A coaxial cable is a specific type of cable that consists of four layers of material. There is an inner conductor, a dielectric insulating layer, another conductive layer, and an insulating layer. The cable is called coaxial because both the inner and outer conductive layers are on the same geometric axis. A geometric axis is a line passing through the length of the material.
These cables are designed to be used for radio frequency transmissions. The purpose of the multiple layers is to restrict the electromagnetic field generated by the signal to interior of the cable itself. Using this development, the amount of electromagnetic interference through the cable is reduced.
The inner conductor can be either solid or stranded in design. Stranded is the preferred wire type, due to its greater degree of flexibility. An option to improve performance is to purchase a coaxial cable with a silver plated inner conductor. The other option is a copper-plated iron wire.
The next layer is insulation, which can be made from foam plastic, air with spacers to hold the inner wire and stop it from touching the shield, solid plastic or solid Teflon®. In cables with a low level of electrical loss, a polyethylene insulation is often used. The higher quality the insulation, the greater the cost.
In a standard coaxial cable, the shield is formed from copper wire that is braided to improve flexibility. The braided wire can be silver-plated, double-layered or covered in foil to improve shield performance. Depending on the required level of signal shielding, the shield can be a solid metal tube.
The risk of using this type of hard line cable is the inability to accommodate sharp bends. Any kink in the shield results in signal loss within the cable. This type of installation is most frequently seen in cable television distribution systems, due to their requirement for a lower level of signal loss.
The insulation jacket is frequently made from polyvinyl chloride (PVC), but can also be made from a wide range of materials. It can include properties of fire resistance, anti-oxidation or ultraviolet light resistance. The type of insulation required depends on the installation and the environment.
The materials used in the composition of the coaxial cable must comply with government regulations on the acceptable level of electromagnetic signal leakage. These signals interfere with a wide range of other signals. The type of insulation required to reduce the level of signal leakage to zero is both expensive and unpractical. The cables made today are a combination of features and are deigned to reduce the levels of interference as much as possible without incurring disproportionate costs and creating unpractical cable properties.