[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.


--- 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

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