AX.25

[C2]

I think that is the protocol for APRS.

I'm interested in the RF end of it. Does it modulation various tones and how to decode them?

I know a TNC or soundard can, but I want to build my own decoder, so I need to know exactly what is happening.

 

[SR385]

The AX.25 specification itself, for the data format transmitted can be found at tapr.org As for the hardware or software design to do the demodulation of the audio signal, I believe they have books they sell describing that.

A better bet may be the open source software in linux that deals with ax.25 and the 'soundmodem' modules, either the kernel module or the user space soundmodem utility.

 

[SR385]

http://www.tnc-x.com/dcc2.doc

 

[C2]

Now that is cool. I also found the WhereAVR