Hello, If it helps the FDMDV demod can sync up with up to +/- 200Hz frequency offset at present. Its probably possible to make this several kHz if reqd. After that a few Hz/s drift is no problem, so a LC oscillator would be OK :-)
If the analog channelization is wider, it would be possible to "find" the correct freq offset by looking at other activity on the band and derive our tuning from off air signals. It would also be possible to tune multiple signals at once, say find some one "calling" for us anywhere in the 2m band by simultaneously demodulating "the band" all signals and looking for a text string with our call sign in it. Cheers, David On Wed, 2012-05-16 at 14:22 -0400, [email protected] wrote: > > I'm thinking about technical issues of purpose-built VHF/UHF radios for > > Codec2. We can deliver a modem capable of a 2 KHz digital voice channel > > on VHF/UHF. But can we get mobile oscillators precise enough to actually > > tune to that channel without resorting to external precision sources > > like GPS? In general, the oscillator would be the time-base for a DDS > > ASIC. > > > > I think that we would need to be clearer in a definition of how we intend > to use bandwidth and how this matches with existing VHF/UHF band plans. > > For example if the rest of the HAM-iverse is using 10KHz channel spacing, > why would we limit our codec/modem to a 2KHz channel. > > If we take the model of using a hard/soft modem with an exist RF front > end, we should have a fair wide (compared to 2KHz) sample. So at least for > RX we can fix/track any drifting in the software of the demodulator. > > For TX we could possibly use on-air references for correction, ie. trust > that a 'control channel' would be on the frequency it was saying it was > on. > > > Would 'purpose built' be from the ground up, or as a module (similar to > the UT-118 used for D-Star in ICOM receivers)? > Simon. > > > ------------------------------------------------------------------------------ > 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 ------------------------------------------------------------------------------ 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
