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Coaxial Cable

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  Coaxial cable Coaxial cable also called coax cable are gaining acceptance for use in existing telecommunications and LAN networks. Coaxial cables are most popular using in medium of television. Coaxial cables have a many kinds. Some designed for use with baseband systems, other use in broadband system networks. However, the main differences among various kinds of coaxial cable are in the materials used for the components of cable. Figure 1: side view of coaxial cable Figure2: cross-section of coaxial cable Coaxial cable comes packaged in a variety of ways, but essentially it consists of one or two central data transmission wires surrounded by an insulating layer, a shielding layer, and an outer jacket. The center of coaxial cable is conductor wire that caries the transmission signal. The conductor wire is insulated by nonconducting materials such as PVC or Teflon and then is surrounded by another conducting material  usually solid copper or woven mesh. All encased in another layer of insulation, sometimes called a sleeve. The outer sleeve may be extruded aluminum. The one advantage of coaxial cable is that it is widely used in non-LAN applications. So, it is widely available, which helps bring down the cost and it relies on what is already a mature technology. Coaxial cable shielding provides high degree immunity to externally caused signal distortion. Because coaxial cable offers higher immunity than twisted- pair cable to noise, it afford higher bandwidth and higher speed. It costs three to four times as much to install this medium. In LANs of less than a half-mile range, signal loss or attenuation is not concern, for no longer distances. However, repeaters that enhance the signals are necessary. Data transmission rates over coaxial cable of up to 100Mbps are not uncommon, and the theoretical bit rate is more than 400Mbps. Coaxial cable is most commonly used in two types of LANs, Ethernet and ARCNET. Ethernet is widely used and supports speed of 10Mbps, 100Mbps, and 1000 Mbps. Coaxial cable was specified for early Ethernet LANs operating at 10Mbps. Thus, coaxial cable is now infrequently used in the foremost LAN implementations. For early Ethernet, it supports two types of coaxial cable, thick and thin. LANs using the thick cable are called thicknets and those using thin cables are called thinnets. The main difference between these two types of coaxial cable is the thickness of cable or the diameter of the center. Coaxial cable is not as easy to tap as twisted-pair cable. Usually tapping a coaxial cable requires piercing and coring the cable and then clamping on a tap. Coaxial cable usually an unbalanced cable as the outer conductor has the effect of a screen and is earthed. The two main parameters of coaxial cable are attenuation and characteristic impedance. Generally the larger the cable may be improved by having several layers of braid screens. Coaxial cables have a very good high frequency, broadband performance and still greatly used for video transmission such as in CATV distribution, CCTV and RGB graphics systems. As the overall, the highlight characteristics of coaxial cable are widely available. Coaxial cable is good noise immunity, high usable bandwidth. The speed data is up to 10 Mbps. Besides that, it difficult to tap than twisted-pair wiring and more expensive than twisted-pair wiring.  Twisted-pair cable Twisted-pair cables a thin-diameter copper cable used for voice and data networks cabling. The wires are twisted around each other to minimize interface from other twisted pairs in the cable. There have two types of cable are found in LANs, there are shielded twisted-pair (STP) and unshielded-twisted-pair (UTP). Even though twisting pairs of wires together minimizes crosstalk, it does not eliminate it, and there are other sources of transmission errors we need to avoid. Some of errors can be reduce by shielding the wires. There are some different between few type of media. Medium type Common speed(Mbps) Error Characteristic Unshielded twisted-pair( UTP ) 1, 4, 10, 16, 100, 1000 Less capable than other conductor media Shielded twisted-pair ( STP ) 1, 4, 10, 16, 100, 1000 Better than unshielded: less capable than fiber optic or coaxial cable. Coaxial cable 10, 16, 50 Good: less capable than fiber optic cable Unshielded twisted-pair cable (UTP) Unshielded twisted-pair cable (UTP) is a popular cable type made up of two unshielded wires twisted around each other. UTP is the most frequently used network cable because it is relatively inexpensive and easy to install. Figure below show the diagram of UTP. Figures3: unshielded twisted-pair wire  UTP cabling is available in seven standard categories defined by the Telecommunications Industry Associations 568 (ANSI/EIA/TIA-568). The differences of category can be indicates the number of twisted per inch. The more twist in the cabling, the more immune of cable from interference, and the faster cable can transmit. Shielded Twisted-pair cable Shielded twisted-pair cable consists of pairs of insulated solid wire surrounded by a braided or corrugated shielding. This shielding may be a metallic foil or copper braid. It function is rather simple. It shields the individual twisted pairs as well as the entire cable from either cable from either electromagnetic interference (EMI) or radiofrequency interference (RFI).installation of shielded twisted pair can be tricky. Figure 4: shielded twisted-pair cable Figure above show the diagram of shielded twisted-pair cable. It is consists of jacket, braided shield, foil shield and the twisted pairs. The differences between UTP and STP are the twisted pair of STP is surrounding by foil shield. The extra covering in STP wiring protects the transmission line from electromagnetics interference (EMI) from leaking into or out of the cable that could result in signal degradation or loss.
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