> Nice! This kinda makes me want to try FreeDV on VHF/UHF now (even if > just with 2400B to start). It might even be easier to get people to > adopt it around here if they don't need to set up a HF station in their > small to nonexistent back yard :)
You cna also try the OFDM modes if youhe a SSB radio. > BTW, I wonder what happened with the SM2000 > (http://www.rowetel.com/?p=4694). Brady and I managed to get about half of it working then life got in the way and we moved onto other projects. Cheers, David > > -Mooneer K6AQ > > On Tue, Mar 31, 2020 at 1:56 PM Jeroen Vreeken <[email protected] > <mailto:[email protected]>> wrote: > > Hi all, > > During the last few weeks I had some more time available than > expected (working from home for obvious reasons) and finally got > around to do an experiment I wanted to do for a while now: implement > and test a new mode for use on VHF/UHF. > I really liked the idea of mode 2400B, but it is relativly wastfull > with bandwidth, and I also wanted to have a bit higher quality > codec2 mode so it can actually compete with analog FM. > So I tried something different: a 6000baud mode with raised cosine > symbols. > A zero is encoded as an inversion, ones as a continuous level. > To prevent to much DC in the signal after each 9 bits a zero is > inserted. > > Originally I wanted to use a higher bitrate LPCNet mode, but > couldn't figure out how to set it to anything other than 1733bps > yet. So for the time being I am using mode 3200, but can still swap > it out later as there is 4666bps available. > I used a frame length of 120ms, partially to reduce overhead, but > also to make it easier to switch to another codec later, 120ms can > handle all the current codec sizes: 20ms, 30ms, 40ms etc... > > In order to make each identification more standardised and to always > have a data channel available each frame has data. > Either 64bits in case of a voice frame, or 608 in case of a full > data frame. > > Yesterday I did some on-air tests between my home and our local 70cm > repeater (the discriminator output is connected to the controller > and can be sampled directly). At home I used the packet input of my > ft-817. Using 5W this resulted in a near perfect (might need some > finetuning) signal over a distance of 11km. > > My current status can be found at > https://github.com/JeroenVreeken/codec2 in the m6000 branch. Be > aware that I have not extensively tested with real audio data yet, > my tests were with artificial voice data to be able to test easily. > Next step is to use the new lib for the actual repeater. It is > currently configured to receive both analog FM and mode 2400B, but > it should not be hard to switch 2400B out for 6000. Just need to > check that the correct amount of samples is used everywhere. That > should enable some real world tests. > > 73s, > Jeroen > > > p.s. some values from the README: > | second | frame > ----------------|---------|------ > baud | 6000 | 720 > inserted 0s | 600 | 72 > sync bits | 133.33 | 16 > --------------------------------- > voice bits | 4666.67 | 560 > used voice bits | 3200 | 384 > codec2 frames | 50 | 6 > extra data bits | 533.33 | 64 > control bits | 50 | 6 > reserved bits | 16.67 | 2 > --------------------------------- > data frame bits | 5066.67 | 608 > control bits | 83.33 | 10 > reserved bits | | 14 > > > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > <mailto:[email protected]> > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
