PhosphorRTTY decodes RTTY (Radio Teletype) signals in real time using your iPhone's microphone. Hold your phone near a shortwave radio tuned to an RTTY signal and watch the text appear on an authentic phosphor CRT display, character by character.
No internet connection required. No external hardware. No account. Just your iPhone and a radio.
FEATURES
- Real-time RTTY decoding via microphone — ITA2 (Baudot) and ASCII modes
- Automatic frequency control (AFC) acquires and tracks drifting signals
- Auto-baud detection: 45.45, 50, 75, 100 Bd
- Auto-shift detection: 85, 170, 450, 850 Hz
- Live FFT spectrum display, scrolling waterfall, and paper punch tape visualisation
- Bit period histogram with baud rate markers
- Session logging with full decoded text, timestamps, and signal parameters
- Amber and green phosphor CRT themes with scanlines, vignette, and glow effects
- USB and LSB conventions supported
- No accounts, no tracking, no network access
DSP ENGINE
Per-sample I/Q quadrature demodulation with biquad low-pass filtering, W7AY Automatic Threshold Correction, and a digital phase-locked loop (DPLL) for timing recovery. 512-point FFT for frequency analysis and AFC. All signal processing runs entirely on-device.
DECODER ACCURACY
PhosphorRTTY has been tested against real over-the-air HF recordings and synthetic test signals. Detailed test results, methodology, and decoded output samples are available in the decoder test report.
WHERE TO FIND RTTY
- 20m band: 14.080–14.099 MHz
- 40m band: 7.080–7.100 MHz
- 15m band: 21.080–21.100 MHz
A shortwave receiver, SDR, or WebSDR audio played through a speaker is all you need.
SUPPORT
Need help? Have a question, bug report, or feature request?
- Ask a question — get help with using PhosphorRTTY
- 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.