EXFO FTB-5600 Distributed PMD Analyzer - Manual (Page 130)

Optimizing Measurements
124 FTB-5600
Select an Optimized PMD Scale for the Acquisition
Select an Optimized PMD Scale for the
Acquisition
Using an appropriate PMD scale is very important. This is because selecting
the most appropriate PMD scale regarding the total PMD from an FUT can
improve the signal to noise ratio so as to have better measurement
dynamics, as well as ensure a signal level that is higher than a coherence
noise level.
For example, if the total PMD of an FUT is of 11 ps, an appropriate PMD
scale should be of 10 ps, and, if a total PMD of an FUT is of 22 ps, an
appropriate PMD scale is of 20 ps.
Note: Make sure not to select a PMD scale that is too high when measuring low
PMD.
To use an appropriate PMD scale for the acquisition is important for the
instrument to obtain a maximum signal level (that is, a mean square
transmission difference), thereby to ensure the signal is larger than a
coherent noise level. A signal level that is too poor due to a too short
beating length in a test fiber section, especially for high depolarization
fibers, in comparison with one with a coherence noise level would result in
the instrument not being able to measure cumulative PMD correctly along
this section of fiber correctly.