SSTV on 20 metres: 14230 kHz, pictures sent by sound

What you hear

A burst of tones that sounds like nothing else on the band: a steady whistle for a second, a short stutter of beeps, then two minutes of rising and falling warble with a sharp tick in it about every half second. That tick is the sync pulse at the start of each picture line; the warble between ticks is the brightness and colour of the pixels, coded as audio frequencies from 1500 Hz for black to 2300 Hz for white. On the waterfall the transmission is a wide, rippling band with a regular comb of pulses on its lower edge. When the warble stops, the picture is complete.

Put a decoder on it and the sound turns into an image of about 320 by 256 pixels, painted from the top down over the length of the transmission. The pictures are whatever amateurs choose to send: a photo of the station, a view from the window, a holiday snapshot, a cat, or a CQ card with the callsign in large letters over a background, often with a signal report and a greeting added on top. Common formats are Martin M1 and Scottie S1, each about two minutes per picture, and the faster Robot 36, which takes thirty-six seconds at lower quality. The decoder works out which one was sent from the short beep sequence at the start, so the listener never has to choose.

Who transmits and why

Licensed amateurs who like the idea that a picture can travel across an ocean through a three-kilohertz voice channel. SSTV dates from the late 1950s, when the pictures were monochrome and shown on long-persistence oscilloscope tubes; today the sound is produced and decoded by software, and colour is standard. A typical contact is unhurried: one station sends a CQ picture, another answers with its own, and the two swap a few images with reports written as RSV, readability, strength and video quality, spoken or placed as text on the picture itself. There are SSTV contests and award programmes, and the International Space Station sends SSTV pictures on VHF a few times a year, which brings newcomers to the mode on shortwave.

14230 kHz is the agreed SSTV frequency on 20 m worldwide, and the activity spreads a few kilohertz around it when it gets busy.

When and where to listen

Daytime and evening, when 20 m is open; weekends are busiest, and the afternoon hours in Europe bring pictures from the whole continent and, later on, from across the Atlantic. Activity comes in bursts: nothing for twenty minutes, then three stations in a row. A picture needs a steady signal for two minutes, so receivers that hear the sender well give clean images, and a fading signal shows as bands of noise across the picture. The dial is 14230 kHz in USB, and the exact frequency matters: a few hundred hertz off and the colours shift or the picture slants.

In ShackDeck

Station catalogue → Amateur radio → SSTV 20 m. The program picks a public receiver that covers 14230 kHz, tunes it, sets the SSTV mode and starts the SSTV decoder on the audio. From the first sync pulse the picture builds line by line on screen, and the finished image stays there. No receiver, antenna or account of your own is needed. The program only receives; to send a picture back you need a transmitter and a licence of your own.