Forum: GNU Radio USRP producing samples larger than 2^8

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Chris S. (Guest)
on 2007-03-15 04:32
(Received via mailing list)
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
Eric B. (Guest)
on 2007-03-15 06:09
(Received via mailing list)
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
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