On Wed, Dec 07, 2005 at 02:51:58AM -0500, Blue Sky wrote: > I am trying to build a AM receiver by using USRP. I did setup the IF > frequency to 1.43 MHz by using set_rx_freq. I was sending a 1 Khz signal 90% > modulated at 1.43 MHz carrier. I should get something from the USRP output > just the 1 KHz sine wave. But for some strange reason I am not getting that. > I am getting some extra 333 Hz freq signal with it. I dont' know where is > the problem. So, I am guessing the NCO-CORDIC is not completely removing my > carrier frequency. I saw the waveform just after the USRP it's the same with > some extra frequency. Anybody's help and thought would be highly > appreciated. Thanks.
The FPGA DDC has a finite frequency step. If you're worried about the 333 Hz, you'll need to follow it up with a software DDC (gr.freq_xlating_fir_filter_xxx: s/w DDC plus channel selection filter). Take a look at gnuradio-examples/python/usrp/usrp_nbfm_rcv.py Skip all the GUI cruft, and look at the set_freq method. It uses the high level daughterboard independent method to control the (possibly null) analog front end and the FPGA DDC, then follows it up with a software DDC to handle any residual frequency offset. Eric _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
