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