Cable television headend is a master facility for receiving television signals for processing and distribution over a cable television system. The headend facility is normally unmanned and surrounded by some type of security fencing and is typically a building or large shed housing electronic equipment used to receive and re-transmit video over the local cable infrastructure. One can also find headends in power line communication (PLC) substations. Coaxial cable is often used to transmit cable television into the house. ... It has been suggested that Mains network be merged into this article or section. ... A 115 kV to 41. ...

Reception

The cable TV headend will normally have several large FSS-type television receive-only satellite television dishes for reception of cable/satellite TV networks such as ESPN, CNN, or HBO; a dedicated, non-movable dish is required for each satellite that the cable TV utility wishes to receive cable channels from for distribution over its system. For reception of signals from several adjacent satellites, a larger non-parabolic multi-satellite dish (such as the Torus or Simulsat) that can see up to 3 or more satellites is often used. Many digital cable systems use services like HITS ("Headend In The Sky", a unit of Comcast), which carry hundreds of channels on just a few satellites; this is commonly used by small systems to expand service without adding expensive new dishes or other equipment. Fixed Service Satellite (or FSS), is the official classification for geostationary communications satellites used chiefly for broadcast feeds for television and radio stations and networks, as well as for telephony, data communications, and also for direct-to-home (DTH) cable and satellite TV channels (although this role has been somewhat... Television receive-only, or TVRO is a term used in North America to refer to the reception of satellite television from FSS-type satellites, generally on C-band analogue; free-to-air and unconnected to a commercial DBS provider. ... Artists impression of a Boeing 601 satellite, as configured for digital television transmission by SES Astra Satellite television is television delivered by way of communications satellites, as compared to conventional terrestrial television and cable television. ... This article needs to be cleaned up to conform to a higher standard of quality. ... U.S. military MILSTAR communications satellite A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications. ... Wikisource has an original article from the 1911 Encyclopædia Britannica about: Parabola A parabola The parabola (from the Greek: παραβολή) is a conic section generated by the intersection of a right circular conical surface and a plane parallel to a generating straight line of that surface. ... Simulsat is a quasi-parabolic satellite earthstation antenna that is capable of receiving satellite transmissions from 35 or more C and Ku Band satellites simultaneously. ... Digital cable is a term for a type of cable digital television that delivers more channels than possible with analog cable by using digital video compression. ... Comcast Corporation, (NASDAQ: CMCSA) based in Philadelphia, Pennsylvania, is the largest cable company and the largest broadband (second overall) Internet service provider in the United States. ...

Cable TV systems usually also carry local over-the-air television networks for distribution. Since each terrestrial channel represents a defined frequency, a dedicated commercial-grade receiving antenna is needed for each channel that the cable company wishes to receive and distribute. These antennae are often built into a single tower structure called a master antenna television structure. Often, commercial TV pre-amplifiers are used to strengthen weakened terrestrial TV signals as much as possible before distribution. Terrestrial television (also known as over-the-air, OTA, or broadcast television) is the traditional method of television broadcast signal delivery, by radio waves transmitted through open space, usually carrying unencrypted signals. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ...

Some cable TV systems receive the local television stations' programming by instead having a dedicated coaxial or fiber-optic line installed between the local station and the headend. A device called a modulator is installed at the local station's facilities to feed their programming over this line to the cable tv headend, which in turn receives it with another device called a de-modulator. It is then distributed through the cable tv headend to the subscriber. This is usually a more reliable method than receiving the local stations' broadcasts over the air with an antenna, however, off-air reception is used as a backup by the headend if the dedicated line, modulator, or demodulator were to fail. Radio-grade flexible coaxial cable. ... Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ...

Other sources of programming include those delivered via fiber optics, telephone wires, the Internet, microwave towers and local community access channels that are sent to the cable headend on an outbound frequency over the cable system itself (known in the industry as "T"-channels), or via a dedicated line set up by the cable company, as mentioned earlier for reception of local television stations' programming by the headend. Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ... The telephone or phone (Greek: tele = far away and phone = voice) is a telecommunications device which is used to transmit and receive sound (most commonly voice and speech) across distance. ... Microwave image of 3C353 galaxy at 8. ... North America cable television broadcast band Channels T-7 through T-14 are sub-band channels and are not used for normal television channel distribution. ...

Signal processing

Once a television signal is received, it must be processed. For satellite TV signals, a dedicated commercial satellite receiver is needed for each channel that is to be distributed by the cable system; these are usually rack-mountable receivers that are designed to take up less space than consumer receivers. Analog terrestrial TV signals do not need a special receiver for reception.

Once received, cable television signals are then mixed into the cable system's channel numbering scheme using a series of cable modulators (one for each channel), which is in turn fed into a frequency multiplexer. Once processed, the television signals are sent over the cable system's coaxial cables and continuously re-amplified as needed.

See also

• North American broadcast television frequencies
• North American cable television frequencies

In North America, terrestrial television is broadcast on designated channels numbered 2 through 69. ... North America cable television broadcast band Channels T-7 through T-14 are sub-band channels and are not used for normal television channel distribution. ...

External links

• HITS website