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Re: [Discuss-gnuradio] Efficient notch filters

From: Martin Dvh
Subject: Re: [Discuss-gnuradio] Efficient notch filters
Date: Tue, 31 Jul 2007 01:29:02 +0200
User-agent: Icedove (X11/20070607)

Marcus Leech wrote:
> Is there a way to produce an efficient notch filter with the bandpass
> filter designer in Gnu Radio?
You can use a resonating IIR filter for that.
They are very efficient for building a notch or narrowband filters (single out 
a single frequency)
The filter designers in gnuradio can not design it yet for you unfortunatly.
(I am working on source which can design them.)

I do already have an optimized implementation of a resonating IIR filter.
(Several of the taps are +1, -1 and 0)

This filter only uses 2 multiplies to get very nice and narrow filters.

ALso note that the current standard multitap IIR implementation probably has a 
bug, (See my mail with a fix for that in the mailinglist archive)

> I'm seeing narrowband interfering signals that are in-band (with respect
> to the bulk filtering in front
>   of the receiver), and I want to notch one or more of them into
> oblivion.  I'd previously used an
>   FFT filter, and set zeros in the bins where I wanted notches, but it
> wasn't very efficient.
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