Hi,
I tested LimeSDR-USB output using SoapySDR API to send sine IQ samples .
Center frequency 2.45GHz; sine tone offset +1MHz; antenna BAND2; sample rate 10MHz; bandwidth 10 MHz.
I got the following levels reported by spectrum analyser.
Soapy gain=52 -> ~ -7.0dBm
Soapy gain=55 -> ~ -4.0dBm
Soapy gain=58 -> ~ -2.0dBm
Soapy gain=61 -> ~ -1.0dBm
distortion (additional harmonics) above gain setting 55 was clearly visible.