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E8362B phase not coherent sweep to sweep.

Question asked by Spedboy on Sep 13, 2006
Latest reply on Sep 13, 2006 by jvall
I have an interesting problem.

I've got a signal source connected to a 1:2 0-degree splitter. The splitter has a pair of 10 dB pads on the outputs for better isolation between the split outputs. One leg of the splitter goes through the pad directly into the A receiver port of my E8362B. The other leg of the splitter goes through the other pad, into a dial type phase trimmer and then directly into the B receiver port.  The E8362B is centered on the frequency of the signal source, and the span set to zero. The IF BW is set to 100 Hz. The points per sweep is 51.  The signal source is phase locked to the 10 MHz reference on the E8362B. 

The traces I'm observing are A and B receivers, both formatted to phase. The relative phase between the A and B inputs is constant point to point across the sweep, and I can trim the offset with the phase trimmer, but the absolute phase of both A and B is not repeatable from sweep to sweep. Why is this? It's as though the digitizer or LO in the Network Analyzer is not locked to its own reference. 

Any insight would be grand.

Pat Tanner