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[Discuss-gnuradio] PMR data decode

From: Matthew Burnham
Subject: [Discuss-gnuradio] PMR data decode
Date: Mon, 8 Jul 2002 22:42:59 +0100

Is anyone working on deocding of data found in the PMR bands (e.g. MDT
terminals, pagers, etc.). I'm quite impressed with GNU Radio so far
having got a nice display of the waveforms using the audio scope
example. I'm not sure how to proceed in decoding in terms of the modules
to link together. I envision something along these lines:

VrAudioSource -> VrSigProc      -> VrSigProc -> VrFileSink
                 (zero-crossing)   (manchester)
                 (detection    )   (decode)

This example is for data where the bits are manchester encoded in
amplitude when viewed on the scope. (I originally believed this to be
FSK, but now I'm not sure as I've seen some other data signals that seem
to be a sinewave at two discrete frequencies, which would necessitate
further FSK decoding first. Anyway, that's a side issue on my lack of
understanding of FSK modulation.)

I've got my head around a lot of the architecture having read through
the entire mailing list archive and the (limited) documentation, but I'm
not sure how I would go about getting from an audio input to a data
output. I connected a VrAudioSource to a VrFileSink, but I'm not sure of
the format of the data in the file (I could look at the data that way if
I knew this, but I guess there is a better way within the architecture)
other than the values get larger with modulated input rather than no

Mat Burnham

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