On 06/11/15 19:01, madengr wrote: > Marcus Müller-3 wrote >> Hi Lou, >> >> that's a pretty good application of the spectrum, I agree. One could >> certainly modify the freq_sink to do that, however, as it is now, the >> PSD calculation (based on the fft result) is done in a single VOLK >> kernel, 32fc_s32f_x2_power_spectral_density_32, which probably has some >> performance advantages, so changing that would mean to either abandon >> that benefit or introduce a new "processing path" inside the frequency >> sink. >> >> I'm a bit confused, though: The DFT is a linear operation. So averaging >> k FFT vectors (linear operation) before or after the DFT wouldn't make a >> difference, because >> >> $\sum_{n=1}^k \mathrm{DFT}(x_n) = \mathrm{DFT}(\sum_{n=1}^k x_n)$, with >> $x_n$ being our DFT length-sized input sample vectors. >> >> You should be able to do $\sum_{n=1}^k x_n$ with a stream to vector->add >> block combination in front of the normal frequency sink. > > Hmm.. maybe it is. I have done it in (shudder) LabView and it's nice since > noise reduces at 1/N instead of 1/sqrt(N); N is number of averages. Maybe > I'll try it tonight with just discrete blocks to compare them side by side. > Just something that can't be done with a normal spectrum analyzer.
Why does that hold true? I don't think it is possible, at least in the general case. Cheers, Daniele _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio