Italy LRC Marine Radio key terms

The Global Maritime Distress and Safety System: an international framework of radio equipment, frequencies, and procedures that lets ships alert shore stations and other vessels and conduct search and rescue coordination at sea.

A sea area covered by at least one VHF coast station with continuous DSC alerting, giving a ship reliable shore contact on VHF channel 70 and radiotelephony.

A sea area outside A1 that is covered by at least one MF coast station with continuous DSC alerting, typically extending to roughly 100 to 150 nautical miles from the coast.

A sea area outside A1 and A2 where an Inmarsat geostationary satellite system provides continuous alerting, covering roughly the band between about 70 degrees north and 70 degrees south.

The remaining sea areas outside A1, A2, and A3, essentially the polar regions, where GMDSS alerting relies on HF DSC and other long-range means rather than satellite coverage.

Digital Selective Calling: an automatic signalling method that sends coded alert, acknowledgement, and routine messages on dedicated channels, including a distress button that transmits a ship's identity and position without voice contact.

A priority transmission signalling grave and imminent danger and requesting immediate assistance, sent by DSC, Inmarsat, or voice and normally including the vessel identity, position, and nature of distress.

The spoken radiotelephony distress signal used three times at the start of a distress call to announce that a vessel or person is in grave and imminent danger and needs immediate help.

The spoken urgency signal, repeated three times, used when a station has an important but not immediately life-threatening message, such as a breakdown or a person needing medical advice.

The spoken safety signal, repeated three times, announcing a navigation or weather safety message, for example a drifting hazard, a storm warning, or a temporary channel closure.

Maritime Mobile Service Identity: a unique nine-digit number stored in DSC and AIS equipment that identifies a ship, coast station, or group, and is used in all digital alerting and identification.

The single VHF channel reserved exclusively for DSC alerting, on which voice transmission is prohibited because digital signalling occupies the channel and voice would block distress alerts.

The international VHF radiotelephony distress, safety, and calling channel, monitored continuously by ships at sea, used to establish contact before moving to a working channel.

The continuous listening duty on designated frequencies, such as VHF 16 or DSC 70, required of ships at sea so that distress and safety calls are heard and answered promptly.

Digital selective calling on medium and high frequencies, using dedicated distress frequencies such as 2187.5 kHz and the 8 MHz band to alert coast stations and ships over long distances.

Narrow-band direct printing: a telex-over-radio technique on MF/HF that sends text error-corrected between stations, historically used for distress traffic, navigational warnings, and ship-to-shore messages.

A narrow-band direct printing service that delivers typed text over HF or MF radio links, often used for weather bulletins, navigational warnings, and shore-to-ship administrative messages.

A store-and-forward satellite messaging terminal used in the GMDSS for distress alerting, two-way text messaging, and reception of enhanced group call safety information at sea.

The Inmarsat enhanced group call service that broadcasts maritime safety information to defined sea areas, received automatically by Inmarsat terminals such as Inmarsat-C.

An automatic narrow-band direct printing system that receives coastal maritime safety information on 518 kHz in English, typically within about 200 nautical miles of a transmitter.

Maritime Safety Information: navigational warnings, meteorological warnings and forecasts, search and rescue notices, and other urgent safety broadcasts distributed to ships by NAVTEX, SafetyNET, or voice.

Emergency Position-Indicating Radio Beacon: a float-free transmitter that, when activated, sends a distress alert with the vessel identity via the Cospas-Sarsat satellite system to rescue coordination centres.

An international satellite system that detects and locates distress beacons on 406 MHz, forwards the alert and identity data to rescue authorities, and supports Doppler or GNSS-based position fixing.

Search and Rescue Radar Transponder: a device that, when interrogated by a nearby radar, transmits a response producing a line of dots on the radar display to mark the survivor's position.

The frequency used by Cospas-Sarsat distress beacons, carrying digitally encoded identity and position data that let rescue authorities identify and locate a vessel quickly.

The aeronautical emergency frequency carried by many EPIRBs as a homing signal, allowing search aircraft to direction-find the beacon during the final phase of a rescue.

The alphanumeric identifier assigned to a radio station by its administration, used in voice communications to identify the ship or coast station during a call and in the sign-off.

The authorisation issued by a national administration permitting a vessel to operate radio equipment, listing the station details, permitted frequencies, and the equipment covered.

A personal qualification, such as the GMDSS General Operator Certificate, proving the holder is trained and authorised to operate ship radio equipment and handle distress traffic.

The international treaty rules governing frequency use, station operation, distress priorities, and interference avoidance, binding on administrations and reflected in national licensing law.

The way radio waves travel from transmitter to receiver, including ground wave along the surface, sky wave refracted by the ionosphere, and line-of-sight paths at VHF and above.

A radio path in which the signal travels up to the ionosphere, is refracted back to earth, and can thus cover very long distances, especially on HF at night.

The portion of a radio signal that follows the earth's surface and provides reliable short-range communication, strongest on MF and lower frequencies and fading quickly at VHF.

Maximum Usable Frequency: the highest frequency that the ionosphere will refract back to a given point at a given time, above which a sky-wave path fails.

The conductor or assembly that radiates and receives radio energy, whose length, height, and grounding strongly affect range, efficiency, and the standing wave ratio of a transmitter.

Voltage Standing Wave Ratio: a measure of how well an antenna system matches the transmitter, where a value near 1:1 is good and a high value wastes power and may damage equipment.

Unwanted radio energy that degrades reception, caused by other transmitters, faulty equipment, or electrical noise, and which must be avoided or reported under radio regulations.

Electromagnetic compatibility: the ability of electronic equipment to work without emitting excessive radio noise and without being disturbed by the emissions of nearby equipment on board.

The connection of radio and electrical equipment to a common reference such as the hull or a dedicated earth plate, reducing noise, improving antenna performance, and limiting shock and fire risk.