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

Raydel Abreu Espinet cm2esp at frcuba.co.cu
Fri May 31 06:31:50 PDT 2013

Hi Bob,

Yes I remember reading about your proposal few months ago and I think it is a nice idea. Even with user collaboration it can be shared both digital and voice communication. If the digital signals are on the 200 ~~ 500 Hz section of the pass band and the voice in 600 ~~ 3 KHz (it would not sound perfect, but yet understandable) So the system is also versatile.

I always try to keep voice on mind because in all over the world there will be always someone who prefer voice over different modes, it is a big crowded planet. So with shared channel, user collaboration and patience it can be done.

It would not had 30 users simultaneously, but perhaps up to 5 or 6? Users should respect frequency plan and accept the digi or voice sounds in both cases that may be annoying but it could "theoretically" work also.

Just thinking how to keep everyone happy is a hard work, but not impossible!!!


Raydel, CM2ESP

----- Mensaje original -----
De: Robert Bruninga <bruninga at usna.edu>
Para: amsat-bb at amsat.org
Enviado: Fri, 31 May 2013 09:04:33 -0400 (CDT)
Asunto: [amsat-bb] Re: Is there anyway to get a linear transponder on the ISS? (PSK31)

> 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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