Television broadcasting is the transmission of video and audio to a geographic area that is intended for general reception by the public, funded by commercials or government agencies. Television broadcasters transmit at high power levels from several hundred foot high towers. A high-power television broadcast station can reach over 50 miles.
The standard television system used in the Americas is the National Television Standards Committee (NTSC) system. The first version of this system used 6 MHz RF channels to provide black and white television. The NTSC standard was later modified to allow color television signals to co-exist on the same type of video channel. The television system used in Europe and other parts of the world is phase alternating line (PAL).
The PAL television system was developed in the 1980’s to provide a common television standard in Europe. The PAL system uses 7 or 8 MHz wide radio channels.
Several enhancements have been added to this basic television broadcasting system, including audio stereo sound, additional audio programming channels, very low data rate digital transfer (closed captioning), and ghost canceling.
The NTSC and PAL enhancements are minor when compared to the technological improvements represented by HDTV proposed to provide significantly higher resolution audio and video, as well as data services. A consortium called the Grand Alliance has produced a standard called Grand Alliance HDTV for digital television. The FCC plans to introduce HDTV initially by allowing broadcasters to offer a simulcast of their regular programming, transmitted on UHF television assignments. The period of simulcast will continue for up to 15 years as old broadcast facilities and receivers are phased out. Receivers for the HDTV system will also include the capability to receive and display regular analog broadcasts.
Figure 1 shows a television broadcast system. This television system consists of a television production studio, a high-power transmitter, a communications link between the studio and the transmitter, and network feeds for programming. The production studio controls and mixes the sources of information including videotapes, video studio, computer created images (such as captions), and other video sources. A high-power transmitter broadcasts a single television channel. The television studio is connected to the transmitter by a high bandwidth communications link that can pass video and control signals. This communications link may be a wired (coax) line or a microwave link. Many television stations receive their video source from a television network. This allows a single video source to be relayed to many television transmitters.
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