Navtex
“Navtex” is an abbreviation for Navigation Teletext. It delivers written navigational warnings and weather forecasts to vessels within a few hundred miles of most of the world’s coastlines.
Navtex transmitters are dotted around the world coastlines, typically a couple of hundred miles apart, but all transmitting on one of two frequencies: 518kHz or 490kHz. Operating at the lower end of the MF band (see page 9) means that each transmitter has a range of several hundred miles, but they don’t interfere with each other because they are divided into groups, in which each transmitter has its own twenty minute “slot” once every four hours.
When its turn comes, each transmitter broadcasts all the messages it has on hand, giving each one a “header” that identifies where it has come from, what subject it covers (weather, navigation, ice etc.,) and a serial number.
Dedicated Navtex receivers can decode the messages, either printing them out on paper, or displaying them on a screen.
The receiver can be programmed to ignore certain types of massage, or to ignore messages from certain stations. If you are cruising the Irish Sea, for instance, you probably don’t want weather forecasts for Portugal or ice warnings for northern Norway.
It will also ignore repetitions of messages which it has already received.
If possible, leave your Navtex receiver switched on. If you switch it on and off during a cruise, it will “forget” which messages it has already received, and subject you to numerous repetitions.
One of the best features of Navtex, for British users, is that all transmissions on the “standard” Navtex service (518kHz) everywhere in the world, are in English. The other frequency (490kHz) is used for a “local” Navtex service. Some countries use this to provide a service in their own language, but in the UK it is used for supplementary information, such as the Inshore Waters weather forecast.
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