[amsat-bb] FO-29 transponder block diagram

Robert Bruninga bruninga at usna.edu
Mon Oct 30 22:23:57 UTC 2017

Im not following this closely, but the transponder I think is inverting.
Thus the uplink dopper is subtracted from the downlink dopper whereas the
beacon on the satellite is impacted by the full dopper of the speed of the
spacecraft.  So they will not be the same.  Do the math and see if that
comes out to the 1.26  you observed.


-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Dani
Sent: Monday, October 30, 2017 5:53 PM
To: amsat-bb at amsat.org
Subject: [amsat-bb] FO-29 transponder block diagram

Hi all,

A few days ago I have transmitted and recorded a (low-power) FT8 signal
through the FO-29 linear transponder to test some Doppler correction
algorithms I'm developing (see

After Doppler correction, I'm left with a linear frequency drift both in
my downlink signal and in the satellite CW beacon. However, the drift rate
of my signal and the beacon are different. Specifically, my signal drifts
1.26 times faster than the beacon. I suspect that this drift is due to one
of the local oscillators in FO-29.

To understand this better, I need to look at a block diagram of the
FO-29 linear transponder. The best I've found is this:


However, I need something similar to this:


Since I need to see the frequencies of all the local oscillators involved
in the transponder and CW beacon.

Is there a more detailed block diagram for FO-29 or does anyone know
something about this information?


Dani EA4GPZ.
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