Television station
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A television station is a type of broadcast station that broadcasts both audio and video to television receivers in a particular area. Traditionally, TV stations made their broadcasts by sending specially-encoded radio signals over the air, called terrestrial television. Individual television stations are usually granted licenses by a government agency to use a particular section of the radio spectrum (a channel) through which they send their signals. Some stations use LPTV broadcast translators to retransmit or rebroadcast to further areas. Television stations are a form of television channel, but not all television channels are necessarily stations.
Many television stations are now in the process of converting from analogue (NTSC, PAL, or SECAM) to digital (ATSC, DVB, or ISDB). In some countries, this is being forced on consumers and stations, while in others it is entirely voluntary.
In countries such as the United States, television stations usually just have one transmitter (or, more recently, two transmitters if the station broadcasts a digital signal in addition to its standard analog signal); most of these stations should be independent or affiliated to a television network such as ABC, CBS, Fox, or NBC.
Outside the US, television stations are generally associated with a nationwide television network, through which they get all of, or at least significant amounts of, their programming. In those countries, the signals broadcast in different areas have no well-known callsigns or other individual traits known to the general public (although a network might have regional variations, possibly broadcast from several different transmitters) and therefore from a consumer's point of view, there is no practical distinction between a network and a station.
In the United States, each nationwide terrestrial broadcast network can have a few "O&Os" — stations that it owns and operates, usually in the larger broadcast markets, like New York or Chicago. They can only own a limited number of stations because of FCC regulations.
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[edit] Facilities
[edit] Production
Large television stations usually have some sort of television studio, which on major-network stations is often used for newscasts or other local programming. There is usually a news department, where journalists gather information. There is also a section where electronic news gathering operations are based, receiving remote broadcasts via remote pickup unit or satellite TV. Vans, trucks, or SUVs with this equipment are sent out with reporters, who may also bring back news stories on videotape rather than sending them back live.
Weather is also a significant part of the station. Stations with newscasts also have their own meteorologists and Doppler weather radar, and produce their own forecasts, which often vary from station to station. In the U.S., most NBC stations now carry Weather Plus on a second digital channel, which mixes national and local segments.
Stations not affiliated with major networks generally do not produce news or weather, or much other programming. Some stations (known as repeaters or translators) only simulcast another, usually the programmes seen on its owner's flagship station, and have no production facilities of their own. This is common in most countries outside of the U.S., Canada, U.K. and Australia. Low-power stations typically also fall into this category worldwide.
Most stations which are not simulcast produce their own station identifications, using digital TV graphics. TV stations may also advertise on or provide weather (or news) services to local radio stations, particularly co-owned sister stations. This may be a barter in some cases.
[edit] Transmission
As with other stations, the radio antenna is often located on a summit, the top of a high skyscraper, or on a tall radio tower. A studio/transmitter link (STL), via either radio or T1/E1, is used to get the signal there. A transmitter/studio link (TSL) may also send telemetry back to the station, but this may be embedded in subcarriers of the main broadcast. Stations which retransmit or simulcast another may simply pick-up that station over-the-air, or via STL or satellite. The license usually specifies which other station is it allowed to carry.
VHF stations often have very tall antennas due to their long wavelength, but require much less effective radiated power (ERP), and therefore use much less transmitter power output, also saving on the electricity bill and emergency backup generators. In North America, full-power stations on band I (channels 2 to 6) are generally limited to 100 kW analog video (VSB) and 10 kW analog audio (FM), or 20 kW digital (8VSB) ERP. Stations on band III (channels 7 to 13) can go up by 5dB(W) to 316 kW video, 31.6 kW audio, or 63.2 kW digital. Low-VHF stations are often subject to long-distance reception just as with FM. There are no stations on channel 1.
UHF, by comparison, has a much shorter wavelength, and thus requires a shorter antenna, but also higher power. North American stations can go up to 5000 kW ERP for video and 500 kW audio, or 1000 kW digital. Low channels travel further than high ones at the same power, but UHF does not suffer from as much electromagnetic interference and background "noise" as VHF, making it much more desirable for TV. Despite this, in the U.S., the FCC is taking another large portion of this band (channels 52 to 69) away, in contrast to the rest of the world, which has been taking VHF instead. This means that some stations left on VHF will be harder to receive after the analog shutdown. Since at least 1974, there are no stations on channel 37 in North America for radioastronomy purposes.
[edit] In numismatics
Television has had such an impact in today's life, that it has been the main motif for numerous collectors' coins and medals. One of the most recent ones is the The 50 Years of Television commemorative coin minted in March 9, 2005. The obverse of the coin shows a "test pattern", while the reverse shows several milestones in the history of television.
[edit] See also
- Class A television service
- Low-power broadcasting
- List of broadcast station classes
- Fernsehsender Paul Nipkow: the first[citation needed] television station in Germany
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