Power measurement with USRP2 and XCVR2450 (units issue)


I’m a newbie GNU Radio student, and I’m trying to measure the received
signal power with an USRP2(using XCVR2450 as daughterboard and VERT2450
Setting up an ad-hoc network with two computers and using a third one
running the GNU Radio flowgraph, I intend to
detect the channel usage with the USRP2 while one computer is sending
continuous PING messages to the other computer.
To reach this goal, I designed the following graph:

[USRP2 source(f=5.2GHz,decimation=16, gain=46dB)]–>[Head(1024)]–>[FFT
filter(taps=1024,decimation=16)]–>[Complex to Mag^2]–>[Number Sink]

  1. The output of Complex to Mag^2 block, what is the data format (Watts,
    mW, dBm, dB)?

  2. Why the gain parameter of USRP2 source block is between 0 and 92?
    What’s the influence of this value to the measurements?

Thank you for your help.