USRP producing samples larger than 2^8


#1

Hi,

Should I get samples with a magnitude > 128 from the USRP no FPGA gain?
I believe the answer is no. Take a look at these plots of the data I
am getting (plot of real portion only):

http://img157.imageshack.us/img157/8648/plot1gi6.gif

http://img245.imageshack.us/img245/8528/plot2fp1.gif

I collected the data using this method:

./usrp_rx_cfile.py -d 16 -f 1575420000 -g 0 -N 4000000 file.dat

Furthermore, I created a test jig which wrote USRP output to stdout and
verified these spikes are not in the binary file or the binary file
reader. I’m using the DBSRX with a GPS antenna and a low noise
amplifier.

Thank you!

Chris


#2

On Wed, Mar 14, 2007 at 07:31:33PM -0700, Chris S. wrote:

I collected the data using this method:

./usrp_rx_cfile.py -d 16 -f 1575420000 -g 0 -N 4000000 file.dat

Furthermore, I created a test jig which wrote USRP output to stdout and
verified these spikes are not in the binary file or the binary file
reader. I’m using the DBSRX with a GPS antenna and a low noise amplifier.

Thank you!

Chris

Chris,

Does it only occur once, and does it occur in the first 1024 samples?
That is, if you look at, say 1M points, is there only a single
occurrence?

If yes to all 3 questions, then I think you’re seeing a known problem
where for some not fully understood reason (but probably related to
failing to properly reinit the FX2 buffers and/or the FPGA) you get
the sinc looking spike.

Eric