FDMDV uses a 1400 bps codec, occupies only 1100 Hz and operates with any SSB transceiver. Comunications doesn't have to be full duplex. At 12-16 kbps the satellite and ground stations could alternate with short bursts of voice or text. This wouldn't fit in a 2.4 kHz SSB bandwidth but would require a 16-20 kHz wide filter or use of a transverter and a simple SDR radio like the SoftRock.
73,
John KD6OZH
----- Original Message ----- From: "Gordon JC Pearce" gordonjcp@gjcp.net
KD6OZH's mentioning of a 1200 bps voice codec is very interesting, too. I see that DSTAR's AMBE is down to 2000 with error correction, and Speex operates down to 2000, too, though I think without error correction. (I find the latter much more engaging as a ham, since it is open source.) It would be a hoot to do a voice conference over the Internet using a sample of low bitrate codecs and just get a sense of what might be possible. One downside of voice is that it would occupy the transponder far more than messaging, and Bob's favorable power calculations would need to be estimated downwards.
Would the packet satellite be capable of bent-pipe operation though? You'd need to transmit and receive simultaneously to get that working. I'd far prefer to use Speex rather than the locked-down proprietary AMBE codecs.