[USRP-users] [Discuss-gnuradio] USRP2 + WBX - Power measurement with different decimation rates

Vlad Stoianovici stoianovici_vlad at yahoo.com
Tue Nov 23 15:52:59 EST 2010


Dear Marcus,
Thanks for the reply,
I used decimation values of 8 and 12 (both multiples of 4), for measuring the bandpower for the exact same band, but different values come out at the end.
I will try to use a spectrum analyzer as a reference, but so far it seems that for different decimations, the measurement of the same band yields different output values.
Thanks for your answer.

Vlad

--- On Tue, 11/23/10, Marcus D. Leech <mleech at ripnet.com> wrote:

From: Marcus D. Leech <mleech at ripnet.com>
Subject: Re: [Discuss-gnuradio] USRP2 + WBX - Power measurement with different decimation rates
To: discuss-gnuradio at gnu.org
Date: Tuesday, November 23, 2010, 6:38 PM

On 11/23/2010 07:17 AM, Vladutzzz wrote:
> Dear all,
> I am using an USRP2 module with a WBX daughterboard.
> I am currently interested in power level measurements, and have tried
> measuring band power with different decimations.
> I've noticed, that if I try to measure the same exact band using different
> decimation rates and their appropriate FIR filters, the results differ.
> Has anyone else come across this?
> Does anyone know why this happens?
>
>
>
>   
Two things:

Different decimations may use one, two , or no half-band filters in the
decimator.  For decimations
  that are even and a multiple of 4, two half-bands are used.  For
decimations that are simply
  even, a single half-band is used, and for odd decimations, no half
bands are used.  Odd
  decimation is not recommended.


Also, total measured power is proportional to bandwidth.


-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org



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