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Re: [Discuss-gnuradio] Squelch block, AGC function and scanner example

From: Martin Dvh
Subject: Re: [Discuss-gnuradio] Squelch block, AGC function and scanner example
Date: Wed, 19 Jan 2005 20:04:08 +0100
User-agent: Mozilla Thunderbird 0.9 (X11/20041124)

Frank Brickle wrote:
Martin Dvh wrote:

> I hope also to find a way to determine what kind of signals they are (FM, AM, TV, FSK)
> This way you get a list of everything there is to receive with your current frontend.

A non-trivial task. Robust classification in this setting means doing selective channel downconversion and making repeated sequential spectral observations on the channels.
I was thinking of the following:
Find parts of the spectrum that are significantly above the noise level (peaks) 
and add these to a list.
After that process them one at a time (estimate bandwidth and do selective 
channel downconversion)
Then try AM-demod, FM-demod, (LSB-demod, USB-demod)
If one of these has a outputlevel above a certain threshold then mark it as 
AM-like, FM/FSK-like etc.
All of this does not have to be in realtime. Just save the 
powerspectra/original signal and process them later.

In broadband, this usually requires maintaining a substantial delay line from which to grab and process the selected channels. In commercial systems like the Agilent E3238S the delay line has been the one of the most expensive components.

If you're interested, I wrote a brief expository article about automatic signal classification using probability models of power spectra that appeared in the December 2003 QEX.
Thanks for the tip.
Do you know if QEX is available in europe. (I live in the Netherlands)?
If I order a back-issue-article from the united states it takes a while to get 
here and shipping costs tend to rise.


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