On Wed, 2008-11-12 at 20:00 -0800, dan s wrote: > I'm puzzled why the number of counts I measure is not constant even > though I have a constant amplitude sinewave signal fed into the LFRX. >
It appears you are seeing the non-uniform passband of the decimation filter in the USRP FPGA. At a decimation of 128, your 250 KHz signal is right at the edge, and is probably about 6dB down from something near the center (DC or 5 KHz.) This is a combination of a 4-stage CIC filter/downsampler and half-band FIR filter without further droop compensation. Try setting the decimation lower, to say, 16, to give you 4 Msps over the USB. If the delta between a 5 KHz signal and a 250 KHz signal becomes smaller, than this is likely the reason. -Johnathan _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
