[amsat-bb] Design The Next AMSAT Satellite

[Tom Schuessler]

Hello all,

This is relating to the brainstorming activity that AMSAT-NA is promoting to
design the next AMSAT satellite.  I know there is lots of talk about using
10Ghz for HEO birds doing yet to be developed digital communications modes
that can carry multitudinous amounts of digital communications on a
transponder, but I would like to reinvigorate a thread that Bob Brunnings,
WB4APR tossed out over a year ago on this forum and have heard nothing about
it since.  

Bob suggested a satellite that would have a linear to FM transponder
specifically to run PSK31.  This "Analigital" mode is very efficient in
spectrum usage as anyone has seen during a contest like Field Day, where 30
or more signals can coexist in a 3KHz chunk of 20 meters around 14.070.

As I remember his idea was to allow for uplink to the satellite on 2 meters
into a linear transponder with a downlink on FM 435Mhz.  The BFO audio
output would be decoded and re-applied to an FM (Always on) transmitter.
Because the output would be FM, the only hard Doppler correction would need
to be on the uplink side and decode could be on nothing more than an HT
connected to a computer sound card with the only need to do the 2.5 or 5 Khz
step tuning we all use with our HTs for SO-50 passes to keep signals coming
in clear.  Perhaps, and somebody could speak to this area, perhaps the
uplink could be on the 10 meter satellite sub-band or an arranged portion of
the higher side of the 10 meter phone band, away from other terrestrial PSK
activity.  10 meter Doppler to the satellite would be quite small and would
minimize the amount of AFC that the PSK RX software would have to negotiate.
Even a non-full-length receive whip on the satellite should be able to pick
up the uplink signals transmitted at normal PSK levels below 30 watts.
listening to the audio output of the FM radio, would make it easy to keep
ones drifting signal in place for decode.  The normal 3Khz bandwidth pass
band for FM will work just wonderfully for PSK 31. For this up/down
configuration In full duplex, you would be able to hear your own PSK signal
and keep in place relatively easy with just a bit of practice.  Oh yeah,
there would be signals floating across the band but that is how it is now on
SSB and CW when operators cannot use full computer aided correction.

Here is the real plus to this idea;  We would open up the world of Amateur
radio satellites to a whole new collection of operators around the world who
love these digital modes and would relish a challenge of learning how to do
PSK in a different way.  It would be much more efficient than a pure FM
voice transponder yet it still will be VERY accessible to the vast majority
of Hams like me who are under significant budgetary constraints on equipment
purchases.  Also bringing satellite accessibility to a new segment of the
Ham community could increase the support level for AMSAT projects and that
would bring more dollars to build more elaborate ideas.

I wonder if since Fox 1D is still uncommitted for launch if it could not be
reconfigured to a 2 up SSB/70 down FM configuration to give this a try?
Might be interesting.

I really think Bob was on to something here and I have been surprised that
nobody else has picked up on it or that I heard nothing about this coming
out of the AMSAT Symposium that last October.

Here's hoping that the discussion will continue and that we can see
something like this get flown.  Just a few thoughts from a little guy.

73 de Tom, N5HYP