Re: [Discuss-gnuradio] peak near center freq for noise signal, how to fix it

[Marcus D. Leech]

On 04/26/2013 12:56 PM, Marcus D. Leech wrote:

On 04/26/2013 12:52 PM, vegihat vegihat wrote:

i use the following command to capture some samples of noise

uhd_rx_cfile -a serial=4759a751 -N 100000 -f 2.48G --samp-rate=2M noise.dat

then using matlab i read the samples
 y=read_complex_binary ('noise.dat');

and i do plotfft
plotfft(y,2000000)

the plot shows a peak near the center. I don't know why. what could i do on the samples y so that the peak not appeared?

i attach the figure of plotfft

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That is the residual DC offset.

UHD allows you to use offset tuning to arrange for the DC offset to be outside your passband, but you'd have to modify uhd_rx_cfile to use that
  feature of UHD.

http://files.ettus.com/uhd_docs/manual/html/general.html#two-stage-tuning-process

-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

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Actually, just noticed that uhd_rx_cfile now has a --lo-offset option, so you don't even need to modify the code, just specify the LO offset -- typically I set
  it to a little bit more than half my sampling bandwidth.

-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org