Coaxial cable, or coax, is an electrical cable with an inner conductor surrounded by a tubular insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer (typically of fine woven wire for flexibility, or of a thin metallic foil), and finally covered with a thin insulating layer on the outside. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, who first patented the design in 1880.
Coaxial cable is used as a transmission line for radio frequency signals, in applications such as connecting radio transmitters and receivers with their antennas, computer network (Internet) connections, and distributing cable television signals. One advantage of coax over other types of transmission line is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors. This allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other transmission lines, and provides protection of the signal from external electromagnetic interference.
Coaxial cable should not be confused with other shielded cable used for carrying lower frequency signals such as audio signals. Shielded cable is similar in that it consists of a central wire or wires surrounded by a tubular shield conductor, but it is not constructed with the precise conductor spacing needed to function efficiently as a radio frequency transmission line.
Twisted pair
Twisted pair cabling is a form of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from Unshielded Twisted Pair (UTP) cables, and crosstalk between neighboring pairs.
UTP
STP
Fiber Optic
A fiber optic cable transmits a signal using a wave of light, while copper wires transmit a signal using an electric current. (Palais, 1998). A typical fiber optic wire consists of a plastic sheath surrounding a glass tube. Inside the tube is a tiny core in which the light waves travel. Separating the core and the tube is a cladding that prevents the light waves from escaping. One wire design has a core diameter of 125 microns and a sheath diameter of 2.5 millimeters.
The wire’s small size provides an advantage over copper wires. Fiber optic cables weigh less than copper wires, which makes installation easier and allows the wires to be placed in smaller areas. (Palais, 1998). Although the wires are made of glass, they are extremely flexible therefore easing the problems involved with installation.
Although the core of a fiber optic cable is very small, large amounts of information can be transported at one time. In copper wires, only one signal can be sent across the wire at a single time but in a fiber optic cable, many light waves can be sent at once. This allows the wires to be more cost effective. Silicon oxide is the material used to make fiber optic wires. This material is less expensive than the copper used in coaxial cables making fiber optics less expensive to make. Also, fewer fiber optic cables are needed for mass communication.
Fiber optic cables also have disadvantages. Because they use light to transmit information they are incompatible with the old copper wires. This creates a problem because telephone companies cannot use the wire system that is already present. They must build a new system using fiber optics. Fiber optic cables are also very difficult to connect. In order to connect the wires, the glass tube must be broken and then melted together with the new wire. With copper wires, you simply cut away the plastic coating and join the wires. This also creates a problem when repairing fiber optic wires. A copper wire is much easier to repair than a fiber optic wire. Special tools and highly trained professionals are needed to repair the damaged fiber wires.
In a fiber optic cable, many light waves of information are transmitted at one time. Sometimes so much information comes in that the cable becomes jammed and the information slows down. This cannot occur in copper wires because only one signal is generated at a time. Often, at points in the cable where traffic is heavy, bottlenecks occur. A bottleneck is when so much information tries to squeeze through but is lost.
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