Re: [Discuss-gnuradio] signal strength block

[Eric Blossom]

On Tue, Sep 12, 2006 at 07:33:20AM -0700, Johnathan Corgan wrote:
> Ben Olsen wrote:
> 
> > I'm trying to determine the strength of a complex filtered signal from a
> > USRP board; that is, I take the data from the USRP board and I lowpass
> > filter it, and now I'd like to either fft then integrate the complex
> > output to get the signal energy, or just straight away do a  sum on the
> > sequence (a la Parseval's theorem).  Which method would be easier?  Are
> > there any blocks that do this already? 
> 
> The "quick and dirty" method would be to run the signal through
> gr.complex_to_mag() and then through gr.single_pole_iir_filter_ff() with
> a suitable time constant.  This would give you a running average of the
> signal magnitude.

> The latest SVN code has a complex_to_mag_squared block; you do the same
> as the above to get a running average of the RMS value.  You can use
> gr.nlog10_ff() to convert either of these to a log scale.

This is all good info.  If you think about computational efficiency,
you probably don't want to be computing the square root and log on
every sample, thus the complex_to_mag_squared followed by
gr.single_pole_iir_filter_ff is probably the way to go.  When you care
you can compute the sqrt and possibly log on a possible decimated stream, etc.

Eric