[Discuss-gnuradio] usrp_fft.py axis values and units

[bjoernm]

Hi,

I'm currently using USRP, GNU Radio and the file usrp_fft.py to find  
the Signal-to-noise ratio, Noise- and Signal-power.
I use the ZigBee PHY from Thomas Schmid to generate the signals at 2.412GHz.

My questions are the following:
1. In usrp_fft.py are the axis denoted as "amplitude [db]" and of  
course "frequency". Now in order to deduce the signal strength or the  
noise strength respectively, I need the reference amplitude used to  
compute the db value. In the code there is the setting "--ref-scale"  
and it's default value is 13490.0. Now is this reference Amplitude  
13490.0 mV? (look at units -> milli-volts)

2. How can I get from here to the signal-power and noise-power? Or  
maybe the signal-strength isn't bad either... (I need those values to  
find the transmitting power of the USRP, I guess it could be 1mW, but  
don't know how to check that)

Thanks a lot for your help!
best,
Björn