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 :)
BTW, I wonder what happened with the SM2000 (http://www.rowetel.com/?p=4694 ). -Mooneer K6AQ On Tue, Mar 31, 2020 at 1:56 PM Jeroen Vreeken <[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] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >
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