Re: [Discuss-gnuradio] NBFM

[Chuck Swiger]

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.

--Chuck