CBT Equipment & Troubleshooting 4

Question 1

A cable TV headend technologist discovers the downstream QAM channel has a high MER (Modulation Error Ratio) degradation. Which impairment is LEAST likely to cause this?

Accepted Answer

Correct input signal level within specification

Answer

A signal level within specification does not cause MER degradation; noise, phase noise, and other impairments do.

Question 2

An IP-based broadcast router using SMPTE ST 2110 is dropping multicast packets intermittently. What network component should be checked first?

Accepted Answer

IGMP snooping configuration on the network switch

Answer

SMPTE ST 2110 relies on IP multicast, and incorrect IGMP snooping configuration is a common cause of dropped or undelivered multicast streams.

Question 3

A technologist is using a Bird wattmeter to measure power. The element reads lower than expected. What is a common reason for this discrepancy?

Accepted Answer

The element is inserted in the reverse direction

Answer

Bird thruline wattmeters are directional; inserting the element reversed causes it to read reflected power instead of forward power.

Question 4

Which protocol is used to synchronize clocks in an IP broadcast facility to sub-microsecond accuracy for SMPTE ST 2110?

Accepted Answer

PTP (Precision Time Protocol) IEEE 1588

Answer

PTP IEEE 1588 provides the sub-microsecond synchronization required for sample-accurate media transport in professional IP broadcast environments.

Question 5

A broadcast technologist notices hum bars rolling through a video monitor. The hum frequency is 60 Hz. What is the MOST likely cause?

Accepted Answer

Ground loop introducing AC power-line interference into the video path

Answer

60 Hz hum bars in video are a classic symptom of a ground loop where different ground potentials create a current path through the video cable shield.

(CBT) Certified Broadcast Technologist Practice Test

(CBT) Certified Broadcast Technologist Practice Test

CBT Equipment & Troubleshooting 4