Monitoring Antennas and Receivers?


#1

I’ve just started using SatNOGS. Congratulations to those who started this project as you have achieved a huge amount.

I have a couple of newbie questions. From my passes so far, only one has returned data values - this used FSK9k6. Another used GFSK9k6 and appears from the waterfall to show packets – but maybe the SNR is too low? I realise that other modulations like MSK and BPSK are not decoded at present - I guess there is ongoing development in these areas?

Partly related to the above, is there a way to monitor (say) SNR or even input signal amplitude during a pass? In other projects I’ve found that, since the RTL dongles are only 8 bits, it’s very useful to monitor rms amplitude eg for adjusting SDR gain and even checking that the LNA is working by seeing the amplitude increase! As present I wait for the waterfall to appear, but of course that doesn’t help during a pass. Perhaps a simple sox-like amplitude indicator that could be running over an ssh session to the RPI would be a useful real-time indicator?

One of my passes failed due to my home-brew rotator not tracking, after some initialisation problem. Does SatNOGS software use rotctld to measure pointing error? (and if so, can it be displayed in any fashion). Is it possible to see the rotctl (and rigctl) traffic - just to observe what is happening during a pass? BTW the yagi doesn’t seem to move to the initial position until the pass starts – is it possible to setup the position (say) a minute beforehand? This would give confidence that flaky rotators will work during the pass :slight_smile:

Please keep up the great work!
Thanks, Bill


#2

Hi Bill,

I’m not 100% sure the FSK demodulator is performing as well as it should. I believe it is searching over pretty much the entire receiver passband (to enable decoding of off-frequency packets) so that may explain it. One of the devs would be able to shed some more light on that. Also, if the framing format is not known, then no data packets will be decoded.

There’s currently no way to dump SNR during the pass. I guess it would be possible to modify the flow-graphs to add some more debug outputs. Not sure if the FSK demod blocks will give a SNR estimate.

As for the rotator, satnogs simply sends position update commands, and assumes the rotator is functioning correctly. There’s currently no facility within satnogs-client to set it up before a pass.
I have written a script that will set up a rotator ready for the next pass, which is available here: https://github.com/darksidelemm/satnogs-unwinder/

The current position of the satellite during the pass can be seen on the web GUI: http://<your_satnogs_ip>:5000/

73
Mark VK5QI