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Amateur television

Amateur television ('''ATV''') is the transmission of Broadcasting|broadcast-quality video and Sound reproduction|audio over radio waves allocated for amateur radio using the broadcast standards of NTSC in North America and Japan, and PAL or SECAM elsewhere, using the full refresh rates of those standards. ATV includes the study of building of such transmitters and receiver (radio)|receivers and the radio propagation|propagation between these two. ATV is an extension of amateur radio. It is also called HAM TV or Fast Scan TV (FSTV) (as opposed to slow-scan television (SSTV), which can be transmitted on any ham frequency due to its narrowband structure, but is not decodable by a television).

North American context

In North America, Amateur radio frequency allocations|amateur radio bands that are suitable for a television signal (capable of the necessary wideband signal) fall in between the UHF and VHF range, between channels 13 and 14, in the 70 cm ham band. While outside of broadcast television channels, this frequency falls into Cable television|CATV North American cable television frequencies|frequencies, on channels 57 to 60 (420-444 Megahertz|MHz). As such, ATV transmissions are viewed by setting a television to cable input, and attaching an antenna. Individual channels (with center frequency for video and Sound reproduction|audio) are:
- 57: 420-426 MHz (421.25 video, 425.75 audio)
- 58: 426-432 MHz (427.25 video, 431.75 audio)
- 59: 432-438 MHz (433.25 video, 437.75 audio) - offset to 434.0 and 438.5 to clear the satellite sub-band (435-438).
- 60: 438-444 MHz (439.25 video, 443.75 audio) All of these fall within the range between T.V. broadcast channels 13 and 14, which are:
- 13: 210-216 MHz (211.25 video, 215.75 audio)
- 14: 470-476 MHz (471.25 video, 475.75 audio) Other amateur radio bands also have ATV usage with Single-sideband modulation#vestigal sideband|vestigal sideband (North American analog TV broadcast modulation standard) on 919.25 MHz, 1241.25 MHz, 1253.25, MHz, 1277.25 MHz and 1289.25 MHz usually for cross band ATV repeater outputs. 1265 MHz is a wider channel (10 MHz) for AM or FM ATV. Some areas in North America use 1255 MHz FM. Most of the FM ATV is on 2441.5 MHz with 6.0 MHz audio subcarrier and 4 MHz deviation. ATV links are on 2417.5 MHz, 3GHz and 5 GHz bands have links in some areas. 10.4 GHz is a wideband FM and used in some ATV repeater inputs. The distance record for ATV is between Hawaii and California on 434 MHz. Experiments with Digital_television|digital modes have lagged somewhat behind those in Europe, but have taken on some new urgency given the DTV_transition_in_the_United_States|transition of broadcast television. WR8ATV currently has an output using DVB-S, which is believed to be the first, and currently only, D-ATV repeater in the US.

European context

In Europe, which generally has a narrower UHF allocation than the USA, the majority of amateur television operation is currently FM on 1.2GHz and above. The frequencies in use depend on national permissions. In most of mainland Europe, the most common frequency is 1255MHz. Other bands commonly used for ATV are the 13cm (~2.3-2.45GHz) and 3cm (~10GHz) bands, although ATV is used on most of the microwave bands. In several countries cross-band repeaters are used, with Amplitude Modulation|AM inputs on 430 MHz and FM outputs on 1255 MHz, others have FM-ATV inputs on 13 cm and outputs on 3 cm. In the United Kingdom, much activity occurs using in-band repeaters. These generally have an input of 1248, 1249 or 1255MHz and typically output at 1308, 1312 or 1316 MHz, although other frequencies are also used. Simplex operation occurs on these or other frequencies chosen to avoid interference with other users of the band, e.g. 1285MHz. Recent experiments have been done with digital television|digital modes following widely-adopted DVB-S and DVB-T standards.

Transmission standards

Typically frequency modulated television|TV is used on frequencies above 1200 MHz (1.2 Hertz|GHz), where there is enough Bandwidth (signal processing)|bandwidth for such wideband transmission (telecommunications)|transmissions. This is often used as a repeater's input frequency, with output being standard Single-sideband modulation#Vestigial sideband|VSB on the four channels listed above. In a nutshell
- below 1.2 GHz: Vestigial Sideband
- above 1.2 GHz: FM, Phase-shift keying|PSK etc... The quality of transmission is expressed as a "p-level"; "p" standing for "picture". P-levels range from zero to five, increasing as the picture becomes more viewable. P-0 signifies a state in which sync bars are visible, but the picture is too snowy to be seen; this occurs at a minimum signal strength of 3db. Each level represents an increase of 6db over the previous; P-5 is 30db above P-0 and represents a perfectly clear picture.ATV P level illustration

Content

Content produced by ATV has included:
- From 1968 to about 2004 amateur TV provided behind-the-scenes co-ordination for the annual New Year's Day Tournament of Roses Parade in Pasadena, CA.
- HAM TV - as it is also called - provides video co-ordination of many public service events and, along with traditional amateur radio, provides much needed "eyes" in natural disasters.
- U.S. stations often retransmit NASA TV while they are not in use, especially if there is currently a Space Shuttle Space exploration|mission.