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. …