Eric Thanks！Now I get it. Ling Eric Blossom wrote: > > On Tue, Dec 23, 2008 at 05:52:03AM -0800, Ling Huang wrote: >> >> Hi,all >> >> I've change the usrp_spectrum_sense.py to print out the m.data. And I got >> the numbers like 9376200 2976546 34170452.... But I just don't understand >> what these numbers stand for . Are they stand for the power or the >> energy? >> And what's these numbers' dimension? >> Sorry for my bad English. >> >> Ling > > They are the single precision floating point magnitude squared of the > FFT output. That is, for each FFT bin[i], mag_squared[i] = re[i]*re[i] + > im[i]*im[i]. > If you want power, take the square root. We don't do it by default > since most users are going to be computing a log somewhere downstream, > and the square root can be trivially folded into that calculation. > > To see what the FFT bins contain, see the FFTW documentation (fftw.org). > > The actual mapping from the levels at the daughterboard antenna port > to sample values depends on a lot of factors including any > daughterboard gain and decimation specific gain in the digital down > converter. You'll need to calibrate the system if you need something > that maps to dBm. > > Eric > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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