OTDR Testing

By Jim Hayes | Nov 15, 2006




You’re reading an older article from ELECTRICAL CONTRACTOR. Some information, such as code-related information, may be outdated. Find the most up-to-date content in our latest issues.


We have covered optical time domain reflectometer (OTDR) testing a few times this year. Plus, we devote a lot of space to it in our books and online at Let’s see how well you understand OTDRs.

1. OTDRs use the ____________ in the fiber to make measurements.

    A. Bandwidth

    B. Backscatter

    C. Absorption

    D. Dispersion

2.OTDRs cannot measure ____________.

    A. Distance

    B. Attenuation

    C. Dispersion

    D. Reflection

3. Length measurements by the OTDR are shorter than the actual cable because the fiber is longer than the cable itself.

    True ❏     False ❏ 

4. OTDRs should always use launch cables to ____________.

    A. Prevent errors caused by the launch pulse overloading the OTDR receiver

    B. Avoid damaging the OTDR launch and receive connectors

    C. Extend the range of the OTDR to longer distances

    D. Allow the OTDR display to show the whole cable plant

5. Launch cables on the OTDR also allow ____________.

    A. Calibrating the OTDR

    B. Setting a loss reference

    C. Measuring the loss of the first connector on the cable plant being tested

    D. Using two OTDRs, one at each end of the cable

6. Multiple reflections in a cable may cause ____________.

    A. Backscatter
    B. Ghost

    C. Distance errors

    D. Loss

7. A receive cable on the other end of the cable plant will allow the OTDR to ____________.

    A. Extend its range by the length of the cable

    B. Reduce the effects of reflectance

    C. Use a longer pulse width

    D. Measure the loss of the connector on that end

8. OTDR connector or splice loss measurements are only accurate if you ____________.

    A. Put index matching fluid on the connector

    B. Use reference quality connectors

    C. Have a matching launch cable

    D. Test both ways and average the reading

9. Unless a mode conditioner is used, OTDRs will usually ____________ the loss of a cable plant compared to insertion loss testing.

    A. Overestimate

    B. Underestimate

    C. Equal

10. TIA 568B allows OTDRs to be used instead of a light source and power meter or OLTS (optical loss test set) to test a cable plant.

    True ❏            False       

Hayes is a VDV writer and trainer and the president of the Structured Cabling Association ( Find him

Answers: 1.B, 2.C, 3.F, 4.A, 5.C, 6.B, 7.D, 8.D, 9.B 10.F



About The Author

HAYES is a VDV writer and educator and the president of the Fiber Optic Association. Find him at





featured Video


New from Lutron: Lumaris tape light

Want an easier way to do tunable white tape light?


Related Articles