|  | 5.1 | Most Common LAN Media
| 5.1.3 | Coaxial cable

Coaxial cable consists of a hollow outer cylindrical conductor that surrounds a single inner wire made of two conducting elements. One of these elements - located in the center of the cable - is a copper conductor. Surrounding it is a layer of flexible insulation. Over this insulating material is a woven copper braid or metallic foil that acts as the second wire in the circuit, and as a shield for the inner conductor. This second layer, or shield, can help reduce the amount of outside interference. Covering this shield is the cable jacket.

For LANs, coaxial cable offers several advantages. It can be run, without as many boosts from repeaters, for longer distances between network nodes than either STP or UTP cable. Repeaters regenerate the signals in a network so that they can cover greater distances. Coaxial cable is less expensive than fiber-optic cable, and the technology is well known. It has been used for many years for all types of data communication. Can you think of another type of communication that utilizes coaxial cable?

When working with cable, it is important to consider its size. As the thickness, or diameter, of the cable increases, so does the difficulty in working with it. You must remember that cable must be pulled through existing conduits and troughs that are limited in size. Coaxial cable comes in a variety of sizes. The largest diameter was specified for use as Ethernet backbone cable because it had historically a greater transmission length and noise rejection characteristics. This type of coaxial cable is frequently referred to as thicknet. As its nickname suggests, this type of cable, because of its thickness, can be too rigid to install easily in some situations. The rule of thumb is: "the more difficult the network media is to install, the more expensive it is to install." Coaxial cable is more expensive to install than twisted-pair cable. Thicknet cable is almost never used anymore, except for special purpose installations.

In the past, coaxial cable with an outside diameter of only .35 cm (sometimes referred to as thinnet) was used in Ethernet networks. It was especially useful for cable installations that required the cable to make many twists and turns. Since it was easier to install, it was also cheaper to install. This led some people to refer to it as cheapernet. However, because the outer copper or metallic braid in coaxial cable comprises half the electrical circuit, special care must be taken to ensure that it is properly grounded. This is done by ensuring that there is a solid electrical connection at both ends of the cable. Frequently, installers fail to do this. As a result, poor shield connection is one of the biggest sources of connection problems in the installation of coaxial cable. Connection problems result in electrical noise that interferes with signal transmittal on the networking media. It is for this reason that, despite its small diameter, thinnet is no longer commonly used in Ethernet networks.