RTTY on 20 metres: 14083 kHz, radioteletype at 45 baud

What you hear

A rapid, hard two-tone chatter, like a very fast telephone bell or a mechanical trill. That is radioteletype idling, switching between its two tones with nothing to say; when text flows, the rhythm breaks up into bursts. On the waterfall each station is a pair of parallel lines 170 Hz apart, flickering between the upper and the lower one. Tune so that the pair sits on the decoder's marks and the trill turns into capital letters marching across the screen.

The text is terse. RTTY uses the five-bit teleprinter alphabet of the 1930s, capitals only, with figures and punctuation reached through a shift character, and runs at 45.45 baud, about sixty words a minute. A weekday contact looks like a PSK31 one with the small talk cut down: callsigns, a report, name, location, equipment, 73. In a contest the whole exchange is one line, callsign, 599, a serial number or a zone, repeated hundreds of times an hour.

Who transmits and why

Amateurs have used teleprinters on the air since the late 1940s, when surplus machines from newsrooms and the military became available. For decades it was the only digital mode, and the habits formed then survive: the segment just above the CW part of each band, the 170 Hz shift, the mark tone on the higher radio frequency, which is why RTTY is traditionally worked as if on the lower sideband even where voice uses the upper one. The machines are gone and software does the keying, but the signal on the air is exactly what a 1950s teleprinter would print.

What keeps the mode alive is contesting. Several large RTTY contests a year, the Roundup in January, the WPX in February and the CQ World Wide at the end of September among them, fill 14080 to 14099 kHz with hundreds of stations for a weekend, and expeditions to rare places still run RTTY alongside CW and voice, because many award hunters need a digital contact in a mode older than FT8. Between contests the segment is quiet, with a handful of regulars on weekend afternoons.

When and where to listen

On contest weekends, any time 20 m is open; outside them, European afternoons and evenings and the weekends. The catalogue's 14083 kHz is a representative spot in the RTTY segment, 14080 to 14099 kHz, and in a contest stations stand every few hundred hertz from the bottom to the top of it. Receivers anywhere in Europe or North America hear plenty. RTTY wants a strong, steady signal: a station fading in and out comes out as a line with holes in it, and a station tuned a little off prints the wrong letters until the two lines sit exactly on the marks.

In ShackDeck

Station catalogue → Amateur radio → RTTY 20 m. The program picks a public receiver that covers 14083 kHz, tunes it, sets the RTTY mode with the standard 45 baud and 170 Hz shift and runs the RTTY decoder on the audio. The text prints on screen as it arrives, and the callsigns the decoder recognises go to the On air list and the map. No receiver, antenna or account of your own is needed; the program only listens.