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Concept
Cable television headend
Summary
A cable television headend is a master facility for receiving television signals for processing and distribution over a cable television system. A headend facility may be staffed or unstaffed and is typically surrounded by some type of security fencing. The building is typically sturdy and purpose-built to provide security, cooling, and easy access for the electronic equipment used to receive and re-transmit video over the local cable infrastructure. One can also find head ends in power-line communication (PLC) substations and Internet communications networks.
Nearly all cable TV systems carry subscription content that is relayed from a satellite in geosynchronous orbit. Encrypted to prevent unauthorized use, this content is uplinked from one or more earth stations operated by various content delivery companies. The content is then analog or digitally modulated and transmitted through the cable network (the OSP or "OutSide Plant") to subscriber homes by means of coaxial or fiber-optic cables buried underground or strung from utility poles.
Most cable TV systems also carry local over-the-air television stations for distribution. While each terrestrial channel represents a defined frequency, one or more commercial-grade receiving television antennas are used to receive the multiple channels that the cable company wishes to distribute. These antennas are often built into a single tower structure called a master antenna television structure. Commercial TV pre-amplifiers strengthen the weakened terrestrial TV signals for distribution, usually after re-modulation using a cable-specific analog or digital scheme.
Some cable TV systems receive the local television stations' programming by dedicated coaxial cable, microwave link or fiber-optic line, installed between the local station and the headend. A device called a modulator at the local station's facilities feed their programming over this line to the cable TV headend, which in turn receives it with another device called a demodulator.
Official source
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