SELCAL Monitor

SELCAL Monitor listens to the audio of one browser tab you choose and decodes ICAO SELCAL calls in real time, so you do not have to sit and listen to an HF channel waiting for your aircraft. == What it does == - Detects all 16 ICAO SELCAL tones (A-H, J-M, P-S) and reports complete four-character codes such as AF-DE. - Decodes the full SELCAL32 32-tone plan (T-Z and 1-9) by default, and can fall back to the original 16 tones for receivers that cannot be tuned as precisely. - Logs every call with the time, the receiver frequency, the detection confidence, and the measured frequency offset. - Shows a desktop notification the moment a code is decoded. - Reads the tuned frequency and mode from the receiver's own display at each detection, so retuning mid-session is logged correctly. - Keeps the tab audio audible while it monitors, so you can still listen. == Watchlist == Register the SELCAL codes you are waiting for, with a note against each one. When a registered code is decoded the extension sounds a chime, and the notification stays on screen until you dismiss it. The alarm works with the popup closed. == Built for real HF == Detection uses a windowed FFT with a common frequency-offset search, so it tolerates the tuning error and fading typical of shortwave reception. A sensitive mode loosens the thresholds for weak and fading signals. Live peak, RMS, and near-clipping meters let you tell a weak signal from a bad audio level. The receiver must be tuned accurately: within about 10 Hz in normal mode or 16 Hz in sensitive mode, and only 5 and 8 Hz respectively with SELCAL32, whose tones sit half as far apart. This is a limit of the signal rather than the software. The two closest SELCAL tones are only 34 Hz apart, so a larger tuning error is genuinely ambiguous between codes and no decoder can resolve it. == Privacy == Nothing leaves your browser. The extension makes no network requests, records no audio, and contains no analytics. Your history and watchlist are stored locally and are deleted when you uninstall it. Built for and tested with KiwiSDR receivers. Not affiliated with or endorsed by KiwiSDR. Requires Chrome 116 or newer.