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In North America, broadcasts are typically sent from repeaters on four UHF channelFor the geographical meanings of this word, see channel (geography). In communications, a channel is the "path" or "route" which a message follows, as it is transmitted between a communication source and a receiver. More specifically, in telecommunications below the UHF TV broadcast band (air channels 14 to 69). These can be received on a cable-ready NTSCNTSC is the analog television system in use in the United States and many other countries, including most of the Americas and some parts of East Asia. It is named for the National Television System(s) Committee the industry-wide standardization body that-format TV or set-top boxThe term set-top box describes a device that connects to a television and some external source of signal, and turns the signal into content then displayed on the screen. The signal source might be a satellite dish, a cable (see cable television), a teleph tuned to cable channels 57 to 60 (420-444 MHz). Individual channels (with center frequencyThe center frequency f ( resonant frequency) is the geometric mean between the lower cutoff frequency f and the upper cutoff frequency f of a frequency band. See also: Band-pass filter. f2 f1 is called the bandwidth B. Only if the bandwidth f f is very sm for video and audio) are:
Typically frequency modulated TV is used on frequencies above 1200MHz (1.2 GHz), where there is enough bandwidth for such wideband transmissions. This is often used as a repeater's input frequency, with output being standard VSB on the four channels listed above. An ATV repeater may also broadcast a noncommercial TV network which does not include music (a U.S. requirement also part of amateur radio). U.S. stations often transmit NASA TV while they are not in use, especially if there is currently a Space Shuttle mission.
In Europe, recent experiments have been done with digital modes following widely-adopted DVB-S and DVB-T standards. Currently, digital ATV modes have not been approved by the FCC in the U.S.
See also: SSTV