Thursday, November 1, 2012


The Navtex system provides reception of local Maritime Safety Information (MSI) by Navtex Receiver on board ship. Navtex Transmitters are situated along the coast in various Navarea and the normal coverage is up to 400 NM range. The broadcast is automated direct printing service (RAdio Telex emission F1B) and the mode is FEC (Forward Error Correction) i.e, each character in the message is transmitted twice. MSI broadcast consists of SAR, navigational, metrological warnings and urgent information to ships.

The Navtex receiver is a unit comprises a pre tuned radio receiver, signal processor and dedicated display device. The Printer can be an integral parts of the equipment or can be an external printer. The Navtex unit should be programmed to display or print only message from stations that are of interest to the user. The latest Navtex Receiver are having user friendly function controls accessible by few buttons, up/down/side arrow keys and displayed menu Tree.

The NAVTEX system is designed to be used in GMDSS Sea Area A2, and is utilised mainly by those countries with relatively small areas of coastline and/or sea areas to cover.

Major areas of NAVTEX coverage include the Mediterranean Sea, the North Sea, coastal areas around Japan and areas around the North American continent.

NAVTEX message format

NAVTEX messages are transmitted using the following format:

in which

ZCZC defines the end of the phasing period,

the B1 character is a letter (A-Z) identifying the transmitter coverage area,

the B2 character is a letter (A-Z) for each type of message.

B3B4 is a two-character serial number for each message, starting with 01 except in special cases where the serial number 00 is used.

The transmitter identification character (B1) is a single letter allocated to each NAVTEX shore station transmitter. NAVTEX receivers allow the operator to accept or reject messages from any station, based on this single letter code.

The subject indicator character (B2) is also single letter code which serves to identify the message subject. NAVTEX receivers also allow the operator to reject certain messages based on the subject indicator character. However, messages concerning Navigational Warnings, Meteorological Warnings, and Search And Rescue information can not be rejected.

Subject indicator characters assigned to the NAVTEX system are as follows:

A - Navigational warnings
B - Meteorological warnings
C - Ice reports
D - Search and rescue information
E - Meteorological forecasts
F - Pilot service messages
G - Decca messages
H - Loran messages
I - Omega messages
J - Satnav messages
K - Other electronic navaid messages
L - Additional navigational messages
V - Special services
W - Special services (possible other languages use)
X - Special services
Y- Special services
Z - No message on hand (QRU)
Shipboard NAVTEX equipment

A NAVTEX receiver is normally a compact unit, with an integrated display and keyboard.

Once programmed with appropriate station codes and subject indicator characters, the unit is left unattended - messages are received automatically.
Frequency of operation

The NAVTEX system uses three broadcast frequencies:

518 kHz - the main NAVTEX channel

490 kHz - used for broadcasts in local languages (ie: non-English)

4209.5 kHz - allocated for NAVTEX broadcasts in tropical areas - not widely used at the moment.

All broadcasts from stations within the same NAVAREA must be coordinated on a time sharing basis to eliminate interference.

In addition, power outputs from each station are adjusted to control the range of each broadcast.  This is particularly important during night-time hours, as Medium Frequencies always travel further after dark.