--- 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
