[Discuss-gnuradio] RDS reception

[Marcus D. Leech]

I managed to get gr-rds built tonight, and was able to test it planted
inside my FM receiver.

Even for a local station, there are *lots* of errors, and more distant
stations get even more.
  I'm going to play around a bit with filter bandwidths, etc, to see if
I can improve it.

Looking at the modulation technique, it's no big surprise--they use a
bi-phase baseband coding
 (basically like differential Manchester), that drives a DSB-SC
modulator with a carrier at
 57kHz.  But that signal is generally about 20dB below the other audio
sub-channels on the
 FM demodulator output. So the SNR is generally *terrible*.

I'm rather surprised, after looking at it, that anyone bother deploying
RDS. It seems utterly
 crappy.  It's generally broadcast with fairly-low SNR, and there's no
FEC built in, only CRC.

I re-jigged the XML for the demodulator part so you can reset the
demodulator state machine
 from within a GRC flow-graph (there was a reset() method on the demod,
but it wasn't exposed
 within the XML framework for GRC).

Also, I may re-jig the decoder portion--it currently injects decoded
frames into a message queue and
  to stdout.   Might be useful to do other things with those messages. 
Like is there a simple way to
 have a message dequeuer within a GRC flow-graph so that one could stuff
messages into a variable?


-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org