Using satnogs groundstation for APRS satgate

I was about to order another RPi to build a Sgate for APRS which would have needed yet another QFH antenna. I already have a working ground-station for receiving VHF satellites so why duplicate the hardware?

Has anyone successfully modified a SatNOGS ground station to do double duty by also acting as a APRS Satgate by decoding and sending APRS packets to via direwolf.

I read somewhere that audio could be taken from the fm_demod.grc flowgraph and fed to direwolf via a Float to short block and a UDP sink.… Thanks Mark.

I have spent days googling but found nothing with clear enough instructions for me to follow. I’m not a programmer. I usually come unstuck by not getting the path right, for instance I couldn’t find fm_demod.grc but I did find /usr/local/bin/ I know GRC can use this file but I don’t know how to get it out of the RPi SD card and into my Linux PC so I can use it to edit the flowgraph.

I have played with building flow graphs on GRC but I don’t want to risk stuffing up my working ID-568 ground station so I would need step by step instructions.

Thanks for your time and expertise.

Bob vk2byf

You can also specify an optional “UDP:” port for Direwolf audio device input (like ADEVICE UDP:7355 default ) and additional UDP sink port in AFSK1200 flowgraph.udp

I would probably suggest not modifying the FM demod flowgraph, and instead using a RF splitter and another RTLSDR to do AFSK reception.

It’s fairly trivial to use rtl_fm and direwolf to do the APRS reception. The direwolf user manuals include such an example.
It doesn’t use a whole of CPU, and it doesn’t tie up a SatNOGS ground-station that could be otherwise used for possibly more important telemetry gathering. Plus you’re also not having to patch satnogs-flowgraphs every time there’s an update.

Thanks Mark, good advice, I think especially seeing how I already have a LNA at the antenna, a home made splitter followed by another LNA to feed the SDRPlay receivers. I can afford to add one more receiver load here as I have more than enough gain from the second LNA.
Way to go

It would be very helpful to allow the end user to select the audio UDP source - option for monitor or remote using as it is done for raw IQ file.

It would be equally important from time to time to use the capabilities of the existing Satnogs base as iGate, equipped with a directional antenna (since the AFSK 1200 requires more signal power for the same performance in terms of error rate).