Cisco Systems UBR10012 manual Testing with TDRs and OTDRs, Testing with OTDRs

Appendix B Recommended Tools and Test Equipment

Testing with TDRs and OTDRs

Test fiber-optic cable both before installation (on-the-reel testing) and after installation. Continuity testing of the fiber requires either a visible light source or a reflectometer. Light sources capable of providing light at the three predominant wavelengths, 850 nanometers (nm), 1300 nm, and 1550 nm, are used with power meters that can measure the same wavelengths and test attenuation and return loss in the fiber.

Testing with TDRs and OTDRs

This section describes time domain reflectometers (TDRs) and optical time domain reflectometers (OTDRs), which are typically used to detect cable defects.

Testing with TDRs

Use time domain reflectometers to test for the following cable defects:

•Open and short circuits

•Crimps, kinks, and sharp bends

•Impedance mismatches

•Other defects

A TDR works by “bouncing” a signal off the end of the cable. Open circuits, short circuits and other problems reflect the signal back at different amplitudes, depending on the problem.

A TDR measures:

•the amount of time it takes for the signal to reflect

•The physical distance to a fault in the cable

•The length of a cable

Some TDRs can also calculate the propagation rate based on a configured cable length.

Testing with OTDRs

Use optical time domain reflectometers to:

•Locate fiber breaks

•Measure attenuation

•Measure the length of a fiber

•Measure splice or connector losses

An OTDR can be used to identify the “signature” of a particular installation, noting attenuation and splice losses. This baseline measurement can then be compared with future signatures if you suspect a problem in the system.

Cisco uBR10012 Universal Broadband Router Troubleshooting Guide

B-2 OL-1237-01