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Re: [Discuss-gnuradio] USRP2 Spectrum Sensing Help

From: Julio Hector Aguilar Rent
Subject: Re: [Discuss-gnuradio] USRP2 Spectrum Sensing Help
Date: Fri, 5 Aug 2011 15:55:09 -0700 (PDT)

hello, how you did it, that changed in the sensing spectrum, I'm using the
module FLEX900?

devin kelly-2 wrote:
> Hello,
> I've created a spectrum sensor with the USRP2, my python script uses the
> same idea as usrp_spectrum_sense.py found in gnuradio.  That is, it tunes,
> takes an FFT, records, retunes, etc.
> I have two problems with my data though.  In the file attached is some TV
> spectrum (left half) and noise (right half).
> My first question is this: why isn't the spectrum for the TV signal flat,
> it
> seems to bob up and down.  Note that each segment is from a different FFT,
> that is each FFT produces that oval shape.  At first I thought this had
> something to do with the window I was using but I've tried hamming,
> blackman-harris, and rectangular windows and they all have this effect.
> My second question is why isn't the transition between TV spectrum and
> noise
> more smooth? It looks like it could be smooth but the gain seems to jump
> for
> an FFT right after 566 MHz and then settle down again.  I thought this
> might
> be the AGC but I've tried different attack/decay rates, different
> reference
> levels, etc with the agc2_cc block but the problem remains.
> Any help with either of these questions would be appreciated,
> Devin
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