FCC MROP key terms

An FCC-issued operator license required to operate radiotelephone equipment on large commercial vessels and on vessels subject to GMDSS carriage rules; it is separate from the station's own radio license.

An FCC authorization for a vessel's radio equipment to transmit in the maritime mobile service. It names the station, lists its call sign, and specifies the frequencies and modes the vessel may use.

The unique letters-and-numbers identifier the FCC assigns to a licensed radio station. Operators give it at the beginning and end of a radiotelephone contact so the station can be identified.

A land-based maritime radio station, such as one operated at a harbor, port, or rescue center, that communicates with ships for distress, safety, navigation, and public correspondence traffic.

Radio traffic that a ship station exchanges with a coast station on behalf of passengers or crew, such as ship-to-shore telephone calls, as opposed to distress, urgency, or safety messages.

A nine-digit Maritime Mobile Service Identity programmed into a vessel's DSC radio and other equipment. It uniquely identifies the station in digital distress alerts and routine calls.

A GMDSS sea area within continuous VHF DSC alerting range of at least one shore station, in practice roughly 20 to 30 nautical miles from the coast, where alerting is by VHF Channel 70.

The section of the Federal Communications Commission's rules covering the maritime radio services, including station licensing, permitted frequencies, operating procedures, and required equipment aboard ships.

The VHF maritime channel at 156.800 MHz reserved for distress, urgency, and safety calling and for initial contact between stations. Routine conversations must move to a working channel.

The international spoken distress signal, transmitted three times in a row. It is used only when a vessel or person faces grave and imminent danger and immediate assistance is needed.

The international spoken urgency signal, repeated three times. It announces a serious situation about the safety of a vessel or person that has not yet become an immediate distress.

The international spoken safety signal, pronounced 'say-cure-ee-TAY' and repeated three times. It introduces an important navigational or weather warning that other stations should hear.

The first transmission announcing that a vessel is in distress, sent either as a spoken MAYDAY call on radiotelephone or as a digital DSC alert carrying the vessel's identity and position.

A distress call repeated on behalf of another station, used when a vessel hears a MAYDAY but cannot itself reach the distressed craft or a coast station to pass the information along.

All radiotelephone messages connected with a distress incident. It has absolute priority over every other kind of traffic, and other stations must keep silent until it ends.

Digital Selective Calling, a system built into marine VHF and MF/HF radios that sends a formatted digital message, including identity and position in distress, without anyone speaking.

An Emergency Position Indicating Radio Beacon. When activated in the water it transmits a satellite distress signal carrying the vessel's identity and position to search-and-rescue authorities.

A Search and Rescue Transponder carried in survival craft. When triggered it answers a searching radar with a distinctive row of dots on the radar screen, helping rescuers find the craft.

A receiver system that automatically prints or displays navigational warnings, weather forecasts, and search-and-rescue notices broadcast on a dedicated MF frequency, without the operator tuning anything.

The Global Maritime Distress and Safety System, an international framework of satellite and terrestrial radio equipment and procedures that lets vessels alert shore authorities and communicate during emergencies.

The VHF channel at 156.525 MHz set aside for Digital Selective Calling. No voice transmissions of any kind are allowed on this channel.

Three-minute intervals of radio silence observed at the start of each half hour on the MF radiotelephone distress frequency, reserved for distress calls and related traffic.

A written or electronic record kept at the station containing required entries such as distress and safety communications, equipment breakdowns, and the times of watches maintained.

Continuous monitoring of a designated frequency, typically VHF Channel 16 or the vessel's DSC channel, so that distress, urgency, and safety calls are heard and answered.

The VHF radiotelephone required on larger vessels for short, direct conversations between ships and with shore traffic services about navigation safety, normally conducted on Channel 13.

The VHF channel at 156.650 MHz designated for bridge-to-bridge navigation safety communications, kept to brief exchanges about course, speed, and passing arrangements.

A mode in which both stations transmit and receive on the same frequency, so only one station can speak at a time and the other must listen.

A mode in which the ship transmits on one frequency and receives on another, so both stations can speak at once through the paired frequencies of a shore station.

The button on a radiotelephone handset that must be held while speaking and released to listen. Pausing briefly after pressing it prevents the first word being cut off.

Standardized procedure words such as OVER, ROGER, and OUT used in radiotelephone traffic. OUT ends the exchange and means no reply is expected.

Voltage Standing Wave Ratio, a measure of how well the antenna and feed line match the transmitter. A high reading means power is reflected back, reducing range and possibly damaging the transmitter.

The amount by which an antenna concentrates radiated power in a particular direction compared with a reference antenna, expressed in decibels; higher gain means a narrower, longer-reaching pattern.

The shielded feed line that carries radio-frequency energy from a transmitter to an antenna: an inner conductor, insulation, a braided outer shield, and a protective jacket.

A receiver control that mutes the loudspeaker unless a signal strong enough to be understood is received, so background noise stays quiet between transmissions.

The radio-frequency power a transmitter delivers to the antenna system, usually selectable on marine VHF radios between about 1 watt for short range and 25 watts for maximum range.

Connecting radio equipment, antennas, and their power returns to the vessel's common ground or hull so that stray currents, static charges, and interference have a safe path.

A protective device in a power lead that melts and opens the circuit when current exceeds its rating, protecting the radio and wiring from overheating and fire.

The absorption of radio-frequency energy by people near transmitting antennas. Operators should stay clear of antennas while transmitting to keep exposure within safe limits.