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Why is the Fund Power of the FMCADC4 different for VA & IIO?

Question asked by ALU on Feb 3, 2017
Latest reply on Feb 20, 2017 by ALU

Hello EZ!


I have successfully managed to make Visual Studio interface with my AD-FMCADC4 board. However, there seems to be a problem with the FFT data:



As you can see, the Fund Power measured is approximately -14 dBFS. However, this contradicts the measurement taken using the IIO Oscilloscope:



According to the IIO Oscilloscope, the Fund Power should be approximately -3 dBFS. Why is there such a large discrepancy in fundamental power? I've tried using other channels and the data also do not match up.


Here is my setup, for reference:

For Visual Analog, I simply used the AD9680 Average FFT template, adjusted the FFT to do 10 iterations, and replaced the 'ADC DataCapture' block with the 'IIO Client' block. By the way, I've also attached the vac file to this post in case you want to take a look at it.


For IIO Oscilloscope, I did not change any settings aside from the FFT Average (I set this to 10).


Input signal came from a R&S SMBV100A and was set at 450 MHz, -12 dBm. This was fed directly to the SMA connectors.


Do you guys have any idea what the issue is? I want to use Visual Analog to get the SNR, SINAD, and SFDR of the on-board AD9680.


Thank you for any input you could provide on this!