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Re: [Discuss-gnuradio] NBFM

From: Chuck Swiger
Subject: Re: [Discuss-gnuradio] NBFM
Date: Thu, 17 Feb 2005 20:39:02 -0500

At 11:54 AM 2/17/2005 -0800, you wrote:

I realized about an hour before a demo last night that we didn't have narrowband
FM (like ham and public safety), so I coded it up.  Its in the
gnuradio-examples package, and it is commented rather liberally.

It will require an update on the gr-wxgui stuff too.

Love it - picked up the local noaa weather (162.4 here) wx right off.

I get some kind of strong 1Kz 'noise peak' that's pretty annoying, almost
a constant whistle - have no idea where it's coming from (maybe my
hardware) - it's on local police too.

Anyway, quick software mod: add a notch (comb) filter!

        # notch filter, 1Khz at 16K sample rate
        taps = [1]              # original signal, no delay
        for i in range(1,8):    # .5mSec ( 1/2 cycle at 1Khz ) = 8/16000
            taps = taps + [0]
        taps = taps + [1]       # signal delayed .5mSec cancels self at 1Khz
        notch = gr.fir_filter_fff (1, taps)

then wire it in - end of problem.


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