RadioReference.com Forums

(edit: Whoops, meant to post this in the UniTracker thread... guess my excitement at getting it working has turned my brain to mush. :) )

OK, you gotta share your secret.

I can't possibly fathom how you are able to decode the APCO P25 CQPSK control channel with pretty decent accuracy (I get about 65% average on the notoriously mistuned Austin system). This is not a simple 2-level FSK signal like a Motorola or EDACS control channel signal. Please tell us how you determine the phase shifts in the acquired sound card signal--are you using some kind of time-based algorithm where you look at each sample or is there more advanced DSP involved like FFTs and getting the phase shift from the output of the FFT or something? Do you convert the samples to I/Q and do your work from there? I'm dying to know!

Whatever you're doing, it's incredible. I write device drivers for a living and have even written a couple of sound card Motorola/EDACS decoders in the past, but that is nothing compared to what your software is doing.

Superb job.
Top