Problem about the LMS6002 - 50Hz interference on the receiving signal

I am doing a project on the bladerf board, bladerf-x115. which using lms6002d, the system performance is far worse than I expected, about 6db worse than the comparable system.

I checked the output signal, found that there is a strong 50Hz interference on the output, then I do a test as following:
RX input is 786MHz sine wave. set the LO to 781MHz, and then I should get the 5MHz signal on the adc output. the result is 5MHz signal, but modulated with 50Hz signal. the data is shown as pic

BladeRF is not a Myriad-RF project and would suggest posting to the BladeRF forum.