Re: [Discuss-gnuradio] Bandpower measurment USRP2

[Marcus D. Leech]

On 11/28/2010 06:53 PM, Vladutzzz wrote:
> Marcus,
> 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.
>
> Vlad.
>
>    
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
http://www.sbrac.org