Re: [Discuss-gnuradio] Interpretting results from usrp_rx_cfile.py

[Eric Blossom]

On Wed, Jan 17, 2007 at 04:37:58PM -0700, Bahn William L Civ USAFA/DFCS wrote:
> I have a function generator outputting a sine wave into the RX-B
> connector of the BasicRX board connected to the RX-B side of a USRP. I
> am trying to capture the waveform and store it to a file.
> 
> Here are the commands I tried:
> 
> # ./usrp_rx_cfile.py -R B -d 256 -f 1000 sine_1k1.dat
> # ./usrp_rx_cfile.py -R B -d 256 -f 10000 sine_1k10.dat
> # ./usrp_rx_cfile.py -R B -d 256 -f 15000 sine_10k15.dat
> 
> The function generator was producing a 1kHz sine wave for the first two
> and a 10kHz sine wave for the third.
> 
> Each time I captured a few seconds worth of data. I then took the data
> files and extracted two streams of single precision floats for each of
> the first ten thousand 8-byte groups in the file and plotted them. The
> results were very similar regardless of the frequency specified on the
> command line (and I have no idea what that frequency is for) or the
> actual frequency of the signal that was applied to the inputs.
> 
> What I got in all cases was basically a flat line (-3 to +3) except for
> in the vicinity of sample #530, which looks like an inverted sinc pulse
> with a peak amplitude of about -10000 (the first stream, which is made
> up of the first float value in each sample pair), and what looks like an
> extremely heavily damped sine wave (the second stream) with a peak
> amplitude of about 20,000 and roughly centered at the same place as the
> sinc pulse. 
> 
> This makes absolutely no sense to be whatsoever. Can anyone shed any
> light on this?
> 
> Thanks

The Basic RX only passes signals > 100kHz.

Eric