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FFT shape using AD9364/FMCOMMS4/Zeboard/IIO

Question asked by chris.blyseth on Mar 2, 2016
Latest reply on Mar 24, 2016 by chris.blyseth

What causes this distinct shape? This is with 20dB manual gain. Same pattern with no signal or CW. I really want to understand what causes this to better understand the device.

 

Using:

  • AD9364
  • FMCOMMS4
  • Zeboard
  • IIO
  • All pretty much configured "right out of the box'

 

We get this with IIO-Oscilloscope FFT or with our own client app and FFT.

 

I was hoping to get a flatter response across the full bandwidth (with manual gain) before we apply application-level calibration logic. It does flatten out with AGC turned on. We can't really make use of automatic gain control in our application, though.

 

Is this something that can be overcome with the right filter setup? I have not tried the filter design wizard yet since I don't have Matlab (yet).

20db_manual_gain.png

Thanks!

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