PhosphorCW
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Description
PhosphorCW — Morse Code Decoder
Decode CW (Morse code) signals in real time using your iPhone or iPad's microphone. PhosphorCW listens to radio audio and prints decoded text on screen with the warm glow of a vintage phosphor terminal.
REAL-TIME DECODING
Point your device at a radio speaker or feed audio via a line-in adapter. PhosphorCW's DSP engine continuously processes the audio stream, detecting CW tones and decoding them into readable text as they arrive. Characters appear on a teleprinter-style display that scrolls automatically, just like the machines that once clattered in radio rooms and newsrooms worldwide.
AUTOMATIC SIGNAL TRACKING
Auto Frequency (AFC) — Automatically finds and locks onto the CW sidetone using FFT peak detection. No need to know the exact tone frequency. The tracker adapts as conditions change.
Auto Speed — Measures dit and dah timing to determine sending speed in words per minute. Adapts continuously from around 5 to 60 WPM as the operator's speed varies.
Both can be switched to manual mode for fixed-frequency or fixed-speed operation.
ON-DEVICE DSP ENGINE
All signal processing happens locally on your device. Nothing is recorded, transmitted, or stored externally.
The decoding pipeline includes:
Bandpass filtering centred on the detected tone frequency
Goertzel-based tone detection with adaptive noise floor tracking
Envelope extraction with slow-decay peak tracking for reliable squelch
Adaptive timing estimation for dit/dah discrimination and character/word gap detection
Full ITU Morse code table including prosigns
SIGNAL ANALYSIS
A dedicated signal view provides:
Live FFT spectrum display showing the audio frequency content
Scrolling waterfall display for visualising signal activity over time
Tone level indicator
Real-time WPM, tone frequency, and SNR readout
Lock status indicator showing when AFC has acquired a signal
DISPLAY
Choose from multiple phosphor colour themes — green, amber, white, and blue — inspired by the CRT terminals of the Cold War era. Adjustable decoder font size. Text selection enabled for copying decoded output.
SESSION LOG
Each decoding session is automatically logged with timestamp, duration, character count, WPM, and tone frequency. Review past sessions and their decoded text at any time.
CONFIGURATION
Input gain control (0.1x to 20x)
Auto/manual frequency detection (300–1500 Hz range)
Auto/manual speed tracking (5–60 WPM)
Colour theme selection
Font size adjustment
USE CASES
Monitor amateur radio CW transmissions
Practice copying Morse code from on-air signals
Decode CW practice recordings and training files
Analyse CW signal characteristics
Learn Morse code by watching the decoder work
ABOUT CW
Continuous Wave — the original digital mode. Samuel Morse's code has been the universal language of radio since the 1840s. From clipper ships to Cold War submarines, from Bletchley Park to amateur radio contests, CW remains the most efficient and reliable communications mode ever devised. This app decodes it from your microphone or line input.
Requires microphone access for audio input. iOS 18.0 or later.