FT8 on 20 metres, 14.074 MHz: the busiest digital frequency in the world

What you hear

In USB the frequency sounds like a chorus of thin warbling tones, a ragged wall of sound that stops and starts again every 15 seconds, on the quarter minute, with a short gap in between. On the waterfall it is dozens of vertical stripes between 200 and 3000 Hz above the dial, each only 50 Hz wide: one set of stripes lights up in the even slots, another in the odd ones, because the two sides of a contact take turns. By ear none of it means anything; it is written for the decoder.

Decoded, the traffic is short, fixed-form messages. A CQ with a callsign and a four-character grid square. An answer with both callsigns and a signal report in decibels. The report acknowledged with an R. Then RR73 and 73, and the contact is over. Six messages, about a minute and a half, often run half-automatically by the software on both ends. Signals as weak as twenty decibels below the noise still decode, which is why the frequency is full even when the band sounds empty.

Who transmits and why

Radio amateurs everywhere. FT8 was released in 2017 by the team behind WSJT-X and within a year it was the most used mode on shortwave. Its appeal is simple: a contact that would never get through by voice with a small antenna and a few watts goes through on FT8, so countries and grid squares for awards pile up even during the quiet years of the solar cycle. The price is that nothing beyond the fixed exchange is said; the messages are the whole contact. 20 metres is the main long-distance band of the day, and 14.074 is its FT8 frequency by convention the world over.

When and where to listen

20 metres is open to somewhere almost all the time. From Europe the morning brings Asia and the Pacific, midday Europe and Africa, the afternoon and evening North and South America; near the peak of the solar cycle the band stays open late into the night. Weekends and contests are busier, but even at three in the morning UTC the slots carry decodes. Any receiver with 20 metres works, and the receiver's location is a lever: a receiver in Japan in its morning shows the Asian and Pacific side of the band, a receiver in the United States in its evening shows the Americas.

FT8 depends on accurate time. The decoder cuts the audio into 15-second slots by UTC, and if the clock of the computer doing the decoding is a few seconds off, nothing decodes. Keep the Mac's clock synchronised and the problem never appears.

In ShackDeck

Station catalogue → Fax and digital signals → FT8 20 m (14.074). The program picks a public receiver that has 20 metres, tunes it to 14.074 MHz in USB and sets the FT8 mode; no receiver, antenna or account of your own is needed. Every 15 seconds a new batch of decodes appears in the Activity view, time, signal level, frequency offset and the message, coloured by what matters: a CQ, a new country, a new grid square, a station worked before. Each station lands on the map in its grid square with its flag, and a line joins the two sides of an exchange. A click on a station puts its callsign into the entry panel and narrows the receiver's passband to that one signal, so you hear it on its own. Stations fade from the map after a couple of minutes, everything heard goes into the Heard log, and alerts can be set for a new country or grid or a callsign you are waiting for.