Co-Axial Cable

Introduction of Co-axial cables:

Coaxial cable is a two conductor electrical cable, which consists of a center conductor and an outer conductor with an insulating dielectric material between the two. It is also referred as "Coax".

Coaxial cable is called "coaxial" because one would find a single center solid wire symmetrically surrounded by another concentric physical channel, both running along the same axis.

Data is transmitted through the center wire, while the outer braided layer serves as a line to ground. The dielectric has a large effect on the fundamental characteristics of the cable, where dielectric is an insulator that separates the center conductor and shielding.

Coaxial cable was invented in 1929 and first used commercially in 1941. AT&T established its first cross-continental coaxial transmission system in 1940 which could carry 8.5-kHz broadcast channel and seven telephone channels. At present, Co-axial can transmit information at the max frequency range of upto 2000GHz.

The characteristic impedance is on of the characteristic of co-axial which is defined as the ratio of the amplitudes of a single pair of voltage and current wave propagating along an infinitely long transmission line with absence of any reflections. It measures like resistance when dealing with co-axial cable.The characteristic impedance of this cable depends on the dielectric material and the radii of each conducting material.

It is least expensive, most reliable, more convenient, and easily maintained way of transferring electronic Information.

The advantage of the braided shield is that it protects the information transferred from the center conductor from the external electromagnetic interference.

Co-axial have standard impedance of 50 ohms to 75 ohms.

Classification of Co-axial cables:

Various types of coax are Hard Line, Radiating or Leaky,RG-6, Triaxial, Twin-axial, Bi-axial, Semi Rigid ,Rigid Line.

RG-6 and RG-59/U are widely used coax where "RG" stands for Radio Guide and 'U'stands for A universal specification.

Co-Axial Connector:

At each end of a cable, connectors are required for further interface of cable with other system. The various kind of connectors used are BNC, SMA, SMB, F, etc.

Important Concepts:

1.Skin Effect:

The skin effect is the description given to the phenomenon where electromagnetic fields (and therefore the current) decay rapidly with depth inside a good conductor in other words it is the tendency of an alternating electric current(AC) to become spread within a conductor in such a way that the current density is largest near the surface(skin) of the conductor, and decreases with greater depths in the conductor.

The electric current flows mainly at the "skin" of the conductor, between the outer surface and a level called the skin depth.

The effect becomes more and more apparent as the frequency increases.