CBT Equipment & Troubleshooting 3 — Questions and Answers
Question 1: An STL (Studio-Transmitter Link) operating at 950 MHz shows excessive bit errors after a heavy rainstorm. What is the MOST likely cause?
- Increased atmospheric pressure
- Water ingress into waveguide or coaxial connections (Correct answer)
- Frequency drift of the STL transmitter
- Overloaded audio input levels
Correct answer: Water ingress into waveguide or coaxial connections
Water entering RF connectors or waveguide sections dramatically increases signal attenuation and causes multipath interference, raising the bit error rate.
Question 2: A technologist measures -10 dBu on an unbalanced consumer audio output but expects +4 dBu on a balanced professional input. What device is needed to interface them correctly?
- Equalizer
- Active balun or line-level matching transformer (Correct answer)
- Noise gate
- A/D converter
Correct answer: Active balun or line-level matching transformer
A balun or active matching device converts the unbalanced consumer level to balanced professional level, correcting both impedance and level differences.
Question 3: In an ATSC 3.0 broadcast system, what is the role of the bootstrap signal?
- It carries the primary audio essence
- It provides receiver synchronization and system discovery information (Correct answer)
- It controls transmitter power output
- It encodes closed-caption data
Correct answer: It provides receiver synchronization and system discovery information
The ATSC 3.0 bootstrap signal allows receivers to synchronize with the OFDM signal and discover system parameters without prior knowledge of the configuration.
Question 4: A transmitter's forward power reads 10 kW but the reflected power meter reads 2 kW. What is the net delivered power to the antenna?
- 12 kW
- 10 kW
- 8 kW (Correct answer)
- 5 kW
Correct answer: 8 kW
Net delivered power equals forward power minus reflected power: 10 kW − 2 kW = 8 kW.
Question 5: Which piece of test equipment is used to verify proper color burst phase and subcarrier frequency in an analog NTSC composite video signal?
- Waveform monitor only
- Vectorscope (Correct answer)
- Spectrum analyzer
- Audio phase meter
Correct answer: Vectorscope
A vectorscope displays the chrominance phase and amplitude, allowing technologists to confirm correct color burst and subcarrier alignment.
Question 6: A broadcast facility's UPS system shows an abnormally high battery discharge rate during a utility power outage. What should the technologist investigate first?
- Adjust the UPS output frequency
- Check for overloaded circuits or failed battery cells (Correct answer)
- Recalibrate the bypass switch
- Replace the static transfer switch
Correct answer: Check for overloaded circuits or failed battery cells
Excessive discharge rate typically indicates either more load than rated capacity or degraded battery cells that cannot hold full charge.
Question 7: What is the purpose of a pre-emphasis circuit in FM broadcasting?
- To boost low-frequency audio before transmission to improve SNR
- To boost high-frequency audio before transmission to improve SNR (Correct answer)
- To limit the total modulation of the FM carrier
- To equalize the stereo pilot tone level
Correct answer: To boost high-frequency audio before transmission to improve SNR
FM pre-emphasis boosts high frequencies at the transmitter; corresponding de-emphasis at the receiver restores flat response while reducing high-frequency noise.
CBT Equipment & Troubleshooting 3
An STL (Studio-Transmitter Link) operating at 950 MHz shows excessive bit errors after a heavy rainstorm.
What is the MOST likely cause?