JS8Call on 20 metres: 14078 kHz, keyboard chat built on FT8

What you hear

On 14078 kHz in upper sideband the sound is FT8: warbling chords in fifteen-second blocks, thin fifty-hertz stripes on the waterfall. The difference is in the rhythm. An FT8 station sends one message and waits for a reply; a JS8 station, once it has something to say, sends frame after frame in consecutive slots, so one stripe keeps going for a minute or two while a sentence crosses. Between conversations the channel carries heartbeats, short automatic transmissions that say "I am here" and collect signal reports from whoever hears them, and the replies to those, so the frequency is rarely silent for long even when nobody is actually chatting.

JS8 has several speeds. Normal is the FT8 timing, fifteen seconds per frame; fast and turbo squeeze a frame into ten or six seconds for stronger signals, and slow stretches it to thirty for the weakest. The slot structure is the same for everyone, so a receiver clock has to be within a second or so of true time, as with FT8.

Who transmits and why

JS8Call is a program released in 2018 that borrowed the FT8 modulation from WSJT-X and replaced the fixed messages with free text and a small set of commands. The result is a chat mode that works at FT8 signal levels, far below where voice or PSK31 give up, with features the fixed-message modes lack: a station can leave a message for another that is away from the radio, ask a distant station to relay to a third it cannot hear, query another station's heard list, or send its position. All of that runs unattended, which is why the mode attracted emergency-communications groups, people in remote places and operators who like the idea of a low-power messaging network that needs no internet.

14078 kHz is the agreed JS8 frequency on 20 m, chosen to sit right above the FT8 slice at 14074 so the two do not overlap. It is the busiest JS8 frequency, with a few to a dozen stations visible at once in Europe and North America and heartbeats from further away as the band opens.

When and where to listen

The hours of 20 m: from mid-morning to late evening, longer in summer, with the most conversations in the North American evening, which is the European night. Heartbeats run around the clock wherever the band is open. A receiver with a quiet location shows the most, since many JS8 stations run a few watts. The dial is 14078 kHz in USB, and the passband 200 to 3000 Hz above it holds the whole channel.

In ShackDeck

Station catalogue → Amateur radio → JS8Call 20 m. The program picks a public receiver that covers 14078 kHz, tunes it and sets USB with the standard digital passband, so you hear the tones and see the stripes on the waterfall. The program has no JS8 decoder, and the FT8 decoder cannot read JS8 frames, since the two protocols differ on purpose: to read the text you need the JS8Call program itself, fed with the receiver's audio. No receiver, antenna or account of your own is needed to listen.