The variety of fiber optic cables and connectors has required several methods to test the insertion loss. Industry standards have been developed that offer options for all these methods, which use reference cables at both ends of the cable under test and require using either one, two or three reference patchcords to set a 0-dB reference. The installer of fiber optic cable plants often encounters situations that require using specific test methods, so let’s see how well you understand them. Answers and explanations are in red.

1. If your test equipment has fiber optic connector interfaces (e.g., ST connectors) that match the installed cable plant being tested, you can follow the recommendations of TIA-568 and use a __________ to set a 0-dB reference according to OFSTP-14, Method B.

A. One cable reference

B. Two cable reference

C. Three cable reference

D. Cable substitution test

If the cable plant, reference cables and instruments have the same connector, a single cable can be used for setting the “0 dB” reference.

2. If your test equipment has fiber optic connector interfaces (e.g., ST connectors) that do not match the installed cable plant being tested (e.g., LC connectors), you can use a __________ to set a 0-dB reference according to OFSTP-14, Method A.

A. One cable reference

B. Two cable reference

C. Three cable reference

D. Cable substitution test

Since the reference cables must match the cable plant on one end and the test equipment on the other, using a one cable reference is not possible, so a two cable reference can be used.

3. If the installed cable plant being tested has “plug-and-jack” connectors that require reference cables that cannot be mated directly to either test equipment or another reference cable (e.g., MTP connectors), you can use a __________ to set a 0-dB reference according to OFSTP-14, Method C.

A. One cable reference

B. Two cable reference

C. Three cable reference

D. Cable substitution test

The reference cables must match the cable plant on one end and the test equipment on the other. The cable plant will have jacks on the end but the reference cables must have plugs, which means the reference cables cannot be mated to each other. Only a three cable reference can be used.

4. The two cable reference method (OFSTP-14, Method A) is used in testing long-distance networks where the reference is set by bringing a meter and source together then separating the instruments with reference cables attached to carry to each end of the cable plant.

True

False

It’s common with long distance networks to connect one reference cable to the source and another to the meter, join them to set the “0 dB” reference, then take them to remote locations to test cables.

5. If the cable being tested has connectors that cannot be mated directly to another, such as some plastic optical fiber (POF) connectors, you can use a __________, which is not covered in most industry standards.

A. One cable reference

B. Two cable reference

C. Three cable reference

D. Cable substitution test

Some connectors are only designed to be used to connect to transceivers, not other cables. So only a cable substitution test is possible.

6. When testing a cable plant, a __________ will give a higher loss

reading than other methods.

A. One cable reference

B. Two cable reference

C. Three cable reference

D. Cable substitution test

With a one cable reference, not connections are included in the reference. With a two cable reference, one fiber connection is included in the reference and with a three cable reference, two connections are included. When tests are performed, the measured loss results will be reduced by the loss in the connections included when setting the  “0 dB” reference.

7. If connectors on the reference cables are dirty when setting the 0-dB reference by the __________ method, measurements of cable plant will be in error and may even show a gain if the connectors are cleaned after setting the reference.

A. One cable reference

B. Two cable reference

C. Three cable reference

D. Any of the above

Dirt on the connectors will reduce the power measured for the  “0 dB” reference. Cleaning them will increase the power, reducing the measured connector loss, sometimes enough to show a gain, not a loss.

8. Some industry standards, such as TIA-568, require controlling multimode fiber source launch conditions using a __________ to reduce measurement uncertainty.

A. Controlled output source

B. Known output source and mandrel wrap on the launch cable

C. Special reference cable

D. Laser source

TIA-568 calls for a source of known modal output followed by a mandrel wrap on the launch cable.

9. End-users contracting for a cable installation will be aware of these options and will specify the test methods in the contract for installation services.

True

False

Few users are aware of these options. Since the test method can affect the measured loss, reviewing these options with the user during the design phase of the project is important.

10. All of these test methods depend on having reference patchcords that are __________.

A. Matching the fiber in the cable being tested

B. Low loss

C. Clean and in good condition

D. All of the above

Patch cords must meet all three conditions.

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