C7 Signal Transmission & Cabling Techniques 2 — Questions and Answers
Question 1: What is the maximum segment length specified for Cat 6 horizontal cabling in a structured cabling system?
- 55 meters
- 90 meters (Correct answer)
- 100 meters
- 150 meters
Correct answer: 90 meters
TIA-568 specifies 90 meters for horizontal permanent link runs, leaving 10 meters for patch cords.
Question 2: Which type of crosstalk is measured at the far end of a cable from the signal source?
- NEXT
- FEXT (Correct answer)
- ANEXT
- PSNEXT
Correct answer: FEXT
FEXT (Far-End Crosstalk) is measured at the opposite end of the cable from the transmitter.
Question 3: A technician needs to run coaxial cable through a plenum space. Which cable type is required?
- RG-6 PVC jacket
- RG-59 plenum-rated (CMP) (Correct answer)
- RG-6 riser-rated (CMR)
- Any coax with a foil shield
Correct answer: RG-59 plenum-rated (CMP)
Plenum spaces require CMP-rated cables with low-smoke, low-flame-spread jackets per NEC Article 820.
Question 4: What does the term 'propagation delay skew' refer to in twisted-pair cabling?
- Signal attenuation over distance
- Difference in signal travel time between the fastest and slowest pairs (Correct answer)
- Impedance mismatch at a connector
- The delay caused by NIC processing
Correct answer: Difference in signal travel time between the fastest and slowest pairs
Propagation delay skew is the difference in arrival time between the fastest and slowest pairs, which affects gigabit Ethernet that transmits simultaneously on all pairs.
Question 5: Which shielding designation indicates a cable with an overall foil shield and individually foil-shielded pairs?
- F/UTP
- U/FTP
- SF/FTP
- S/FTP (Correct answer)
Correct answer: S/FTP
S/FTP (or SF/FTP) denotes an overall braid shield (S) with individually foil-shielded (FTP) pairs per ISO/IEC 11801.
Question 6: When terminating Cat 6A cable, why is maintaining twist to within 13mm of the termination point critical?
- To prevent the insulation from cracking
- To preserve the cable's rated impedance and reduce crosstalk (Correct answer)
- To comply with NEC color coding
- To ensure the conductors reach the punch-down block
Correct answer: To preserve the cable's rated impedance and reduce crosstalk
Untwisting pairs beyond the allowed distance degrades crosstalk performance and can fail certification testing.
Question 7: What is the primary purpose of a balun in a low-voltage signal system?
- Amplify signal strength over long runs
- Convert between balanced and unbalanced transmission (Correct answer)
- Provide surge protection on coaxial lines
- Split one signal into multiple outputs
Correct answer: Convert between balanced and unbalanced transmission
A balun (balanced-unbalanced transformer) converts signals between balanced twisted-pair and unbalanced coaxial formats.
C7 Signal Transmission & Cabling Techniques 2
What is the maximum segment length specified for Cat 6 horizontal cabling in a structured cabling system?