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Extra Frequency Component in 9361 DDS

Question asked by htorke on Sep 16, 2016
Latest reply on Sep 27, 2016 by larsc

I have attempted to use the FMCOMMS3 board using the standard boot image and ADI Linux distribution. Using the Oscilloscope program, I set the channel 1 DDS frequency at approximately 100 kHz  and set a TX frequency of 2450 MHz. I see this output on my scope:


DDS Sine Wave


The sinusoid is clearly visibule, but there is some high frequency component disturbing the signal. Zooming in, this is what the noise looks like:


TX Noise


Some sort of periodic disturbance is present in addition to the DDS wave. This is not the carrier, as if I zoom in further:


Carrier Wave


I see the fairly clean 2.45 gHz carrier sine.


Other than setting the DDS and TX characteristics, all other settings are left at default.


What would be the cause of this intermediate interfering signal?