GROL General Radiotelephone 3 — Questions and Answers
Question 1: What is the primary purpose of the Global Maritime Distress and Safety System (GMDSS)?
- To provide commercial ship-to-shore telephone service
- To automate distress alerting and improve coordination of SAR operations (Correct answer)
- To replace VHF channels for routine port operations
- To provide weather routing advice to vessel masters
Correct answer: To automate distress alerting and improve coordination of SAR operations
GMDSS automates distress alerting using DSC, EPIRBs, and satellite systems to rapidly coordinate search-and-rescue operations.
Question 2: What is the internationally designated distress frequency for MF (medium frequency) radiotelephony?
- 2182 kHz (Correct answer)
- 156.8 MHz (Channel 16)
- 406 MHz
- 8291 kHz
Correct answer: 2182 kHz
2182 kHz is the international distress and calling frequency for MF radiotelephony, used for watch-keeping at sea.
Question 3: In a superheterodyne receiver, what is the purpose of the IF (intermediate frequency) stage?
- To amplify and filter the signal at a fixed, lower frequency for better selectivity (Correct answer)
- To convert the received RF signal directly to audio
- To mix the incoming signal with the local oscillator
- To provide automatic frequency control of the local oscillator
Correct answer: To amplify and filter the signal at a fixed, lower frequency for better selectivity
The IF stage amplifies and filters the down-converted signal at a constant frequency, providing consistent selectivity and gain.
Question 4: Which antenna has a radiation pattern that is omnidirectional in the horizontal plane?
- Yagi-Uda antenna
- Corner reflector antenna
- Vertical whip antenna (Correct answer)
- Rhombic antenna
Correct answer: Vertical whip antenna
A vertical whip antenna radiates equally in all horizontal directions, making it ideal for ship and land mobile use.
Question 5: What does the term 'selectivity' refer to in a radio receiver?
- The ability to detect very weak signals
- The ability to reject adjacent channel interference (Correct answer)
- The range of frequencies the receiver can tune
- The ratio of signal power to noise power at the output
Correct answer: The ability to reject adjacent channel interference
Selectivity is the receiver's ability to separate the desired signal from nearby interfering signals on adjacent frequencies.
Question 6: What safety precaution must be observed when working on a transmitter's high-voltage power supply?
- Wear rubber-soled shoes only
- Work with one hand in your pocket to avoid creating a path across the chest (Correct answer)
- Always use a wooden stick to change settings
- Remove the antenna before energizing
Correct answer: Work with one hand in your pocket to avoid creating a path across the chest
Keeping one hand in your pocket prevents current from flowing through your chest (heart) if you contact a high-voltage point.
Question 7: What is the main advantage of using SSB over double-sideband AM for long-distance voice communication?
- SSB has a wider bandwidth allowing higher audio quality
- SSB requires less bandwidth and transmits all power in one sideband (Correct answer)
- SSB is immune to selective fading on HF bands
- SSB equipment is simpler and cheaper to manufacture
Correct answer: SSB requires less bandwidth and transmits all power in one sideband
SSB suppresses the carrier and one sideband, reducing bandwidth by half and concentrating all transmitter power into the voice-modulated sideband.
GROL General Radiotelephone 3
What is the primary purpose of the Global Maritime Distress and Safety System (GMDSS)?