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RE: Question On Passband noise with IF off



Gary,
You can check the telemetry archive on the web site and check the Matrix
status at that general position within the orbit. Occasionally, when the
transponder is turned off, and just the Telemetry beacon is on, the
matrix has the MB routed thru the Leila to the S-Band Tx. When that is
the case the noise floor jumps way up, even though a receiver is not
patched through.. I have noticed it many times.. It does not represent
any sort of a problem, just a quirk as the result of the configuration.
It is most dramatically noticed near Perigee..
Regards,
Gunther Meisse
W8GSM


-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org] On
Behalf Of Gary Gonnella
Sent: Sunday, October 05, 2003 5:40 PM
To: Amsat-Bb
Subject: [amsat-bb] Question On Passband noise with IF off


I have noticed a curious thing on the AO40 Passband. Under normal
conditions when the squint is low I hear the pass band noise at about
3db or so above the receiver noise. Today (9/05/03) I noticed that after
the transponder was shut off and the bird was at a low altitude there
was a significant noise level on the output. The readings were taken at
MA 244 with an altitude of about 7000 miles and a squint of about 50
degrees. The telemetry at this time showed that no receiver was
connected to the transmitter.

My understanding of the noise floor is that is the noise from the
receiver being passed through the IF matrix and being "repeated" at a
low level. Under this assumption there should be no "repeated" noise
floor on the S2 transmitter when the IF matrix is off.  So the question
is this noise coming from a connected receiver or is this some noise
being generated in the S2 transmitter?

BandScope images can bee see on my site here
http://www.w6ryo.com/passband.htm

Any information on this would be appreciated.

Gary Gonnella W6RYO
http://www.w6ryo.com


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