Subtract carrier and noise from signal source and measure noise caused by the DUT using phase detector.
Strict adjustment between two paths is required to get enough compensation.
The same signal frequency should be input on both RF inputs 1 and 2,
When the DUT is a frequency conversion device, the Two DUTs configuration is required.
When the DUT has an extremely low residual noise, external source is required.
See the RF path tab in Phase Noise Setup dialog.
Source signal purity (Phase noise, AM noise, harmonics, sub-harmonics)
Source out of E505xA covers most application but for devices with extremely low residual noise, consider use external sources, insert LPF/HPF at the input and/or output of the device
Input/Output power of DUT (= input power at RF1/2 Input)
For high gain DUT, the input power is set low, which is also the input of RF1 input and will degrade the sensitivity
Compression of DUT gives unexpected and unwanted result.
Baseband noise and/or noises close to harmonics from source out or from external sources may be self converted and appears around fundamental carrier frequency.
Measurement with 2-DUT configuration gives the some of the two DUTs.
To Estimate contribution of each DUT, subtract 3db from the result.
Bandpass filters have large group delay, which make loss of correlation of two signals.
Compression of DUT will suppress AM noise from the source, while reference (RF1) input measures raw AM noise of the source, which leads loss of correlation of two signals and shows extra noise as residual noise of the DUT.