" It turns out that there is a undocumented DIAG command for setting the ref level in the phase noise personality. It is as follows:
SENSe:LPLot:DIAG:GRAPh:Y:REFerence?
An example of setting the ref level to -50 dBc/Hz is as follows:
SENSe:LPLot:DIAG:GRAPh:Y:REFerence -50
Notice that there are no units in the command. "
Using an undocumented DIAG command places the instrument into an unspecified state. The commands are undocumented for a reason and Agilent Technologies does not recommend their use. Please remember that any instrument specificies will no longer apply once a DIAG command is sent to the instrument
For what it's worth, I have recently added SCPI support to my host-based phase-noise measurement app (downloadable here). It is probably not as capable as the PSA noise-measurement personality, but it does give you some control over the reference level relative to the carrier power.
Nobody has tested this code on a PSA-series analyzer as far as I know, but it does work well on the ESA-E series.
SENSe:LPLot:DIAG:GRAPh:Y:REFerence?
An example of setting the ref level to -50 dBc/Hz is as follows:
SENSe:LPLot:DIAG:GRAPh:Y:REFerence -50
Notice that there are no units in the command.