A nice write up David, good work. my 2c as usual, the "always decodable header" should contain all the information for the decoder to figure out what mode is being transmitted. Like DVBT- there is a TPS pilot system transmitted BPSK at multiple carriers. From this, the receiver can determine the main payload channel QAM type, code rates, bit rates, interleavers etc.
Static crashes on 80m : I designed a proprietary data system for 2-6 MHz 10 years ago and there are similarities here... on 80m , 3.6 MHz, at night time in summer, the static crashes from lightning from everywhere in the country is the problem. There is great signal to noise, >15-20dB was no problem .....then nothing for 200-500 mS. The most effective way I was able to overcome it (one way data system, no ARQ) was a deep interleaver- a full 1.5 seconds...... so a interleaver might be a good option for people. (header should indicate interleaver in use) In the daytime, where D layer absorption was the limit, and there was very very low BUT consistent SNR, the system switched to BPSK 1/3 code... the channel at midday almost gaussian in character. glen On 16/02/2017 9:34 AM, David Rowe wrote: > Part 2 (of 2) in my write up/tutorial of where I'm at with HF modems: > > http://www.rowetel.com/?p=5448 > > OK - now onto the work of improving low SNR performance of FreeDV 700C. > > Cheers, > > David > > > > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, SlashDot.org! http://sdm.link/slashdot > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
