Long before FT8 took over the digital segments of every HF band, PSK31 was already doing keyboard-to-keyboard chat over weak, narrow signals. Released by Peter Martinez, G3PLX, in 1998, it’s still around today, and it’s worth understanding even if you never plan to make it your primary mode.
How PSK31 actually works
PSK31 uses phase-shift keying rather than the frequency-shift approach RTTY and FT8 use, encoding data as phase changes in a continuous carrier. The 31 in the name refers to its roughly 31 baud data rate, deliberately chosen to match typical human typing speed. That narrow bandwidth, about 60 Hz, is the mode’s biggest advantage: you can pack dozens of PSK31 conversations into the same spectrum a single SSB signal would occupy.
Real-time conversation, not structured exchanges
This is where PSK31 genuinely differs from FT8. There’s no fixed message format and no 15-second transmit windows. You type, and the other station reads it in something close to real time, the same way an instant message conversation works. That makes PSK31 far better suited to an actual rag chew than FT8 ever will be, even though FT8 pulls weaker signals out of the noise more reliably.
Is it still worth learning
PSK31 activity has thinned out considerably since FT8 arrived, but it hasn’t disappeared. If you already run Fldigi or a similar digital mode suite, PSK31 costs you nothing extra to try, and it’s a genuinely different experience from FT8’s automated exchanges. I’d treat it as a mode worth having in your toolkit rather than a primary destination, useful for the nights you actually want to type a real conversation instead of trading grid squares and signal reports.
Related reading: What Is RTTY? · VarAC: The Modern Chat Mode Built on VARA · JTDX vs WSJT-X