Exfo FTB-5600 Distributed PMD Analyzer Bedienungsanleitung PDF herunterladen (Seite 125)

Acquisition Data

Distributed PMD Analyzer 119

To measure the PMD, you need to take the frequency step according to the

PMD value. The reason is that the frequency sampling step must be less

than one half the period of DGD fluctuation to obtain the best

measurement.

A lower sampling rate will not allow a correct measurement, because of

the violation of the Nyquist sampling criteria. A sampling rate that is too

high will result in a measurement that is too noisy.

The figure below gives an example of a correct step and of a step which is

too large to measure the variation of the signal properly.

For example, if a PMD curve can span from 0 to 20 ps, one sampling step is

not enough to compute the curve over the entire PMD span. This is why

many scales are necessary to build the PMD curve.

One frequency step can measure from 20 % and saturates at 240 % of its

value. As an example, the 20 ps step can measure from 5 to 48 ps.

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Exfo FTB-5600 Distributed PMD Analyzer Bedienungsanleitung Seite 125