PhosphorTEX

PhosphorTEX decodes NAVTEX maritime safety broadcasts in real time on your iPhone or iPad. Tune a receiver to 518 kHz, 490 kHz or 4209.5 kHz, hold your device near the speaker, and watch navigational warnings, gale warnings, ice reports and search-and-rescue notices arrive on an authentic phosphor CRT display.

No internet connection required. No account. Nothing leaves the device.


WHAT NAVTEX IS

NAVTEX (Navigational Telex) is the worldwide maritime safety broadcast of the IMO's Global Maritime Distress and Safety System (GMDSS). Coast stations send storm warnings, navigational hazards, search-and-rescue notices and weather forecasts to ships at sea, each station in its own ten-minute slot. PhosphorTEX puts that live feed on your screen.


SIGNAL PROCESSING

PhosphorTEX decodes CCIR 476 SITOR-B entirely on the device, with signal processing written for the app:

Synchronous 7-bit decoding with phase-locked clock recovery
Automatic character alignment that finds the character boundary on its own
Automatic polarity detection, so maritime receivers and SDR tuning both work with no toggles
Automatic frequency control that finds and tracks the 170 Hz tone pair anywhere from 800 to 2500 Hz
Every character checked against the NAVTEX error code, with errors shown rather than guessed
Error statistics for every message, measured against the second copy NAVTEX sends of each character
Live 512-point FFT spectrum and scrolling waterfall


FIVE TABS

DECODE: every message as a colour-coded card, with the station letter, subject, serial number, UTC time, a signal quality badge and the full text. Switch to TAPE for the raw teleprinter stream.

SIGNAL: FFT spectrum with mark and space cursors, a scrolling waterfall, mark and space tone bars, and an FEC HEALTH panel showing how cleanly each character arrived.

SCHEDULE: a built-in database of 43 NAVTEX coast stations across thirteen NAVAREAs, from Cullercoats, Niton and Malin Head to Reykjavik, Las Palmas, Singapore and Valparaíso. A live grid shows which stations transmit in the current ten-minute slot against a running UTC clock.

LOG: every decoded message kept on the device, with its header, time, full text and error statistics. Copy, share or delete a message, or export them all as text.

CONFIG: amber or green phosphor, three text sizes, automatic or manual tuning, mark and space inversion, alert colours for search-and-rescue and vital messages, and a mute list for subjects you do not want on the cards. Search-and-rescue messages can never be muted.


IPHONE AND IPAD

On iPad PhosphorTEX runs natively in every orientation, with larger type and the cards, spectrum, waterfall and station schedule opened out across the full width of the screen.


PRIVACY

PhosphorTEX makes no network requests. No account, no cloud, no analytics, no tracking, no third-party code. Audio is processed in memory as it arrives and is never recorded, stored or sent anywhere. The microphone is used only while decoding.


WHERE TO FIND NAVTEX

518 kHz carries the international service in English, 490 kHz carries national services in local languages, and 4209.5 kHz carries the tropical HF service. Any receiver that covers these frequencies with SSB will do, and so will WebSDR audio played through a speaker.


REQUIREMENTS

iPhone or iPad with a microphone
iOS or iPadOS 26.4 or later
A receiver tuned to a NAVTEX frequency, or WebSDR audio played through a speaker
No in-app purchases. No subscriptions. No tracking. No network access.

PhosphorTEX is part of the Phosphor range of retro-CRT radio tools, alongside PhosphorRTTY, PhosphorCW, PhosphorFeld and PhosphorSSTV.