DCI Testing & Troubleshooting 2 — Questions and Answers
Question 1: A cable tester reports a 'split pair' fault. What does this indicate?
- Two conductors from different pairs are wired together at one end (Correct answer)
- A wire is broken inside the cable jacket
- The cable exceeds maximum length limits
- Incorrect termination polarity on both ends
Correct answer: Two conductors from different pairs are wired together at one end
A split pair occurs when conductors from different pairs are used together, maintaining continuity but severely degrading crosstalk performance.
Question 2: What does OTDR stand for in fiber optic testing?
- Optical Time Domain Reflectometer (Correct answer)
- Optical Transmission Data Recorder
- Output Terminal Data Reader
- Optical Transfer Distance Ratio
Correct answer: Optical Time Domain Reflectometer
An OTDR (Optical Time Domain Reflectometer) sends pulses of light and measures reflections to locate faults and measure loss along a fiber.
Question 3: When testing insertion loss on a fiber link, the measured value exceeds the channel limit. Which is the MOST likely cause?
- Excessive number of connections or splices in the link (Correct answer)
- Incorrect polarity at the patch panel
- A split pair condition in the cable
- The fiber was tested using 850 nm instead of 1300 nm
Correct answer: Excessive number of connections or splices in the link
Each connector or splice adds loss; too many in a link can push total insertion loss beyond the channel budget.
Question 4: A technician finds that wire map shows pins 1 and 2 are reversed at the far end. This is called a:
- Reversed pair (Correct answer)
- Split pair
- Transposed pair
- Open circuit
Correct answer: Reversed pair
A reversed pair (also called a polarity reversal) occurs when both conductors of a pair are swapped at one end.
Question 5: Which parameter measures the signal strength difference between the transmitted signal and the near-end crosstalk?
- NEXT (Correct answer)
- FEXT
- Attenuation
- Return loss
Correct answer: NEXT
NEXT (Near-End Crosstalk) measures unwanted signal coupling from one pair to another at the same end where the signal is transmitted.
Question 6: A fiber optic link fails the insertion loss test after cleaning the connectors. What is the next troubleshooting step?
- Inspect connector end faces with a fiber scope (Correct answer)
- Replace the entire cable run
- Re-test using a different wavelength
- Check the wire map with a copper tester
Correct answer: Inspect connector end faces with a fiber scope
Inspecting end faces with a fiber microscope reveals scratches, cracks, or contamination that cleaning alone may not resolve.
Question 7: What is the primary purpose of a tone generator and probe in cable testing?
- To identify and trace cable routes without damaging the jacket (Correct answer)
- To measure attenuation on copper pairs
- To certify a cable against TIA standards
- To test fiber optic insertion loss
Correct answer: To identify and trace cable routes without damaging the jacket
A tone generator and inductive probe (toner/probe) is used to identify and trace specific cables or pairs without requiring access to both ends simultaneously.
DCI Testing & Troubleshooting 2
A cable tester reports a 'split pair' fault.
What does this indicate?