NAVTEX

Navtex is an international, automated system for instantly distributing maritime navigational warnings, weather forecasts and warnings, search and rescue notices and similar information to ships. A small, low-cost and self-contained "smart" printing radio receiver installed in the pilot house of a ship or boat checks each incoming message to see if it has been received during an earlier transmission, or if it is of a category of no interest to the ship's master. The frequency of transmission of these messages is 518 kHz in English, while 490 kHz is use to broadcast in local language.
The messages are coded with a header code identified by the using alphabets to represent broadcasting stations, type of messages, and followed by two figures indicating the serial number of the message.