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High frequency DDS signal distortion when observed by spectrum

Question asked by RobertYJ on Jun 12, 2018
Latest reply on Jun 13, 2018 by DragosB

Hi everyone,

 

In my job I have to use AD9361 FMCOMMS3 to sent DDS signal to observe the time domain and frequency domain.

But when I use the higher frequency of dds the time domain is became distortion.

 

Below is my setting and spectrum diagram.

 

My baseband sample frequency is 20MHz, and Spectrum's sample frequency is approximated 56MHz.

 

0.3M DDS

 

1MHz DDS

 

 

5M DDS

 

As diagram above can see that when I use the higher frequency dds the time domain is distortion, but frequency domain is normal.

Why would this phenomenon happened?

 

Hope someone can help me to solve this issue.

Thanks a lot. 

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