Gr_remez insufficient extremals

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
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

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:

Flowgraph: http://dl.dropbox.com/u/8898915/FMstereotxrx2.grc
Generating: “/home/mula/Dropbox/Public/top_block.py”

RuntimeError: gr_remez: insufficient extremals – cannot continue


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

Dipl.-Ing. Martin B.
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

Thanks Martin,

Thanks for the idea… and, yes, 1kHz for audio stop isn’t a good idea.
I’ve
reinstalled the 3.2.2 and it really works fine. Anyway, I’ll be trying
to do
a filter as you recommended.

Thanks!
Bernardo

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