DCI Testing & Troubleshooting 3

Question 1

ACR-N is calculated by subtracting which two measurements?

Accepted Answer

NEXT minus attenuation

Answer

ACR-N (Attenuation-to-Crosstalk Ratio at Near End) equals NEXT minus attenuation, indicating the usable signal margin at the near end.

Question 2

A Category 6 channel certification test fails for PS NEXT. What does PS NEXT measure?

Accepted Answer

The combined crosstalk from all disturbing pairs onto one pair simultaneously

Answer

PS NEXT (Power Sum NEXT) measures the cumulative crosstalk effect of all disturbing pairs on a single victim pair at the near end.

Question 3

What condition does 'return loss' measure in a copper cable?

Accepted Answer

The portion of transmitted signal reflected back toward the source due to impedance mismatches

Answer

Return loss measures impedance discontinuities that cause signal reflections back toward the transmitter, which can disrupt data transmission.

Question 4

An OTDR trace shows a large reflective event followed by no backscatter. What does this indicate?

Accepted Answer

A break or cleaved end of the fiber at that distance

Answer

A large Fresnel reflection followed by the absence of backscatter indicates the fiber has a break or open end at that location.

Question 5

A cable tester shows 'FAIL – Length' even though the physical cable appears short enough. What is the most likely cause?

Accepted Answer

The nominal velocity of propagation (NVP) is set incorrectly

Answer

NVP (Nominal Velocity of Propagation) calibrates the tester's time-to-distance calculation; an incorrect NVP produces inaccurate length readings.

(DCI) Data Cabling Installer Practice Test