Iir filter in spectrum analyzer

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

View this message in context:
http://old.nabble.com/iir-filter-in-spectrum-analyzer-tp28791867p28791867.html
Sent from the GnuRadio mailing list archive at Nabble.com.

Marcus D. Leech wrote:

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

so it is a filter to filter the noise at the noise floor level am i
correct?
but there is also a windowing in the flow graph… I think this windowing
is
also used for the filtering the noise including noise in the noise floor
level (please fix me). if not, may i know what is the usage of this
window
and what is the different between this window and the iir filter used in
this flowgraph?


Mohd Adib Sarijari
Universiti Teknologi Malaysia
www.fke.utm.my
www.utm.my

View this message in context:
http://old.nabble.com/iir-filter-in-spectrum-analyzer-tp28791867p28803709.html
Sent from the GnuRadio mailing list archive at Nabble.com.

(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