Cable television

Cable television is a sophisticated system for delivering programming to consumers. It uses radio frequency (RF) signals to transmit data. These signals travel through coaxial cables or modern fiber-optic cables. This method differs from terrestrial television, which uses over-the-air radio waves and antennas. It also differs from satellite television, which uses dishes to receive signals from space. Beyond television, these cable systems can provide high-speed Internet and telephone services.

The process begins at a local facility called a headend. At the headend, engineers receive signals from communication satellites using dish antennas. These signals include national channels and local broadcast stations. They also include community access channels and educational programming. To send many channels through one cable, the system uses frequency division multiplexing. This technique assigns each channel a specific frequency slot. This ensures that the different signals do not interfere with one another.

Most modern networks use a hybrid fiber-coaxial (HFC) distribution method. In an HFC system, the signal starts as an electrical signal at the headend. This is converted into an optical signal, which is a pulse of light. The light travels through optical fiber trunklines to reach local neighborhoods. These trunklines provide high bandwidth and capacity for future growth. At a local optical node, the light is translated back into an electrical signal. This electrical signal then travels through coaxial cables to individual homes.

Once the signal reaches a home, it enters through a service drop. This is an overhead or underground cable connected to the building. In the United States, the standard cable is RG-6. This cable has a 75 ohm impedance and uses a type F connector.

Inside the building, the signal moves through wiring in the walls to different rooms. A small device called a splitter is used to divide the signal among multiple jacks. This allows different televisions in the house to receive the signal separately.

To view digital channels, subscribers usually need a set-top box. This electronic device is often called a cable converter box. Most digital channels are encrypted, which means the signal is scrambled. This encryption helps prevent cable service theft. The set-top box decodes the signal so the television can display it.

Because the box only decodes one channel at a time, each TV needs its own box. Some unencrypted broadcast channels can be viewed without a receiver. However, digital channels on older analog TVs require a digital television adapter.

Cable television has a long and evolving history. The earliest local networks appeared in 1936 in London and Berlin. In the United States, the industry grew as a commercial business in the 1950s. Early systems were often called community antenna television, or CATV. These systems helped people in mountainous areas or distant locations receive signals. In 1968, only 6.4% of Americans had cable television. This number grew to 52.8% by 1988 and reached 62.4% by 1994.

Modern systems are massive and serve entire metropolitan areas. A single coaxial cable can carry as many as 500 channels. The system also manages two-way communication through upstream and downstream channels. Downstream channels, which carry incoming data, occupy frequencies from 50 MHz to 1 GHz. Upstream channels, which send data from the home to the headend, occupy 5 to 42 MHz. This upstream capability allows for features like pay-per-view movies and internet access. This complex network keeps millions of people connected to information and entertainment.