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E5052B Phase Noise Measurement Problem

Question asked by MPF on Sep 1, 2016
Latest reply on Sep 23, 2016 by MPF

We are using E5052B to measure the output phase noise of a DDS module. At 300.01MHz output the measured Phase Noise at 10 KHz offset is -142dBc/Hz. However, when I configure the DDS module for 300MHz Output, phase noise will increase to -130dBc/Hz (12dB Difference). The only difference between these two tones is several near-carrier spurs (less than “100Hz” offset) with level of -80dBc at 300MHz signal spectrum.

Is it possible that E5052B, not being able to resolve this spurs, so shows them as a spread out noise spectrum close to the carrier at 300 MHz (and causing 12dB increase in phase noise at 10 KHz offset)?