Thank you to Simpli for writing in and sharing a set of free radio decoders that run entirely in the browser. There are pages for Morse, RTTY, PSK31, SSTV, weather fax, NAVTEX, APRS and the DCF77/MSF time signals, plus a signal identifier that tries to name an unknown mode and links to the matching decoder.

Audio can come from your SDR program via a virtual audio cable, a microphone, a WAV or MP3 recording, or a WebSDR playing in another browser tab (this needs a desktop browser with screen sharing), so no hardware is needed to try them. Simpli tested them on DWD RTTY on 4583 kHz and DWD weather fax on 3855 kHz via the Twente WebSDR, as well as on live PSK31 and an ISS SSTV recording in PD120 mode.

Simpli writes:

A detail you might find interesting: the WebSDR player inserts 128 zero samples about once a second, and its playback speed wanders by up to half a percent. That's enough to tear a fax picture apart. The fax decoder cuts those gaps out and tracks the speed from the white tone, so the chart comes out straight. The RTTY page also switches to reversed polarity by itself when it sees too many framing errors.

All decoding happens locally with nothing uploaded, and the tools are free with no sign-up. This is similar in spirit to OFFgrid-SDR, which we just posted about, as both run in the browser and can automatically identify a mode. However, OFFgrid-SDR connects directly to an RTL-SDR via WebUSB and is open source under the GPLv3, while Clever Quest Lab's decoders work on audio from any receiver and do not appear to be open source.