Re: [Discuss-gnuradio] Frequency discriminator using a frequency to voltage converter

[madengr]

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.

Thanks,
Lou

 

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.
> 
> Cheers,
> Marcus





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