Hi, Why is the M&M algorithm discouraged? I use successfully both in FSK and PSK demodulators. It seems to perform fine.
Regards, Adrian On April 2, 2018 8:48:00 AM UTC, Thomas Habets <[email protected]> wrote: >Hi. > >As an experiment I'm trying to decode an FT8 signal I've captured. I've >gotten far enough that I can clearly see the packet ( >https://blog.habets.se/tmp/ft8_packet.png), but now I want to actually >turn >that into bits. > >I know it's 8FSK (the above screenshot is quad demod of that), but I >have a >few questions on clock recovery: > >* Is the GFSK block only for BFSK? If so then that's out. >* Is there a "best" clock recovery block nowadays? I seem to recall >"Clock >Recovery MM" being discouraged in favor of "Polyphase Clock Sync". >* I'm trying to read up on the parameters Polyphase Clock Sync wants, >but >any pointers would be helpful. >* Would it be a good idea to throw in a costas loop for frequency >tuning? >* Does Polyphase Clock Sync have the same dislike of "staircase" >inputs? >That is, I should try to make the center of the bits more "pointy"? >(e.g. >lowpass filter them) > >I've done some custom OOT decoders before, so I'm not shy about that. >Maybe >the best thing is some whole-packet clock recovery[1]. But if I just >write >a block that takes the quad demod (see above screenshot) and finds the >"platforms", outputting a message that is a list of floats, and then >another block that takes a list of floats and the number 8 and decodes >it >as 8FSK, well it seems like I may be reimplementing things where I'm >guessing someone might say "oh just use this block". > >Also for experimentation and my own understanding I'd like to turn it >into >bits using in-tree blocks, if possible. > >Maybe a correct Polyphase Clock Sync of the quad demod followed by a >Constellation decoder? I could use the float as the phase, with >magnitude >1. Does that make sense? Is it a good idea? > >What I have so far is: >Data: > https://blog.habets.se/tmp/ft8-burst-10k.raw (10k samp_rate) > >GRC: > https://blog.habets.se/tmp/ft8_decode.grc > >Screenshot: > https://blog.habets.se/tmp/ft8_decode_grc.png >(everything off-screen to the right is failed clock recovery >experiments) > >Quad demod > https://blog.habets.se/tmp/ft8_packet.png > > >[1] Like https://www.youtube.com/watch?v=rQkBDMeODHc which I turned >into >https://github.com/ThomasHabets/radiostuff/blob/master/ >gr-habets/python/magic_decoder.py > >-- >typedef struct me_s { > char name[] = { "Thomas Habets" }; > char email[] = { "[email protected] <[email protected]>" }; > char kernel[] = { "Linux" }; > char *pgpKey[] = { "http://www.habets.pp.se/pubkey.txt"; }; > char pgp[] = { "9907 8698 8A24 F52F 1C2E 87F6 39A4 9EEA 460A 0169" }; > char coolcmd[] = { "echo '. ./_&. ./_'>_;. ./_" }; >} me_t;
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