On Thu, Mar 19, 2009 at 05:43:56PM -0400, Erich Stuntebeck wrote: > Hi, > > I'm trying to calibrate the USRP so I can get true dBm readings out of > it. I'm using an LFRX card with 16 decimation and a center frequency > of 2 MHz so I can look at the range from DC - 4 MHz. I hooked up a > signal generator and swept it through the DC - 4 MHz range at 100 kHz > intervals and generated the plot here: > > http://ice.cc.gt.atl.ga.us/usrp_adc_response.jpg > > The signal generator produced a -36 dBm signal for each frequency, and > the y-axis of this plot is the output of the USRP's ADC in dB. (20 * > log10 of the appropriate FFT bin for the frequency of interest, using > an 8192 point FFT). > > My question is what is causing the particular shape of this response. > I'm guessing it has to do with the CIC filter, but I can't seem to > reconcile my output with the plots from this post on the CIC filter's > response: > > http://lists.gnu.org/archive/html/discuss-gnuradio/2007-05/msg00191.html >
What is the daughterboard gain set to? If you look at the time domain samples, what is their range? You might try increasing the power a bit and see if anything changes. Did you collect that data with usrp_rx_cfile.py? If so, what was the exact command line that you used? What kind of a signal generator are you using? Have you tried sweeping the same way into a spectrum analyzer? If so, what did you see? Eric _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
