Cable television is a television program delivery system to paying customers via radio frequency (RF) signals transmitted through coaxial cable, or in newer systems, light pulses through fiber optic cables. This is in contrast to television broadcasts, where television signals are transmitted over the air by radio waves and received by television antennas attached to the television; or satellite television, where television signals are transmitted by communications satellites orbiting the Earth and received by a satellite dish on the roof. FM radio programming, high-speed Internet, telephone service, and similar non-television services can also be provided through this cable. Analog television is standard in the 20th century, but since the 2000s, cable systems have been upgraded to digital cable operations.
"Cable channels" (sometimes known as "cable networks") are television networks available on cable television. When available via satellite television, including direct broadcast satellite providers such as DirecTV, Dish Network and BSkyB, as well as through IPTV providers such as Verizon FIOS and AT & amp; T U-verse is called a "satellite channel". Alternative terms include "non-broadcast channels" or "programming services", most recently used in legal contexts. Examples of cable/satellite/cable networks available in many countries are HBO, MTV, Cartoon Network, E!, Eurosport, and CNN International.
Abbreviations CATV are often used for cable television. It originally stood for the Community Television Access or Antenna Television Community , from the origin of cable TV in 1948. In areas where over-the-air TV reception is limited by distance from the transmitter or mountainous areas, large "community antennas" are built, and cables run from them to individual homes. The origins of broadcasting cable for radio are even older as radio programming is distributed by cable in several European cities as far back as 1924.
Video Cable television
History in North America
Cable television began in the United States as a commercial business in 1950, although there was a small-scale system by fans in the 1940s.
The initial system receives only weak channels (broadcasts), amplifies them, and sends them wirelessly to a subscriber, limited to nearby communities or communities. The receiving antenna will be higher than any customer can reach, thus carrying a stronger signal; in hilly or mountainous areas it will be placed at high altitudes.
Initially, cable systems served only smaller communities without their own television stations, and who could not easily receive signals from stations in cities due to terrain or hilly terrain. But in Canada, people with their own signals are a fertile cable market, because viewers want to receive American signals. Rarely, as in the Alfred university city of New York, US cable systems retransmit Canadian channels.
Although the initial television receiver (VHF) can receive 12 channels (2-13), the maximum number of channels that can be broadcast in one city is 7: channels 2, 4, either 5 or 6, 7, 9, 11 and 13, it can not receive strong (local) signals on adjacent channels without distortion. (There is a frequency gap between 4 and 5, and between 6 and 7, which allows both to be used in the same city.)
When the equipment is upgraded, all twelve channels can be used, except the local VHF television station is broadcast. Local broadcast channels can not be used for signals that are considered a priority, but technology allows low priority signals to be placed on the channel by synchronizing the discharge interval. Similarly, a local VHF station can not be performed on its broadcast channel because the signal will arrive on the TV a little separately in time, causing "ghosting".
The bandwidth of the amplifier is also limited, which means frequencies above 250 MHz are very difficult to transmit to distant parts of coaxial networks, and UHF channels can not be used at all. To expand more than 12 channels, non-standard "midband" channels must be used, located between FM and Channel 7 bands, or "superband" outside Channel 13 to about 300 MHz; this channel can initially only be accessed using a separate tuner box that sends the selected channel to the TV set on Channel 2, 3, or 4.
Before being added to the cable box itself, this midband channel is used for the initial incarnation of pay TV, e.g. The Z Channel (Los Angeles) and HBO but transmitted in a clear that is not randomized because the standard TV sets of the period can not catch the signal or the average consumer can 'cancel' the normal station to be able to receive it.
Once a tuner that can receive selected mid band and super band channels begins to be incorporated into a standard television set, the broadcaster is forced to install a scrambler circuit or move these signals farther from the reception range for the pre-set TV and VCR cables. However, once all 181 cable channels allocated have been entered, the premium broadcaster has no choice but to scramble.
Unfortunately for pay TV operators, descrambling circuits are often published in electronic hobby magazines such as Popular Science and Popular Electronics that allow anyone with something more than just basic knowledge about electronic broadcasting for can build their own and receive programming at no cost.
Later, cable operators began carrying FM radio stations, and encouraged customers to connect their FM stereo devices to the cables. Before stereo and bilingual TV sound becomes common, the sound of Pay TV channels is added to the FM stereo cable channel. Around this time, operators expanded beyond a 12-channel dial to use the "VIRF" and "superband" channels adjacent to the "high band" 7-13 North American television frequencies. Some operators such as in Cornwall, Ontario, use a dual distribution network with Channels 2-13 on each of two cables.
During the 1980s, United States regulation was no different from public access, education and government (PEG) which created the beginning of cable-based live television programs. As cable penetration increases, many cable TV stations are launched, many with their own news agencies that can provide more direct and local content than provided by the nearest network news.
Such stations may use the same branding as used by the affiliates of the nearest broadcast network, but the fact that these stations are not airborne and not regulated by the FCC, their call sign is meaningless. These stations have partially evolved into today's over-the-air digital sub-channels, where major broadcast TV stations for example. NBS 37 * will - in the absence of any available local CNB or ABS stations - re-broadcast programming from nearby affiliates but fill it with its own news and other community programs to fit its own location. Many local programs that live with local interests were then made throughout the United States in most major television markets in the early 1980s.
It evolved into many current cable broadcasts from a variety of programs, including only cable-produced movies and miniseries. Cable-only channels, starting with oriented channels to feature movies and sporting events or big shows, further diversification, and "narrowcasting" become common. In the late 1980s, cable signals only exceeded the number of broadcast signals on cable systems, some of which have now exceeded 35 channels. In the mid-1980s in Canada, cable operators were allowed by regulators to enter into distribution contracts with their own cable networks.
In the 1990s, levels became common, with subscribers being able to subscribe to different levels to get a selection of different additional channels above the basic options. With an additional subscription level, subscribers can get custom channels, movie channels and foreign channels. Large cable companies use descrambler that can be addressed to limit access to premium channels for unsubscribed subscribers to higher levels, but the magazines above often publish solutions for that technology as well.
During the 1990s, the pressure to accommodate an increasing supply structure resulted in digital transmission that made the use of VHF signal capacity more efficient; Optical fibers are common to carry signals to areas near the home, where coax can carry higher frequencies over the remaining distance. Although for a time in the 1980s and 1990s, television receivers and VCRs were equipped to receive mid-band and super-band channels. Due to the fact that descrambling circuits are for the time being present in these tuners, depriving cable operators of most of their revenue, such cable-ready tuners are rarely used now - requiring a return to the set-top boxes used from the 1970s. advanced.
Conversion to digital broadcasting has put all signals - broadcast and cable - into digital form, rendering analog cable television services largely obsolete, functional in the market supply is diminishing. The analog television set can still be accommodated, but the tuner is mostly outdated, often hanging entirely on the set-top box.
Maps Cable television
Distribution
To receive cable television in certain locations, cable distribution lines should be available at local utility poles or underground utility channels. Coaxial cables carry signals to customers' premises via a drop of service , cable above or below ground. If the customer's building does not have a drop in cable service, the cable company will install it. The standard cable used in the US is RG-6, which has a 75 ohm impedance, and is connected with an F-type connector. The cable company's part of the cable usually ends in the distribution box on the exterior of the building, and the cable wires embedded in the wall typically distribute the signal to the jack in various rooms connected to the television. Some cables to different rooms are separated from the incoming cables with a small device called a splitter. There are two standards for cable television; older analog cables, and new digital cables that can carry data signals used by digital television receivers such as HDTV equipment. All cable companies in the United States have switched to or are switching to digital cable television since it was first introduced in the late 1990s.
Most cable companies require set-top boxes to view their cable channels, even on newer televisions with digital cable QAM tuners, as most digital cable channels are now encrypted, or "scrambled", to reduce cable service theft. The cable from the wall jack is attached to the input of the box, and the output cable from the box is attached to the television, usually RF-IN or composite input on an older TV. Since the set-top box translates only one channel being watched, every television in the house needs a separate box. Some unencrypted channels, usually traditional over-the-air broadcast networks, can be displayed without a receiver. The cable company will provide set top boxes based on customer-purchased service levels, from basic set top boxes to standard definition images connected via standard coaxial connections on TV, to high-definition wireless DVR receivers connected via HDMI or components. The older analog TV sets are "ready cables" and can accept old analog cables without a set-top box. To receive digital cable channels on analog television sets, even unencrypted ones, require different types of boxes, digital television adapters provided by cable companies. A new distribution method that utilizes low-cost low cost DVB distribution to residential areas, using a TV gateway to convert DVB-C, DVB-C2 to IP streams for TV distribution over home IP networks.
Principle of operation
In the most common system, some television channels (as many as 500, though this varies depending on the available channel capacity of the provider) are distributed to the customer's residence via coaxial cable, derived from the trunkline supported on power lines originating from the cable company's local distribution facility , called "headend". Many channels can be transmitted through a coaxial cable with a technique called frequency division multiplexing. In the headend, each television channel is translated to a different frequency. By giving each channel "slot" different frequencies on the cable, separate television signals do not interfere with each other. In the outdoor cable box at the customer's residence, the company's drop-down service cable is connected to a cable that distributes signals to different rooms in the building. On every television, customer television or set-top box provided by the cable company translates the desired channel back to its original frequency (baseband), and it is displayed on the screen. Due to widespread cable theft in earlier analog systems, signals are usually encrypted on modern digital cable systems, and set-top boxes must be activated by the activation code sent by the cable company before functioning, which is only sent after the subscriber registers. If a customer fails to pay his billing, the cable company can send a signal to disable the customer's box, preventing reception.
There is also usually a channel "upstream" on the cable to send data from the customer's box to the cable headend, for advanced features such as requesting a pay-per-view or movie show, wired internet access, and cable phone service. The "downstream" channel occupies the frequency band from about 50 MHz to 1 GHz, while the "upstream" channel occupies frequencies from 5 to 42 MHz. Customers pay for a monthly fee. Customers can choose from multiple levels of service, with "premium" packages including more channels but higher costs. In the local headend, the feedback signal from each television channel is received by the dish from the communication satellite. Additional local channels, such as local broadcast television stations, educational channels from local universities, and community access channels intended for local government (PEG channels) are usually included in cable services. Commercial advertisements for local businesses are also included in programs in the headend (individual channels, nationally distributed, also have nationally-oriented ads).
Hybrid-coaxial fiber
Large modern cable systems, with one network and headend often serving the entire metropolitan area. Most systems use hybrid fiber-coaxial (HFC) distributions; this means the trunklines that carry signals from the headend to the local environment are optical fibers to provide greater bandwidth and also additional capacity for future expansion. In headend, the radio frequency electrical signal carrying all channels is modulated on the rays and transmitted through the fiber. The fiber trunkline goes to several distribution hubs, from which some fibers spread to carry signals to a box called optical nodes in the local community. At the optical node, the light beam of the fiber is translated back to the electrical signal and carried by the coaxial cable distribution line on the power line, from which the cable branches into signal amplifier circuit and line extension. This device carries signals to customers via a passive RF device called a tap.
Distribution by continent
Cable television is mostly available in North America, Europe, Australia and East Asia, and less so in South America and the Middle East. Cable television has little success in Africa, as it is not cost-effective to install cables in sparsely populated areas. The so-called "wireless cable" or microwave-based system is used instead.
Other cable-based services
Coaxial cable capable of transporting two-way signal and transmission of large amounts of data. Cable television signals only use a portion of the available bandwidth through coaxial channels. This leaves plenty of space available for other digital services such as cable internet, wired phones and wireless services, using unlicensed and licensed spectrum. Broadband internet access is achieved through coaxial cable by using cable modem to convert network data into digital signal types that can be transferred through coaxial cable. One problem with some cable systems is the old amplifiers that are placed along a unidirectional cable route so as to allow for uploading customer data will need to use an analog phone modem to provide upstream connections. It limits the upstream speed to 31.2k and prevents the convenience of broadband internet typically provides. Many large cable systems have upgraded or updated their equipment to allow for two-way signals, allowing for greater upload speed and convenience always, although this increase is expensive.
In North America, Australia and Europe, many cable operators have introduced cable phone services, operating like fixed-line carriers. This service involves the installation of a special telephone interface where customers convert analog signals from subscriber cables into digital signals, which are then sent on local loops (replacing last mile analogs or regular old telephone service (POTS) to the company's switching center, where it is connected to the public switched telephone network (PSTN). The biggest obstacle to cable phone service is the need for nearly 100% reliable service for emergency calls. One of the standards available for digital cable phones, PacketCable, seems to be the most promising and able to work with the demanding quality of service (QOS) of traditional traditional long-distance telephone service (POTS) services. The greatest advantage for digital cable phone service is similar to the advantages of digital cable, ie that data can be compressed, resulting in far less bandwidth being used than special analog circuit-switched services. Other benefits include better voice quality and integration into Voice over Internet Protocol (VoIP) networks that provide cheap and unlimited national and international calls. In many cases, digital cable telephone services are separate from cable modem services offered by many cable companies and do not rely on Internet Protocol (IP) or Internet traffic.
Traditional cable television providers and traditional telecommunications companies are increasingly competing in providing voice, video and data services to residence. The combination of television, telephones, and Internet access is commonly called "triple play", regardless of whether CATV or telcos offer it.
See also
References
Further reading
- Rediffusion History by Gerald K Clode
- Eisenmann, Thomas R., "Cable TV: From Community Antenna to Wired City", Bulletin Bulletin Harvard Business School , July 10, 2000
- Moss, Mitchell L.; Payne, Frances, "Can Cable Keep Its Promise?", New York Affairs , Volume 6, Number 4. New York University. 1981
- Smith, Ralph Lee, "The Wired Nation", The Nation magazine, May 18, 1970
- Smith, Ralph Lee, Wired Nation; Cable TV: electronic communication highway . New York, Harper & amp; Line, 1972. ISBN: 0-06-090243-4
- Herrick, Dennis F. (2012). Media Management in the Age of the Giant: The Dynamics of Business Journalism . UNM Press. ISBN 978-0-8263-5163-0.
External links
- Cable Television in Curlie (based on DMOZ)
Source of the article : Wikipedia
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