EXFO FTB-5600 Distributed PMD Analyzer - Manual (Page 135)

Optimizing Measurements
Distributed PMD Analyzer 129
Use an Appropriate Spatial Smoothing Filter Value
Use an Appropriate Spatial Smoothing Filter
Value
The spatial filter for the FTB-5600 was designed to suit the filtering needs of
the cumulative PMD curve. The filter preserves sharp transition, which
often appears in cumulative PMD measurements; the sharp transition
position will not be changed by the filter.
³
An anti-causal filter has the property to remove the delay of the filter
from the filtering effect of the signal. This means that it has an effect
before the transition occurs.
In the example below, we can see the blue curve, which is the raw
data, while the black curve is a causal moving average filter and the
red one is an anti-causal moving average filter.
Note: The black and red curves are the same, but the black curve was shifted to
the left to remove the delay.