Television station
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.
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.
In other countries such as the
United Kingdom, 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 there is no strong network/station split.
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
Los Angeles.
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
newscasters also have their own
meteorologists and
Doppler 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, whhich mixes national and local segments.
Stations not
affiliated with major networks generally do not produce news or weather, or much other programming. Some stations only
simulcast another and have no production facilities of their own. This is common in most countries outside of the U.S., Canada, 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.
Transmission
As with other stations, the
radio antenna is often located on a
summit 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 100kW analog video (
VSB) and 10kW analog audio (
FM), or 20kW digital (
8VSB) ERP. Stations on
band III (channels 7 to 13) can go up by 5
dB(
W) to 316kW video, 31.6kW audio, or 63.2kW 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 5000kW ERP for video and 500kW audio, or 1000kW 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.
*
Class A television service*
Low-power broadcasting*
List of broadcast station classes
