Are you asking about the IF? The USRP does not really use an IF, it does
direct up/down conversion using a rough Hartley modulator/demodulator
architecture. When you tell it to plot spectrum over a certain frequency
band it will behave like a swept-tuned spectrum analyzer by sweeping
through
the band-of-interest (BOI) in amounts equal to its bandwidth (datarate /
decimation ratio / 2). If you want to see a single band which is within
its
real-time bandwidth capabilities it sets the local-oscillator to the
lowest
frequency in your BOI. Then you get, after down-conversion, baseband’s
DC =
f_BOI_min and baseband’s max = f_usrp_max_bandwidth. I’m not sure if
that
answers your question, but please feel free to post a follow-up.
Cheers,
-Jonathan
Jonathan F.
Networked and Embedded Systems Lab (NESL)
University of California, Los A. (UCLA)