Thuraya ARFCN

Sylvain Munaut 246tnt at gmail.com
Thu Apr 30 16:53:17 UTC 2020


Hi Johann,

So, first wrt to different formula, the spec is definitely right ...
(I mean it's the spec ...).
However they are narrow channels and if your B210 is not GPS
disciplined, its oscillator could be out quite a bit. It's default
xtal is only rated to +- 20ppm and that's a 30 kHz error at 1.5 GHz
... so you can be off by a full channel just with that.

Second, the frequency you give to gmr1_rx_sdr.py is where to tune. In
reality you want to tune not to the channel directly but a bit to the
side so that the DC offset and 1/f noise at the center of the capture
don't mess up the data. The script will automatically filter and
recenter the proper frequency depending on the -a argument you passed
to it.

Finally that python script only does the sample and channelization,
and saves to a cfile in /tmp it doesn't do any of the decoding at all.
For that you need to also run gmr1_rx binary ( or gmr1_rx_live , see
the live branch ) on the recording. And it's that one that will take
the raw samples do all the demod and decoding of the channels and send
the data to wireshark.

Cheers,

    Sylvain


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