PhosphorTEX decodes NAVTEX (Navigational Telex) broadcasts in real time using your iPhone's microphone. Hold your phone near a shortwave receiver tuned to 518 kHz, 490 kHz, or 4209.5 kHz and watch gale warnings, nav warnings, and maritime safety information appear on an authentic amber phosphor display.
No internet connection required. No external hardware. No account. Just your iPhone and a maritime receiver.
FEATURES
- Real-time NAVTEX decoding via microphone — CCIR-476 SITOR-B, 100 Bd, 170 Hz shift
- Time-diversity FEC: 5-character DX/RX pair-merge per CCIR-476 spec
- 7-way phase-ambiguity disambiguator picks the correct character-boundary phase automatically
- Automatic frequency control with FFT peak-pair search locked to 170 Hz shift
- ZCZC…NNNN message framer with B1/B2/B3B4 header parsing
- CARDS view: message cards coloured by subject (SAR/piracy, nav warning, met warning, ice report …)
- TAPE view: raw teleprinter stream, character-by-character, including FEC ERR markers
- Live FFT spectrum display and scrolling waterfall (SDR-style colour palette)
- FEC health panel: DX valid %, RX fallback %, ERR %, alternation lock status
- NAVAREA station schedule tab: 24-slot grid, current-slot highlight, UTC clock
- Per-subject mute list (D-category SAR/piracy messages always override)
- Full message log with search, share, and export
- Amber phosphor CRT theme with scanlines, vignette, and glow effects
- No accounts, no tracking, no network access
DSP ENGINE
Per-sample I/Q quadrature demodulation with biquad low-pass filtering and W7AY Automatic Threshold Correction. Synchronous 7-bit SITOR-B framer with DPLL clock recovery. Seven parallel character-phase candidates scored by DX/RX mismatch rate on real message content — the winning phase commits and its buffered history replays through the framer so the ZCZC header is never lost. 512-point FFT for frequency analysis and AFC. All signal processing runs entirely on-device.
DECODER ACCURACY
PhosphorTEX is verified against real over-the-air 518 kHz WebSDR recordings of live maritime-safety traffic (Netherlands Coastguard and NCC-Hamburg nav warnings). Detailed test results and decoded output samples are available in the decoder test report.
WHERE TO FIND NAVTEX
- 518 kHz — International (English). The primary NAVTEX band.
- 490 kHz — National language broadcasts (Dutch, French, Portuguese, etc.)
- 4209.5 kHz — HF, tropical / long-range coverage.
A shortwave receiver (or SDR / WebSDR audio played through a speaker) tuned in USB with carrier positioned so the mark tone is around 1615 Hz is all you need. NAVTEX stations broadcast in assigned 10-minute slots within a 4-hour cycle — check the SCHEDULE tab for current and upcoming slots.
SUPPORT
Need help? Have a question, bug report, or feature request?
- Ask a question — get help with using PhosphorTEX
- Report a bug — let us know if something isn't working
- Request a feature — suggest improvements or new functionality
You can also browse existing issues to see if your question has already been answered.