[USRP-users] Band power measurement.

Vlad Stoianovici stoianovici_vlad at yahoo.com
Mon Nov 29 04:50:56 EST 2010


Dear Mike,
Thank you for your reply.
I am actually trying to measure a complex 8 MHz signal band. I am more interested in getting an output value of the bandpower, not just visualizing it on a spectrum scope, and therefore I was interested in the hole flow from USRP2 sample to dBm value, block by block.
I got a good reply here http://old.nabble.com/Bandpower-measurment-USRP2-td30323488.html but I am still digging, as I am not so experienced and am still struggling with some aspects of this.
Thank you for your time.

Vlad. 





--- On Mon, 11/29/10, Mike McLernon <Mike.McLernon at mathworks.com> wrote:

From: Mike McLernon <Mike.McLernon at mathworks.com>
Subject: RE: [USRP-users] Band power measurement.
To: "Vlad Stoianovici" <stoianovici_vlad at yahoo.com>
Cc: "usrp-users at lists.ettus.com" <usrp-users at lists.ettus.com>
Date: Monday, November 29, 2010, 5:38 AM

Hi Vlad,  For a simple signal such as a sine wave, you can use the Spectrum Scope block to essentially do the measurement for you.  The attached model, mMeasureSignalPower_10b.mdl, is meant to be run in the R2010b version of MATLAB.  The sine wave source is at 100 Hz, with an amplitude of 1.  With that amplitude, the power is 0.5 W, assuming a load impedance of 1 ohm.  That 0.5 W translates into 27 dBm.   Note the FFT plot of the signal:    The two signal spikes at +/-100 Hz are at 24 dBm, giving a total power of 27 dBm.  If you are using a more complicated signal than a sine wave, then you can simply reckon the Simulink signal values as having units of sqrt(watts).  In that case, you can get the power Px of signal x in dBm according to  Px (dBm) = 10*log10(var(x)) + 30.  Hth,Mike    From: usrp-users-bounces at lists.ettus.com [mailto:usrp-users-bounces at lists.ettus.com] On Behalf Of Vlad Stoianovici
Sent: Sunday, November 28, 2010 8:37 AM
To: usrp-users at lists.ettus.com
Subject: [USRP-users] Bandpower measurement.  Dear all,
I would like to receive as many suggestions as possible on how to accurately measure bandpower with a USRP2 + WBX setup.
I know I should use a block that does the square magnitude (FFT squared) and sum the resulting coefficients but after this I don't really know what the correct procesure is. I would like to have the value in dBm and I know I'm suppose to use 30 dBm + 10log10, but the resulting value is not the correct one.
Please help me by offering your insight on this matter.
Thanks!

Vlad.  


      
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