Cable television: Difference between revisions
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Although early ([[VHF]]) television receivers could receive 12 channels (2–13), the maximum number of channels that could be broadcast in one city was 7: channels 2, 4, either 5 or 6, 7, 9, 11 and 13, as receivers at the time were unable to receive strong (local) signals on adjacent channels without distortion. (There were frequency gaps between 4 and 5, and between 6 and 7, which allowed both to be used in the same city). |
Although early ([[VHF]]) television receivers could receive 12 channels (2–13), the maximum number of channels that could be broadcast in one city was 7: channels 2, 4, either 5 or 6, 7, 9, 11 and 13, as receivers at the time were unable to receive strong (local) signals on adjacent channels without distortion. (There were frequency gaps between 4 and 5, and between 6 and 7, which allowed both to be used in the same city). |
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As equipment improved, all twelve channels could be utilized, except where a local VHF television station broadcast. Local broadcast channels were not usable for signals deemed to be priority, but technology allowed low-priority signals to be placed on such channels by synchronizing their [[blanking interval]]s. |
As equipment improved, all twelve channels could be utilized, except where a local VHF television station broadcast. Local broadcast channels were not usable for signals deemed to be priority, but technology allowed low-priority signals to be placed on such channels by synchronizing their [[blanking interval]]s. TV's were unable to reconcile these blanking intervals and the slight changes to due to travel through a medium, causing [[ghosting (television)|ghosting]].<ref>{{cite web |title=ELIMINATION OF GHOST IN TELEVISION PICTURE |url=http://zwiki.org/Elimination%20of%20Ghost%20in%20television%20picture%20-%20GCR.pdf |website=zwiki.org |access-date=29 January 2021}}</ref> |
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The bandwidth of the amplifiers also was limited, meaning frequencies over 250 MHz were difficult to transmit to distant portions of the coaxial network, and UHF channels could not be used at all. To expand beyond 12 channels, non-standard "midband" channels had to be used, located between the FM band and Channel 7, or "superband" beyond Channel 13 up to about 300 MHz; these channels initially were only accessible using separate tuner boxes that sent the chosen channel into the TV set on Channel 2, 3 or 4.{{Citation needed|date = November 2017}} Initially, UHF broadcast stations were at a disadvantage because the standard TV sets in use at the time we’re unable to receive their channels. Around 1966 the FCC mandated that all TV sets sold after a certain date were required to have the capability of receiving UHF channels. |
The bandwidth of the amplifiers also was limited, meaning frequencies over 250 MHz were difficult to transmit to distant portions of the coaxial network, and UHF channels could not be used at all. To expand beyond 12 channels, non-standard "midband" channels had to be used, located between the FM band and Channel 7, or "superband" beyond Channel 13 up to about 300 MHz; these channels initially were only accessible using separate tuner boxes that sent the chosen channel into the TV set on Channel 2, 3 or 4.{{Citation needed|date = November 2017}} Initially, UHF broadcast stations were at a disadvantage because the standard TV sets in use at the time we’re unable to receive their channels. Around 1966 the FCC mandated that all TV sets sold after a certain date were required to have the capability of receiving UHF channels. |
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Revision as of 20:52, 29 January 2021
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Cable television is a system of delivering
A "cable channel" (sometimes known as a "cable network") is a television network available via cable television. When available through
The abbreviation CATV is often used for cable television. It originally stood for Community Access Television or Community Antenna Television, from cable television's origins in 1948. In areas where over-the-air TV reception was limited by distance from transmitters or mountainous terrain, large "community antennas" were constructed, and cable was run from them to individual homes. In 1968 6.4% of Americans had cable television. The number increased to 7.5% in 1978. By 1988 52.8% of all households were using cable. The number further increased to 62.4% in 1994.[1]
Distribution
To receive cable television at a given location, cable distribution lines must be available on the local utility poles or underground utility lines. Coaxial cable brings the signal to the customer's building through a service drop, an overhead or underground cable. If the subscriber's building does not have a cable service drop, the cable company will install one. The standard cable used in the U.S. is RG-6, which has a 75 ohm impedance, and connects with a type F connector. The cable company's portion of the wiring usually ends at a distribution box on the building exterior, and built-in cable wiring in the walls usually distributes the signal to jacks in different rooms to which televisions are connected. Multiple cables to different rooms are split off the incoming cable with a small device called a splitter. There are two standards for cable television; older analog cable, and newer digital cable which can carry data signals used by digital television receivers such as high-definition television (HDTV) equipment. All cable companies in the United States have switched to or are in the course of switching to digital cable television since it was first introduced in the late 1990s.
Most cable companies require a
Principle of operation
In the most common system, multiple television channels (as many as 500, although this varies depending on the provider's available channel capacity) are distributed to subscriber residences through a
There are also usually "
Hybrid fiber-coaxial
Modern cable systems are large, with a single network and headend often serving an entire metropolitan area. Most systems use hybrid fiber-coaxial (HFC) distribution; this means the trunklines that carry the signal from the headend to local neighborhoods are optical fiber to provide greater bandwidth and also extra capacity for future expansion. At the headend, the electrical signal is translated into an optical signal and sent through the fiber. The fiber trunkline goes to several distribution hubs, from which multiple fibers fan out to carry the signal to boxes called optical nodes in local communities. At the optical node, the optical signal is translated back into an electrical signal and carried by coaxial cable distribution lines on utility poles, from which cables branch out to a series of signal amplifiers and line extenders. These devices carry the signal to customers via passive RF devices called taps.
History in North America
Cable television began in the United States as a commercial business in 1950, although there were small-scale systems by
The early systems simply received weak (
At the outset, cable systems only served smaller communities without television stations of their own, and which could not easily receive signals from stations in cities because of distance or hilly terrain. In Canada, however, communities with their own signals were fertile cable markets, as viewers wanted to receive American signals. Rarely, as in the college town of Alfred, New York, U.S. cable systems retransmitted Canadian channels.
Although early (
As equipment improved, all twelve channels could be utilized, except where a local VHF television station broadcast. Local broadcast channels were not usable for signals deemed to be priority, but technology allowed low-priority signals to be placed on such channels by synchronizing their
Before being added to the cable box itself, these midband channels were used for early incarnations of
but transmitted in the clear i.e. not scrambled as standard TV sets of the period could not pick up the signal nor could the average consumer `de-tune' the normal stations to be able to receive it.Once tuners that could receive select mid-band and super-band channels began to be incorporated into standard television sets, broadcasters were forced to either install scrambling circuitry or move these signals further out of the range of reception for early cable-ready TVs and VCRs. However, once consumer sets had the ability to receive all 181 FCC allocated channels, premium broadcasters were left with no choice but to scramble.
Unfortunately for pay-TV operators, the descrambling circuitry was often published in electronics hobby magazines such as Popular Science and Popular Electronics allowing anybody with anything more than a rudimentary knowledge of broadcast electronics to be able to build their own and receive the programming without cost.
Later, the cable operators began to carry
During the 1980s, United States regulations not unlike
Such stations may use similar on-air branding as that used by the nearby broadcast network affiliate, but the fact that these stations do not broadcast over the air and are not regulated by the FCC, their call signs are meaningless. These stations evolved partially into today's over-the-air digital subchannels, where a main broadcast TV station e.g. NBS 37* would – in the case of no local CNB or ABS station being available – rebroadcast the programming from a nearby affiliate but fill in with its own news and other community programming to suit its own locale. Many live
This evolved into today's many cable-only broadcasts of diverse programming, including cable-only produced television movies and miniseries. Cable specialty channels, starting with channels oriented to show movies and large sporting or performance events, diversified further, and "narrowcasting" became common. By the late 1980s, cable-only signals outnumbered broadcast signals on cable systems, some of which by this time had expanded beyond 35 channels. By the mid-1980s in Canada, cable operators were allowed by the regulators to enter into distribution contracts with cable networks on their own.
By the 1990s, tiers became common, with customers able to subscribe to different tiers to obtain different selections of additional channels above the basic selection. By subscribing to additional tiers, customers could get specialty channels, movie channels, and foreign channels. Large cable companies used addressable descramblers to limit access to premium channels for customers not subscribing to higher tiers, however the above magazines often published workarounds for that technology as well.
During the 1990s, the pressure to accommodate the growing array of offerings resulted in digital transmission that made more efficient use of the VHF signal capacity; fibre optics was common to carry signals into areas near the home, where coax could carry higher frequencies over the short remaining distance. Although for a time in the 1980s and 1990s, television receivers and VCRs were equipped to receive the mid-band and super-band channels. Due to the fact that the descrambling circuitry was for a time present in these tuners, depriving the cable operator of much of their revenue, such cable-ready tuners are rarely used now – requiring a return to the set-top boxes used from the 1970s onward.
The conversion to digital broadcasting has put all signals – broadcast and cable – into digital form, rendering analog cable television service mostly obsolete, functional in an ever-dwindling supply of select markets. Analog television sets are still[when?] accommodated, but their tuners are mostly obsolete, oftentimes dependent entirely on the set-top box.
Deployments by continent
Cable television is mostly available in
Other cable-based services
Coaxial cables are capable of bi-directional carriage of signals as well as the transmission of large amounts of
In
Traditional cable television providers and traditional telecommunication companies increasingly compete in providing voice, video and data services to residences. The combination of television, telephone and Internet access is commonly called "triple play", regardless of whether CATV or telcos offer it.
See also
- AllVid
- CableCARD
- "CCTV" as closed-circuit television—not to be confused with CATV
- DOCSIS
- DVB-C
- European cable television frequencies
- List of cable television companies
- Multichannel video programming distributor
- North American television frequencies
- Private cable operator
- QAM (television)
- Satellite television
- Switched video
- Tru2way
References
- JSTOR 23785961.
- ^ Tynan, Dan (23 May 2007). "New Choices Coming for Cable TV Users". TechHive. Retrieved 3 April 2019.
- ^ "ClearQAM – What It Is And Why It Matters". Retrieved 19 June 2015.
- ^ https://www.cisco.com/c/dam/en/us/solutions/collateral/service-provider/cable-access-solutions/cable-ebook.pdf
- ^ "ELIMINATION OF GHOST IN TELEVISION PICTURE" (PDF). zwiki.org. Retrieved 29 January 2021.
Further reading
- The history of Rediffusion by Gerald K Clode
- Eisenmann, Thomas R., "Cable TV: From Community Antennas to Wired Cities", Harvard Business School Weekly Newsletter, 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, The Wired Nation; Cable TV: the electronic communications highway. New York, Harper & Row, 1972. ISBN 0-06-090243-4
- Herrick, Dennis F. (2012). Media Management in the Age of Giants: Business Dynamics of Journalism. UNM Press. ISBN 978-0-8263-5163-0.
External links
- Cable Television at Curlie