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Re: [Discuss-gnuradio] Sample audio from my FM stereo receiver

From: Alberto Albiol
Subject: Re: [Discuss-gnuradio] Sample audio from my FM stereo receiver
Date: Thu, 1 Aug 2013 09:08:53 -0700 (PDT)

I found a bug with de-emphasis, the coefficients in de denominator should
change their sign in gnuradio....

One question. I have tried your simple_fm_rcv and a similar version that I
made on my own. In both cases I have found that there is a phase shift in
the pilot tone. In the image the red curve is the L-R modulated signal and
the green line is the recovered 38Khz carried recovered after squaring the
pilot tone. It looks like the zero crossings are pi/2 rad shifted so the
demodulated signal is almost zero. 


By delaying the pilot by one sample (which is almos pi/2) the problem
solves, but I do not see any reason for doing this :-(

Of course, I have been careful and all the filters to split the mux signal
have the same delay and have linear phase

Any idea?

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