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RYA SRC/VHF study materials
RYA SRC/VHF study resources

RYA SRC/VHF practice questions

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Question 1General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which frequency band is assigned to the VHF maritime mobile service used by small craft radio installations?

  1. 156.000 MHz to 174.000 MHz Correct answer.
  2. 121.500 MHz to 136.975 MHz
  3. 406.000 MHz to 406.100 MHz
  4. 1.605 MHz to 4.000 MHz

Explanation

The maritime VHF band runs from 156 MHz to 174 MHz and is the band in which channelised ship and coast stations, including channel 16, operate. The other ranges belong to aeronautical, MF/HF or satellite distress services.

Question 2General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

On which VHF channel is the distress, safety and calling frequency located, and what is its frequency?

  1. Channel 16, 156.800 MHz Correct answer.
  2. Channel 6, 156.300 MHz
  3. Channel 70, 156.525 MHz
  4. Channel 13, 156.650 MHz

Explanation

Channel 16 at 156.800 MHz is the international distress, safety and calling channel, monitored by coast stations and ships. It is used to establish contact, after which traffic is moved to a working channel.

Question 3General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What does the abbreviation GMDSS stand for?

  1. Global Marine Data and Safety Service
  2. General Maritime Digital Signalling System
  3. General Marine Distress Signalling Standard
  4. Global Maritime Distress and Safety System Correct answer.

Explanation

GMDSS is the Global Maritime Distress and Safety System, an internationally agreed framework for distress alerting, search and rescue coordination and the broadcast of maritime safety information. It is built on both terrestrial radio and satellite communications.

Question 4General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which unit is used for radio frequencies in the VHF maritime band, and what does one such unit represent?

  1. The megahertz, representing one million cycles per second Correct answer.
  2. The hertz, representing one cycle per minute
  3. The watt, representing one joule per second
  4. The kilohertz, representing one thousand cycles per hour

Explanation

Frequency is measured in hertz, and one megahertz equals one million cycles per second. Marine VHF channels are therefore expressed in MHz, for example 156.800 MHz for channel 16.

Question 5General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What does the working channel selected after a DSC alert on VHF channel 70 normally carry?

  1. Satellite position reports
  2. Digitally encoded distress and routine calls only
  3. Voice radiotelephony traffic Correct answer.
  4. Navigational telex broadcasts

Explanation

Channel 70 is reserved exclusively for digital selective calling and carries no voice. Once a DSC link is established, the parties move to a voice working channel such as channel 6 or 72 for the actual radiotelephony.

Question 6General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

A small craft without DSC wishes to make an urgency call. Which VHF channel and signal should be used?

  1. Channel 16 with the words 'MAYDAY MAYDAY MAYDAY'
  2. Channel 16 with the words 'PAN PAN PAN' Correct answer.
  3. Channel 13 with the word 'SECURITE'
  4. Channel 70 with a digital urgency alert

Explanation

The urgency signal is PAN PAN, repeated three times, and it is transmitted on channel 16 to announce a serious situation that does not yet threaten immediate loss of life. The distress signal MAYDAY is reserved for grave and imminent danger.

Question 7General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the purpose of the Sea Area A1 designation in the GMDSS?

  1. An area within MF coverage of a coast station
  2. An area covered by the Inmarsat geostationary satellites
  3. An area beyond 100 nautical miles from the coast
  4. An area within VHF coverage of a coast station equipped with DSC alerting Correct answer.

Explanation

Sea Area A1 is the area within radiotelephone coverage of at least one VHF coast station with continuous DSC alerting, roughly 20 to 30 nautical miles offshore. A2 and A3 describe MF and satellite coverage respectively.

Question 8General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which statement correctly describes the function of a Maritime Mobile Service Identity, or MMSI?

  1. It is the callsign allocated to the radio operator on watch
  2. It is the IMO number painted on the hull
  3. It is the vessel's official number issued by the ship registry
  4. It is a nine-digit number that uniquely identifies a station for DSC and digital communications Correct answer.

Explanation

An MMSI is a nine-digit identity stored in the DSC controller and used to address and identify stations automatically. It is programmed into the radio and must match the vessel's registration details.

Question 9General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

A vessel in distress has an EPIRB and a portable VHF. Which action is most appropriate for alerting rescue services?

  1. Transmit a MAYDAY RELAY on channel 70
  2. Broadcast a SECURITE message on channel 6
  3. Activate the EPIRB and transmit a MAYDAY on channel 16 with position and nature of distress Correct answer.
  4. Wait for another vessel to notice the situation

Explanation

Activating a 406 MHz EPIRB sends a distress alert via the COSPAS-SARSAT system, while a MAYDAY on channel 16 gives nearby stations and coast radio the details needed for an immediate response. Using both methods maximises the chance of a rapid rescue.

Question 10General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the correct content of a MAYDAY distress message after the signal has been sent?

  1. Vessel name, position, nature of distress and assistance required Correct answer.
  2. The weather forecast for the area
  3. The vessel's port of registry and owner's name
  4. Only the vessel's MMSI and callsign

Explanation

The distress message gives the identity of the vessel, its position, the nature of the distress and the assistance required, followed by any other useful information such as number of persons on board. This lets rescuers plan the response.

Question 11General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which VHF channel is designated for inter-ship communication and is also used for bridge-to-bridge safety traffic?

  1. Channel 70
  2. Channel 28
  3. Channel 16
  4. Channel 13 Correct answer.

Explanation

Channel 13 at 156.650 MHz is the inter-ship navigation safety channel, often used for bridge-to-bridge communication about manoeuvring. Channel 16 is for calling and distress, and channel 70 is DSC only.

Question 12General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What does a DSC distress alert transmitted on VHF contain?

  1. A spoken description of the emergency
  2. The vessel's cargo manifest
  3. The names of the crew on board
  4. The vessel's MMSI, the nature of distress and the position with time Correct answer.

Explanation

A VHF DSC distress alert carries the vessel's MMSI, the selected nature of distress and the position with the time of the fix, all in a single digital burst. It does not carry voice or detailed crew information.

Question 13General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

A vessel receives a DSC distress alert from another station. What is the correct immediate action on VHF?

  1. Acknowledge the alert by DSC and prepare to assist, then monitor channel 16 Correct answer.
  2. Switch off the radio to avoid interference
  3. Ignore the alert because it is not addressed to the vessel
  4. Retransmit the alert on channel 70

Explanation

A station receiving a distress alert should acknowledge it by DSC where appropriate and then keep a listening watch on channel 16 for the distress traffic and for instructions from a coast station or rescue coordination centre. Silence or retransmission can delay the rescue.

Question 14General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which of the following is a function of the Maritime Safety Information broadcasts received on VHF?

  1. Engine maintenance schedules
  2. Private telephone calls to shore
  3. Navigational warnings and weather forecasts for the area Correct answer.
  4. Commercial advertising by marinas

Explanation

Maritime Safety Information includes navigational warnings, meteorological warnings and forecasts, and urgent safety information broadcast to ships. It is received through NAVTEX, SafetyNET or VHF voice broadcasts depending on the area and equipment.

Question 15General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What does the term 'duplex' mean when applied to a VHF marine channel?

  1. The vessel transmits and receives on the same frequency
  2. The channel carries only digital data
  3. The channel is shared between two vessels only
  4. The vessel transmits and receives on two different frequencies Correct answer.

Explanation

On a duplex channel the ship transmits on one frequency and receives on another, allowing simultaneous two-way communication through a repeater or coast station. Simplex channels use a single frequency for both directions.

Question 16General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which power setting should normally be selected for a short-range VHF call between two nearby vessels?

  1. Maximum power with the antenna disconnected
  2. Low power, typically 1 watt Correct answer.
  3. High power, typically 25 watts
  4. The setting does not affect range

Explanation

Low power, usually 1 watt, is sufficient for short-range communication and reduces interference to other stations on the same channel. High power is used when contact cannot be made at low power or when range requires it.

Question 17General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the main purpose of the COSPAS-SARSAT system in the GMDSS?

  1. To relay routine weather reports
  2. To provide telephone calls to shore
  3. To detect and locate distress beacons and pass alerts to rescue coordination centres Correct answer.
  4. To broadcast navigational warnings

Explanation

COSPAR-SARSAT is a satellite system that detects 406 MHz distress beacons, determines their position and forwards the alert to the appropriate rescue coordination centre. It is a core element of GMDSS distress alerting.

Question 18General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which of these is a correct way to test a VHF radio without causing interference?

  1. Transmit a MAYDAY and cancel it
  2. Use channel 70 for a voice test
  3. Make a short test transmission on a working channel, identifying the station and stating that it is a test Correct answer.
  4. Transmit continuously on channel 16

Explanation

A radio check should be brief, made on a suitable working channel and should identify the station and state that it is a test. Channel 16 and channel 70 must not be used for routine testing.

Question 19General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the function of the automatic identification system, AIS, in relation to VHF communications?

  1. It replaces the VHF voice radio entirely
  2. It broadcasts vessel identity, position and course on VHF data channels for collision avoidance Correct answer.
  3. It provides satellite distress alerting
  4. It broadcasts weather forecasts to all vessels

Explanation

AIS transmits vessel identity, position, course and speed over VHF data channels so that other stations can display traffic information. It supports collision avoidance but does not replace voice communication or distress alerting.

Question 20General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which of these statements about the use of channel 16 is correct?

  1. It is used for routine chat between vessels throughout a voyage
  2. It is used to establish contact and for distress, urgency and safety traffic, then traffic moves to a working channel Correct answer.
  3. It is used only for public correspondence calls
  4. It is used only for digital selective calling

Explanation

Channel 16 is the international distress, safety and calling channel. Initial contact is made there, but the conversation should then move to a working channel to keep channel 16 clear for emergencies.

Question 21General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the correct phonetic spelling of the distress signal MAYDAY when transmitted by voice?

  1. M'AIDER, spoken once
  2. MAY DAY, spoken as two separate English words
  3. MAYDAY, spoken as the French expression m'aidez, repeated three times Correct answer.
  4. MAYDAY, spoken once only

Explanation

The distress signal is the word MAYDAY, derived from the French m'aidez, and it is repeated three times in the initial call. Repeating it three times makes the distress call unmistakable.

Question 22General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

A vessel's VHF radio has a DSC controller. What should be done before transmitting a routine DSC call to another vessel?

  1. Transmit a MAYDAY first
  2. Enter the other station's MMSI and select a working channel for the subsequent voice contact Correct answer.
  3. Switch to channel 70 for voice
  4. Disconnect the antenna

Explanation

A routine DSC call is addressed to the other station's MMSI and proposes a working channel for the voice conversation that follows. Channel 70 itself carries only the digital call.

Question 23General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which of the following best describes the term 'simplex' in marine VHF operation?

  1. Transmission and reception on two separate frequencies
  2. Communication through a satellite link
  3. Communication using only digital data
  4. Transmission and reception on the same frequency, one direction at a time Correct answer.

Explanation

In simplex operation the same frequency is used for both transmitting and receiving, so only one station can transmit at a time. Most ship-to-ship VHF channels are simplex.

Question 24General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

A vessel is 15 nautical miles offshore and wishes to send a routine DSC call to a coast station. Which sea area is this most likely to be?

  1. Sea Area A4, in polar regions
  2. Sea Area A3, within satellite coverage
  3. Sea Area A2, within MF coverage
  4. Sea Area A1, within VHF DSC coverage Correct answer.

Explanation

At 15 nautical miles offshore the vessel is normally within VHF coverage of a coast station with continuous DSC alerting, which defines Sea Area A1. MF and satellite areas apply further offshore.

Question 25General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the purpose of the 406 MHz frequency used by distress beacons?

  1. It is the frequency for public correspondence calls
  2. It carries voice communication between vessels
  3. It carries the digital distress message detected by the COSPAS-SARSAT satellites Correct answer.
  4. It is used for navigational telex broadcasts

Explanation

A 406 MHz beacon transmits a digital distress message that the COSPAS-SARSAT satellites detect and relay to rescue coordination centres. The 121.5 MHz signal is used for local homing by rescue aircraft.

Question 26General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Under the GMDSS, which equipment is mandatory for a vessel operating exclusively within Sea Area A1?

  1. A VHF radio installation with DSC and a 406 MHz EPIRB Correct answer.
  2. A NAVTEX receiver and an HF radiotelephone
  3. An Inmarsat-C ship earth station
  4. An MF/HF radio installation with DSC and NBDP

Explanation

Sea Area A1 is defined by continuous VHF DSC alerting coverage from at least one coast station, so the core carriage requirement is a VHF DSC installation plus a satellite EPIRB operating on 406 MHz. MF/HF and Inmarsat equipment become necessary only when the vessel operates outside A1 into A2 or A3. NAVTEX is part of the MSI reception requirement but does not by itself satisfy the A1 distress alerting requirement.

Question 27General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the primary purpose of the dedicated DSC distress button on a VHF radio?

  1. To activate the EPIRB and AIS simultaneously
  2. To switch the radio to maximum power for long-range calling
  3. To transmit a pre-formatted distress alert on channel 70 without voice procedure Correct answer.
  4. To open a voice channel to the nearest coast station for a routine report

Explanation

The distress button sends a digital distress alert on VHF channel 70 containing the vessel's MMSI and the nature of distress if selected, without the operator needing to speak. It does not itself establish voice contact; a follow-up distress call on channel 16 is normally made afterwards. It is not linked to EPIRB or AIS activation.

Question 28General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which frequency band does the GMDSS use for on-scene communications between survival craft and rescue units?

  1. Satellite L-band only
  2. LF and MF only
  3. HF single sideband only
  4. VHF and 9 GHz radar transponders Correct answer.

Explanation

On-scene communications in the GMDSS are carried out on VHF radiotelephone, particularly channel 16 and the associated working channels, supported by the 9 GHz radar transponder (SART) for locating survival craft. These two means are complementary and are the standard fit for on-scene coordination. LF, HF only, and satellite-only solutions do not provide the short-range ship-to-survival-craft link.

Question 29General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the function of the DISTRESS category in a DSC transmission?

  1. It is used to test the DSC controller without transmitting
  2. It indicates a safety broadcast about navigation hazards
  3. It marks the message as an immediate distress alert requiring no further confirmation Correct answer.
  4. It requests a routine commercial call to a coast station

Explanation

The distress category in DSC identifies the alert as an immediate distress situation and gives it priority handling by all stations receiving it. It is distinct from urgency, safety, and routine categories, which cover lesser priorities. A distress alert should not be used for testing or for ordinary traffic.

Question 30General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

A vessel receives a DSC distress alert on VHF channel 70 from a station whose MMSI is unknown. What should the watchkeeper do first?

  1. Retransmit the alert on channel 16 to widen the search
  2. Switch off the DSC controller to avoid further alerts
  3. Acknowledge the alert by DSC and then listen on channel 16 for the distress traffic Correct answer.
  4. Ignore the alert because the MMSI is not recognised

Explanation

A DSC distress alert should be acknowledged by DSC, after which the station should keep a listening watch on channel 16 for the distress call and traffic. Acknowledging does not commit the vessel to rescue but confirms reception and allows coordination by the rescue authority. Ignoring, retransmitting, or disabling the controller would delay or disrupt the distress response.

Question 31General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which statement correctly describes the use of VHF channel 13 in the GMDSS?

  1. It is used only for DSC distress alerts
  2. It is designated for bridge-to-bridge navigational safety communications Correct answer.
  3. It is reserved exclusively for public correspondence
  4. It is the primary channel for maritime safety information broadcasts

Explanation

VHF channel 13 is designated for bridge-to-bridge communications concerning the safe navigation of vessels, such as passing arrangements. It is not a public correspondence channel, a DSC channel, or an MSI broadcast channel. Channel 16 remains the distress and calling channel, and channel 70 is used for DSC.

Question 32General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the correct procedure for a routine DSC call to another vessel when no working channel has been agreed?

  1. Send the DSC call on channel 70 and remain on channel 70 for the voice conversation
  2. Send the DSC call on the working channel and speak on channel 70
  3. Send the DSC call on channel 70 proposing a working channel, then switch to that channel for the voice conversation Correct answer.
  4. Send the DSC call on channel 16 and then speak on channel 70

Explanation

Routine DSC calls are sent on channel 70, and the call should propose a working channel for the subsequent voice communication. Once the DSC exchange is complete, both stations move to the proposed working channel. Channel 70 must not be used for voice, and channel 16 is not used for routine DSC calls.

Question 33General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

A vessel is in Sea Area A2. Which GMDSS communication capability must it have in addition to VHF?

  1. HF radiotelephone only
  2. Inmarsat-C only
  3. A second VHF DSC radio only
  4. MF radiotelephone with DSC and, where required, NBDP Correct answer.

Explanation

Sea Area A2 is defined by continuous MF DSC coverage, so a vessel operating there must carry MF equipment with DSC, and NBDP where the applicable carriage requirements call for it. HF and Inmarsat are associated with A3 and A4 rather than being the A2 baseline. A second VHF set does not extend coverage beyond A1.

Question 34General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which statement correctly describes the purpose of a NAVTEX receiver in the GMDSS?

  1. It transmits distress alerts to coast stations
  2. It provides two-way voice communication with rescue coordination centres
  3. It tracks vessel position for AIS reporting
  4. It automatically receives and prints maritime safety information broadcasts on 518 kHz Correct answer.

Explanation

NAVTEX is a receive-only system that automatically receives and prints or displays maritime safety information, including navigational warnings and weather, on the international frequency 518 kHz. It does not transmit distress alerts, provide voice communication, or perform AIS position reporting. Those functions belong to DSC, radiotelephony, and AIS respectively.

Question 35General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

When should a vessel transmit a MAYDAY RELAY?

  1. When the vessel is entering a foreign port
  2. When another vessel is known to be in distress and no acknowledgement has been heard Correct answer.
  3. When the vessel wishes to test its distress equipment
  4. When the vessel needs a routine weather forecast

Explanation

A MAYDAY RELAY is used to relay a distress alert when a station in distress is not able to communicate directly or when no acknowledgement has been heard. It informs other stations and the rescue authority that a distress exists and that relay assistance is being provided. It is not a test, a weather request, or a port entry procedure.

Question 36General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which of these is the correct way to pronounce the figures in a spoken distress message?

  1. As a single whole number in the normal language
  2. Each digit spoken separately using the standard phonetic digit words Correct answer.
  3. Only in Morse code
  4. As Roman numerals

Explanation

In radiotelephony, figures in distress and safety traffic are spoken digit by digit using the standard phonetic digit words so that each figure is clearly understood. This avoids confusion between similar-sounding numbers. Reading a whole number, using Roman numerals, or using Morse code is not the radiotelephone procedure.

Question 37General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

A vessel's VHF DSC controller displays an incoming distress alert with a nature of distress of 'fire'. What does this indicate?

  1. The transmitting station has declared a fire as the reason for distress Correct answer.
  2. The transmitting station is testing its fire alarm system
  3. The alert is a routine fire drill notification
  4. The alert is a safety message about a fire ashore

Explanation

The nature of distress field in a DSC distress alert communicates the reason the distress alert was sent, and 'fire' indicates that fire is the declared cause. It is not a test, a drill, or a shore safety message. Receiving stations should treat it as a genuine distress alert and respond accordingly.

Question 38General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Which of these best explains why channel 70 must not be used for voice communication?

  1. It is limited to 1 watt output by regulation
  2. It is a duplex channel that cannot carry voice
  3. It is used only for public correspondence
  4. It is reserved exclusively for DSC and voice would interfere with digital distress and routine signalling Correct answer.

Explanation

Channel 70 is the dedicated DSC channel and carries digital distress, urgency, safety, and routine signalling. Voice transmissions on it would interfere with these digital messages, including distress alerts. Duplex status, public correspondence, and power limits are not the reason for the prohibition.

Question 39General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

What is the correct action when a DSC distress alert is received and the vessel is more than 100 nautical miles from the distress position?

  1. Proceed immediately at maximum speed to the distress position
  2. Retransmit the alert on channel 16
  3. Acknowledge by DSC and maintain a listening watch on channel 16 for further instructions Correct answer.
  4. Ignore the alert because of the distance

Explanation

Even at long range, a station receiving a DSC distress alert should acknowledge by DSC and keep a listening watch on channel 16 so that it can follow the distress traffic and any instructions from the rescue authority. Immediate high-speed passage is not automatically required at that distance, and ignoring or retransmitting the alert is incorrect.

Question 40General knowledge of radio communications and the Global Maritime Distress and Safety System (GMDSS)

Under the GMDSS, what does the MMSI number programmed into a vessel's VHF DSC radio identify when a distress alert is transmitted?

  1. The nearest coast station, so the alert is routed to the correct rescue coordination centre
  2. The vessel itself, so the coast station and other units know which ship is in distress Correct answer.
  3. The nationality of the skipper, so the alert is passed to the correct flag state authority
  4. The satellite system used, so the alert reaches the correct search and rescue region

Explanation

A Maritime Mobile Service Identity is a nine-digit number assigned to the ship station (or to a coast station, group or person depending on its format) and stored in the DSC controller. When the distress button is pressed, the alert carries this identity so that rescue authorities know exactly which vessel is in distress and can look up its details. The MMSI belongs to the station, not to a coast station, a satellite system or the skipper's nationality.

Question 41VHF radio operation, controls and channel usage

On a standard fixed VHF/DSC set, which control adjusts the receiver sensitivity so that weak signals are amplified more than strong ones?

  1. The clarifier control
  2. The volume control
  3. The RF gain control Correct answer.
  4. The squelch control

Explanation

The RF gain control sets how much amplification is applied to incoming signals, so reducing it can suppress background noise while strong local stations remain audible. Squelch is different: it mutes the receiver until signal strength exceeds a threshold. Volume only affects loudspeaker output, not receiver sensitivity.

Question 42VHF radio operation, controls and channel usage

What is the purpose of the squelch control on a VHF radio?

  1. It reduces the transmitter power to save battery
  2. It locks the keypad to prevent accidental transmission
  3. It silences the loudspeaker when no signal is being received Correct answer.
  4. It selects the duplex channel pair

Explanation

Squelch mutes the audio output until the received signal rises above a chosen threshold, so the operator does not have to listen to continuous background hiss. Setting it too high can cause weak but important transmissions to be missed. It has no effect on transmit power or channel selection.

Question 43VHF radio operation, controls and channel usage

Which channel is designated worldwide for distress, safety and calling on marine VHF?

  1. Channel 70
  2. Channel 16 Correct answer.
  3. Channel 13
  4. Channel 06

Explanation

Channel 16 (156.800 MHz) is the international distress, safety and calling channel, monitored by coast stations and vessels. Initial contact is made there, then traffic is normally moved to a working channel. Channel 70 is reserved for DSC only and must not be used for voice.

Question 44VHF radio operation, controls and channel usage

Why must Channel 70 never be used for voice communication?

  1. It is allocated exclusively to digital selective calling Correct answer.
  2. It is limited to low power and short range
  3. It is reserved for port operations traffic
  4. It is a receive-only channel for weather broadcasts

Explanation

Channel 70 is reserved internationally for DSC digital transmissions, and voice or other analogue use would interfere with the automated distress and calling system. DSC alerts are transmitted there automatically, so keeping it clear protects the integrity of the alerting service.

Question 45VHF radio operation, controls and channel usage

You are hailing another vessel on Channel 16. What is the correct procedure once contact is established?

  1. Ask the coast station to relay the conversation
  2. Move to a working channel agreed between the two vessels Correct answer.
  3. Switch to Channel 70 to continue by voice
  4. Remain on Channel 16 for the whole exchange

Explanation

Channel 16 is a calling and distress channel and must be kept clear for emergencies, so routine exchanges are moved to an agreed working channel such as 06, 08 or 72. The station initiating the call normally proposes the working channel. Prolonged conversation on 16 is contrary to the Radio Regulations.

Question 46VHF radio operation, controls and channel usage

What does the 'dual watch' function on a VHF radio do?

  1. It scans all international channels in sequence
  2. It monitors Channel 16 while the set is tuned to a selected working channel Correct answer.
  3. It transmits on two channels simultaneously
  4. It compares signal strength on two antennas

Explanation

Dual watch keeps the receiver checking Channel 16 at intervals while the operator works on another channel, so a distress or calling signal is not missed. It does not transmit on two channels at once. Full scanning of many channels is a different function, usually called scan or memory scan.

Question 47VHF radio operation, controls and channel usage

Which of these is a simplex channel commonly used for ship-to-ship conversation?

  1. Channel 72 Correct answer.
  2. Channel 60
  3. Channel 24
  4. Channel 16

Explanation

Channel 72 is a simplex inter-ship channel widely used for routine ship-to-ship working traffic. Channels 60 and 24 are duplex channels used for public correspondence through coast stations, so both stations do not transmit and receive on the same frequency. Channel 16 is reserved for calling and distress.

Question 48VHF radio operation, controls and channel usage

What is the effect of selecting low power on a VHF radio?

  1. The receiver sensitivity is increased
  2. The channel spacing is halved
  3. The transmission is converted to single sideband
  4. The range is reduced, which is useful for short-range ship-to-ship contact Correct answer.

Explanation

Low power, typically around 1 watt, reduces the range of the transmission, which helps avoid unnecessary interference with distant stations when only short-range contact is needed. High power, usually 25 watts, is selected when greater range is required. Power selection does not change the modulation mode or channel spacing.

Question 49VHF radio operation, controls and channel usage

In the phonetic alphabet, which word represents the letter Q?

  1. Queen
  2. Quota
  3. Quincy
  4. Quebec Correct answer.

Explanation

The standard ICAO phonetic alphabet uses Quebec for Q, which is essential when spelling out call signs, names and positions over a noisy channel. Using non-standard words defeats the purpose, since the receiving operator may not recognise them. The other spellings are not part of the recognised alphabet.

Question 50VHF radio operation, controls and channel usage

A vessel's DSC controller is prompting for the type of call to be sent. Which call type should be selected to request an urgent medical evacuation?

  1. Urgency Correct answer.
  2. Safety
  3. Routine
  4. Distress

Explanation

Urgency calls, announced by the spoken signal PAN PAN, cover serious but non-immediate danger such as medical evacuation or a disabled vessel not in immediate peril. Distress is reserved for grave and imminent danger requiring immediate assistance. Safety covers navigational warnings and similar advisory traffic.