# FSK Demodulation trouble

**URL:** <https://www.ruby-forum.com/t/fsk-demodulation-trouble/240336>\
**Category:** GNU Radio\
**Created:** [April 9, 2014, 12:36am UTC](https://www.ruby-forum.com/t/fsk-demodulation-trouble/240336 "2014-04-09T00:36:22Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\
**Post date:** [April 9, 2014, 12:36am UTC](https://www.ruby-forum.com/t/fsk-demodulation-trouble/240336/1 "2014-04-09T00:36:22Z")

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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. 😉

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](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,  
[GitHub - jboone/tpms: Tire Pressure Monitoring System decoding tools.](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:  
removed\_email\_address@domain.invalid[https://mail.google.com/mail/?view=cm&fs=1&tf=1&to=removed\_email\_address@domain.invalid](https://mail.google.com/mail/?view=cm&fs=1&tf=1&to=removed_email_address@domain.invalid)  
LinkedIn + Resume: [http://www.linkedin.com/in/jradcliffe02](http://www.linkedin.com/in/jradcliffe02)