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
tv-spectrum.png