Testing & Troubleshooting Flashcards

A technician is using a time domain reflectometer (TDR) on a coaxial cable and the display shows a positive reflection spike. What does a positive reflection indicate?

Answer: An open circuit or high-impedance fault

A positive reflection on a TDR trace indicates an open circuit or impedance higher than the cable's characteristic impedance, such as a missing terminator.

Which fiber optic test is used to verify the end-to-end optical loss budget of a newly installed link before connecting active equipment?

Answer: Optical loss test using a light source and power meter (insertion loss test)

An insertion loss test using a calibrated light source and optical power meter directly measures the total end-to-end attenuation against the system's loss budget.

A BNC connector on a 75-ohm coaxial cable shows 50 ohms impedance on a TDR. What is the most likely problem?

Answer: A 50-ohm BNC connector was mistakenly installed instead of a 75-ohm connector

50-ohm and 75-ohm BNC connectors are physically compatible but electrically mismatched; using a 50-ohm connector on 75-ohm cable creates a measurable impedance discontinuity.

During troubleshooting, a technician discovers that a Cat5e cable run passes all wire map tests but fails the Power Sum ELFEXT (PS-ELFEXT) test. What does this failure indicate?

Answer: Excessive far-end crosstalk which degrades signals at the distant end of the cable

PS-ELFEXT measures power sum equal-level far-end crosstalk; a failure indicates the cable or terminations are coupling noise onto pairs at the far end, impairing high-speed data transmission.

A technician notices that a wireless access point connected to a PoE switch port does not power on. After confirming the AP supports PoE, what is the NEXT step?

Answer: Test the patch cable with a cable tester and verify the switch port PoE output with a PoE tester

A faulty patch cable or a non-functional switch PoE port are common causes; verifying the cable and measuring the PoE output isolates the fault before replacing equipment.

When performing a signal level measurement on a CATV drop, the technician finds the downstream level is -12 dBmV at the outlet. What is the appropriate action?

Answer: Add an amplifier to boost the signal, as -12 dBmV is below the -8 dBmV minimum for good reception

Cable television outlet signal levels should typically be between -8 dBmV and +8 dBmV; -12 dBmV is below minimum and requires amplification or reduction of splitter/cable losses.

An OTDR shows a flat line with no return signal after a certain distance on a multimode fiber. What does this indicate?

Answer: A complete fiber break or macrobend causing total signal loss beyond that point

A flat line (noise floor) after a point on an OTDR trace indicates no backscatter is returning, which means the fiber is broken or has a severe bend causing complete signal loss.