Shows RMS audio level bar and SSTV tone classification (leader/sync/noise)
via SSE during detecting mode, replacing the static "Listening..." state
with actionable signal feedback.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
slowrx is a GTK GUI app that doesn't support CLI usage, so the SSTV
decoder was silently failing. This replaces it with a pure Python
implementation using numpy and Pillow that supports Robot36/72,
Martin1/2, Scottie1/2, and PD120/180 modes via VIS header auto-detection.
Key implementation details:
- Generalized Goertzel (DTFT) for exact-frequency tone detection
- Vectorized batch Goertzel for real-time pixel decoding performance
- Overlapping analysis windows for short-window frequency estimation
- VIS header detection state machine with parity validation
- Per-line sync re-synchronization for drift tolerance
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Adds a general-purpose SSTV decoder alongside the existing ISS SSTV mode,
supporting USB/LSB/FM modulation on common amateur radio HF/VHF/UHF
frequencies (14.230 MHz USB, 3.845 MHz LSB, etc.) with auto-detection
of modulation from preset frequency table.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
