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N5244A PNA-X 2-port and relative phase

Question asked by RROSS02 on Mar 1, 2010
Latest reply on Mar 10, 2010 by RROSS02
I have two PLL's tied to the same 10 MHz source (PNA-X is tied to it also) and I'm looking at the relative phase using frequency offset relative to port 1 (PLL input) and their outputs (x8 of port 1) using B/R2. 

1) I notice there is some delay over frequency that I attribute to the internal PNA-X cables that I can reliably measure with a power divider at room temperature and remove.  Any idea on variation over temperature?
2) Once I remove the delay, I also enter a phase offset to get it to read zero degrees for the relative phase as I then change the phase input to one of the PLL inputs to verify if moves relative to my changes.  It works, I'm happy.
3) Now, I want to add some modulation (the same) to the PLL's and see the relative phase still measure properly.

Where does the PNA-X start to break down as to keeping up with the relative phase as to the modulation, BW, etc?  I'm doing this as a CW measurement with a time sweep and thinking I should adjust the IF bandwidth to keep up with the modulation rate I intend to use.