PSK31 on 20 metres: 14070 kHz, keyboard conversations in thirty hertz

What you hear

Tune to 14070 kHz in upper sideband and listen just above the dial: a soft, warbling hum, one steady note that seems to shimmer, sometimes two or three of them at different pitches. Each is a PSK31 signal, and on the waterfall it shows as a thin bright line, about thirty hertz wide, with a faint pair of sidebands while the station is sending text and a clean single trace while it idles. The signals gather in the first kilohertz above the dial, 14070.0 to 14071.5 kHz, several at once on a busy evening, none of them interfering with the others because each is so narrow.

Decoded, the hum becomes text, letter by letter at typing speed, about fifty words a minute. A contact reads like a slow chat: a CQ, an answer, then name, location, signal report, a description of the station and antenna, the weather, and a 73. Many operators keep prepared paragraphs for these, so the same words come up often, but the exchanges in between are live typing, mistakes and all.

Who transmits and why

PSK31 appeared at the end of 1998 and was the first digital mode built for the sound card rather than for a dedicated modem. The idea was a mode as easy as a conversation and as narrow as possible: it shifts the phase of a single tone at 31.25 baud, matching the speed of a touch-typist, and codes letters so that the common ones are the shortest, in the spirit of Morse. The result fits in thirty-one hertz, so a hundred stations can share the space one voice signal takes, and it decodes a few decibels below what an ear can copy.

For a decade it was the mode everyone tried first. FT8 took most of that traffic after 2017, but PSK31 kept the people who wanted to actually talk: it is the mode for an operator who likes to tell you about their antenna, and it still fills up during the PSK contests and on winter evenings. The operators are ordinary amateurs, often with low power, since a few watts go a long way in such a narrow signal.

When and where to listen

Whenever 20 m is open, which from Europe means mid-morning until late evening, with the most stations in the European evening and on weekends. Because contacts last ten or fifteen minutes, a quiet hour can still hold two or three conversations in progress. The dial is 14070 kHz in USB; the signals sit in the audio range 500 to 2500 Hz above it. Tuning accuracy matters less than for voice, but the receiver must be stable: a drift of a few hertz breaks the text.

In ShackDeck

Station catalogue → Amateur radio → PSK31 20 m. The program picks a public receiver covering 14070 kHz, sets the PSK31 mode and runs the PSK31 decoder on the audio: the decoder follows a signal and prints its text as it is typed, and the callsigns it finds go to the On air list and the map. No receiver, antenna or account of your own is needed; the program listens only, and joining the conversation takes a transmitter and a licence.