Hello,
I'm having a ton of trouble with the USRP/LFRX daughterboard setup. I am
trying to calibrate the counts that are stored as integers when I use the
usrp_rx_cfile.py script.
I am using an HP waveform driver with 50 ohm output impedance to feed single
frequency sinewaves to the LFRX channel A. I am generating sinewaves with an
amplitude of 50 mV peak to peak. I tried measuring several frequencies from 5
to 250 kHz. I am using a decimation of 128 (500 kHz) and the default gain of
10dB.
I recorded the data for each frequency and used matlab to perform an FFT
(normalized) to receive my peak counts for each case. The number of counts I
measure is not the same for all the frequencies. I noticed the number of
counts stays constant from 5 to 20 khz, then drops from 20 to 150 khz, then the
number of counts rises slightly from 150 to 240 kHz.
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.
I also tried performing the same tests with an HP spectrum analyzer. The
analyzer measured a response of 16 mVrms (which corresponds to 50mV peak to
peak) at each of the frequencies. I am 100 percent confident the signal I am
feeding into the LFRX is perfect.
Thanks,
Dan Sura
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