Gang -- I have submitted a paper to the Amsat Space Symposium this October with the topic of the potential applications and benefits of Codec2 in amateur satellite voice communications. I hope the tenor of this piece will be as a report from the C2 community, since I can't possibly claim to know enough about all of C2's aspects to speak authoritatively.
My starting point, however, will be that, unlike with HF communications, e.g., a great majority of satellite stations (esp. for linear birds) has a computer attached in order to perform doppler correction and demodulation of other digital signals. Moreover, there has been a long-standing tension between those who advocate and launch digital birds, which have the advantage of simplicity and generally lower power requirements, and satellites that include voice communications, which traditionally have been more complex. This tension has not abated with the rising popularity of cubesat projects among universities, projects that have focused usually on digital modes. C2 provides a means of reconciling these two. If a primarily digital cubesat provided: 1) a modem of sufficient bandwidth; 2) a repeater mode, it could, on the end of its primary mission, be repurposed as an digital voice satellite. I think getting a nascent cubesat project to buy into this idea would be a great boon to C2; and what graduate student would not like to *talk* through his bird after it has downloaded all that great telemetry? Additionally, of course, the narrow bandwidth of a modem like David's would be beneficial for linear birds, especially if the modem could provide some degree of carrier frequency searching (to compensate for doppler shift), as did the highly successful BPSK1000 modem by KA9Q on ARISSAT-1. If I remember correctly, he used a 2000 kHz bandwidth for his 1000 baud in order to provide an aggressive FEC compensating for fades. In voice communications, I think you'd just give up on the fades. These are some preliminary thoughts. I'd also like to have some red-hot video of a C2 QSO through, say, VO-52 :-) 73, Bruce VE9QRP On Tue, May 22, 2012 at 6:33 PM, Trevor . <[email protected]> wrote: > --- On Tue, 22/5/12, Kristoff Bonne <[email protected]> wrote: >> Conventional wisdom says that you cannot relay D-STAR >> signals over a traditional FM relais. Would a digital protocol at >> 2400 baud any better of in this? And, if yes, would this -if you >> ignore the issue of doppler-shift for the time being- this mean that >> would also work over a satellite FM relais? > > The first amateur satellite QSO using D-STAR digital voice was through the FM > satellite AO-27 in 2007, details at > > http://www.southgatearc.org/news/july2007/dstar_satellite_qso.htm > > The D-STAR GMSK modulation signals could be demodulated up to 1.5 kHz off > frequency. The D-STAR rigs used could only tune in 5 kHz steps and the > Doppler shift on the AO-27 436.795 MHz downlink caused the signal to vary > over 16 kHz during a 15 minute pass so inevitably they were times when the > signal couldn't be demodulated. > > Arguably a narrow-band (<1.5 kHz) digital voice modem that used VHF/UHF SSB > equipment would be better for satellite use since it could use the linear > transponder satellites which permit multiple QSO's instead of the single QSO > permitted by FM sats such as AO-27. > > A 1400 bps modem would seem a good choice if it could also sync onto a signal > over a "wide" frequency range to facilitate manual Doppler correction. (wide > = at least +/- 250 Hz and a far greater sync range would be better). > > 73 Trevor M5AKA > > > ------------------------------------------------------------------------------ > Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. Discussions > will include endpoint security, mobile security and the latest in malware > threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 -- http://ve9qrp.blogspot.com ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
