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Table 3-7. Diagnosing Faults on OTDR Traces
Large reflective event with high loss (top), excessive tailing (middle), or a hook on the falling edge of
the trace (bottom). May be identified as an end event though it occurs before the end of the cabling.
May be caused by the following:
•
A dirty, scratched, cracked, misaligned, or unseated connector. Misaligned or unseated
connectors can also cause large reflections that produce ghosts. Bad connectors should be
cleaned, repolished, or replaced. A hook, as shown in the bottom example, can occur when a
large reflection causes the OTDR detector's gain to become non-linear.
•
A good connector with a sharp bend or crack within its deadzone. If the cable is tightly bent the
tester may indicate a break, especially at longer wavelengths or in Manual OTDR mode with
smaller resolution settings. Use a visual fault locator to precisely locate the fault.
•
A crack in the fiber. Use a visual fault locator to precisely locate the fault.
•
A connection between mismatched fibers (different backscatter coefficients, core sizes,
numerical apertures, or other parameters). The top example could be caused by a larger core
(on the left) connected to a smaller core.
Using the OTDR
Diagnosing OTDR Test Failures
3
-continued-
3-53
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