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Technology
The elements of a simple television system are:
An image source - this may be a camera for live pick-up of images or VTR or a
Film Chain-Telecine-flying spot scanner for transmission of films.
A sound source.
A transmitter, which modulates one or more television signals with both picture
and sound information for transmission.
A receiver, which recovers the picture and sound signals from the television
broadcast.
A display device, which turns the electrical signals into visible light.
A sound device, which turns electrical signals into sound waves to go along with
the picture.
Practical television systems include equipment for selecting different image
sources, mixing images from several sources at once, insertion of pre-recorded
video signals, synchronizing signals from many sources, and direct image
generation by computer for such purposes as station identification.
Transmission was originally over the air from land-based transmitters. The
quality of reception varies greatly, and this led to the proliferation of large
antennas on house roofs for best signal in the 1960s. In most cities today,
cable systems deliver television over metal or optical cables, but for a fee. It
can be delivered by radio from synchronous satellites, which were large for
analog, and smaller dishes for digital broadcast, also for a fee, often less
than cable systems, which has led to the appearance of small dishes outside of
houses and apartments.
Digital systems may be inserted anywhere in the chain to provide better image
transmission quality, reduction in transmission bandwidth, special effects, or
security of transmission from reception by non-subscribers. A home today might
have the choice of receiving analog or HDTV over the air, analog or digital
cable with HDTV from a cable television company over coaxial cable, or even from
the phone company over fiber optic lines. On the road, television can be
received by pocket sized televisions, recorded on tape or digital media players,
or played back on wireless phones over a high speed network or the internet.
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