Also known as: NAVTEX
NAVTEX is an international system for broadcasting maritime safety information — navigational warnings, weather forecasts and gale warnings, and search-and-rescue notices — as printed text to ships automatically. It sends narrow-band FSK teleprinter data with forward error correction, chiefly on 518 kHz for English-language international traffic, so a shipboard receiver can print bulletins around the clock without an operator.1 NAVTEX is a core component of the Global Maritime Distress and Safety System (GMDSS) and complements voice and DSC alerting.
Overview
Every NAVTEX message begins with a four-character technical header — a transmitter identity letter, a subject-indicator letter (navigational warning, meteorological warning, ice report, and so on), and a two-digit serial number. Receivers use the header to reject messages from out-of-range stations, on unwanted subjects, or already printed, so the crew sees only relevant, un-duplicated bulletins. Transmissions are time- scheduled so that many stations in a region share one frequency without colliding.
Technical characteristics
| Property | Value |
|---|---|
| Frequencies | 518 kHz (international), 490 kHz (national language), 4209.5 kHz (tropical) |
| Modulation | FSK, 170 Hz shift, 100 baud |
| Coding | SITOR collective (FEC) mode with character repetition |
| Header | Station + subject + serial (B1B2B3B4) |
| Access | Scheduled time-sharing by station |
History
NAVTEX was developed in the 1970s and adopted by the IMO and ITU as part of GMDSS, replacing manual receipt of safety traffic. The international 518 kHz service uses English; 490 kHz was later added for broadcasts in national languages, and 4209.5 kHz serves some tropical regions.
Deployment
Coast and coastguard stations worldwide broadcast NAVTEX; SOLAS vessels carry dedicated NAVTEX receivers that print continuously. Its forward-error-corrected mode is the same SITOR-B / RTTY-family teleprinter coding used elsewhere in maritime HF.
Decoding it with GopherTrunk
GopherTrunk is a land-mobile trunking scanner and does not decode NAVTEX. The signal sits well below GT’s target VHF/UHF trunking bands, and its teleprinter FEC decoding is outside GT’s scope. Enthusiasts typically receive NAVTEX with a general-coverage HF SDR and a dedicated SITOR-B/NAVTEX decoder.