VDV Testing and Certification 2 — Questions and Answers
Question 1: What does a wiremap test verify in a structured cabling installation?
- Signal attenuation on each pair
- Correct pin-to-pin continuity and absence of miswires (Correct answer)
- Cable impedance matching
- Power over Ethernet voltage levels
Correct answer: Correct pin-to-pin continuity and absence of miswires
A wiremap test checks that each conductor connects to the correct pin at both ends and identifies faults like opens, shorts, reversed pairs, and split pairs.
Question 2: Which ANSI/TIA standard defines the minimum performance requirements for field testing of balanced twisted-pair cabling?
- TIA-568-C.0
- TIA-606-C
- TIA-568-C.2 (Correct answer)
- TIA-526-14-B
Correct answer: TIA-568-C.2
TIA-568-C.2 specifies performance standards and field testing requirements for balanced twisted-pair telecommunications cabling.
Question 3: A technician measures -3 dBm at the end of a fiber run and the source was +2 dBm. What is the link loss?
- 3 dB
- 5 dB (Correct answer)
- 2 dB
- 1 dB
Correct answer: 5 dB
Link loss equals input power minus output power in dBm: +2 dBm − (−3 dBm) = 5 dB total loss.
Question 4: During coaxial cable testing, a return loss of 20 dB is measured. What does this indicate?
- Severe impedance mismatch
- Acceptable impedance matching with minimal reflections (Correct answer)
- Total signal loss
- Open circuit condition
Correct answer: Acceptable impedance matching with minimal reflections
A return loss of 20 dB means only 1% of the signal is reflected, indicating good impedance matching in the cable system.
Question 5: What is the purpose of an Optical Time Domain Reflectometer (OTDR) trace in fiber certification?
- Measure chromatic dispersion
- Locate faults and measure splice/connector losses along a fiber link (Correct answer)
- Test the optical power budget
- Verify fiber core diameter
Correct answer: Locate faults and measure splice/connector losses along a fiber link
An OTDR sends pulses into the fiber and analyzes backscattered light to locate faults, measure attenuation, and evaluate splice and connector losses at specific points.
Question 6: Which parameter measures the difference in propagation delay between the fastest and slowest pairs in a Cat 6 cable?
- Propagation Delay
- Delay Skew (Correct answer)
- NEXT
- Insertion Loss
Correct answer: Delay Skew
Delay skew is the difference in propagation delay between the pair with the shortest delay and the pair with the longest delay, critical for applications using all pairs simultaneously.
Question 7: A VDV technician is field-testing a Cat 6A channel and the tester reports a FAIL for Alien Crosstalk (AXT). What is the most likely cause?
- Cable pairs are reversed
- Excessive bundling of Cat 6A cables without adequate separation (Correct answer)
- The cable run exceeds 90 meters
- Connectors are not shielded
Correct answer: Excessive bundling of Cat 6A cables without adequate separation
Alien crosstalk in Cat 6A is caused by electromagnetic coupling between adjacent cables, and tight bundling without separation significantly worsens this interference.
VDV Testing and Certification 2
What does a wiremap test verify in a structured cabling installation?