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From: | dan s |
Subject: | [Discuss-gnuradio] Problems with the USRP/LFRX at lower frequencies |
Date: | Wed, 12 Nov 2008 20:00:30 -0800 (PST) |
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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