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Appendix A: Tests on Long Fiber Links
with the OptiFiber Pro OTDR
The OptiFiber Pro OTDR can do tests on multimode links up to
35 km and on singlemode links up to 130 km at 1550 nm. This
appendix gives information on how to set up the tester and select
launch cords to do OTDR tests on links longer than approximately
27 km.
Make a Custom Fiber Type, If Necessary
If the list of fiber types in the tester does not include the fiber
type used in the link, make a custom fiber type. For instructions
on how to make a custom fiber type, see Chapter 19.
Get these values from the manufacturer of the fiber:
 Index of refraction: This setting affects the length
measurement. It is important to have the correct value for the
fiber when you do tests on long fibers.

Backscatter coefficient: This setting affects reflectance and
optical return loss measurements.
Use a Launch Cord of the Correct Type
Select a launch cord that has properties that are similar to the
link. If the launch cord is not similar, the OTDR will show loss
measurements that are higher or lower that the actual loss of the
link. This can cause a “gainer” in the test results from one
direction.
If the launch cord is similar to the fiber in the link, but you still see
a difference in the backscatter from the fibers, you can use
LinkWare PC software to do bi-directional averaging.