Re: [Discuss-gnuradio] How to simulate a Zoom in FFT display ?

[Ryan Connelly]

In the Frequency Xlating FIR filter just put a decimation factor and
output that to FFT. This will be "zoomed" to the center frequency by
the decimation factor. For example if you have a 1M sample rate file,
and pass it through a decimation of 4, you will get an FFT "zoomed" to
a 250 kHz bandwidth. Is that what you want to achieve?

Also the center frequency parameter (in that FIR filter) can be a
variable linked to a GUI slider so that you can interactively move the
center frequency you are zoomed on.

On Sun, Aug 12, 2012 at 1:28 PM, William Pretty Security
<address@hidden> wrote:
> Hello all;
>
>
>
> I have a 40KHz carrier that I want to be able to check for modulation.
>
> The ‘source’ is the audio source in GnuRadio Companion.
>
>
>
> I have tried a number of things and nothing seems to work for me.
>
> I have the source, followed by a 40KHz Bandpass filter and a frequency
> translating FIR filter block.
>
> The output of the BPF and FIR filters go to separate FFT GUI’s so that I can
> see what is going on.
>
>
>
> What I am trying to implement is the equivalent of the “Span” and “Center
> Frequency” functions on a spectrum analyzer.
>
> The Center Frequency is easy, using the Translating FIR block, but I can’t
> figure out how to do the Span/Zoom function.
>
>
>
> I Google searched and found a couple of SDR’s with this function, but it
> appears to be “hard coded”.
>
>
>
> Does anybody know how to this in GnuRadio Companion ??
>
>
>
> Thanks …
>
>
>
> Bill
>
>
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