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The UK Hidrographic Office series of ALRS publications (6 Volumes) is
a comprehensive source of information covering all aspects of Maritime
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:
AOR-E is Atlantic Ocean Region East. This region is one of the four Inmarsat satellite coverage area's
AOR-W is Atlantic Ocean Region West. This region is one of the four Inmarsat satellite coverage area's
Automatic Request for Repetition, telex mode used to send mainly routine message from one transmitter to one receiver
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.
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).
Space System for the Search of Vessels in Distress
DTE, Data Terminal Equipment is an end instrument that converts user information into signals or reconverts received signals.
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.
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.
Forward Error Correction, telex mode used to send mainly priority message (distress, urgency or safety) from one transmitter to many receivers
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.
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.
Gross Tonnage - Size of the ship, calculated as a function of the volume of all ship's enclosed spaces.
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.
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 is the connector by which a computer exchanges information with the outside world e.g. GPS position information.
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).
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 is Indian Ocean Region. This region is one of the four Inmarsat satellite coverage area's
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.
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).
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.
Lowest Usable Frequency is defined as the frequency at below which the signal falls below the minimum strength required for satisfactory reception.
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.
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.
Medium frequency - same mean as medium wave (MW). Frequency bands from 300 to 3000 kHz. For distress calls in sea area A2 Mfrequencies should be used.
MF/HF DSC radio
MF/HF RT radio
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.
Maritime Safety Information - Navigational and meteorological warnings, meteorological forecasts, and other urgent safety-related information broadcast to ships.
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)
Narrow Band Direct Printing
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.
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 Network Operations Centre. This centre is monitoring the entire network in relation to the communication.
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 is Pacific Ocean Region. This region is one of the four Inmarsat satellite coverage area's
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.
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.
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.
Search and Rescue Satellite-Aided Tracking
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 is the Satellite Control Centre. This centre is monitoring all the satellites of the entire network in relation to their proper functioning.
Ship Earth Station - Ship's device used to communicate via an Inmarsat
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.
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.
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.
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.
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.
Very High Frequency - frequency band extending between 156 MHz and 174 MHz that contains 57 individual VHF CH (channels).
VHF DSC 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.