[Discuss-gnuradio] Harmonics of the sampling freqeuncy

[devin kelly]

Hello,

I'm doing a spectrum sensing project and I'm testing both the USRP 1
and USRP 2.  So far, I've modified usrp_scectrum_sense.py to do use
the USRP2 with the WBX

Right now I'm doing this is what I'm doing with what gr_bin_statistics
gives me (as discussed in a previous post)

         signalPower=0
         const = -20*math.log10(tb.fft_size)-10*math.log(tb.power/tb.fft_size)
         for bin in m.data:
                 signalPower += 20*math.log10(bin/tb.fft_size) + const


I then save each of the signalPower variables to a file and plot them
using matlab.  The attached is what I get when I plot, this is the
results of one sweep with the USRP2 and WBX.  I have several questions
about my results.

1) There are harmonics at multiples of the sampling frequency (100
MHz) which I have pointed arrows at.  Has anyone encountered this
before?  Are there any solutions?

2) This sweep was done with a constant gain (31) on the WBX.  Should I
be changing the gain as a function of the frequency I'm scanning?  I
ask because after 1.5 GHz power seems to decrease quickly.

3) In this sweep I had a terminated all ports with 50 ohm terminators,
so I would expect my sweep to be fairly flat.  However, there peaks
and troughs.  Does anyone know how I could get a flatter response?


Any help is appreciated,
Devin

usrp2-with-wbx-2.png
Description: PNG image