The coaxial cable was invented in 1929. However, its commercial use started only in 1941. Coaxial cables consist of round, cylindrical shaped wires which is covered by a spacer, a cylinder shaped sheath which in turn is surrounded by an insulating jacket. Coaxial cable is basically an electrical cable and is used to transfer high frequency signals. The electromagnetic field generated is present in between the inner and the outer conductors. There is therefore less interference from outer electromagnetic fields. This type of cabling is used for industries like cable TV and networking. Coaxial cabling is a bit more costly than normal telephone cabling. However, it is preferred because it allows maximum transmission of data and information with the least interference.
These cables are normally of two types- flexible and rigid. Rigid cables consist of solid type of sheath and flexible cable consists of braided type sheath of copper. The inner insulator (or dielectric) affects the cable's properties, such as attenuation and impedance. RF connectors are used to connect the ends of coaxial cables. Dielectric may be solid or perforated with small holes.
The RF connector is a short and a rigid type of cable having the same impedance as that of cable with which it is associated. However, the dielectric may not be same. The connectors with high quality are normally coated with gold, but lower quality cables are coated with nickel. Silver is also used (but only in case of high-end connectors) as its conductivity is really good. Silver plating normally requires additional coating because of its oxidation in air.
A full list of the various type of coaxial cable can be found at category5-cable.com/plenum-cat-5.html, and are summarized below:
Hard Line - These are the powerful cables with rigid outer shield and with minimum loss. Normally used to connect a transmitter and an antenna. These cables consists of high dielectric in high temperature as well.
Tri axial - Cable with three layers of shielding and the outermost shielding protecting the inner layers from from outer electromagnetic interference.
Twin axial - This cable consists of a twisted pair covered by a shield.
Bi axial - Consists of two 50O coaxial cables used for networking.
Semi rigid - It is a coaxial cable with solid outer copper sheath.
Short type of coaxial cables are basically used for home video, ham radio and some small computer networks while long coaxial cables connect radio or television networks. Micro coaxial cables are used by the military or medical use.
Micro coaxial cables are used in a range of consumer devices, military equipment and also in ultra-sound scanning equipment. The cables with impedances of 50/52 and 75 ohms are commonly used. 50/52 ohm cables are normally used for commercial purposes while 75 ohm cables are used for domestic purpose.
