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Re: [Discuss-gnuradio] Bandpower measurment USRP2

From: Vladutzzz
Subject: Re: [Discuss-gnuradio] Bandpower measurment USRP2
Date: Mon, 29 Nov 2010 14:53:53 -0800 (PST)

Thanks Marcus.
You did manage to tie up several loose ends, and I really appreciate it!
All the best.


Marcus D. Leech wrote:
> 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
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> Discuss-gnuradio mailing list
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