Fluke Networks CertiFiber Pro Users Manual - Manual (Page 275)

Chapter 9: How to Use the OptiFiber Pro OTDR Module
OTDR Results
253
Gainer
An apparent gain in the
strength of the returned
signal. A gainer shows
as a negative value of
loss. Page 297 shows
OTDR traces gainers.
Caused by a splice or connection between two
fibers that have different backscatter
coefficients, numerical apertures, core diameters,
or mode field diameters.
The tester compares the loss of non-reflective
gainers to the limits for splice loss to give the
event a PASS/FAIL status.
If a gainer occurs at a connection, the gainer
shows as a Reflection event with negative loss.
The tester compares reflective gainers to the
limits for reflective events to give the event a
PASS/FAIL status.
Strong reflections at or before an event can
cause tailing after the event, which can cause a
measurement of negative loss.
To find the cause of a gainer, see if the fiber type
is different before and after the splice or
connection. Replace fiber if necessary. Fibers that
are the same can possibly have different
tolerances, which can cause gainers at a splice.
When this occurs, the splice is usually good and
does not require rework.
If you do the OTDR test from the other end, the
gainer event will show a loss. If you add this loss
to the gain from the other direction, you get the
true loss of the event. If you upload the results to
LinkWare software, you can use the bi-
directional averaging utility in LinkWare to
calculate the true loss of gainers.
Gainers at launch events can occur when the
launch cord does not have the same properties as
the fiber under test. In this situation, you can get
more reliable results if you do a bi-directional
test and calculate the true loss as described
above. Use a tail cord that has the same
properties as the launch cord and use Launch +
Tail compensation.
(continued)
Table 11. Event Types (continued)