Exfo FTB-5600 Distributed PMD Analyzer Manuale Utente Scaricare il pdf (Pagina 136)

Optimizing Measurements

130 FTB-5600

Use an Appropriate Spatial Smoothing Filter Value

³ A median filter provides the medium of a group of points. The median

filter will preserve sharp transition, whereas the moving average filters

will not.

In the figure below, you can see that the sharp transition is still

preserved and that there are no delays.

When filtering a cumulative PMD curve, you must take into account the

behavior of the filters. You might have to adjust the positions of the markers

after you have applied a filter.

In the figure below, you can see how the filter behaves when encountering

a small and a large step compared to the noise variance. The red curve is

the anti-causal median filter and the blue curve is the causal moving

average.

In the case of the small step, the moving average and the median filtering

show the same behavior, that is a ramp equal to the filter length to reach

the top of the step.

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Exfo FTB-5600 Distributed PMD Analyzer Manuale Utente Pagina 136