Amateur television
| Amateur television (ATV) | |
|---|---|
| Mode type | Full-motion video with sound, analog or digital |
| Also called | Fast-scan television; DATV for the digital form |
| Bands | 70 cm and higher |
| US license | Technician and above |
| Technical | |
| Analog | AM (vestigial sideband) in 6 MHz channels on 70 cm; FM, wider, on 23 cm and up |
| Digital | DVB-S, DVB-S2 and DVB-T broadcast standards |
| Common 70 cm segments | 420–426 MHz and 438–444 MHz in many areas |
| Infrastructure | ATV repeaters, often receiving and transmitting on different bands |
Amateur television, or ATV, is the transmission of moving pictures with sound by amateur radio. It is often called fast-scan television to distinguish it from slow-scan television, which sends still pictures over a voice channel. ATV uses the same picture standards as broadcast television, so a signal that takes up a few kilohertz on SSTV needs several megahertz as ATV, and it is therefore confined to the UHF and microwave bands. Hams use it for live video from their shacks, regular ATV nets, high-altitude balloons and model aircraft, and for public-service events, where a camera at a parade route or marathon finish can send pictures back to the organizers.
Bands and channels
The lowest band wide enough for ATV is the 70-centimeter band. In the US it runs from 420 to 450 MHz, and an analog TV channel there is 6 MHz wide, the same width as an over-the-air broadcast channel. Many local band plans place ATV between 420 and 426 MHz and between 438 and 444 MHz, but arrangements differ from region to region, and ATV must fit around repeaters, weak-signal work and the 435–438 MHz satellite segment. Hams are secondary users of 70 centimeters, sharing it with government radar, and transmitting on 420–430 MHz is not permitted north of a boundary near the Canadian border known as Line A.
Above 70 centimeters there is more room. The 33-centimeter (902–928 MHz) and 23-centimeter (1240–1300 MHz) bands are also used for ATV, especially 23 centimeters, as are the microwave bands from 2.4 GHz up. Signals on these bands travel mostly by line of sight, so range depends heavily on antenna height; with high-gain Yagis at both ends, a few watts can cover tens of miles.
Because the US Technician license carries full privileges on these bands, ATV is open to new hams from the start.
Analog ATV
Traditional ATV is analog, using the NTSC standard of US analog broadcasting. On 70 centimeters it is usually sent as AM with a vestigial sideband, one sideband partly trimmed away, exactly as broadcast stations once did, so an older analog television set could display it, often through a converter. On 23 centimeters and higher, ATV is more often sent as FM, which gives a cleaner picture but occupies a wider channel. In both cases the sound travels on a subcarrier alongside the picture.
Analog ATV degrades gracefully. A weak signal produces a snowy but watchable picture, which makes it forgiving for portable and balloon use, and it needs no special decoder.
Digital ATV
Digital amateur television (DATV) uses digital broadcast standards, mainly DVB-S and DVB-S2 from satellite television and DVB-T from terrestrial television. Digital signals give a perfect picture until the signal falls below a threshold, then freeze or vanish. Their main advantage is efficiency: with modern video compression, a DATV signal can carry a good picture in a channel of 2 MHz or less, and experimenters have pushed reduced-bandwidth DATV much narrower still. That makes room for more stations in crowded bands and allows longer paths at the same power.
DATV equipment has become far more accessible thanks to software-defined radios, which can generate and receive these signals under the control of a small computer, and to consumer satellite TV receivers, some of which can tune DATV signals on 23 centimeters directly.
ATV repeaters
An ATV repeater receives a video signal and retransmits it from a high site, extending the range of low-power stations much as a voice repeater does. Because ATV signals are so wide, an ATV repeater normally listens on one band and transmits on another, for example receiving on 23 centimeters and transmitting on 70 centimeters. Many ATV repeaters show a test pattern or a rotating display of club information when idle, and some also stream their output on the internet. Voice coordination usually takes place on a separate 2-meter or 70-centimeter frequency.
The International Space Station also carries a digital television transmitter for amateur use, called HamTV, which works in the 2.4 GHz band and has sent video during some school contacts organized by ARISS. As of October 2026 ARISS listed it as transmitting a test signal on 2395.00 MHz; check the ARISS status page for its current state.