Re: [Discuss-gnuradio] gr_remez insufficient extremals

[Martin Braun]

Hi Bernardo,

I'm pretty sure the filter code hasn't changed too much since 3.2.2.
However, I'm surprised it worked before: Your FM demodulator requires a
pretty steep filter (the transition width is less than 0.005 normalised
to the sampling frequency). I only had a quick peek, but since your
decimation in the FM demod is 1, you could use a frequency demod instead
and couple it with your own (custom) filter.
The gr_remez code is a bit unstable in this respect. You normally have
to fiddle around with the parameters until you get a good filter, and
the FM demod block doesn't give you enough knobs.

MB


On Mon, Feb 28, 2011 at 11:25:54AM -0300, Bernardo Guadagnin Gonçalves wrote:
> Hello,
> 
> 
> Until last week I was using the Gnu Radio 3.2.2 (which is ready for use in
> ubuntu), then I decided to try the latest version (v3.3.1git-147-g5a23954a).
> The flowgraph was working perfectly. It's for "in" GRC simulation only. I know
> it's very simple and the 38kHz recovery (at the receiver) is not the
> recommended way.
> 
> 
> Flowgraph: http://dl.dropbox.com/u/8898915/FMstereotxrx2.grc
> 
> .Wav for simulation: http://dl.dropbox.com/u/8898915/sine4k.wav
> 
> 
> The messages that are now shown are:
> 
> 
> Showing: "/home/mula/Dropbox/Public/FMstereotxrx2.grc"
> 
> 
> Generating: "/home/mula/Dropbox/Public/top_block.py"
> 
> 
> Executing: "/home/mula/Dropbox/Public/top_block.py"
> 
> 
> gr_remez: insufficient extremals -- cannot continue
> 
> Traceback (most recent call last):
> 
>   File "/home/mula/Dropbox/Public/top_block.py", line 361, in <module>
> 
>     tb = top_block()
> 
>   File "/home/mula/Dropbox/Public/top_block.py", line 193, in __init__
> 
>     tau=tau,
> 
>   File 
> "/usr/local/lib/python2.6/dist-packages/gnuradio/blks2impl/fm_demod.py",
> line 65, in __init__
> 
>     60)   # Stopband attenuation
> 
>   File "/usr/local/lib/python2.6/dist-packages/gnuradio/optfir.py", line 53, 
> in
> low_pass
> 
>     taps = gr.remez (n + nextra_taps, fo, ao, w, "bandpass")
> 
>   File "/usr/local/lib/python2.6/dist-packages/gnuradio/gr/
> gnuradio_swig_py_general.py", line 432, in remez
> 
>     return _gnuradio_swig_py_general.remez(*args, **kwargs)
> 
> RuntimeError: gr_remez: insufficient extremals -- cannot continue
> 
> 
> >>> Done
> 
> 
> Thanks!
> 
> 
> Regards,
> Bernardo
> 

> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio


-- 
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

pgpgVfpBxhld2.pgp
Description: PGP signature