RYA SRC/VHF key terms

The worldwide system that uses satellite and terrestrial radio to automate distress alerting and ensure that ships and shore stations can always reach each other for rescue coordination.

A sea area within continuous coverage of at least one shore-based VHF station with DSC alerting, normally about 20 to 30 nautical miles from the coast, where VHF is the primary means of alerting.

A situation in which a vessel or person is threatened by grave and imminent danger and requires immediate assistance, giving the highest priority on all radio frequencies.

A condition concerning the safety of a vessel or person but not requiring immediate assistance, such as a serious illness or a breakdown that does not threaten the vessel.

A message about navigational warnings, weather warnings or other important information that does not involve danger to a vessel or person but affects safe navigation.

The spoken distress signal, repeated three times, used on VHF to announce that a vessel is in grave and imminent danger and needs immediate help.

The spoken urgency signal, repeated three times, used to announce a serious situation that does not yet require immediate distress assistance.

The spoken safety signal, repeated three times, used to introduce a navigational or weather warning that other vessels should listen to.

Digital Selective Calling: a digital signalling method on VHF and other bands that sends pre-formatted alerts and calls to specific stations, including distress alerts with position and identity data.

A one-button digital transmission, normally on VHF Channel 70, that tells the coastguard and other stations the vessel's identity, position and nature of distress without using voice.

The red, protected key on a DSC controller that, when pressed and held for several seconds, transmits a distress alert; it must only be used in a genuine grave and imminent danger.

Maritime Mobile Service Identity: a unique nine-digit number programmed into a radio that identifies the vessel or station in DSC calls and is also used by AIS and other systems.

A nine-digit number beginning with a zero that identifies a group of stations, such as a rally fleet or club, so one DSC call can reach all its members.

Automatic Transmitter Identification System: a digital identifier used on inland waterways in some European countries, required instead of or alongside DSC on certain inland passages.

The international distress, safety and calling channel on 156.800 MHz, monitored continuously at sea and used to make initial contact before moving to a working channel.

The frequency 156.525 MHz reserved solely for DSC on VHF; voice transmissions are prohibited on it because they would interfere with digital alerting.

A VHF channel other than 16 or 70 used for routine conversation after initial contact, so that the calling and distress channels stay clear.

The bridge-to-bridge navigation safety channel, used for ship-to-ship manoeuvring communications, especially in busy or restricted waters; it is not for general chat.

A radio function that alternates monitoring between Channel 16 and a selected working channel so the operator keeps a listening watch on distress frequencies while using another channel.

A receiver function that cycles through a chosen list of channels, stopping on one that is receiving, so several working channels can be monitored at once.

A control that silences the receiver when no strong signal is present, suppressing background noise; set too high it can hide weak but important transmissions.

The transmit power selection on a VHF set, typically 25 watts high and 1 watt low; low power is used for short-range contact to reduce interference to other stations.

The national licence authorising a vessel to carry and operate radio equipment, usually issued with the vessel's call sign and required to be available on board.

A personal qualification, such as the Short Range Certificate, proving the holder has been trained and examined to operate a marine VHF radio and DSC equipment legally.

Short Range Certificate: the operator qualification for non-commercial craft using VHF and DSC equipment, covering radio theory, channel use, distress procedures and regulations.

The unique letters and numbers assigned to a vessel or station, used in voice radio to identify the transmitting station clearly at the start and end of a call.

A shore organisation that coordinates search and rescue operations, receives distress alerts and directs vessels and aircraft responding to an incident.

The spoken signal used by a station that is not itself in distress to pass on a distress message it has received on behalf of another vessel or station.

An accidental distress transmission, for example from a misused distress button; it must be cancelled immediately by radio so rescue services are not launched unnecessarily.

Emergency Position Indicating Radio Beacon: a float-free transmitter that, when activated, sends a distress alert with the vessel's identity and position via the Cospas-Sarsat satellite system.

The international satellite system that detects and locates signals from distress beacons and passes the alert and position to the relevant rescue authorities.

The frequency used by modern satellite distress beacons to carry a digitally coded alert containing the beacon identity, and often the vessel identity and position.

Search and Rescue Transponder: a radar transponder carried by the vessel that, when interrogated by a nearby radar, displays a line of dots pointing toward the casualty.

Radio detection and ranging: equipment that transmits pulses and displays echoes from objects, used for navigation and collision avoidance and to trigger a SART response.

The date by which a radio, EPIRB or SART battery must be replaced or the equipment serviced; it is marked on the unit and checked during pre-departure checks.

A built-in check that verifies a radio, EPIRB or SART is functioning without transmitting a real distress signal, normally performed regularly and before departure.

The conductor that radiates and receives radio energy; its height, condition and correct connection strongly affect range, and a damaged cable can stop transmission entirely.

A short test call to a coastguard or marina asking for a signal report, made on a working channel or as directed, to confirm the set and antenna are working.