NAVTEX

NAVTEX is an international service for the broadcast and automatic receipt of Maritime Safety Information (MSI). NAVTEX broadcasts are telex transmissions and are normally received by a dedicated receiver. The receiver either contains a printer on which it records the messages or it stores the messages in local memory for later review on a display. The purpose of the NAVTEX system is essentially to provide MSI relevant to the coastal areas within the range of the MF NAVTEX transmitter network.

NAVTEX operates worldwide in the MF band on 518 kHz. The NAVTEX transmissions are in English. However, for MSI broadcasts in the local language, an alternative frequency of 490 kHz is available or, in the tropical regions, 4209.5 kHz.

NAVTEX broadcast can contain different classes of messages. Each class of messages has its own identification. The receiver can be programmed to print or display only certain classes of messages and reject the other messages. Messages that are safety related can not be rejected. The message classes are as follows:

* These messages cannot be rejected by the receiver
A*	Navigational warnings
B*	Meteorological warnings
C	Ice reports
D*	Search and Rescue information and piracy warnings
E	Weather forecasts
F	Pilot service messages
G	DECCA messages
H	LORAN messages
I	OMEGA messages (not in use anymore)
J	Satellite navigation messages
K	Other navigational messages
L*	Rig movements
V	Amplification of NAV WARNINGS in A
Z	No message on hand

All NAVTEX messages begin with a 4-character group.

the first denotes the transmitting station,
the second the message category,
the third and fourth the serial number.

The serial number 00 is used for urgent traffic and will always be printed.

The messages are transmitted with a simple FSK modulation, with a frequency shift of 170 Hz at a speed of 100 bits/s.