FSK Demodulation trouble

Hello All,

I am working on learning gnuradio and getting a grip on demodulating
digital communications. I’ve been a ham for a long time, and this seems
far from my days as a kid running 1200 baud half duplex AFSK. :wink:

What I have is a toy with a cc1101 chip in it that transmits @ 19.2 k
baud,
2-FSK, 16.5 khz deviation. The sync word is the default 0xD3 0x91.
Here
is a link to the capture file I am working with:
https://dl.dropboxusercontent.com/u/37979208/ping_903.020m_0.400m_20140403_000000z_rtlsdr.cfile

I started out by trying to get Jared B.'s TPMS code to work,
https://github.com/jboone/tpms but it doesn’t like me or my system at
all.
(Ubuntu 12.04, gnuradio built with the build-gnuradio script). I really
like his reverse engineering methods that he talked about in the talk he
gave at toorcon. I also like the ability to analyse the captures
offline
with a CLI interface.

When I have worked with the GRC, I run the file source through a
throttle,
then through the quadrature demod block, then to a Scope Sink to try and
see the bits on the scope. I am a little lost on a couple things: 1. I
know i need to provide some information about the signal (data rate,
deviation, offset) but I don’t see any place to add those values. 2.
Can I
use the squelch block to limit the demodulation to only look at signals
above a certain signal strength?

Ideally, I would love to get a GRC or script that worked on the capture
file, then I can have a good example to learn from. Most of the posts I
see from googleing show really incomplete work, or just the final
product,
without explanation of how to get there (the dreaded “self-documenting
code”).

Any help would be greatly appreciated. beer is on me if I see you at a
conference or swap.

73

Jay n8os

Jay R.
Twitter: @jradcliffe02
E-Mail:
[email protected]https://mail.google.com/mail/?view=cm&fs=1&tf=1&[email protected]
LinkedIn + Resume: http://www.linkedin.com/in/jradcliffe02

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