issues related to the amplitude of the output measured in ev-adar-2s connected to eval-radar-mmic2

we are testing the EVAL-RADAR-MMIC2 board.  we have looped back the TX2 to one of the RX port(J4) using 1.8m long cable through a 20 dB attenuator. power measured at reciever input is -20dbBm(Tx power 7 dbm-(20dbm attenuator 7 dbm cable loss). We are measuring the beat frequency in the EV-ADAR-D2S board @O6 connector. The beat frequency is coming correctly (in KHz range) but the magnitude of the beat frequency is 60mv pk-pk. This doesn't seems to match with gain of ADF5904. How do i correlate the measured output with receiver gain(ADF5904)?