NAVTEX
What the exam tests here
NAVTEX is the short-range, automatic, narrow-band direct-printing system for MSI in coastal waters. The exam tests frequencies, message types, station/time-sharing identifiers, and how a receiver filters what it prints.
Technical basics
NAVTEX is an MF system using narrow-band direct printing with a 500 Hz shift: 518 kHz for the international service in English, 490 kHz for national services in the local language, and 4209.5 kHz for tropical waters. Usable range is typically 200-400 nm from the transmitter, so it is a coastal service and not a substitute for SafetyNET on ocean passages. Receivers print automatically, with no operator action, and reject messages already received.
Message types and identifiers
Each transmission starts with a station identifier letter and a message-type letter. Key types: A navigational warning, B meteorological warning, C ice report, D SAR information, E weather forecast, F pilot service, L additional navigational warning, V special (e.g. an important advisory). Messages of types A, B, D and L cannot be rejected by the receiver - they are always printed - and a "vital" message is printed regardless of the operator's settings.
Setting up the receiver
Select the correct station list for the voyage, choose the message types you want (A, B, D and L are compulsory), and check that the display shows the station identifier and the time-sharing slot so you know which transmitter you are hearing.
Worked example
A ship leaves Mumbai for the Gulf. The navigator keeps the receiver on 518 kHz and adds the relevant stations along the route to the station list; A, B, D and L are automatically printed. On approaching an area with no 518 kHz station in range, the navigator knows NAVTEX has lapsed and relies on SafetyNET for ocean MSI.
Traps
- Assuming NAVTEX covers ocean passages.
- Rejecting type A or D messages; the receiver will either refuse or a vital message will override.
- Ignoring 490 kHz, which carries national-language warnings you may need in coastal waters.