EXFO FTB-5600 Distributed PMD Analyzer - Manual (Page 131)

Optimizing Measurements
Distributed PMD Analyzer 125
Use an Appropriate Residual PMD for the Acquisition
Use an Appropriate Residual PMD for the
Acquisition
A residual PMD is designed where a limited small PMD value cannot be
measured properly. If you want to measure the PMD value on high PMD
sections over a few ps and are not interested in low PMD values, for
example <1 ps, then you should select a residual PMD that is just smaller
than 1 ps.
On the other hand, if you are interested in measuring PMD the value of few
hundreds fs, then you should set a residual PMD of less than 100 fs.
Note: An appropriately selected residual PMD can result in a lower acquisition
time.
More generally, if the PMD curve is very wavy and at the same level as the
PMD resolution, then it is the sign of a bad PMD scale. It should be set to a
lower value.