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Re: [Discuss-gnuradio] Bandpower measurment USRP2

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Bandpower measurment USRP2
Date: Sun, 28 Nov 2010 19:26:10 -0500
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On 11/28/2010 06:53 PM, Vladutzzz wrote:
First of all thank you for your reply!
I have some questions about your very much appreciated explanations:
After using the complex-to-mag-squared block, should I consider the
coefficients as being in W or mW (should I use 10*log10 or 30 + 10*log10 to
get the power value in dBm)?
What is the function of the single-pole-iir_filter? What does it actualy do?
I'm asking this so I will know how to calculate its parameters. Does it give
the frequency bin based signal band, a more rounded appearance?
Again thank you for your help!
I hope other people will also find this useful.


You expressed a desire to measure power over a finite bandwidth (at least, that's what I think
  you were asking).

The values after the complex-to-mag-squared block are *unscaled* total power estimates over the input bandwidth. The IIR filter is used to smooth the result--in a hardware power detector, it would be a simple R-C network, here we use a simple single-pole IIR filter, although you could use a simple FIR low-pass as well, but the single-pole IIR is cheap, and has adequate
  behaviour for total-power detection--it's what I use in radiometry.

In order to convert to your favourite units (like dBm), you'll have to take some *experimental measurements*, and scale the output values accordingly. Please re-read
  my original reply, I'm not going to repeat it here.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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