EXFO OTDR 2 - Manual (Page 62)

Testing Fibers
54 OTDR
Defining Launch and Receive Fiber Settings
Defining Launch and Receive Fiber Settings
To define the fiber span start, you can set the launch fiber length. If you do
not know the fiber length, it is also possible to define the launch/receive
fiber by event number.
When you perform tests with your unit, you connect a launch fiber
between your unit and the fiber under test. If the launch and receive fiber
are not defined, the fiber will appear as if it was part of the fiber under test.
When you define the length of the launch fiber, the application sets the
fiber span start at the beginning of the fiber under test. It allows to
characterize the first connector at the beginning of the fiber. Therefore,
only events related to the defined fiber span will be taken into account. The
application will include the loss caused by the span start event in the
displayed values. The span start event will also be taken into account when
determining the status (pass/fail) of connector loss and reflectance.
The span start becomes event 1 and its distance reference becomes 0.
Events excluded from the fiber span are shaded in the event table, and do
not appear in the trace display. The cumulative loss is calculated for the
defined fiber span only.
When you perform tests with your unit, you can connect a receive fiber to
the fiber under test. It allows to characterize the last connector at the end
of the fiber. By default, the fiber span also includes the receive fiber. When
the receive length is mentioned, the application finds the event which is
characterized as the end of fiber and moves the span end according to a
value corresponding to the specified receive fiber length (except for
continuous or end of analysis events).
When the span end is positioned, an event should be near the new
position of the span end. If no event is found, the application will
automatically add an event where there should be one.
The application can also set the span end according to a number of events
instead of using a distance.