Usage
Repeaters are used to boost signals in coaxial and twisted pair cable and in optical fiber lines. An electrical signal in a cable gets weaker the further it travels, due to energy dissipated in conductor resistance and dielectric losses. Similarly a light signal traveling through an optical fiber suffers attenuation due to scattering and absorption. In long cable runs, repeaters are used to periodically regenerate and strengthen the signal. A network hub is one such device.
An optical communications repeater is a piece of equipment that receives an optical signal, converts that signal into an electrical one, regenerates it, and then retransmits it as an optical signal. In contrast, optical amplifiers, which amplify the light beam directly, are often used in transcontinental and submarine communications cables, because the signal loss over such distances would be unacceptable without them.
Radio repeaters are used in radio communication services. A radio repeater consists of a radio receiver connected to a transmitter. The radio signal is received, amplified and retransmitted, usually on a different frequency. Higher radio frequencies are limited to line-of-sight transmission, their range is blocked by mountains and the curvature of the Earth, so repeaters are located on hills and mountains, to retransmit the signal beyond the obstruction. Radio repeaters are also used extensively in broadcasting, where they are known as broadcast relay stations. These extend the broadcast coverage area to remote communities, outside the range of the main broadcast station.
A digipeater is a blend meaning "digital repeater", particularly used in amateur radio. Store and forward digipeaters generally receive a packet radio transmission and then retransmit it on the same frequency.
When providing a point-to-point telecom link using radio beyond line of sight, one uses repeaters in a microwave radio relay. A reflector, often on a mountaintop, that relays such signals around an obstacle, is called a passive repeater.
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