I'm having trouble demodulating the RDS signal that comes along with a lot of broadcast FM signals these days. I know that there's "gr-rds" that has already done this, but I wanted to do my own just for personal education.
I spent a lot of time yesterday playing with it, and I can't get anything but garbage bits out of the DBPSK demodulator in Gnu Radio. I can't find a freely-available version of the RDS standard, so I've been cribbing from the nearly-impenetrable gr-rds implementation.
What I've done is to carve off a few kHz around 57kHz out of the FM demodulator, downconvert to zero Hz, and then resample to exactly 19.0kHz/8, and feed that into a "Digital" DBPSK block, with symbols-per-sample=4. I get nothing but rubbish out the back side of this, even for a strong local signal.
Is there something I'm missing in the way the signal gets modulated?
-Marcus
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