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Information about Navtex

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A NAVTEX receiver prints an incoming message.
NAVTEX 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. It was developed to provide a low-cost, simple, and automated means of receiving this information aboard ships at sea within approximately 370 km (200 nautical miles) of shore. NAVTEX stations in the U.S. are operated by the United States Coast Guard. There are no user fees associated with receiving NAVTEX broadcasts.

Where the messages contain weather forecasts, an abbreviated format very similar to the shipping forecast is used.

NAVTEX is a component of the International Maritime Organization/International Hydrographic Organization 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) mandated certain classes of vessels must carry NAVTEX, beginning August 1, 1993.

NAVTEX receivers which are approved for GMDSS contain an internal printer and cost between $800-$1500. A new generation of NAVTEX receivers intended for non-GMDSS applications such as the recreational community is now entering the marketplace. These receivers include features such as LCD screens and RS-232 output and have a purchase price in the $300-$500 range. In the UK they can be purchased for £115.

NAVTEX Message Format

NAVTEX messages are transmitted using binary frequency-shift keying (BFSK) at 100 bit/s and a 170 Hz frequency shift. The characters are encoded using the 7-bit CCIR 476 character set and basic error detection is enabled by employing forward error correction (FEC). This is the same format as the SITOR-B (AMTOR) format.

Every NAVTEX message is preceded by a phasing signal of around ten seconds then a start of message group, "ZCZC", followed by four characters B1, B2, B3 and B4.

B1 is an alpha character identifying the station, and B2 is an alpha character used to identify the subject of the message. Receivers use these characters to reject messages from certain stations or if the message contains subjects of no interest to the user.

B3 and B4 are two-digit numerics identifying individual messages, used by receivers to keep already received messages from being repeated.

A message containing the B1,2,3,4 characters of 'FE01' from a U.S. NAVTEX Station indicate that this is a weather forecast message from Boston MA.

NAVTEX message example: 
>
(start of phasing signals >=10 seconds)
ZCZC
B1,B2,B3,B4
Time of message transmission in UTC (optional)
Message Text ...
NNNN
(end of message phasing signals for >=5 seconds before next message)

Start of message

ZCZC begins the message.

Transmitter identity (B1)

This character defines the transmitter identity and its associated coverage area.

Subject indicator character (B2)

The subject indicator character is used by the receiver to identify different classes of messages below. The indicator is also used to reject messages concerning certain optional subjects which are not required by the ship (e.g. LORAN C messages might be rejected in a ship which is not fitted with a LORAN C receiver).

NAVTEX broadcasts use following subject indicator characters:

ANavigational warnings 1
BMeteorological warnings 1
CIce reports
DSearch & rescue information, and pirate warnings 1
EMeteorological forecasts
FPilot service messages
GDECCA messages
HLORAN messages
IOMEGA messages (note OMEGA has been discontinued)
JSATNAV messages (i.e. GPS or GLONASS)
LNavigational warnings - additional to letter A (Should not be rejected by the receiver)
VNotice to fishermen (U.S. only - currently not used)
WEnvironmental (U.S. only - currently not used)
X
YSpecial services - allocation by IMO NAVTEX Panel
ZNo message on hand


Note: Receivers use the B2 character to identify messages which, because of their importance, can not be rejected (designated by a 1). The subject indicator characters B, F and G are normally not used in the United States since the National Weather Service normally includes meteorological warnings in forecast messages. Meteorological warnings are broadcast using the subject indicator character E. U.S. Coast Guard District Broadcast Notices to Mariners affecting ships outside the line of demarcation, and inside the line of demarcation in areas where deep draft vessels operate, use the subject indicator character A.

Serial number of message (B3, B4)

These two characters define the serial number of each B2 message type (class). Generally serial numbers start with the numbers '01', however in special circumstances, the numbers begin with '00'. This forces the receiver to print the message.

Time of origin

The time of the transmission of the message is in UTC.

Message text

The full text of the message follows.

End of message

The end of the message is asserted when the characters "NNNN" are received.

Technical Information

NAVTEX broadcasts are primarily made on Medium frequencies of 518 kHz or 490 kHz and using narrow-band direct printing (NBDP), 7-unit forward error correcting (FEC or, Mode B) transmission and the CCIR-476 character set. This type of transmission is also used in Amateur radio, where it is known as AMTOR. AMTOR Broadcasts use 100 baud FSK modulation, with a frequency shift of 170 Hz.

The international NAVTEX frequency is 518 kHz USB. Regional transmission of NAVTEX uses 490 kHz specifically for broadcasts in local languages other than English. It is not used in the U.S.

NAVTEX-type Marine Safety Information (MSI) transmissions also take place on HF at 4209.5 kHz using FEC mode.

Message Reception

Commercial receivers are available for installation into vessels. These are designed to operate unattended and either record messages on to paper or to the receiver's internal memory for later review. There are also a number of software packages available allowing messages to be decoded by a PC with a suitable receiver connected to the computer's soundcard. Any general communications receiver capable of audio reception at 518 kHz or 490 kHz single sideband can be used.

NAVTEX via Internet

Some organisations have gateways through which web users can access the NAVTEX bulletins using a browser:

Sources

NAVTEX MF Transmitters NAVTEX decoders
Medium frequency (MF) refers to radio frequencies (RF) in the range of 300 kHz to 3000 kHz. Part of this band is the medium wave (MW) AM broadcast band.
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United States Coast Guard (USCG) is at all times a branch of the U.S. military, a maritime law enforcement agency, and a federal regulatory body. The Coast Guard has eleven statutory missions: Migrant Interdiction, Defense Readiness, Drug Interdiction, Ports, Waterways and
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The Shipping Forecast is a four-times-daily BBC radio broadcast of weather reports and forecasts for the seas around the coasts of Britain and Ireland.

It is produced by the UK Meteorological Office (part of MOD) and broadcast by BBC Radio 4 on behalf of the Maritime and
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The International Maritime Organization (IMO), formerly known as the Inter-Governmental Maritime Consultative Organization (IMCO), was established in 1948 through the United Nations to coordinate international maritime safety and related practices.
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Headquarters
(and largest city)
Official languages French, English
Establishment 1921
Website
[1] The International Hydrographic Organization
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The Global Maritime Distress Safety System (GMDSS) 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, boats and aircraft.
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The International Convention for the Safety of Life at Sea (SOLAS) is the most important treaty protecting the safety of merchant ships. The first version of the treaty was passed in 1914 in response to the sinking of the RMS Titanic.
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liquid crystal display (commonly abbreviated LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector.
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In telecommunications, RS-232 (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly used in computer serial ports.
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Frequency-shift keying (FSK) is a modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The most common form of frequency shift keying is 2-FSK.
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In telecommunication, forward error correction (FEC) is a system of error control for data transmission, whereby the sender adds redundant data to its messages, which allows the receiver to detect and correct errors (within some bound) without the need to ask the sender for
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AMTOR is a specialised form of RTTY protocol. The term is an acronym for AMateur Teleprinting Over Radio and is derived from the commercial SITOR system (Simplex Telex Over radio) developed primarily for maritime use in the 1970s.
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Loran can refer to one of the following:
  • LORAN, the terrestrial radio-based navigation system.
  • Loran (cassette), a brand of blank audio cassette made out of Lexan plastic.

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The Decca Navigator System was a hyperbolic low frequency radio navigation system (also known as multilateration) that was first deployed during World War II when the Allied forces needed a system which could be used to achieve accurate landings.
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Loran can refer to one of the following:
  • LORAN, the terrestrial radio-based navigation system.
  • Loran (cassette), a brand of blank audio cassette made out of Lexan plastic.

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OMEGA was the first truly global radio navigation system for aircraft, operated by the United States in cooperation with six partner nations.

OMEGA was originally developed by the United States Navy for military aviation users.
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Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). 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
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GLONASS (Russian: ГЛОНАСС - ГЛОбальная НАвигационная
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The three-letter abbreviation IMO may have several meanings, depending on context:
  • Idiopathic Massive Osteolysis (Gorham's Disease)
  • In my opinion – Internet slang
  • Institute for Marketecology

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National Weather Service

Agency overview
Formed February 9, 1870

Jurisdiction Federal government of the United States
Headquarters Silver Spring, Maryland

Annual Budget

Agency Executive
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Amateur radio, often called ham radio, is both a hobby and a service that uses various types of radio communications equipment to communicate with other radio amateurs for public service, recreation and self-training.
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AMTOR is a specialised form of RTTY protocol. The term is an acronym for AMateur Teleprinting Over Radio and is derived from the commercial SITOR system (Simplex Telex Over radio) developed primarily for maritime use in the 1970s.
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HF, Hf or hf can refer to:
  • Hafnium, a chemical element
  • Hartree-Fock, a calculation scheme
  • High frequency, the 3-30 MHz range of radio frequencies
  • Hydrofluoric acid, a highly corrosive solution of hydrogen fluoride in water

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Single-sideband modulation (SSB) is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth. It is closely related to vestigial sideband modulation (VSB) (see below).
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