USRP2 transmission issues

Hi!! I am trying to transmit a complex signal with the USRP2+WBX system.
First I tried transmitting from file, an 8MHz band recorded with the
USRP2, by connecting the “from file” block to the USRP2 transmitter,
with and appropriate interpolation.
When visualizing the output on a spectrum analyzer I can see that the
USRP2 is transmitting a very narrow bell-shaped signal band and on the
sides what seem to be harmonics of the center signal.
Changing the interpolation on the usrp2 seems to affect the bandwidth of
the central signal (the smaller the interpolation the larger the
Any ideas on where I’m going wrong?