[amsat-bb] Repeater interference on AO-92

Burns Fisher wb1fj-bb at fisher.cc
Tue Apr 28 13:36:34 UTC 2020

>Maybe someone here can better explain how the Fox tone squelch
>works, for example how long it stays on after hearing a tone.

The Fox FM satellites (now AO-91 and AO-92) have their receivers on all the
time and listen for the 67Hz tone.  If they do not hear it they turn on the
Tx every 2 minutes for about 10 seconds for a couple frames of telemetry
and a voice ID (without the repeater enabled).   If they do hear a tone,
they turn on the repeater for 1 minute (extended each time they hear the

The tone detector is not too sharp so it might trigger on 69.3 or 71.9 Hz
as well.  It does require that the tone be heard for a bit of time (I don't
remember exactly how long--in the hundreds of ms, I think), so it is not
too likely to be triggered by random noise that has some components in that
frequency range.  Of course it is not impossible.

Unlike many terrestrial repeaters, the Fox repeaters do not transmit a tone
squelch on the downlink.  Those frequencies are right where we stick the

I hope that is helpful...

Burns WB1FJ
AMSAT Fox Flight Software


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