Don Essig
Mahon Communications Corp.
Problem
No matter how carefully work schedules are planned, last-minute changes can sometimes leave a technician alone to complete a task normally assigned to a team. One such example is testing recently terminated fiber-optic cables for mechanical integrity and connector quality.
Solution
A procedure known as a loopback method allows one technician to measure end-to-end attenuation with a fiber-optic power meter. By coupling the fibers?blue to orange, green to brown, slate to white and so on?at each remote end of the cable, you actually send the light source back to the main distribution frame or point of transmission. If you terminate your connectors by using proven installation procedures, this technique can save time.
Note: It is important to test fiber-optic cable when it is received from your vendor and after it has been pulled.
Procedure
1) At each remote fiber location, couple the fibers.
2) With a 100 pocket microscope, examine all connectors to ensure they are clean and have not been contaminated during handling.
3) Calibrate your fiber-optic meter with quality test jumpers. Record your reference level, which is the power-meter output plus jumper loss; for example, -20 decibels. Any level recorded in addition to the reference level is the cable loss plus connector loss.
4) Calculate connector and cable loss according to the manufacturer?s specifications. This loss will vary depending on actual cable length.
5) Transmit your light source into the first fiber (blue) and receive through its corresponding fiber (orange). Repeat this for each respective pair.
6) If attenuation levels fluctuate, you most likely have a problem with the cable at one or more connectors. If a high loss or no loss is recorded, a connector may need to be replaced.
7) As you are testing, compose a list of fibers that do not pass this basic test.
8) Uncouple the fibers back to their original state and test any suspect fibers, one at a time.
9) After completing this process, you may need to address additional problems, such as faulty connectors.
10) If there are still losses after pinpointing and replacing suspect connectors, you will probably need to use an optical time-domain reflectometer to accurately pinpoint the fault.
Don Essig is a fiber-optic technician at Mahon Communications Corp., Boston, MA.