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What to listen to · Fax and digital signals
FT4 on 20 metres, 14.080 MHz: the fast variant of FT8
FT4 exchanges the same callsigns, grids and reports as FT8 in half the time, in 7.5-second turns on 14.080 MHz. ShackDeck decodes the short bursts and shows the stations on the map; busiest during digital contests.
What you hear
Short bursts of warbling tones, each under five seconds long, coming in a quick rhythm of 7.5-second turns: eight exchanges a minute instead of four. On the waterfall the stripes are a little wider than FT8's, about 80 Hz, and there are fewer of them. On an ordinary weekday 14.080 can be almost empty for hours, a stripe here and there; during a digital-mode contest it fills from edge to edge.
The messages are the same as on FT8: a CQ with a callsign and a grid square, an answer with a report in decibels, R and the report, RR73, 73. A full contact takes about 45 seconds, which is the whole point of the mode.
Who transmits and why
FT4 was released in 2019 by the same team that made FT8, for people who wanted the reliability of FT8 at contest speed. It pays for the speed with sensitivity: FT4 decodes to about three and a half decibels less deep than FT8, so a signal that is marginal on 14.074 is lost on 14.080. That trade-off is why the two modes live side by side: FT8 for weak signals and everyday contacts, FT4 when there are many strong stations and the aim is as many contacts as possible in an hour.
When and where to listen
The band hours are those of 20 metres: Europe and Africa around midday, the Americas in the afternoon and evening, Asia in the morning, with the band open far into the night near the solar maximum. The frequency itself lives by the calendar more than by the clock: look at it at the weekend, and above all during digital contests, when the rate of decodes is a sight in itself. Any receiver with 20 metres works. As with FT8, the computer that decodes needs an accurate clock, because the decoder cuts the audio into 7.5-second slots by UTC.
In ShackDeck
Station catalogue → Fax and digital signals → FT4 20 m (14.080). The program picks a public receiver with 20 metres, tunes it to 14.080 MHz in USB and sets the FT4 mode; no receiver, antenna or account of your own is needed. The decodes appear in the Activity view every 7.5 seconds with time, level, frequency offset and the message, coloured for a CQ, a new country, a new grid or a station worked before; each station lands on the map in its grid square with its flag, and a click on one puts its callsign into the entry panel and narrows the passband to that one signal. If the frequency is quiet, the FT8 entry on 14.074 is two clicks away and is never empty.