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Re: [Discuss-gnuradio] RDS demodulation

From: Andrew Davis
Subject: Re: [Discuss-gnuradio] RDS demodulation
Date: Tue, 21 Feb 2012 12:49:58 -0500

If I remember correctly, the original RDS feed the stereo pilot to the
DBPSK block as it had the correct symbol phase. From this
https://www.cgran.org/raw-attachment/wiki/RDS/rds.png it looks just
like band passing the pilot and dividing to the correct rate.

On Tue, Feb 21, 2012 at 12:33 PM,  <address@hidden> wrote:
> I'm not feeding it the stereo pilot.  I just use a fractional resampler to
> resample the few kHz at 19.0kHz/8 --this gives 4 samples/symbol into the
> DBPSK block.
> The spectrum looks roughly correct--a double-humped structure either side of
> zero.
> On Tue, 21 Feb 2012 12:27:54 -0500, Andrew Davis wrote:
> exactly 19.0kHz/8?
> Are you feeding it the stereo pilot or generating your own?
> Have you tried looking at the signal with an FFT scope to see if there
> is anything there or if it looks distorted or something?
> On Tue, Feb 21, 2012 at 10:35 AM,  <address@hidden> wrote:
> 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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