DragonOS Focal Rx and Decode Inmarsat-C Messages w/ SigDigger + STDCDEC (RTLSDR)

This video shows how to get DragonOS setup to receive Inmarsat-C Messages. A command line interface tool called STDCDEC (Open-source Inmarsat-C decoder, based on Inmarsatc library) is used along with a RTLSDR v3 and SigDigger. Everything shown in the video will most likely be included in the next DragonOS release.

You will need a patch panel or other type antenna built to receive Inmarsat and either an external bias-t or internal to power the antenna. In this demonstration I chose to use the internal bias-t provided by the RTLSDR.

SigDigger is used as the front-end to receive and perform USB demodulation of the signal. I chose SigDigger for this video because it has a PSK inspector that allowed me to find the center audio frequency, which is needed to setup the STDCDEC demodulation tool. Once you run and get familiar with this setup, it becomes easier to get the correct signal center freq, bandwidth, and audio center freq. I left in the few attempts I performed while making this video to show what you may encounter while doing it yourself.

Audio needs to be piped over the correct interface, which I show how to use the mixer in DragonOS to get that setup. There's actually several ways to get audio over to STDCDEC, however with SigDigger's current state I went with pulse audio.

Once all the pieces of STDCDEC is up and running AND you have the signal/audio center freq correct, you should start to receive, decode, and see the Inmarsat-C messages.

Enjoy!

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References:
https://github.com/cropinghigh/stdcdec
https://github.com/cropinghigh/inmarsatc
https://en.wikipedia.org/wiki/Inmarsat-C
https://legacy.iho.int/mtg_docs/com_w...