FM stereo problem

Hello everyone,

As Euripedes Rocha told few days ago in the email “Who actually does
use
GNU Radio?”, we’re starting to use it here, but we do not currently have
daughterboards to use with USRP2.

Due to this, specially in my case, I’m building some simple diagrams
using
GRC, and one of them is a FM stereo transmitter/receiver in the same
flow
graph.

Basically, the problem is that it works just as mono, not stereo…

Here is a screenshot of the flow graph:
http://dl.dropbox.com/u/8898915/fmstereotxrx.png

The grc’s file is here:
http://dl.dropbox.com/u/8898915/FMstereotxrx.grc

Thanks!

Regards

schrieb Bernardo Gon

schrieb Patrick S. on 2011-01-25 16:55:

Hi Patrick,

First, thanks for the reply!

But two other things I did notice:

  1. The difference signal, which is shifted down from 38kHz is several
    10dB lower than the sum signal. With different gains I got something
    more stereo-like.

I’ll try to do that, I’ve seen through a FFT after the FM Demod block,
but I
didn’t try to increase the gain of 38-53kHz!

  1. The sum signal is faster than the difference signal. In the
    diff-signal path you have more blocks that are processed. Some delay
    (delay block) could maybe fix this problem, but I did not get the right
    value at a quick try.

Well, wouldn’t that be also a problem during the modulation? Anyway I’ll
also try to look after the Delay block.

I’ll post the results soon!

Thanks for the help!

Regards,
Bernardo

On Tue, Jan 25, 2011 at 10:25 PM, Patrick S. <

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