Question about antenna using on LFRX

Dear all,

If I use usrp_source_c to introduce a complex signal from a USRP1 with
LFRX, and sink into a data file as complex signal, do I have to using
both of the antenna on one LFRX daughter board, one for I channel, the
other one for Q channel. If using usrp_source_c as the source signal,
but only connect one antenna, what would happen?

Really appreciate any of your help!

Yan