Thomas, I think the first step is for you to understanding the reason behind the step function for your measurement. Please lower the output frequency of the DAC, and also perform initialization of the NCOs to make sure the NCO accumulators are initialized correctly. You can try to duplicate the test results for phase noise through the following app note: You will need to refer section 3.4 of the following app note to initialize the NCO correctly: In the past, the E5052 have problems distinguishing the two Nqyuist zone tones from the DAC. You generated the 460.8MHz tone, but there is actually another tone reflecting around 614.4MHz at 768MHz. You may need to add a filter to allow the E5052 to better resolve the Nyquist image. attached are two measurements done a long time ago with a Wenzel 1GHz oscillator with the DAC output at around 400MHz. You can see the DAC itself can achieve much better noise floor. DAC output at 402.59MHz Wenzel oscillator source at 1GHz Is this done on your own PCB or the TI EVM? Please try this also on TI EVM to duplicate the setup.
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