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Three of the principal design techniques are shielding, coaxial geometry, and twisted-pair geometry. Like other types of cables, fibre-optic cables are designed and insulated for various applications overland, underground, overhead, and underwater. With fibre-optic cables, made of flexible fibres of glass and plastic, electrical signals are converted to light pulses for the transmission of audio, video, and computer data. Many aerial cables, especially those operating at high voltages, are bare (uninsulated). Additional local channels, such as local broadcast television stations, educational channels from local colleges, and community access channels devoted to local governments (PEG channels) are usually included on the cable service. Many channels can be transmitted through one coaxial cable by a technique called frequency division multiplexing. Multiple cables to different rooms are split off the incoming cable with a small device called a splitter. The first, and still very common, man-made plastic used for cable insulation was polyethylene.
The insulation of a telephone cable is composed of dry cellulose (in the form of paper tape wrapped around the conductor or paper pulp applied to the conductor) or of polyethylene. The most common type of electric power cable is that which is suspended overhead between poles or steel towers. Broadband internet access is achieved over coaxial cable by using cable modems to convert the network data into a type of digital signal that can be transferred over coaxial cable. The cable core contains a single solid or stranded central strength element that is surrounded by optical fibres; these are either arranged loosely in a rigid core tube or packed tightly into a cushioned, flexible outer jacket. Illustrative of these usages and of the special conditions to be met are cables for use in steel mills and boiler rooms (high temperature), on mobile equipment (vibration and excessive flexing), in chemical plants (corrosion), for submarines and mines (mechanical abuse), near nuclear reactors (high radiation), and on artificial satellites (pressure extremes). The receiving antenna would be taller than any individual subscriber could afford, thus bringing in stronger signals; in hilly or mountainous terrain it would be placed at a high elevation. At the local headend, the feed signals from the individual television channels are received by dish antennas from communication satellites.
Physically, an electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual coverings, assembly protection and protective coverings. These coverings offer some protection against short-circuiting and accidental electric shock. CIGRE International Conference on Large High Voltage Electric Systems, 1984 Session, 29 August – 6 September. Electric communication cables transmit voice messages, computer data, and visual images via electrical signals to telephones, wired radios, computers, teleprinters, facsimile machines, and televisions. 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. Cable television signals use only a portion of the bandwidth available over coaxial lines. This service involves installing a special telephone interface at the customer’s premises that converts the analog signals from the customer’s in-home wiring into a digital signal, which is then sent on the local loop (replacing the analog last mile, or plain old telephone service (POTS) to the company’s switching center, where it is connected to the public switched telephone network (PSTN). Electrical cables are extensively used in building wiring for lighting, power and control circuits permanently installed in buildings.
Analog television sets are accommodated, their tuners mostly obsolete and dependent entirely on the set-top box. The cable company will provide set-top boxes based on the level of service a customer purchases, from basic set-top boxes with a standard-definition picture connected through the standard coaxial connection on the TV, to high-definition wireless digital video recorder (DVR) receivers connected via HDMI or component. Since the set-top box only decodes the single channel that is being watched, each television in the house requires a separate box. Before being added to the cable box itself, these midband channels were used for early incarnations of pay TV, e.g. The Z Channel (Los Angeles) and HBO 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. 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. Tight lays during stranding makes the cable extensible (CBA – as in telephone handset cords). Electrical cables may be made more flexible by stranding the wires.
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