Digital communication between two USRP1

Hi all,

I want to send and receive data between two different USRP1 (both
directly connected) using the GMSK modulation at 30 MHz. I am using the
GMSK modulation implemented in GNU Radio. For transmission, I am using
the LFTX daughterboard and for reception, the BasicRX.
As a result, when I transmit at low frequencies(e.g. 10 MHz), all the
data is always correctly received. However, when I use 30 MHz, the PC
can receive the data correctly most of the time, but sometimes it
doesn’t receive anything at all. I’ve also tried with other modulations
(the types of PSK and QAM implemented in GNU Radio), different rates,
different longitude of the cables, but the problem persists. When tested
in a loop using the same USRP for transmission and reception, all the
data was always correctly received.
Is there a way to do digital communications using two USRP 1 at 30 MHz?
Was that done before? If so, is there anything I should take into