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 _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
