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ALRS

The UK Hidrographic Office series of ALRS publications (6 Volumes) is
a comprehensive source of information covering all aspects of Maritime
Communications.

ALRS Volume 5

Admirality List of Radio Signals Volume 5 is a publication published by The United Kingdom Hydrographic Office. It contains a lot of up to date and well structured information about GMDSS:
  • Worldwide communication requirements for distress, search and rescue,
  • The only SOLAS compliant guide for GMDSS published in English,
  • Colour diagrams depicting worldwide operational DSC ranges,
  • Essential information for GMDSS students,
  • Easily updated from weekly Admirality Notices for Mariners,
  • Revised annually.

AOR-E

AOR-E is Atlantic Ocean Region East. This region is one of the four Inmarsat satellite coverage area's

AOR-W

AOR-W is Atlantic Ocean Region West. This region is one of the four Inmarsat satellite coverage area's

ARQ

Automatic Request for Repetition, telex mode used to send mainly routine message from one transmitter to one receiver

CER

CER (Character Error Rate/Ratio) : The CER, an indication of the radio signal reception property can also be added to the NAVTEX message. Usually it is added as text in the line before ZCZC indicator.


CES

CES means a Coast Earth Station working within the Inmarsat Network providing the connection between Inmarsat mobile users to other Inmarsat mobile users or the the landbased communication network. These stations are also called LES meaning Land Earth Stations.

CG

Coast Guard - A coast guard is a national organization responsible for various services at sea. However the term implies widely different responsibilities in different countries. In most countries is concerned with SAR (for example in the UK).

COSPAS

Space System for the Search of Vessels in Distress

CRS

Coast Radio Station - They are a maritime radio stations situated on shore which monitors radio distress frequencies, coordinate the radio traffic and relays ship-to-ship and ship-to-land communications. Some of CRSs are categorised as MRCCs or MRSCs or NAVTEX CRSs.

DSC

Digital Selective Calling - Broadcasting and receiving DSC Alerts is one of the major facilities on a VHF radio that is possible by VHF DSC controller. DSC alerts are used to “switch people on” to follow on with voice communication.

DTE

DTE, Data Terminal Equipment is an end instrument that converts user information into signals or reconverts received signals.

Duplex

Duplex channels are normally only used for communication between vessels and CRS and for port operations and ship movement. With duplex channels our transmission can only be heard by the CRS. However, all ship stations listening to the same channel can hear the CRS transmission.

EGC

EGC, enhanced group call transmitted via the Inmarsat C system. The messages which are broadcasted via this system are FleetNET or SafetyNET messages. The SafetyNET messages are used for transmission of MSI for area's outside the range of the NAVTEX stations within the coverage of Inmarsat satellites.

EPIRB

Emergency Position Indicating Radio Beacon - It is used as a distress alerting system, indicating to SAR authorities both the identity and position of a person or a vessel, which is in grave and imminent danger and requires immediate assistance.

FEC

Forward Error Correction, telex mode used to send mainly priority message (distress, urgency or safety) from one transmitter to many receivers

FleetNET

FleetNET are messages are messages adressed to a dedicated group of mobile stations like all ships from the same company or all ships from the same country (having the same nationality) transmitted via the Inmarsat C EGC system.

GMDSS

Global Maritime Distress and Safety System - The GMDSS is an important part of the IMO (International Maritime Organisation) SOLAS (Safety Of Life At Sea) convention. It is an internationally agreed-upon set of safety procedures, types of equipment, and communication protocols used to increase safety and make it easier to rescue distressed ships.

GPS

Global Positioning System - Utilizing a constellation of at least 24 Medium Earth Orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its location, speed, direction, and time. GPS receivers may be found also on ships, for example as a part of navigational equipment and in some models of EPIRBs. They are usualy connected to DSC radio communication equipment, for example VHF radio.

GT

Gross Tonnage - Size of the ship, calculated as a function of the volume of all ship's enclosed spaces.


HF

High frequency - same mean as long wave (LW). Frequency bands from 3 to 30 MHz. For distress calls in sea areas A3 and A4 HF frequencies should be used.


HRU

Hydrostatic Release Unit - It is a device that will automatically release the EPIRB once a depth of approximately 4-5 m is reached.

I/O connector

I/O connector is the connector by which a computer exchanges information with the outside world e.g. GPS position information.

IMO

International Maritime Organisation - IMO is the source of approximately 60 legal instruments that guide the regulatory development of its member states to improve safety at sea, facilitate trade among seafaring states and protect the maritime environment. The most well known is the International Convention for the Safety of Life at Sea (SOLAS).

INMARSAT

International Maritime Satellite Organisation - Inmarsat provides telephony and data services to users world-wide, via special terminals. An Inmarsat terminal contacts the satellite and communicates to a ground station through the satellite. It provides reliable communications services to a range of governments, aid agencies, media outlets and businesses needing to communicate in remote regions or where there is no reliable terrestrial network. Aside from its commercial services, Inmarsat provides GMDSS services to ships at no charge, as a public service.


IOR

IOR is Indian Ocean Region. This region is one of the four Inmarsat satellite coverage area's

ITU

International Telecommunication Union - the United Nations agency for information and communication technology issues

ITU List of Coast Stations and Special Services (List-IV)

ITU List of Coast Station and Special Service Station (List-IV) : Tariffs and Taxes. Particulars of stations participating in GMDSS: MF, HF and VHF Digital Selective Calling; Coast Earth Stations; Stations broadcasting Maritime Safety Information (MSI); including those of NAVTEX service. call sign; selective call number and MMSI; hours of operation; frequencies in use; type and classes of emissions; hours of traffic lists and watch-keeping; etc. Particulars of stations used for maritime radio-navigation and of stations providing special transmissions for use by ship and other stations. Information provided: Direction finding and DF calibration stations; Radio beacons and radar beacons stations;
Stations transmitting time and standard frequencies; Stations transmitting Ursigrams (bulletin about solar activities and the ionosphere); Stations transmitting regular meteorological bulletin and notices to mariners; Stations transmitting medical advice.

LES

LES means a Land Earth Station working within the Inmarsat Network providing the connection between Inmarsat mobile users to other Inmarsat mobile users or the the landbased communication network. These stations are also called CES meaning Coast Earth Stations.

LRC

Long Range Certificate. Just as every driver needs a license to drive a car, operators of marine radios also require a license. Radio operators on leisure or commercial vessels not under the regulation of the SOLAS convention that are fitted with long range communications (MF/HF radio) or satellite equipment must be qualified to a minimum standard. This standard is the GMDSS LRC (Long Range Certificate).

LT

Local Time - A time zone is a region of the Earth that has adopted the same standard time, usually referred to as the local time. Most adjacent time zones are exactly one hour apart, and by convention compute their local time as an offset from UTC.

LUF

Lowest Usable Frequency is defined as the frequency at below which the signal falls below the minimum strength required for satisfactory reception.

LUT

Local User Terminal - LEOLUT and GEOLUT Earth based ground stations, receive and process Distress alerts from 406 MHz EPIRBs relaying Distress information, comprising casualty ID, Position and UTC time, to MCC.

MCC

Mission Control Centres - Their main purpose and function is to relay EPIRB Distress alert information to the appropriate MRCC who coordinates the deployment of SAR units in the SAR region in which the casualty is located.

MES

Mobile Earth Station - The generic name used to describe an Inmarsat-approved terminal which is allowed to access the network, and applicable to both maritime and land mobile communications.

METAREA

The world is divided into 16 (plus 5 polar - not operational yet) METeorogical AREAs. This are regions of the seas, with same outer boundaries as NAVAREA, for which specified nations have the responsibility for the co-ordination of the provision of meteorological information. METAREAs are usually divided into sea areas for weather forecast broadcast using EGC, NAVTEX or voice messages through VHF, MF or HF.


MF

Medium frequency - same mean as medium wave (MW). Frequency bands from 300 to 3000 kHz. For distress calls in sea area A2 MF frequencies should be used.

MF/HF DSC radio

It is a transmitting-receiving system, which allows the operator to either transmit or receive information on the marine MF (Medium Frequency) and HF (High Frequency) band only by DSC (Digital Selective Calling).

MF/HF radio

is a transmitting-receiving system, which allows the operator to either transmit or receive information on the marine MF (Medium Frequency) and HF (High Frequency) band.

MF/HF RT radio

It is a transmitting-receiving system, which allows the operator to either transmit or receive information on the marine MF (Medium Frequency) and HF (High Frequency) band only by voice.

MMSI

Maritime Mobile Service Identity - MMSI is a unique 9 digit number and acts in the same way as a telephone number. The MMSI allows radio operator to make automatic calls through VHF DSC radio and is the identity that is automatically transmitted within DSC calls. These MMSI numbers are issued by the appropriate authorities in the country of registration of the vessel and can be referenced back to a database of information about the vessel and it’s owners and so forth.

MRCC

Maritime Rescue and Coordination Centre - All SAR activities are organized by MRCCs and MRSCs within specified navigational sea areas normally bordering their coastlines.

MRSC

Maritime Rescue Sub Centres - All SAR activities are organized by MRCCs and MRSCs within specified navigational sea areas normally bordering their coastlines.

MSI

Maritime Safety Information - Navigational and meteorological warnings, meteorological forecasts, and other urgent safety-related information broadcast to ships.

MUF

Maximum Usable Frequency is the frequency at which radio communications just starts to fail. It is caculated by formula: MUF=f0/cos alpha where is
h= layer height
f0= layer density
alpha = arc tg ((d/2)/h)

NAVAREA

NAVigational AREA - Under the WWNWS the world's oceans are divided into 16 geographical sea areas, called NAVAREAs which are identified by Roman numerals and comprises NAVTEX CRS identified by a single letter of the alphabet from A to Z.

NAVTEX

NAVigational TELex - It is a system for transmitting MSI in GMDSS Sea Area A1 and A2.

NBDP

Narrow Band Direct Printing

NCS

NCS Network Co-ordination Station. This is the land earth station within the Inmarsat Oceanan Region which is responsible for a smooth communication proces. This station is directing the mobile users and the Land Earth Stations to the right appointed channel.

NM

Nautical Mile - A nautical mile or sea mile is a unit of length. It corresponds approximately to one minute of latitude along any meridian. The international standard definition is: 1 NM = 1,852 m exactly.

NOC

NOC Network Operations Centre. This centre is monitoring the entire network in relation to the communication.

OTF

Optimum Traffic Frequency is usually the most effective frequency for ionospheric reflection of radio waves between two specified points on Earth. Commonly is taken as 85 % of MUF.

POR

POR is Pacific Ocean Region. This region is one of the four Inmarsat satellite coverage area's

PSA

Point of Service Activation. The PSA is an entity that has concluded a contract with Inmarsat for the activation and maintenance of records and accounts of Inmarsat terminals. A PSA in some cases can be a one-stop shop for service activation, terminal equipment provision and customer support.

PTT

Press To Transmit - PTT or “PRESSEL” switch is usually mounted on one side of the microphone or in the middle of the handgrip of a telephone style handset connected to the marine radio communication equipment. To operate correctly, you have to press it in order to switch the radio from receive mode to transmit mode and release it in order to revert to receive mode.

R/T

Radio Telephony.
Voice communications.

RCC

Rescue and Coordination Centre - This is a centre used for coordination of all SAR activities within specified areas. When a RCC only is operating in the maritime Search and Rescue it's called a MRCC.

Receiver

A receiver is a device, such as a part of a radio, television set, or telephone, that receives incoming radio signals and converts them to perceptible forms, such as sound or light.

RT

Radio Telephony - Radio communication known as RT uses a Tx (radio transmitter) to send out radio waves of a certain frequency and a Rx (radio receiver) to receive the radio waves at the same frequency. Radio waves consist of electro-magnetic energy in specific frequency bands within the radio frequency spectrum. Frequency of waves means the number of occurrences of a wave per second. For example, marine VHF RT works in the VHF part of the marine radio frequency spectrum, which extends between 156 MHz to 174 MHz.

Rx

radio receiver

SafetyNET

SafetyNET is a system that is transmitting EGC MSI messages via the Inmarsat C system which will be received by all vessels that are logged-in to the satellite
that broadcasts MSI for these international NAVAREA/METAREA's.

SAR

Search And Rescue - SAR is an operation mounted by emergency services, often well-trained volunteers, to find someone believed to be in distress, lost, sick or injured at sea, whether close to shore or not.

SARSAT

Search and Rescue Satellite-Aided Tracking

SART

Search and Rescue [Radar] Transponder - It is a portable device, which is used as a complimentary distress alerting system. It enables any ship/airplane/helicopter in the area to locate survivors easily by just the use of their proper radar system.

SCC

SCC is the Satellite Control Centre. This centre is monitoring all the satellites of the entire network in relation to their proper functioning.

SES

Ship Earth Station - Ship's device used to communicate via an Inmarsat

Simplex

Simplex is the communication method where both transmitter and receiver are operating on a single (or the same) frequency. On simplex channels it isn't possible to transmit and receive simultaneously. Simplex channels are mainly used for Distress, Urgency, Safety and Routine Calling purposes, port, pilotage, harbour and inter-ship operations.

SMCP

The SMCP have been constructed considering the most basic knowledge of English and drafted in a simplified version of maritime English. It includes phrases for use in routine situations such as berthing as well as standard phrases and responses for use in emergency situations.

SOLAS

Safety Of Life At Sea - This International Convention is the most important treaty protecting the safety of merchant ships. It divides all vessels in 2 groups: SOLAS and non SOLAS vessels. SOLAS vessels need to comply with GMDSS sattelite and radio equipment carriage requirements. SOLAS vessels are all cargo ships of 300 GT and upwards and all passenger ships with some exceptions. Detailed SOLAS vessels definition may be found in ALRS Volume 5. Non SOLAS vessels do not need to comply with GMDSS radio equipment carriage requirements, but will increasingly use it, because that causes an important increase of the safety at sea. Some countries have incorporated GMDSS radio equipment carriage requirements into their domestic marine legislation that is valid for non SOLAS vessels under their flag.

SRC

Short Range Certificate - Just as every driver needs a licence to drive a car, operators of marine radios also require a licence. The person operating VHF radio system sailing in GMDSS Sea Area A1 must be qualified to a minimum standard. This standard is the GMDSS SRC.

SSB

Single-sideband modulation (SSB) is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth
The method by which audio, (information), is impressed on a radio signal is called modulation. To modulate a radio wave is to add information to it that can be received on a receiver for some useful purpose. It is a very efficient method of superimposing your voice or other information on a radio wave and the transmission of that radio wave.

Tx

radio transmitter

UTC

Coordinated Universal Time - It is a high-precision atomic time standard. Time zones around the world are expressed as positive or negative offsets from UTC. Local time is UTC plus the time zone offset for that location, plus an offset (typically +1) for daylight saving time, if in effect.

VHF

Very High Frequency - frequency band extending between 156 MHz and 174 MHz that contains 57 individual VHF CH (channels).

VHF CH

VHF Channel - The marine frequency band for VHF radio communication, extending between 156 MHz and 174 MHz, contains 57 individual VHF CH (channels) numbered consecutively from VHF CH 1 to VHF CH 28 and from VHF CH 60 to VHF CH 88.

VHF DSC radio

VHF DSC radio: It is a transmitting-receiving system, which allows the operator to either transmit or receive information on the marine VHF (Very High Frequency) band only by DSC (Digital Selective Calling).

VHF radio

is a transmitting-receiving system, which allows the operator to either transmit or receive information on the marine VHF (Very High Frequency) band

VHF RT radio

It is a transmitting-receiving system, which allows the operator to either transmit or receive information on the marine VHF (Very High Frequency) band only by voice.

WWNWS

World Wide Navigation Warning Service - It is a co-ordinated global service for the promulgation of navigational warnings. In GMDSS Sea Area A1 and A2 they are broadcasted via NAVTEX system, and outside given areas via SafetyNET system.


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