VDV Testing & Troubleshooting 2 — Questions and Answers
Question 1: A technician measures -3.5 dB return loss on a coaxial cable connector. What does this indicate?
- Excellent impedance match
- Moderate signal reflection due to impedance mismatch (Correct answer)
- Complete signal absorption
- Normal insertion loss
Correct answer: Moderate signal reflection due to impedance mismatch
A return loss of -3.5 dB indicates significant signal reflection back toward the source, which is caused by an impedance mismatch at the connector.
Question 2: When using a toner and probe kit to trace a cable, the probe produces no tone on any cable in a bundle. What is the most likely cause?
- The cable is shielded and blocking the tone
- The toner is not connected to the correct pair or is faulty (Correct answer)
- The cable bundle is too large
- The probe sensitivity is too high
Correct answer: The toner is not connected to the correct pair or is faulty
If no tone is detected on any cable, the most likely cause is that the toner is not properly connected to the target cable or the toner unit itself is malfunctioning.
Question 3: A VoIP phone loses audio quality intermittently during calls. Which test tool best identifies the root cause?
- Cable certifier
- Network packet analyzer (protocol analyzer) (Correct answer)
- Optical power meter
- Multimeter
Correct answer: Network packet analyzer (protocol analyzer)
A protocol analyzer (such as Wireshark) captures packets to reveal jitter, packet loss, and latency—the primary causes of intermittent VoIP audio degradation.
Question 4: A coaxial cable run tests with higher-than-expected attenuation. Which of the following is the LEAST likely cause?
- Excessive cable length
- Kinked or damaged dielectric
- Incorrect termination impedance
- Low ambient temperature (Correct answer)
Correct answer: Low ambient temperature
Low ambient temperature actually reduces attenuation slightly; excessive length, physical damage, and impedance mismatches are all common causes of elevated attenuation.
Question 5: During a CATV signal level sweep test, a technician notices a 6 dB drop at all frequencies above 550 MHz. What is the most probable cause?
- Faulty splitter on the low-band port
- Water-damaged cable segment acting as a high-frequency low-pass filter (Correct answer)
- Amplifier reverse-path noise
- Incorrect channel plan configuration
Correct answer: Water-damaged cable segment acting as a high-frequency low-pass filter
Water ingress into coaxial cable or connectors creates a low-pass filter effect, causing greater attenuation at higher frequencies.
Question 6: A technician installs a structured cabling system and the cable certifier reports 'FAIL – Near-End Crosstalk (NEXT)'. Which action is MOST likely to resolve this?
- Increase the cable pull tension
- Re-terminate the connectors, ensuring minimum untwisting of pairs (Correct answer)
- Replace the cable with a larger gauge
- Reduce the patch cord length
Correct answer: Re-terminate the connectors, ensuring minimum untwisting of pairs
Excessive untwisting of twisted pairs during termination is the most common cause of NEXT failures; re-terminating with minimal untwist typically resolves this.
Question 7: An OTDR trace shows a spike (gainer) in the middle of a fiber run where no splice or connector exists. What does this indicate?
- A fiber break at that location
- A difference in backscatter coefficients between two fiber sections joined at that point (Correct answer)
- An air gap in the fiber
- Excessive bend radius at that location
Correct answer: A difference in backscatter coefficients between two fiber sections joined at that point
A gainer artifact on an OTDR trace typically results from a splice between fibers with different backscatter coefficients, making the far section appear to have lower loss than it does.
VDV Testing & Troubleshooting 2
A technician measures -3.5 dB return loss on a coaxial cable connector.
What does this indicate?