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# 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.

• 2.Velocity Propagation :
• It is the transmission speed of electrical energy in a determined length of cable as compared to speed of light.

## Mathematics :

Calculation of characteristic impedance:

Calculation of attenuation:

## Applications:

• Wireless and antenna application(connecting from dish to television through co-axial cable. example: Tata sky)
• RF and Microwave transmission
• Video distribution
• Cable television and cable internet

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