I don't know if you saw his presentation but Andy Walls did a talk on the new clock recovery block he wrote to address issues he had with existing ones. I believe it's in tree now?
https://www.gnuradio.org/wp-content/uploads/2017/12/Andy-Walls-Samples-to-Digital-Symbols.pdf On Mon, Apr 2, 2018, 08:55 Adrian Musceac <[email protected]> wrote: > I should add that the main problem I face is getting it synchronized fast > enough for short bursts. > > Adrian > > On April 2, 2018 11:54:21 AM UTC, Thomas Habets <[email protected]> wrote: >> >> I just seem to recall that being said. >> >> I've used M&M successfully in the past, but it does require some >> massaging of the data to not be "square wave" before it'll work. Also does >> it work (well) for M-FSK? >> >> On 2 April 2018 at 11:16, Adrian Musceac <[email protected]> wrote: >> >>> 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; >>>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> [email protected] >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >> >> >> -- >> 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; >> > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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