CodeMonkey

Linux GUI (AppImage)

• 1.Download the AppImage and make it executable: chmod +x CodeMonkey-*.AppImage
• 2.Run it: ./CodeMonkey-*.AppImage
• 3.No installation required. Qt, Hamlib, and PortAudio are bundled inside the AppImage.
• ›The AppImage also includes the codemonkey-decode and codemonkey-encode CLI tools.

CLI tools

• 1.Download and make executable: chmod +x codemonkey-decode codemonkey-encode
• 2.The CLI tools link against system libraries. Install: sudo apt-get install -y libportaudio2
• ›Pipe audio data to codemonkey-decode, or pass text to codemonkey-encode to produce a WAV file.

1. Resampling

Audio from the sound card (at any sample rate the system provides) is resampled to an internal rate of 8 000 Hz. The lower rate reduces CPU load for all downstream stages while comfortably covering the 0–4 kHz audio passband used on HF.

2. I/Q demodulation

The resampled audio is mixed with a cosine and a sine at the selected tone frequency to produce in-phase (I) and quadrature (Q) components. A low-pass Butterworth IIR filter (cutoff ≈ 200 Hz) is applied to both channels to isolate the baseband signal from adjacent QRM. The instantaneous signal strength (envelope) is computed as √(I² + Q²). This narrow, phase-coherent demodulation rejects adjacent signals and achieves a much cleaner envelope than simple rectification or energy detection.

3. Automatic gain control

An AGC stage normalizes the envelope to the 0–1 range using asymmetric time constants: fast attack (proportional to the estimated dit length) to track a suddenly stronger signal, and slow decay to avoid misreading the spaces between characters as signal loss. This makes the decoder insensitive to absolute signal level and allows it to follow fading without requiring manual gain adjustment.

4. Dual-threshold keying detection

A hysteresis comparator with upper threshold 0.60 and lower threshold 0.35 converts the normalized envelope to a binary key stream (mark / space). The gap between thresholds suppresses chatter at transitions caused by noise or signal flutter, producing a clean key-up / key-down event stream.

5. Adaptive timing analysis

The durations of successive marks and spaces form a bimodal histogram: one cluster for dits (and inter-element spaces), another for dahs (and inter-character/inter-word spaces). The decoder continuously fits this histogram to extract the current dit length in real time, tracking speed changes from approximately 5 WPM to 50 WPM without any manual adjustment. The PARIS standard (50 dit-equivalents per word) is used to convert dit length to words per minute.

6. Probabilistic character matching

Each mark or space is scored against the current timing model as a probability of being a dit, dah, inter-element space, inter-character space, or word space. These probabilities propagate through a Morse trie (binary decision tree, depth ≤ 6) to produce a weighted score for every candidate character at each branch. The highest-scoring leaf node wins. This approach — never making a hard timing decision early — is the core insight from CW Skimmer that lets it outperform threshold-only decoders on marginal signals and irregular fists.

7. Farnsworth timing (TX)

When sending, Farnsworth mode transmits each character at the full selected WPM but stretches inter-character and inter-word spaces so that the effective throughput matches a lower “Farnsworth WPM”. The spacing is computed from the PARIS formula: inter-character space = 3× a scaled unit, word space = 7×, where the unit is chosen so that the overall average matches the target Farnsworth rate. This is the standard method used by ARRL code courses for building copy speed.

Hamlib rig control

CodeMonkey integrates with Hamlib, the universal amateur radio control library, which supports over 400 radio models from Icom, Kenwood, Yaesu, Elecraft, FlexRadio, and many others. Set your rig model, serial port, and baud rate in the Radio Setup dialog; CodeMonkey will connect automatically on startup and reconnect every 15 seconds if the link is lost.

Once connected, the frequency display in the status bar shows the current VFO frequency in real time. The Center button retunes the radio so that the decoded signal aligns with your TX tone frequency — one click to zero-beat any station you can hear.

Serial port keying (RTS / DTR)

CodeMonkey can key a CW interface wired to the RTS or DTR line of any serial port. Use the Hamlib-connected rig port (shared mode) or a separate USB-serial adapter for a standalone keyer interface. Both lines support polarity inversion for interfaces that require an active-low key signal. Keying is synchronized with audio output so both paths fire simultaneously.

GPIO keying (Raspberry Pi)

On Raspberry Pi and other Linux single-board computers, CodeMonkey can key a transistor or relay directly from a GPIO pin using the Linux /sys/class/gpio sysfs interface. Select any BCM pin number in the Keying Setup dialog (default: GPIO 17). Polarity inversion is supported for active-low circuits. No additional drivers or libraries are required.