Usrp_spectrum_sense problem

We have an Agilent signal generator and an Agilent transmitter tester in
our lab. We are trying to use usrp_spectrum_sense as a spectrum analyzer
in the ~2.4 GHz range. We have the appropriate 2.4 GHz daughterboard
installed.

When we run spectrum_sense from 2.4 GHz to 2.5 Ghz while transmitting
using our signal generator at 2.45 GHz (which we then verify with out
transmitter tester), we get garbage from spectrum_sense. When we view
the data in MATLAB and apply fftshift it just looks like it ramps up
towards the center frequency and then back down, no peak is present. We
get the same output irrespective of whether the signal is on or not.

In contrast, usrp_fft works very well (although quite slowly).

Why do we only get noise in spectrum_sense and no signal?