The previous SNR formula (cand->score * 0.5 - 29.0) used the adjacent
tone bin as a noise reference. On a crowded FT8 band that bin is often
occupied by another station, inflating the apparent noise floor by
10-15 dB and capping reported SNR at around -10 dB even for strong
signals.
Replace with ftx_post_decode_snr(): re-encode the decoded message to
obtain the exact per-symbol tone sequence, compare each signal bin
against the minimum of the remaining (noise-only) bins, average over
all valid symbols, and apply the WSJT-X 2500 Hz bandwidth correction
dynamically per protocol. This produces accurate SNR estimates for both
FT8 and FT4 regardless of band occupancy.
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>
sjg
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