[Discuss-gnuradio] Demodulating a MPT1327 signal

[Weaver, Tyler [GCS]]

MPT1327 uses MSK on its control channel.  I am attempting to use NBFM Receive to demodulate the signal into a WAV file that I can play back and use sdrtrunk to decode it.  So far my best attempt is set up as follows:

 

USRP

Sample Rate: 250k

Center Freq: 652.625M

Gain: 100

 

Frequency Xlating FIR Filter

Decimation: 1

Taps: firdes.low_pass(100,samp_rate,10e3,1e3)

Center Frequency: 0

Sample Rate: 250k

 

Rational Resampler

Decimation: 250k

Interpolation: 192k

 

NBFM Receive

Audio Rate: 192k

Quadrature Rate 192k

 

Wav File Sink

Sample Rate: 192k

Bits per Sample: 16

 

The output of this seems to be just noise and is not working.

 

Thank you.

 

--tyler