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## Re: [Discuss-gnuradio] mathematics behind probe.level()

 From: Marcus Leech Subject: Re: [Discuss-gnuradio] mathematics behind probe.level() Date: Thu, 29 Aug 2013 14:59:56 +0000 (UTC)

For a complex signal, the instantaneous power level is proportional to (I**2 + Q**2), which you then average.

This is precisely what probe_avg_mag_sqrd does.

And, you shouldn't refer to it as an "energy level", since you're measuring power, not energy.  Those are different (but related) concepts in physics.

Now reducing even further, remember that the ADC is sampling a *voltage* level.  The power flowing through a circuit is proportional to the square of the voltage.
The samples that are coming into the flow-graph are proportional to the voltage seen by the ADC, so in order to calculate the power, you have to square them.
Review Ohms law to see that this is true.

on Aug 29, 2013, dilip thapa <address@hidden> wrote:
Hi,
I want to do energy detection of received signal, And after searching I was advised to use probe block to do the sense. (gr.probe_avg_mag_sqrd_f).

Can anyone explain how this works. How level() method gives the energy level. I need mathematic behind this function. Is this calculates based on FFT or what?

dilip

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