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Re: [Discuss-gnuradio] RDS reception

From: Rafael Diniz
Subject: Re: [Discuss-gnuradio] RDS reception
Date: Fri, 24 Feb 2012 10:23:48 -0800
User-agent: SquirrelMail/1.4.21

It would be great to have the rds code inside the gnuradio tree instead of
in a separate cgran project!
; )

I don't know why, but when I tried the cgran rds code, the grc example
worked much better then the python one.

Best regards,
Rafael Diniz

> Actually, I'm using the blks2 WBFM block, which I believe is a PLL
> demodulator.
> Both of my "test" stations are actually roughly 100km
> away from me, broadcasting from a high point in the Ottawa Valley.
> One
> station comes in about 10dB stronger than the other, although both have
> an ERP of about 100kW, and both are located on the same transmit tower.
> I'll send you my 'stuff' once I'm more comfortable with it. The audio
> quality is actually reasonably good, so I think the FM demodulator
> portion is just fine.
> -Marcus
> On Fri, 24 Feb 2012 11:12:28 -0500,
> Andrew Davis wrote:
>> I think the problems with SNR is with the FM
> Demod, my car stereo can
>> get RDS as the station fades 40 miles away,
> but with my USRP has
>> trouble picking up the stereo pilot from a 50kw
> station one mile away
>> ( -10dBm ). FM demod is hard for software ( I
> think GNUradio just uses
>> a zero-crossing detector ).
>> Do you have
> the code, I would love to test it.
>> On Thu, Feb 23, 2012 at 11:33
> PM, Marcus D. Leech wrote:
>>> 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 [1]
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