Coaxial Cable :: Networks Telecommunications

IntroductionCoaxial cable is an electrical cable consisting of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath, usually surrounded by a final insulating layer. It is utilise as a high-frequency transmission line to carry a high-frequency or wideband signal. Sometimes DC power (called bias) is added to the signal to supply the equipment at the other end, as in direct broadcast satellite receivers. Beca expend the electromagnetic field carrying the signal exists (ideally) only in the space between the inner and outer conductors, it cannot interfere with or suffer interference from external electromagnetic fields.Coaxial cables may be rigid or flexible. Rigid types have a solid sheath, while flexible types have a braided sheath, both usually of thin pig bed wire. The inner insulator, also called the dielectric, has a significant effect on the cables properties, such as its characteristic impedance and its attenuation. The die lectric may be solid or perforated with air spaces. Connections to the ends of coaxial cables are usually made with RF connectors.Radio-grade flexible coaxial cable.A outer plastic sheathB pig screenC inner dielectric insulatorD copper coreThere are two types of coaxial cables1.Thinnet2.Thicknet ThinnetAlso known as Thin Ethernet or Thinnet, 10BASE-2 is an IEEE standard for baseband Ethernet at 10MBps over thick coaxial cable. 10Base2 has a maximum distance of 185 meters. Thin Ethernet is five millimeters in diameter and used to connect machines up to 1,000 feet apart.Thinnet (thin Ethernet) is an incarnation of the Ethernet standard in which coaxial cables are used in a LAN (local-area network) configuration to connect computers together. A Thinnet apparatus is capable of transmitting data at a rate of 10Mbps (megabits per second). It is also cheaper and easier to install than Thicknet.The first variation on the original variety of Ethernet was simply to use a thinner coaxial ca ble and relax the constraints on how and where transceivers can connect. 10BASE-2 does this with coaxial cable that looks just like the cable used for receiving cable television receiver or hooking up a television set to an antenna. The only difference in the cable itself is the impedance rating. A television cable is rated at 75 ohms and a 10BASE-2 cable is rated at 50 ohms. In a pinch, a small length of one can be substituted for the other. The connectors used in 10BASE-2 are called BNC connectors for Berkeley Nucleonics Co. they were originally used in nuclear physics.