PSK31 decoder in the browser
PSK31 is the mode for keyboard conversations on HF: narrow, efficient and readable even with weak signals. Signal-Pirat decodes PSK31 from a recording or live via the receiver output and creates PSK31 audio for practice. Everything runs in the browser.
Open in the browser
No installation, no sign-up needed.
What the page does
- Decode BPSK31 and BPSK63 from WAV or MP3 up to 5 minutes
- Live via microphone or receiver output
- Audio frequency is detected and tracked continuously
- Squelch against false characters in signal gaps
- Also identified in the signal search alongside CW, RTTY and APRS
Background
PSK31 was introduced in 1998 by Peter Martinez (G3PLX) and recommended as ITU-R M.2034 in 2013. It sends 31.25 symbols per second: a phase reversal of the carrier means 0, a steady carrier 1. Characters are encoded in Varicode, where frequent characters have short codes; no code contains two consecutive zeros, so “00” separates characters. As a result PSK31 occupies only about 60 Hz bandwidth.
In practice
How it works: tune the receiver in USB to a PSK31 signal, for example on the usual frequencies in the 20 m or 40 m band, so that it sits at about 1000 Hz audio. Live, the decoder starts at the set audio frequency and tracks it; “Find carrier” takes the strongest signal of the last seconds. In recordings the frequency is found automatically. With a connected radio the page also shows the RF frequency of the signal.
Frequently asked questions
Are QPSK31 and PSK63 decoded too?
BPSK31, BPSK63 and QPSK31 are decoded and generated; the mode is selected at the top of the page. QPSK31 with error correction (Viterbi) and sideband selection.
How weak may the signal be?
In test runs with ten noise sequences each, error-free down to 0 dB (PSK31, QPSK31) or 3 dB (PSK63) SNR referred to 4 kHz bandwidth and with up to ±6 Hz frequency offset.