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On the phenomenon that a sine wave becomes a square at a specific center frequency

Question asked by DolphinSasoh on Dec 6, 2016
Latest reply on Dec 8, 2016 by DolphinSasoh

Hi,

 

If the frequency is set to 201 MHz, the IQ plot of the received 200 MHz sine wave will be square rather than circle.
I have not tried everything, but this phenomenon seems to occur at a specific center frequency setting.
Looking at the spectrum, the harmonic is very big.

 

I am using FMCOMMS 3 and ML 605.
I am using No-OS Software.

 

The setting of the AD9361 is
Center frequency 201 MHz
Sampling frequency 61.44 MHz
Setting bandwidth 56 MHz
Gain 10 dB

 

The input signal is
CW 200 MHz
Power - 10 dBm


The following is the IQ plot and spectrum of the waveform acquired with the Xilinx Chip Scope.

What is the cause? Are there countermeasures?

 

ad9361 freq fmcomms3

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