CBT Equipment & Troubleshooting 2 — Questions and Answers
Question 1: A transmitter's VSWR suddenly spikes to 3:1. What is the FIRST corrective action a broadcast technologist should take?
- Increase transmitter power output
- Inspect the transmission line and antenna for faults (Correct answer)
- Replace the exciter module
- Adjust the audio processing chain
Correct answer: Inspect the transmission line and antenna for faults
A high VSWR indicates an impedance mismatch, most commonly caused by a transmission line or antenna fault that must be located and corrected.
Question 2: Which test instrument is used to measure the frequency response of an audio circuit?
- Spectrum analyzer
- Waveform monitor
- Audio signal generator and analyzer (Correct answer)
- Vector scope
Correct answer: Audio signal generator and analyzer
An audio signal generator sweeps frequencies while an analyzer measures the output level, producing a frequency response curve.
Question 3: An FM exciter's stereo pilot tone is missing. Which subsystem should the technologist check first?
- RF amplifier stage
- Stereo generator (composite encoder) (Correct answer)
- Antenna tuning unit
- Audio limiter
Correct answer: Stereo generator (composite encoder)
The 19 kHz stereo pilot is generated by the stereo composite encoder; its absence points to a fault in that subsystem.
Question 4: A broadcast engineer notices audio is present on a video feed but the waveform monitor shows the video level is 120 IRE. What problem does this indicate?
- Under-modulation
- Video signal is over-deviated
- Video is clipped above white level (superwhite) (Correct answer)
- Improper sync pulse timing
Correct answer: Video is clipped above white level (superwhite)
100 IRE is standard white; a level of 120 IRE means the video exceeds the white clip level, which can cause issues in downstream processing.
Question 5: What does an Optical Time-Domain Reflectometer (OTDR) measure in a fiber optic plant?
- Optical carrier frequency
- Location and magnitude of losses and reflections along a fiber (Correct answer)
- Modulation depth of optical signals
- Chromatic dispersion only
Correct answer: Location and magnitude of losses and reflections along a fiber
An OTDR sends light pulses down the fiber and analyzes backscatter to pinpoint splices, connectors, breaks, and their associated losses.
Question 6: A digital video router experiences intermittent switching errors. Which component is the MOST likely cause?
- SDI cable impedance mismatch
- Power supply voltage ripple
- Reference signal (black burst or tri-level sync) instability (Correct answer)
- Monitor calibration drift
Correct answer: Reference signal (black burst or tri-level sync) instability
A digital router relies on a stable reference signal to synchronize switching; an unstable reference causes unpredictable frame-boundary switching errors.
Question 7: When replacing a power amplifier tube in a high-power AM transmitter, which safety procedure is MOST critical before opening the final amplifier cabinet?
- Disable the remote control interface
- Discharge all high-voltage capacitors using a grounding stick (Correct answer)
- Switch the transmitter to low-power mode
- Remove the antenna feedline
Correct answer: Discharge all high-voltage capacitors using a grounding stick
High-voltage filter capacitors in AM transmitters can retain lethal charges long after power is removed and must be safely discharged before work begins.
CBT Equipment & Troubleshooting 2
A transmitter's VSWR suddenly spikes to 3:1.
What is the FIRST corrective action a broadcast technologist should take?