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Re: [Discuss-gnuradio] NBFM

From: James Cooley
Subject: Re: [Discuss-gnuradio] NBFM
Date: Tue, 22 Feb 2005 07:47:12 -0500
User-agent: Mozilla Thunderbird 1.0 (X11/20041206)

I'm having a bit of trouble getting this one to work...

I'm running the input through a microtune 4937 frontend, so that the IF is 5.75e6. I've changed Matt's nbfm script just to adjust this IF_freq.

Is there anything else that needs to be done? I'm trying to tune to a known station, the weather, 162.475.


Chuck Swiger wrote:

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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