Re: FM stereo receiver distortion

[Jeff Long]

Ah, it's a Python heir block. You could reduce the quadrature rate further so that the quadrature rate is closer to 200 kS/s and/or put a 200 kHz LPF in front of the block. There's internal filtering for the various components of the baseband signal, but no internal filtering before the PLL. It could also be just that FM stereo is more sensitive to noise (try GQRX stereo on a station that sounds good in mono).

On Thu, Jun 18, 2020 at 6:41 AM Jeff Long <willcode4@gmail.com> wrote:

If there's no filter inside "WBFM Receive PLL", place one before it. The example in gr-uhd has a 400 kHz filter there.

On Tue, Jun 16, 2020 at 8:46 PM Barry Duggan <barry@dcsmail.net> wrote:

Hi,

I have a broadcast FM (mono) receiver which works well, with good audio
and clean traces in the Time Domain. See
https://wiki.gnuradio.org/index.php/File:USRP_FM_fg.png

Then I made a stereo version. See
https://wiki.gnuradio.org/index.php/File:USRP_FM_stereo_fg.png  Using
it, the sound has a distortion but does not have any audio underruns.
The traces in the Time Domain have a lot of "fuzz" (noise?).

Do I need a filter? If so, would it come before or after the WBFM
Receive PLL block?

Once I have a good design, I will use it as an Example Flowgraph.

Thanks for your help.
--
Barry Duggan KV4FV