Re: [Discuss-gnuradio] Re: wrong dB

[Marcus D. Leech]

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