WBX Daughter board problem

Hi every body,Now i’ve got a problem that my usrp now has only BasicRX
and WBX
but i want to make a experiment that i want to generate the signal from
the signal generator for 1.5M and 4M through each Daughter board
and i decide to generate the 1.5M to basicRx and i knew that minimum
Rage of WBX is about 50Mhz so i tried to generate 4Mhz to the wbx and
show in the grc scope sink and i saw only noise.Are there another way
that i can do my experiment (i cannot generate up to 50Mhz because of my
function generator) and if i can generate above 50Mhz through the WBX
what will i see in the grc scope sink?

thank you very much for every kindness and advice
Wipat