Optical Backscatter Reflectometer 4600 105
User Guide
Return Loss Type
The software can use two methods to calculate Return Loss:
• Measured Return Loss: The actual power reflected from an event as
detected by the OBR. If Insertion Loss has occurred before a Return
Loss, the power reflected from that event is reduced. The Measured
Return Loss includes this reduction.
• Absolute Return Loss: The amount of loss reflected from an event in
the absence of Insertion Loss up to that event. The Absolute method
shows Return Loss data as if each connection was attached directly to
the front of the OBR, with nothing before it.
You may change the Return Loss calculation method in the Parameter
Specifications window (Figure 6-4 on page 83).
Why is there an asterisk before the RL value?
When the vertical cursors are on in the main window, the Return Loss of a
highlighted feature will be displayed in the upper right of the graph.
Sometimes
there
will be an asterisk (*) before this value, meaning that the Rayleigh scatter just before
that event was not sufficiently flat to allow accurate Absolute Return Loss
calculation.
An asterisk may also be placed before the Return Loss value if the gain is set low
enough that the Rayleigh scatter cannot be detected properly.
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