I need to demodulate and decode a signal.It is transmitted from a satellite using GFSK. The packets are based on AX.25. Could you recommend any out-of-the-box HAM software packages that could do either GFSK demodulation or AX.25 decoding?
This is a bit cobbled together, but sometimes that's the only way to get things done!
Part of this article refers to Dirweolf, a packet AX.25 modem. It is an incredible software modem for packet reception. So for decoding the incoming packet frames, Direwolf may be a good bet.
Dealing with AX.25 is better left to Linux. Attach Direwolf to the Linux AX.25 network stack via the KISS protocol and it can provide you with decoded frames, though only in a specific format when you use the built in tool set, namely "axlisten".
Check out my HALDigital project on Sourceforge if you would like a Linux ax.25 system that is easy to build and configure on a cheap RasberryPi. The current Beta image is running Rasbian Wheezy for an RPi2, and includes the AX.25 linkage with Direwolf and all the standard utilities.
I managed to solve the problem. Basically I implemented the DSP demodulation software in GNU Radio. I then rewrote AX.25 software stack in C++. It is not a very complicated stack and it didnt take a lot of time.