Coaxial Cable
Physical Description: Coaxial cable, like twisted pair, consists of two conductors, but is constructed differently to permit it to operate over a wider range of frequencies. It consists of a hollow outer cylindrical conductor that surrounds a single inner wire conductor (Figure 4.2b). The inner conductor is held in place by either regularly spaced insulating rings or a solid dielectric material. The outer conductor is covered with a jacket or shield. A single coaxial cable has a diameter of from 1 to 2.5 cm. Coaxial cable can be used over longer distances and support more stations on a shared line than twisted pair.
Applications: Coaxial cable is a versatile transmission medium, used in a wide variety of applications.The most important of these are
• Television distribution
• Long distance telephone transmission
• Short run computer system links
• Local area networks
Coaxial cable is widely used as a means of distributing TV signals to individual homes—cable TV. From its modest beginnings as Community Antenna Television (CATV), designed to provide service to remote areas, cable TV reaches almost as many homes and offices as the telephone. A cable TV system can carry dozens or even hundreds of TV channels at ranges up to a few tens of kilometers.
Coaxial cable has traditionally been an important part of the long distance telephone network.Today, it faces increasing competition from optical fiber, terrestrial microwave, and satellite. Using frequency division multiplexing (FDM, see Chapter 8), a coaxial cable can carry over 10,000 voice channels simultaneously.
Coaxial cable is also commonly used for short range connections between devices. Using digital signaling, coaxial cable can be used to provide high speed I/O channels on computer systems.
Transmission Characteristics: Coaxial cable is used to transmit both analog and digital signals. As can be seen from Figure 4.3b, coaxial cable has frequency characteristics that are superior to those of twisted pair and can hence be used effectively at higher frequencies and data rates. Because of its shielded, concentric construction, coaxial cable is much less susceptible to interference and crosstalk than twisted pair. The principal constraints on performance are attenuation, thermal noise, and intermodulation noise. The latter is present only when several channels (FDM) or frequency bands are in use on the cable.
For long distance transmission of analog signals, amplifiers are needed every few kilometers,with closer spacing required if higher frequencies are used.The usable spectrum for analog signaling extends to about 500 MHz.For digital signaling, repeaters are needed every kilometer or so,with closer spacing needed for higher data rates.
Physical Description: Coaxial cable, like twisted pair, consists of two conductors, but is constructed differently to permit it to operate over a wider range of frequencies. It consists of a hollow outer cylindrical conductor that surrounds a single inner wire conductor (Figure 4.2b). The inner conductor is held in place by either regularly spaced insulating rings or a solid dielectric material. The outer conductor is covered with a jacket or shield. A single coaxial cable has a diameter of from 1 to 2.5 cm. Coaxial cable can be used over longer distances and support more stations on a shared line than twisted pair.
Applications: Coaxial cable is a versatile transmission medium, used in a wide variety of applications.The most important of these are
• Television distribution
• Long distance telephone transmission
• Short run computer system links
• Local area networks
Coaxial cable is widely used as a means of distributing TV signals to individual homes—cable TV. From its modest beginnings as Community Antenna Television (CATV), designed to provide service to remote areas, cable TV reaches almost as many homes and offices as the telephone. A cable TV system can carry dozens or even hundreds of TV channels at ranges up to a few tens of kilometers.
Coaxial cable has traditionally been an important part of the long distance telephone network.Today, it faces increasing competition from optical fiber, terrestrial microwave, and satellite. Using frequency division multiplexing (FDM, see Chapter 8), a coaxial cable can carry over 10,000 voice channels simultaneously.
Coaxial cable is also commonly used for short range connections between devices. Using digital signaling, coaxial cable can be used to provide high speed I/O channels on computer systems.
Transmission Characteristics: Coaxial cable is used to transmit both analog and digital signals. As can be seen from Figure 4.3b, coaxial cable has frequency characteristics that are superior to those of twisted pair and can hence be used effectively at higher frequencies and data rates. Because of its shielded, concentric construction, coaxial cable is much less susceptible to interference and crosstalk than twisted pair. The principal constraints on performance are attenuation, thermal noise, and intermodulation noise. The latter is present only when several channels (FDM) or frequency bands are in use on the cable.
For long distance transmission of analog signals, amplifiers are needed every few kilometers,with closer spacing required if higher frequencies are used.The usable spectrum for analog signaling extends to about 500 MHz.For digital signaling, repeaters are needed every kilometer or so,with closer spacing needed for higher data rates.
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