TRANSMISSION MEDIA

Now a days communication is necessary in every field and to communicate a transmission media is needed. Transmission media is classified into two types.

·         Wire communication (a connection between transmitter and receiver.)

·         Wireless communication (no connection between transmitter and receiver.)

1.                                                          In case of wire line communication, nonelectrical signals are converted into electrical signals                         at the entry and these electrical signals(voltage,current) are transmitted with the help of                                   conductor.The device which transforms it is called the “Transducer”

There are 3 major and well known types of wire communication

·         COAXIAL CABLE:

*It is kind of copper cable mostly used by cable tv companies between communicating antenna and user home tv set and is applied by telephone companies from their offices to poles.

*This cable has three layers enclosed in it, inner layer is conducting copper wire and  two outer layers are used to protect the conducting(cu wire) path from outer damages.

*Major disadvantage regarding this cable is electromagnetic induction

HOW? Here it is said that electrical signals are transmitted by inner cu layer ,it means we have electric field and as these electrons are flowing(current) we have magnetic field around the conductor.so both fields exists. whenever another conductor is brought near to it, we may have collision and there is chance of loss of information.

·         TWISTED PAIR:

*To overcome the loss of information in the coaxial cable Twisted pair cable was introduced as name itself indicates pair of wires are twisted one, to collapse electromagnetic interference.

*It is ordinary wire that connects home and many business computers. To reduce  cross talk and electromagnetic induction between pairs of  wires ,two insulated cu wires are twisted. These are sometime enclosed in single cable this acts as a shield for twisted pair cable.

*For secure information this shield acts as ground and is called as shield twisted pair cable and for home transmit information this shield acts as unshielded and is called unshielded twisted pair cable.

*Major advantage is twisted pair is cheaper than coaxial cable and it overcomes EM induction.

*Disadvantage is slow transfer of information.

·         OPTICAL FIBER:

Up to this security is enough and every one needed the speed and thought of using the light as source to transmit the information as we knew that the speed of light is 3*108m/sec. Based on this technique optical fibre was designed. Similar to coaxial cable it also has 3 layers, outer one is buffer or sheath,middle one is cladding and the inner one where the light is gonna transmit is core. For proper transmission refractive index of core must be slightly greater than cladding. To know how light transmits in the core one should know about the critical angle and total internal reflection.

      *critical angle: When a wave is transmitting from one medium to another medium of different refractive indices and if wave incident angle is greater than 90 degrees this angle is referred as critical angle

      *Total internal reflection: When angle of incident is equal to critical angle then no reflection occurs only refraction into medium.

*By using these light parameters transmission is done in optical fiber. *Major advantages is Optical fiber carries much more information than normal cu wire and is not subjected to EM interference, so most telephone companies long distances lines are made of optical fibers by use of Repeaters at regular distances.
 2.     In case of wireless communication no wired media is present between transmitter and receiver. Here communication is by EM waves HOW? As I said before around a conductor both fields exists and these EM waves are necessary for communication.

The first wireless transmission went on air in early 20^th century using morse code. Later by modulation it made possible for transmitting voices and music via wireless.

Modes:

Wireless communication can be via,

·         Radio communication(Radio frequency)

·         Microwave communication(high frequency)

·         Infrared communication

·         Ultrasonic communication.are made of optical fibers by use of Repeaters at regular distances.

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