According to the board manufacturer:
"The receive frontends have 73 dB of available gain; and the transmit frontends have 89.5 dB of available gain. Gain settings are application specific, but it is recommended that users consider using at least half of the available gain to get reasonable dynamic range." [1]
The default values for the config files are around 125 dB for TX and 90 dB for RX. However, if you look at the log file of the eNB software, you can see that the final set values are close the ones reported by the manufacturer.
For example, look at the following lines excerpt from the eNB log:
RX Gain 0 125.000000 (49.000000) => 76.000000 (max 76.000000)
...
Actual RX gain: 76.000000...
Even though the RX gain is set to 125 in the config file, the actual RX gain is 76 dB. To access the actual values, you can take a look at "usrp_lib.cpp" file in "\targets\ARCH\USRP\USERSPACE\LIB\usrp_lib.cpp".
std::cout << boost::format("Actual TX bandwidth: %fM...") % (s->usrp->get_tx_bandwidth(i)/1e6) << std::endl;
References
[1] http://files.ettus.com/manual/page_usrp_b200.html
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