Coaxial Cable :: Networks Telecommunications

Introduction Coaxial 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 used as a high-frequency transmission line to carry a high-frequency or broadband 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. Because 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 copper wire. The inner insulator, also called the dielectric, has a significant effect on the cable's properties, such as its characteristic impedance and its attenuation. The dielectric 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 sheath B: copper screen C: inner dielectric insulator D: copper core There are two types of coaxial cables: 1. Thinnet 2. Thicknet Thinnet Also 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 setup 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 cable 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 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.