PSK31 on 20 metres, 14.070 MHz: keyboard conversations in a 31 Hz signal

What you hear

A single warbling tone with a soft, uneven rhythm, something like a flute with a tremolo. When the operator is not typing the signal idles, a steady warble at the rate of 31 bits a second; when a letter goes out the rhythm breaks for a moment. On the waterfall each station is a thin bright line with two faint lines beside it, a railway track, and on a good day there are several of them side by side between 1000 and 2500 Hz above the dial, 14.071 to 14.0725 MHz. The lines are so narrow that a dozen contacts fit where one voice signal would be.

Decoded, the text comes out letter by letter at the speed the other person types, pauses and corrections included, which is what makes the mode feel like a chat. A typical contact: a CQ repeated three times with the callsign, then names, locations, a signal report, a description of the station, the antenna, the software and the weather, often sent from prepared macros, then 73. The text is in upper and lower case, with punctuation, and reads like a message rather than a telegram.

Who transmits and why

Radio amateurs on 20 metres, the band where PSK31 has lived since the mode appeared in 1998. It was the first digital mode built for an ordinary computer sound card, and for a decade it was the way most amateurs met digital radio: a PC, a cable to the transceiver and a few watts were enough for contacts across continents. Its strength is the bandwidth: 31 Hz means all the transmitter's power goes into a sliver of spectrum, and a weak signal still reads. The arrival of FT8 took away most of its crowd, but 14.070 still carries signals most days, kept alive by people who want to talk rather than exchange reports. Faster relatives, PSK63 and PSK125, are met a little higher, around 14.072.

When and where to listen

The daytime hours of 20 metres: Europe around midday, the Americas in the European afternoon and evening, more on weekends and in the evening hours of whichever region the receiver is in. The waterfall tells you more than the ear here: look for the thin lines first, then pick one. Any receiver with 20 metres works, and because the signals are narrow a receiver with a low noise floor, out in the countryside, shows more of them than a city one.

In ShackDeck

Station catalogue → Fax and digital signals → PSK31 20 m (14.070). The program picks a public receiver with 20 metres, tunes it to 14.070 MHz in USB and sets the PSK31 mode; no receiver, antenna or account of your own is needed. The decoder locks onto the strongest signal in the passband and the AFC holds it there; to read another station, click its line on the waterfall. The text appears in the text panel as it is typed, and callsigns in it are clickable: a click puts the callsign into the entry panel with the station's country, bearing and distance, and looks it up. If the output is garbled for a while, the two sides are simply switching over, or the signal is fading; the decoder picks the text up again when the signal returns.