Spectrum_sense.py for usrp2

Hey!
I am using USRP2 with XCVR2450 daughter board. when i execute the
usrp2_rx_cfile.py it appends the data into a file but the size of file
is
way too big. in fraction of seconds it generates a file of 1 to 2GBs. I
dont
know whats going on in it. I am using the default decimation of 16.
Secondly, I got the modified spectrum sense code for usrp2 from this
forum
i added fft mag_square part in it from usrp_spectrum_sense.py. whenever
i
run this code i get the error Failed to set center frequency.
please help me out. I just want to collect the real time data for 2.4GHz
ISM
band.