Re: [Discuss-gnuradio] Power output RFX2400 and OFDM example

[Marcus D. Leech]

On 07/27/2015 11:56 AM, Jose Perez wrote:
> Hi all,
>
> I am trying to obtain or know how much power output my hardware device is
> transmitting. For this, I am running the example "tx_ofdm.grc" with a USRP1
> and RFX2400 daughterboard. The RFX2400 provides a typical power output of 50
> mW => ~ 17dBm.
> The block "Multiply const" can increase or decrease my transmitted signal
> and I am also using a Spectrum Analyzer to measure the received signal
> according the distance.
> Actually, I need understand how the "Multiply const" block relates with the
> power output ... and what is the exact power that my hardware is
> transmitting.
> If I put 0,5 in "Multiply const" block this means the I am transmitting half
> of my all power output?
>
>
> Thank you in advance.
>
> Cheers,
> José
There's no way to know precisely what your output power will be, just 
from the magnitude of the baseband samples.  In RF, particularly in UHF
  and above, there's *always* device-to-device variability of 1 or 2dB.

Now, since power is proportional to the square of the voltage, and since 
baseband samples represent instantaneous voltages,
  then increasing your baseband magnitude from 0.25 to 0.5 will 
increase the *power* by 6dB (factor of 4).  As you approach magnitudes of
  1.0 it's likely that the TX amplifier will be close to its 
compression point, the exact point can only be verified with external 
measurements.