Gain more than 20 dB in uhd tx dpsk.py

GNU Radio
1

Hi,

I am using gnu 3.7, Ubuntu 13.04, USRP N200 with XCVR2450.

When I run gr-uhd/ examples/grc$ sudo ./uhd_tx_dpsk.py I can increase
tx gain to more than 20 dB. The power of the XCRV2450 is 100mW.
In this case the sink or the source will react to an higher gain
(>20dB).

  1. Why does it happen?

  2. The second question is how about always transmitting with max gain?