On 11/04/2010 01:02 AM, Steve Mcmahon wrote: > Marcus: > > Thank you for your reply. Let me ask you another question to make sure I'm > understanding this correctly. Remember, I have a USRP2 board with a WBX > daughterboard. If I construct a flow graph where a signal source block > generates a 7 khz cosine at a sample rate of 200 khz (100e6/500), and if this > cosine is fed into a USRP2 sink block with its "frequency" parameter set to > "900M", then will I see a spike in the WBX output spectrum at 907 MHz, or at > 893 MHz, or both? (assuming perfect precision of the internal reference clock > on the USRP2) What if it were a sine instead of a cosine? Thanks again for > your help. I really appreciate your time. > > Steve McMahon > You'll see a spectral spike at 900.007Mhz. Regardless of the phase. You keep making the "907MHz" mistake in your posts. Remember that upconversion doesn't "expand" the frequency components. So a spectral component at 7Khz will still be at 7Khz relative to the upconverted "DC" frequency.
Your complex baseband signal has spectral components that stretch from -bandwidth/2 to +bandwidth/2. If you have a component at +7KHz, it'll still be at <upconverted-frequency>+7Khz when it's finished being upconverted. Interpolation also doesn't change the relative spacing of spectral components, only the time-domain resolution of the samples of those spectral components. So your +7Khz signal sampled at 200KHz will still be at +7Khz when sampled at 100MHz. -- Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
