Construction of Coaxial Wire
Posted under: Home Automation
A coaxial cable comprises of two conductors with a common axis. The conductor on the inner side is just a straight wire which can be stranded or solid. The conductor on the outer side is braided or foiled so that it can act like a shield.
The following layers are found in a coaxial cable. The first layer discussed takes up the centre spot and the last layer is the outermost layer. All other layers are found in between these two.
- As mentioned above, the central layer comprises of a conducting material. The preferred choice for the core is solid copper. This layer transmits the baseband video signal. During transmission, a certain amount of signal is lost due to long distance. The main reason for this is resistance, so a bigger conductor should be used. Resistance is inversely proportional to area so it is decreased this way, and most of the signal is retained.
- The dielectric layer surrounds the centre copper core. This is basically the waxy, opaque part of the cable, and is made up of hydrocarbons such as polyolefins, polystyrene and polypropylenes. At times, air is also used as dielectric, but in this case, spacers are used to support the inner wire and to prevent it with from coming in contact with the shield. The function of the dielectric is to separate the inner conductor from the shield and provide physical support.
- The next layer is the metallic shield, generally composed of braided copper. It has two main purposes: to protect the conductor from noise or other unwanted signals, referred to as ingress, and to retain the transmitted signal in the conductor, referred to as egress. On this basis, coaxial cables can also be classified as dual and quad. Dual cables have two layers of shielding and quad cables have four.
- The last layer is the outside insulation which encloses all the inner layers. This is called a jacket and is usually made from PVC.
Attenuation or Insertion Loss:
Attenuation is the process of losing a signal when it is being transmitted. It is caused by long cables, humidity, temperature and excess return loss. Insertion loss is not only present in the coaxial cable, but is also seen in devices connected to the cable such as amplifiers and splitters.
Systems are design such that attenuation is minimized.