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  • 8/11/2019 GMDSS Paper work


    T H E G L O B A L M A R I T I M E D I S T R E S S A N D S A F E T Y S Y S T E MG M D S S

    Student: Constantin Gabriel

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    INTRODUCTIONThe Global Maritime Distress and Safety System is the

    technical, operational and administrative structure formaritime distress and safety communications worldwide. Itwas established in 1988 by the International MaritimeOrganization (IMO) which adopted a revised text of Chapter IVof the International Convention for the Safety of Life at Sea,1974, (SOLAS) - dealing with Radiocommunications - and wasimplemented globally between 1992 and 1997. The GMDSSestablishes the radiocommunications equipment that ships arerequired to carry, how this equipment shall be maintained and

    how it is used, and provides the context within whichgovernments should establish the appropriate shore-basedfacilities to support GMDSS communications.

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    Marine VHF radio refers to the radio frequency range

    between 156.0 and 162.025 MHz, inclusive. In the official language

    of the ITU the band is called the VHF maritime mobile band.

    It's installed on all large ships and most seagoing small

    craft. It is also used, with slightly different regulation, on rivers and

    lakes. It is used for a wide variety of purposes, including

    summoning rescue services and communicating with harbours,

    locks, bridges and marinas, and operates in the very high

    frequency (VHF) range, between 156 and 162.025 MHz. Although it

    is widely used for collision avoidance, its use for that purpose iscontentious and is strongly discouraged by some countries,

    including the UK

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    A marine VHF set is a combined transmitter andreceiver and only operates on standard, international

    frequencies known as channels. Channel 16 (156.8 MHz) is

    the international calling and distress channel. Transmission

    power ranges between 1 and 25 watts, giving a maximum

    range of up to about 60 nautical miles (111 km) between

    aerials mounted on tall ships and hills, and 5 nautical miles (9

    km; 6 mi) between aerials mounted on small boats at sea

    level. Frequency modulation (FM) is used, with vertical

    polarization, meaning that antennas have to be vertical in

    order to have good reception.

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    Modern-day marine VHF radios not onlyoffer basic transmit and receive capabilities.

    Permanently mounted marine VHF radios on

    seagoing vessels are required to have certification

    of some level of "Digital Selective Calling" (DSC)

    capability, to allow a distress signal to be sent with

    a single button press.

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    Marine VHF mostly uses "simplex" transmission, where

    communication can only take place in one direction at a time. A

    transmit button on the set or microphone determines whether it is

    operating as a transmitter or a receiver. The majority of channels,

    however, are set aside as "semi-duplex" transmission channels

    where communication can take place in both directionssimultaneously. Each semi-duplex channel has two frequency

    assignments. Semi-Duplex channels can be used to place calls on

    the public telephone system for a fee via a marine operator. This

    facility is still available in some areas, though its use has largelydied out. Marine VHF radios can also receive weather radio

    broadcasts, where they are available.

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    A Search And Rescue Transponder (SART) is a self-

    contained, waterproof transponder intended for emergency use

    at sea. These devices may be either a radar-SART, or a GPS-

    based AIS-SART (automatic identification system SART).

    The radar-SART is used to locate a survival craft ordistressed vessel by creating a series of dots on a rescuing

    ship's radar display. A SART will only respond to a 9 GHz X-band

    (3 cm wavelength) radar. It will not be seen on S-band (10 cm) or

    other radar. Shipboard Global Maritime Distress Safety System

    (GMDSS) include one or more search and rescue locating


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    The radar-SART may be triggered by any X-bandradar within a range of approximately 8 nautical miles (15

    kilometers). Each radar pulse received causes the SART

    to transmit a response which is swept repetitively across

    the complete radar frequency band. When interrogated, itfirst sweeps rapidly (0.4 microsecond) through the band

    before beginning a relatively slow sweep (7.5

    microseconds) through the band back to the starting


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    This process is repeated for a total of twelvecomplete cycles. At some point in each sweep, the

    radar-SART frequency will match that of the

    interrogating radar and be within the pass band of

    the radar receiver. If the radar-SART is within

    range, the frequency match during each of the 12

    slow sweeps will produce a response on the radar

    display, thus a line of 12 dots equally spaced byabout 0.64 nautical mile (1.2 km) will be shown.

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    When the range to the radar-SART is reduced toabout 1 nautical mile (2 km), the radar display may show

    also the 12 responses generated during the fast sweeps.

    These additional dot responses, which also are equally

    spaced by 0.64 nautical mile (1.2 km), will be interspersedwith the original line of 12 dots. They will appear slightly

    weaker and smaller than the original dots.

    SARTs are typically cylindrical, about the size of a

    person's forearm, and brightly coloured.


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    Portable VHF Transceiver

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    Usual portable VHF transreceiver specifications:

    Built-in Parallel 12 Channel GPS Receiver

    SC-101 DSC Distress Call Automatically BroadcastsLat/Lon and Vessel ID

    6 Watt Transmit power

    Volume & Squelch indication on display

    DSC Position Request

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    NMEA output of DSC, DSE, GLL, RMC, GSA, GSV andGGAChannel names on display

    SOS Strobe light

    Submersible Speaker Microphone Jack 1150 mAh Rechargeable Li-Ion battery

    AC and 12 VDC Chargers included

    Position information shown on the display


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    NAVTEX Receiver

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    NAVTEX (Navigational Telex) is an international automated

    medium frequency direct-printing service for delivery of

    navigational and meteorological warnings and forecasts, as well as

    urgent marine safety information to ships.Navtex was developed to

    provide a low-cost, simple, and automated means of receiving this

    information aboard ships at sea within approximately 370 km (200nautical miles) off shore.

    There are no user fees associated with receiving NAVTEX

    broadcasts, as the transmissions are typically transmitted from the

    National Weather Authority (Italy) or Navy or Coast Guard (as inthe US) or national navigation authority (Canada).

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    Where the messages contain weather forecasts, anabbreviated format very similar to the shipping forecast is


    NAVTEX is a component of the International

    Maritime Organization/International HydrographicOrganization Worldwide Navigation Warning Service

    (WWNWS). NAVTEX is also a major element of the Global

    Maritime Distress Safety System (GMDSS). International

    Convention for the Safety of Life at Sea (SOLAS) mandatedcertain classes of vessels must carry NAVTEX, beginning

    August 1, 1993

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    NAVTEX transmissions are also called narrow-band direct

    printing (NBDP). The transmissions are layered on top of SITOR

    collective B-mode. SITOR-B is a forward error correcting (FEC) broadcast

    that uses the CCIR 476 character set.

    SITOR-B is also used in amateur radio, where it is known as

    AMTOR-B or AMTOR-FEC. NAVTEX / SITOR / AMTOR broadcasts use100 baud FSK modulation with a frequency shift of 170 Hz.

    NAVTEX broadcasts are primarily made on the Medium

    frequencies of 518 kHz and 490 kHz. The international NAVTEX

    frequency is 518 kHz, and these broadcasts should always be in English.National transmission of NAVTEX uses 490 kHz specifically for

    broadcasts in local languages.

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    A NAVTEX message is built on SITOR collective B-mode and consists


    a phasing signal of at least ten seconds;

    the four characters "ZCZC" that identify the end of phasing;

    a single space; four characters B1, B2, B3and B4;

    a carriage return and a line feed;

    the information;

    the four ch