Principle Of Navtex System; How Navtex Works; Navtex System Operation - Furuno NX-900 Operator's Manual

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PRINCIPLE OF NAVTEX SYSTEM

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How NAVTEX Works

NAVTEX is an acronym meaning Navigational Telex, and as its name shows, it is a
kind of narrow band radio teletype system for sending (by frequency shift keying) text
messages expressed in a 7-unit code. The difference is that a NAVTEX transmitter
transmits nine control characters (header code) ahead of the main message, so that
the receiver can identify the station, message type and serial number automatically.
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NAVTEX System Operation

For navigation purposes, the world is divided into 21 areas (called Navareas). Each
Navarea has multiple NAVTEX stations and each NAVTEX station has an identifica-
tion code, from "A" to "Z". The frequency assigned to NAVTEX is 518 kHz (some sta-
tions use 490 or 4209.5 kHz also), and many stations exist in the same Navarea,
If the stations were to transmit without any rule, the system would collapse due to mu-
tual interference. To avoid this problem, the following rules apply.
• The transmission schedule is determined so that two or more stations having a
common service area may not overlap in time.
• Each station transmits with minimum required power to cover its service area (200
to 400 nautical miles nominal).
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