M17 - SDR & GNU Radio

Started by SP5WWP, November 26, 2019, 10:32:33 AM

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November 26, 2019, 10:32:33 AM Last Edit: December 12, 2019, 10:17:43 AM by SP5WWP
M17 compatible radio built using RTL-SDR/HackRF and GNU Radio.


Have you made this/are you making this?


I'm working on it. I think SQ3SWF is trying too.


Sorry for double-posting, but if anyone is familiar with GNU Radio - please stand up :) We need a 4FSK demod block.


I've been meaning to learn GNUradio, maybe this is my motivation.


Been busy with work lately but had some time to start learning GNURadio and sketching out a flowgraph

At the moment all it does is encode audio to raw Codec2, transmit it as 4FSK symbols over FM, simulate a noisy channel, and demodulate it back into bits. Currently missing: Framing that would let me plug those bits back into Codec2 and get audio out of it. When I manually find the correct offset it decodes fine, though, even down to some pretty low SNRs (constellation diagram is basically just 4 pinprick dots even down to 10dB SNR or so). I expect this to get worse with higher symbol rates, but it's a pretty good start. I wager that with ECC we should be able to get quite acceptable decode performance down to 4-5 dB SNR.

It would probably be a good idea to design the function that accomplishes framing and ECC in the M17 codebase, to also work as a GNURadio plugin so that it doesn't need to be written twice and we can be assured that what we are simulating is actually reality.


Can you provide (attach) a .grc file? I have received a HackRF One yesterday and gonna play with it.