APT start/stop signals are not audio-frequency tones — they are
black↔white transition rates in the FM-demodulated output (300, 675,
450 transitions/s). The Goertzel detector was running on the raw ~1900 Hz
carrier where no energy exists at those frequencies, so APT detection
never fired on real HF WEFAX signals.
Replace the Goertzel approach with transition-counting on demodulated
luminance (matching fldigi's decode_apt), and swap the processing order
so FM demodulation runs before APT detection.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>
sjg
a01609212e