M17 - SDR & GNU Radio

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

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SP5WWP

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.

faydrus

Have you made this/are you making this?

SP5WWP

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

SP5WWP

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

KE0WVA

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

KE0WVA

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.

SP5WWP

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

EDIT: