[Discuss-gnuradio] Help decoding Bell 202

[En Shih]

Hi all,

I am trying to decode a Bell 202 signal from a RTL dongle source using GNU
Radio Companion 3.7.8.1.
I am new to GNU Radio and signal processing, and constructed this flow graph
by searching previous topics on AFSK:

<http://gnuradio.4.n7.nabble.com/file/n57483/2015-12-27_20-51-40.png> 
first by passing through a NBFM and then a quadrature demod, but I can't
recover the expected signal, which should have bytes 01 04 or 01 01 at the
start of a packet.

This is how the signal looks like:

1. RTL-SDR source
<http://gnuradio.4.n7.nabble.com/file/n57483/signal1.png> 

2. After NBFM receive
<http://gnuradio.4.n7.nabble.com/file/n57483/3.png> 

3. After quadrature demod
<http://gnuradio.4.n7.nabble.com/file/n57483/5.png> 

4. Final
<http://gnuradio.4.n7.nabble.com/file/n57483/6.png> 

Does it look like I am on the right track? 

The grc file, a dump of the original signal, and a decoded file is stored
here:
https://drive.google.com/folderview?id=0B5T4PFVUKZgmcXlTWnV0VzZFQTg&usp=sharing
<https://drive.google.com/folderview?id=0B5T4PFVUKZgmcXlTWnV0VzZFQTg&usp=sharing>
  
The decoded file was done using a physical modem, and its contents does not
match the dump but is in the same format.

I have also tried using  multimon-ng
<https://github.com/EliasOenal/multimon-ng>   with the following command:
rtl_fm -f 402000000 -s 22050 | multimon-ng -a AFSK1200 -t raw /dev/stdin 
but to no avail.

Thanks.

Regards,
En Shih



--
View this message in context: 
http://gnuradio.4.n7.nabble.com/Help-decoding-Bell-202-tp57483.html
Sent from the GnuRadio mailing list archive at Nabble.com.