Ian Waugh - A Mariner\'s Guide to Marine Communications

Vo!. 5, near the beginning of the NAVTEX section. The two letters are

followed by two numbers (01-99), the numerical sequence being applied

to each subject indicator, individually.

Example:

NAVTEX Message OA22, off the coast of South Mrica, would be

from Durban (station 0) and message type 'Navigation Warning'

(subject indicator A). This particular message is type 'N. (Navigation

Warning) number 22 of 99.

The same message number received near the centre of the

Mediterranean Sea would also be Navigation Warning number 22

of 99, but would come from Malta (Station 0 - see ALRS Vol. 315

NAVTEX map for the Mediterranean Sea area).

Some subjects, namely type A (Navigation Warnings); B (Weather
Warnings); and D (Search & Rescue messages) cannot be rejected by a
GMDSS-approved NA VTEX receiver. Subject indicator 'IJ - 'Navigation
Warnings additional to letter 'N should not be rejected from your
NAVTEX receiver.

Problem: I often receive 'asterisks' in my NAVTEX messages,

especially during the night. Why is this? Can I do anything about it?

Answer: Asterisks '*' in the text of a NAVTEX message indicate

interference - either radio interference, or electrical. If you are

receiving asterisks during the night, but not during the day, your

equipment is OK - what you are experiencing is 'sky wave'

interference from a distant station which happens to broadcast at the

same time as your own, programmed station. If you are experiencing

asterisks night and day within reasonable range of your programmed

station, you may have a problem onboard - see Chapter 9.

Receiving MSI using Marine VHF ISSB Radio (Voice and telexl

NBDP services)

NAVTEX and SafetyNET are the two main 'automatic' methods

of receiving MSI in the GMDSS. Many countries continue to provide

MSI using conventional voice and/or telex broadcasts, using VHF and

SSB radio, for coastal and deep-sea information.

In some countries, the VHF ISSB broadcasts are additional to

NAVTEX/SafetyNET broadcasts (and may be monitored, for example,

if you have a problem with NAVTEXlSafetyNET reception). In other

MARINE COMMUNICATIONS 19