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Navtex

NAVTEX (Navigational Telex) is a international automated medium frequency direct-printing service for delivery of navigational and meterological warnings and forecasts, as well as urgent marine safety information to ships.


NAVTEX is a component of the international Maritime Organization/International Hydrographic Organization Worldwide Navigation warning Service (WWNWS). NAVTEX is also a mojor element of the Global Maritime Distreess Safety System (GMDSS) . International convention ofr the Safety of Life at Sea (SOLAS) mandated certain Classes of vessels must carry NAVTEX beginning August 1,1993.



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 used the CCIR 476 character set.



SITOR_B is also used in amateur radio, where it is known as AMTOR_B or AMTOR-FEC. NAVTES / SITOR /AMTOR broadcasts use 100 baud FSK modulation with a frequency shift of 170 Hz.


NAVTEX is also used in amateur radio, where it is known as AMTOR-B or AMTOR-FEC. NAVTES/SITOR /AMTOR fbroadcasts are 100 baud FSK modulation with a frequency shift of 170 Hz.


NAVTEX broadcost are primarily made on the Medium frequencies of 518 KHz and 490 KHz. The international NAVTEX frequency is 518 KHz. [1} and these broadcasts should always be in English. National transmission of NAVTES uses 490 KHz specifically for broadcasts in local languages. It is not used in the U.S.


NAVTEX Marine Safety informaion (MSI0 national transmissions also take place on HF at 42.9.5KHz using FEC mode.


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.


A NAVTEX messages is built on SITOR 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
  • a single space
  • four charactes B1,B2,B3 and B4 (see below)
  • a carriage return and 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 singal and another message starting with "ZCZC" or
  • either ; an enf of emission idle signal alpha for at least 2 seconds.

  • Subject indicator characters


    A Navigational warnings
    B Meteorological warnings
    C Ice reports
    D Search & rescue information, and priate warnings
    E Meteorological forecasts
    F Pilot service messages
    G AIS messages
    H LORAN messages
    I Not used
    J SATNAV message (i.e. GPS or GLONASS)
    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 NAVTEX Panel
    Y Special services - allocation by IMO NAVTEX Panel
    Z No message on hand

    Inmarsat

    Satellit
    Satellite Coverage Longitude Vehicle Launch date (GMT) Services / notes

    Inmarsat - 4 satellites

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    Country codes

    The permanent telephone country code for calling inmarsat destinations is :
  • 870 SNAC (Single Network Access Code) The 870 number is an automatic locator: SNAC is now usable by all inmarsat services

  • Country codes phased out on 31 December 2008 were
  • 871 Atlantic Ocean Region - East (AOR-E)
  • 872 Pacific Ocean Region (POR)
  • 873 Indian Ocean Region (IOR)
  • 874 Atlantic Ocean Region - West (AOR-W)
  • Existng and Evolved services, based on older technologies
  • Aeronautical (Classic Aero). provides voice/fax /data services for aircraft. Three levels of terminals. Aero -L (Low Gain Antenna) primarily for packet data including ACARS and ADS, Aero-H (High Gain Antenna) for medium quality voice and fex/data at up to 9600 bit/s, and Aero-I (Intermediate Gain Antenna) for low quality voice and fax/data at up to 2400 bits/s. Note, there are also aircraft rated versions of inmarsat-C and Mini-M/M4.The aircraft version of GAN is called Swift64.
  • Inmarsat-B: provides voice services, telex services, medium speed fax/data services at 9.6 kbits/s and high speed data services at 56, 64 or 128 kbit/s. There is also a 'leased' mode for inmarsat-B available on the spare inmarsat satellites.
  • Inmarsat-C: effectively this is a "satellite telex" terminal with store-and-forward, polling etc. capabilities. Certain models of inmarsat_C terminals are also approved for usage in the GMDSS system, equipped with GPS.
  • Inmarsat-M: provides voice services at 4.8 kbit/s and medium speed fax /data services at 2.4 Kbit/s. It paved the way towards inmarsat-Mini-M.
  • Mini-M: Provides voice services t 4.8Kbit/s and medium speed fax/data services at 2.4 Kbits/s. . One 2.4Kbit/s channel takes up 4.8Kbit/s on the satellite.
  • GAN (Global Area Network): provides a selection of low speed services like voice at 4.8Kbit/s. fax & data at 2.4 bits/s ISDN like services at 64 kbit/s (called Mobile ISDN) and shared-channel IP packet-switched data services at 64 kbits/s (called Mobile Packet Data Service MPDS, formerly inmarsat Packet Data Service-1IPDS). GAN is also known as "M4".
  • Fleet: actually a family of networks that includes the inmarsat-Fleet77, Inmarsat-fleet 55 and inmarsat-Fleet33 members .Much like GAN it provides a selection of low speed services like fax/data at 2.4 Kbits/s Medium speed services like fax/data at 9.6 kbits/s . ISDN like services at 64 Kbit/s (called Mobile ISDN) and shared-channel IP Packet-switched data services at 64 kbit/s (called Mobile Packet Data Servic MPDS). However, not all these services are available with all members of the family. The latest service to be supported is Mobile ISDN at 128 Kbits/s on inmarsat-Fleet77 terminals.
  • Swift 64: Similar to GAN, providing voice, low rate fax/data, 64Kbits/s ISDN, and MPDS services, for private, business, and commercial aircraft. Swift 64 is often sold in a mumlti-channel version, tosupport serveral times 64kbits/s .
  • Inmarsat D/D+/IsatM2M: Inmarsat's version of a pager, although much larger than terrestrial versions. Some units are equipped with GPS The original inmarsat-D terminals were one-way (to mobile) pagers. The newer Inmarsat-D+terminals are the equivalent of a two-way (to mobile) pagers.The main use of this technology nowadays is in tracking trucks and buoys and SCADA applications. SKy Wave Mobile Communications is a provider of D/D+/IsatM2M satellite data services with its DMR and SureLnx series products. SKY Wave also provides satellite tracking. monitoring and contril capabilities through its Global Wave MT series Products. Competing Systems such as from Skybitz only operate on the MSAT geostationary satellite over North America.
  • MPDS (Mobile Packet Data Service): Previously Known as IPDS this is an IP- based data service in which several users share a 64kbit/s carrier in a manner similar to ADSL.
  • Isat Phone: provides voice services at 4.8 Kbit/s and medium speed fax/data services at 2.4 Kbits. This service emerged from a collaboration agreement with ACeS, and is available in the EMEA and APAC satellite regious . Coverage is available in Africa, the Middle-East, Asia, and Europe, as well in maritime areas of the EMEA and APAC coverage.


  • Frequencies


    Due to the increased need of more marine VHF channels for VTS, commercial requirements. and port operations , a recent ITU Worls Radio. Conference has authorized and developed a new channel plan for the VHF marine radio frequencies. This new channel plan will take efect january 1,2017.

    Destress Frequencies

  • 2182KHz: MF International distress frequency for ship, aircraft and survival craft.
  • 3023KHz: intercommunications between mobile stations engaged in coordinition of search and rescue.
  • 4125KHz :Distress and safety traffic by adiotelephone.
  • 5680KHz:intercommunications between mobile stations engaged in coordintion of search and rescue.
  • 6125KHz: Distress and safety traffic by radiotelephone.
  • 8364KHz:Designated for use by survival craft stations.

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