[amsat-bb] Re: Is there anyway to get a linear transponder on the ISS? (PSK31)

Robert Bruninga bruninga at usna.edu
Fri May 31 06:04:33 PDT 2013

> The nicest configuration... would be a 2m FM uplink with CTCSS to avoid
interference and a SSB 10m downlink.

The problem with that is the same as all our other FM satellites.  Only a
single user at a time.  Congestion, conflict and little practical value.

The better use of SSB is to use the same single channel FM bandwidth for a
wideband transponder allowing up to 30 or more simultaneous users.  This
is equally trivial to do.  Just connect the output of a 10m SSB receiver
tuned to 28.120 MHz to an FM downlink and use PSK-31 on the uplink.  The
FM downlink gives everyone in the footprint the identical PSK waterfall
spectrum where they can tune all 30 QSO's simultaneously.  Then each
person sets their PSK-31 uplink to an unused 100 Hz wide area in the

Not only can 30 stations participate at once, the fact that they are
transmitting on 10m PSK31 and receiving on 2m or UHF FM at the same time
means they are also operating full duplex during the entire pass.
Everyone can talk to everyone without conflict or congestion.

And no special hardware is required for users.  A PC with a sound card can
do it all.


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