On Tue, Mar 15, 2011 at 4:48 PM, Scott Johnston <scott.johns...@ll.mit.edu> wrote: > Hello, > > I wrote a simple grc graph to compute power spectra of the output of the > usrp. My test setup is a signal generator outputting a tone at the same > frequency that I set as the usrp center frequency, directly connected to the > usrp. But when I examine the output in Matlab, the first vector is exactly > what I expect, a peak at the center and then the noise floor. The following > vectors show the peak at lower and lower power levels until, after 10 or so, > it disappears into the noise. My code is attached. Anybody know what could > be causing this?
My guess is that you are seeing a DC offset correction loop closing. This would occur if the RF tone of interest is downconverted to DC (which sounds like what you described). I don't recall how DC offset correction is actually implemented in USRP land, but it may very well take a few tens/hundreds of samples before it is completely corrected, which lines up with what you're seeing. Try changing your sig gen to output a tone at, say 100 Khz from your RF tuning frequency, and it should not attenuate over time. -- John Orlando CEO/System Architect Epiq Solutions http://www.epiq-solutions.com _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
