Receiver frequency floats when decoding FSK9k6


I have recently changed SDR from RTL to Airspy mini. Works great, with one exception. Whenever there is a satellite that transmit data on 9k6 FSK receiver frequency drifts all over the place, sometimes getting satellite frequency out of the waterfall. I do not know wether there is too much load for my raspberry pi 3B+, or demodulator somehow is trying to compensate frequency. You can see an example for example here:Observation 250289


You will see loads of Overruns (e.g.: “OOOOOOO[…]”) in the journalctl. RaspberryPis are not powerfull enough to demodulate or decode that 3 MSpS where the airspy mini is running at. I have started some experiments on using the internal decimation of the osmocom source to get lower CPU loads with e.g. 500 kHz RF bandwidth, but time is very short these days.

If you can replace that RasPi with a more powerfull board or a PC, you will see it works.

Thanks for your reply.
I’m getting some overruns, but not that much as I was expecting. Also CPU load was about 70% and that was about the same as while tracking satellite with CW decoding.
Can I turn off decoding feature for fsk9k6 - at this stage it is doing more bad than good.


there are options for saying which script will be used in settings, however are not exposed through satnogs-setup.

If you use the rpi image, there is a “” way to edit the in /var/lib/satnogs/lib/python2.7/site-packages/satnogsclient/ . There you can change GNURADIO_FSK9K6_SCRIPT_FILENAME to show at the fm script. After your changes remove settings.pyc and then restart satnogs-client.service by systemctl restart satnogs-client.service. You need to remove .pyc file in order to be build again from .py file after restart the satnogs-client.

Let me know if that works for you.