello, all!
>I am writing with a question about something I observed listening to AO-40
>today.  I was listening to the 2401 MHz downlink and periodically (perhaps
>every few minutes) my received signals (whether my own uplink, another
>station's downlink, or the MB) would shift erratically down in frequency by
>about 300 Hz, and then return to the original frequency.  This happened very
>irregularly, but persistently, until MA 220.  After the passband was turned
>off, the beacon was of course all I could listen to, but whereas it had been
>erratic as well, it was rock solid in frequency (with the expected Doppler
>drift, of course).  There was no change in signal strength or in the
>background noise level as might occur if there were a problem with the DC
>supply voltage to the UEK-3000.  THe whole thing reminded me of how AO-10
>has sounded when it gets 'flaky'.

  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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