Just some obsesrvations... - Why do WBFM to Audio? Shouldn't that be NBFM? - Your post NBFM receive looks good. - Your QD output looks a little strange. Perhaps look at the FFT of your signal before the QD? - In my experience the MM Clock Recovery block likes using ~4 sps. Perhaps use the Rational Resampler to decimate by 10 first? - 2 MHz / 40 = 50 kbps... did you mean to be working with 1200 baud?
I've done my own "1200 baud AFSK" receiver, you may be interested in it. https://github.com/tkuester/gr-bruninga - Tim On Sun, Dec 27, 2015 at 7:52 AM, En Shih <seanstone5...@gmail.com> wrote: > 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. > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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