Navtex
Encyclopedia
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) off 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.
. 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 use 100 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. Regional transmission of NAVTEX uses 490 kHz specifically for broadcasts in local languages. It is not used in the U.S.
NAVTEX Marine Safety Information (MSI) transmissions also take place on HF
at 4209.5 kHz using FEC mode.
(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.
A NAVTEX message is built on SITOR
collective B-mode and consists of:
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.
For example, a message containing B1B2B3B4 characters of 'FE01' from a U.S. NAVTEX Station indicates a weather forecast message from Boston MA.
NAVTEX message example:
C messages might be rejected in a ship which is not fitted with a LORAN C receiver).
NAVTEX broadcasts use following subject indicator characters:
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.
Details of all transmitting stations and their schedules may be found at www.pcnavtex.com
output and have a purchase price in the $300–$500 range. In the UK they can be purchased for £115. There are also a number of NAVTEX engines available that do not have any user interface, and just output decoded data in RS-232
format, either as a simple ASCII
data stream, or using the NMEA NAVTEX sentences, or their own proprietary protocol.
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 MF Transmitters
NAVTEX Control and Monitoring Systems
NAVTEX decoders
NAVTEX Station Lists & Information
Medium frequency
Medium frequency refers to radio frequencies in the range of 300 kHz to 3 MHz. Part of this band is the medium wave AM broadcast band. The MF band is also known as the hectometer band or hectometer wave as the wavelengths range from ten down to one hectometers...
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) off shore. NAVTEX stations in the U.S. are operated by the United States Coast Guard
United States Coast Guard
The United States Coast Guard is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the military branches for having a maritime law enforcement mission and a federal regulatory agency...
. 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
Shipping Forecast
The Shipping Forecast is a four-times-daily BBC Radio broadcast of weather reports and forecasts for the seas around the coasts of the British Isles. It is produced by the Met Office and broadcast by BBC Radio 4 on behalf of the Maritime and Coastguard Agency. The forecasts sent over the Navtex...
is used.
NAVTEX is a component of the International Maritime Organization
International Maritime Organization
The International Maritime Organization , formerly known as the Inter-Governmental Maritime Consultative Organization , was established in Geneva in 1948, and came into force ten years later, meeting for the first time in 1959...
/International Hydrographic Organization
International Hydrographic Organization
The International Hydrographic Organization is the inter-governmental organisation representing the hydrographic community. It enjoys observer status at the UN and is the recognised competent authority on hydrographic surveying and nautical charting...
Worldwide Navigation Warning Service (WWNWS). NAVTEX is also a major element of the Global Maritime Distress Safety System
Global Maritime Distress Safety System
The Global Maritime Distress and Safety System 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....
(GMDSS). International Convention for the Safety of Life at Sea
International Convention for the Safety of Life at Sea
The International Convention for the Safety of Life at Sea is an international maritime safety treaty. The SOLAS Convention in its successive forms is generally regarded as the most important of all international treaties concerning the safety of merchant ships.- History :The first version of the...
(SOLAS) mandated certain classes of vessels must carry NAVTEX, beginning August 1, 1993.
Technical Information
NAVTEX transmissions are also called narrow-band direct printing (NBDP). The transmissions are layered on top of SITOR collective B-modeSITOR
SITOR is a system for transmitting text messages. Although it uses the same frequency-shift keying modulation used by regular radioteletype , SITOR uses error detection, redundancy, and/or retransmission to improve reliability.There are two SITOR modes:* SITOR-A is used for point to point links...
. SITOR-B is a forward error correcting
Forward error correction
In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....
(FEC) broadcast that uses the CCIR 476 character set. SITOR-B is also used in amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
, where it is known as AMTOR-B
AMTOR
AMTOR is a type of telecommunications system that consists of two or more electromechanical teleprinters in different locations that send and receive messages to one another. AMTOR is a specialized form of RTTY protocol...
or AMTOR-FEC. NAVTEX/SITOR/AMTOR broadcasts use 100 baud FSK modulation with a frequency shift of 170 Hz.
NAVTEX broadcasts are primarily made on the Medium frequencies
Medium frequency
Medium frequency refers to radio frequencies in the range of 300 kHz to 3 MHz. Part of this band is the medium wave AM broadcast band. The MF band is also known as the hectometer band or hectometer wave as the wavelengths range from ten down to one hectometers...
of 518 kHz and 490 kHz. The international NAVTEX frequency is 518 kHz, and these broadcasts should always be in English. Regional transmission of NAVTEX uses 490 kHz specifically for broadcasts in local languages. It is not used in the U.S.
NAVTEX Marine Safety Information (MSI) transmissions also take place on HF
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
at 4209.5 kHz using FEC mode.
NAVTEX Message Format
NAVTEX messages are transmitted using binary frequency-shift keyingFrequency-shift keying
Frequency-shift keying is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK . BFSK uses a pair of discrete frequencies to transmit binary information. With this scheme, the "1" is called...
(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
Forward error correction
In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....
(FEC). This is the same format as the SITOR-B (AMTOR
AMTOR
AMTOR is a type of telecommunications system that consists of two or more electromechanical teleprinters in different locations that send and receive messages to one another. AMTOR is a specialized form of RTTY protocol...
) format.
A NAVTEX message is built on SITOR
SITOR
SITOR is a system for transmitting text messages. Although it uses the same frequency-shift keying modulation used by regular radioteletype , SITOR uses error detection, redundancy, and/or retransmission to improve reliability.There are two SITOR modes:* SITOR-A is used for point to point links...
collective B-mode and consists of:
- 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, B3 and B4 (see below)
- a carriage return and a line feed
- the information
- the four characters "NNNN" to identify the end of information
- a carriage return and two line feeds
- either
- 5 or more seconds of phasing signal and another message starting with "ZCZC" or
- an end of emission idle signal α for at least 2 seconds.
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.
For example, a message containing B1B2B3B4 characters of 'FE01' from a U.S. NAVTEX Station indicates a weather forecast message from Boston MA.
NAVTEX message example:
(phasing signals >= 10 seconds)
ZCZC FE01
(message text ...)
NNNN
(end of message phasing signals for >= 2 seconds before next 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. LORANLORAN
LORAN is a terrestrial radio navigation system using low frequency radio transmitters in multiple deployment to determine the location and speed of the receiver....
C messages might be rejected in a ship which is not fitted with a LORAN C receiver).
NAVTEX broadcasts use following subject indicator characters:
| A | Navigational warnings 1 |
| B | Meteorological warnings 1 |
| C | Ice reports |
| D | Search & rescue information, and pirate warnings 1 |
| E | Meteorological forecasts |
| F | Pilot service messages |
| G | AIS Automatic Identification System The Automatic Identification System is an automatic tracking system used on ships and by Vessel traffic services for identifying and locating vessels by electronically exchanging data with other nearby ships and AIS Base stations... messages |
| H | LORAN LORAN LORAN is a terrestrial radio navigation system using low frequency radio transmitters in multiple deployment to determine the location and speed of the receiver.... messages |
| I | Not used |
| J | SATNAV messages (i.e. GPS or GLONASS GLONASS GLONASS , acronym for Globalnaya navigatsionnaya sputnikovaya sistema or Global Navigation Satellite System, is a radio-based satellite navigation system operated for the Russian government by the Russian Space Forces... ) |
| K | Other electronic navaid messages |
| L | Navigational warnings - additional to letter A (Should not be rejected by the receiver) |
| T | Test transmissions (UK only - not official) |
| V | Notice to fishermen (U.S. only - currently not used) |
| W | Environmental (U.S. only - currently not used) |
| X | Special services - allocation by IMO IMO The three-letter acronym IMO may refer to:* International Mathematical Olympiad* International Maritime Organization** IMO ship identification number, unique identity numbers issued to seacraft * International Meteorological Organization... NAVTEX Panel |
| Y | Special services - allocation by IMO IMO The three-letter acronym IMO may refer to:* International Mathematical Olympiad* International Maritime Organization** IMO ship identification number, unique identity numbers issued to seacraft * International Meteorological Organization... NAVTEX Panel |
| Z | No 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
National Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...
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.NAVTEX Transmission Schedule
Each station identifier has a fixed 10 minute time slot, starting with A at 0000UTC. The time slots are repeated at 4 hour intervals. Within each time slot, a mix of navigation warnings, weather forecasts, ice information and other content may be sent, and this is normally according to a structured plan for that specific station. For example, in the first and third time slot they may decide to transmit navigation warnings, and weather forecasts in the others.Details of all transmitting stations and their schedules may be found at www.pcnavtex.com
NAVTEX receivers
NAVTEX receivers which are approved for GMDSS contain an internal printer and/or a scrollable display, 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-232RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
output and have a purchase price in the $300–$500 range. In the UK they can be purchased for £115. There are also a number of NAVTEX engines available that do not have any user interface, and just output decoded data in RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
format, either as a simple ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
data stream, or using the NMEA NAVTEX sentences, or their own proprietary protocol.
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:- United Kingdom Hydrographic Office
- Greece (Hellenic National Meteorological Service HNMS) (click on Maritime Bulletin)
- JCOMM official web site provides the marine weather information broadcast via Inmarsat-C SafetyNET
- Worldwide NAVTEX messages Messages from live receivers across the world including Japanese language messages
- Messages from a live receiver in Suffolk, England.
- Messages from a live receiver in Suffolk, England. sent via Twitter!
Media
External links
- http://www.nws.noaa.gov/om/marine/navtex.htm
- http://www.navcen.uscg.gov/?pageName=NAVTEX
NAVTEX MF Transmitters
- http://www.senderchile.cl
NAVTEX Control and Monitoring Systems
- http://www.icselectronics.co.uk ICS Electronics Home Page
NAVTEX decoders
- http://www.dxsoft.com/en/products/seatty/ (Windows/commercial)
- http://www.frisnit.com/navtex/ (Windows/Mac(Java)/free)
- http://www.winradio.com/home/ads-navtex.htm (Windows/commercial)
- http://www.blackcatsystems.com/software/multimode.html (Mac/commercial)
- http://www.coaa.co.uk/dscdecoder.htm (Windows/commercial)
- http://www.pcnavtex.com (Windows/commercial)
NAVTEX Station Lists & Information
- http://www.ndblist.info/navtex.htm
- http://www.pcnavtex.com/AboutNAVTEX/NAVTEXStations/tabid/63/Default.aspx