On Thu, Apr 28, 2005 at 02:12:37PM -0600, Viktor Przebinda wrote: > Hi, > > I have a simple question on the USRP. When setting fpga digital > down-conversion frequency to zero via set_rx_freq method why do > I get nonzero (and changing) values in the imaginary channel? > Seems like these should all be zero since sin(0)==0 ?? > > Thanks, > Viktor
What's happening is a complex multiply of the incoming I/Q with cos/sin out of the NCO (really all done together in the CORDIC). This effectively rotates the incoming I/Q signal. What you're seeing is that the phase register in the NCO has a non-zero, but constant value (freq == 0) and as such is rotating the input I/Q by a fixed angle on each sample. Right now there's no way to zero the phase register, but you can see this behavior by cycling power on the USRP and then setting the frequency to zero as the first thing (or don't set it at all). In this state Q will be a constant zero. Eric _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
