Re: [Discuss-gnuradio] iir filter in spectrum analyzer

[Marcus D. Leech]

>
> Dear all,
> I have a question regarding the usage of single_pole_iir_ff filter in the
> fftsink_nongl.py which is used to construct the spectrum analyzer in
> gnuradio-3.1.3. what is the usage of this iir filter since the alfa value is
> equal to 1 which give the value of input the same as the value of the output
> (refering to the single pole iir filter explanation in
> https://radioware.nd.edu/documentation/a-dictionary-of-the-gnu-radio-blocks
> -- please fixme if i am wrong). in the previous post, firas told that this
> filter is used for the averaging purposes
> (http://old.nabble.com/question-regarding-usrp_fft.py-td24440532.html#a24466469)
> but what is the value that it average? 
>
> -----
> Mohd Adib Sarijari
> Universiti Teknologi Malaysia
> www.fke.utm.my
> www.utm.my
>   
It averages the values in each of the bins.

If your FFT is 1024 wide, then you essentially have 1024 single-pole IIR
filters, each computing the
  low-pass filtered version of the individual bins.  This is called (at
by me) spectral averaging.
  There will always be a certain amount of "noise" in spectral
estimates, and for weak signals,
  averaging can bring out spectral features that would otherwise be
hidden by the randomness
  of the noise floor.

-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org