CPCT Cable Testing & Troubleshooting 4 — Questions and Answers
Question 1: Which optical power meter measurement is used to verify that a fiber optic link meets the loss budget for a specific application?
- Optical Return Loss (ORL)
- Insertion loss measured end-to-end (Correct answer)
- OTDR event loss at each connector
- Dispersion coefficient of the fiber
Correct answer: Insertion loss measured end-to-end
End-to-end insertion loss measured with a light source and power meter gives the actual total attenuation of the link, which is compared to the application's loss budget.
Question 2: What does a negative dB reading on an optical power meter indicate when measuring a fiber link?
- The link has gain from an amplifier
- The measured power is less than the reference power — indicating loss (Correct answer)
- The meter is connected backwards
- The fiber is single-mode instead of multimode
Correct answer: The measured power is less than the reference power — indicating loss
Optical power meters display loss in negative dB because the received power is always less than the transmitted reference power in a passive link.
Question 3: During certification testing, a technician discovers that a cable run measures 96 meters total channel length. The patch cords account for 7 meters. Does this channel comply with TIA-568?
- Yes, because the total channel length does not exceed 100 meters
- No, because the permanent link portion exceeds 90 meters (Correct answer)
- Yes, because patch cord length is excluded from channel calculations
- No, because the channel maximum is 90 meters
Correct answer: No, because the permanent link portion exceeds 90 meters
With 7 m of patch cords, the permanent link is 89 m, which exceeds the 90 m permanent link limit, even though the 100 m channel limit is met.
Question 4: A multimode fiber link passes the insertion loss test at 850 nm but fails at 1300 nm. Which condition could explain this?
- The connectors are dirty at only one end
- The fiber has a higher attenuation coefficient at 1300 nm than expected, possibly indicating OM1 fiber installed instead of OM3 (Correct answer)
- The OTDR was set to single-mode wavelengths
- The link has too many splices
Correct answer: The fiber has a higher attenuation coefficient at 1300 nm than expected, possibly indicating OM1 fiber installed instead of OM3
OM1 fiber has significantly higher attenuation at 1300 nm compared to OM3/OM4, so using OM1 where OM3 is required would fail at 1300 nm while potentially passing at 850 nm.
Question 5: When performing a wiremap test on a newly punched-down patch panel, a technician finds an 'open' on pin 6. The cable passes the test at the wall plate end. Where is the fault most likely located?
- At the wall plate jack
- At the patch panel punch-down for pin 6 (Correct answer)
- Somewhere in the middle of the cable run
- At the cable's jacket termination point
Correct answer: At the patch panel punch-down for pin 6
Since the open appears only when testing from the patch panel end and the wall plate passes, the fault is isolated to the patch panel termination of pin 6.
Question 6: What is the primary purpose of using launch and receive cables (launch boxes) when performing OTDR testing?
- To extend the test range of the OTDR beyond its maximum distance
- To move the dead zone away from the first connector under test so it can be evaluated (Correct answer)
- To convert from single-mode to multimode fiber
- To boost the OTDR pulse power
Correct answer: To move the dead zone away from the first connector under test so it can be evaluated
Launch cables place the dead zone in the launch cable itself, allowing the OTDR to accurately measure the first connector in the link under test.
Question 7: A coaxial cable segment tested with a TDR shows a reflected pulse at 150 ns. If the cable's NVP is 0.66c, what is the approximate distance to the fault?
- About 15 meters (Correct answer)
- About 14.9 meters
- About 29.7 meters
- About 49.5 meters
Correct answer: About 15 meters
Distance = (time × velocity) / 2 = (150 ns × 0.66 × 3×10⁸ m/s) / 2 ≈ 14.85 m, approximately 15 meters.
CPCT Cable Testing & Troubleshooting 4
Which optical power meter measurement is used to verify that a fiber optic link meets the loss budget for a specific application?