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Re: [Discuss-gnuradio] Re: wrong dB
From: |
Marcus D. Leech |
Subject: |
Re: [Discuss-gnuradio] Re: wrong dB |
Date: |
Tue, 03 Mar 2009 14:20:59 -0500 |
User-agent: |
Thunderbird 2.0.0.19 (X11/20090105) |
Stefan Brüns wrote:
>
> You have to calibrate your USRP to get from the sampling values to input
> power
> in Watts.
>
>
Absolutely!!
You can't get even close to "real" numbers without knowing
reasonably-precise figures for gains (losses) in the entire
chain from the antenna up to the application. Digital filters have
gains/losses, there are gains/losses in all the bits of
analog gear in front of the A/D as well.
For my radio astronomy work, I generally don't pay too much attention to
calibration within the application, but rather
use calibrations when post-processing the logged data. We also use
"calibration sources"--radio sources in the
sky with known, stable, flux densities at the observing frequency.
Radio telescopes regularly measure signals
down in the pico-watts, to a reasonable degree of repeatability and
precision.
--
Marcus Leech
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org