Saturday, 14 April 2012

Hardware Requirements : Transmission Medium

Transmission media can be divided into two broad categories.  
  • Physical transmission media
  • Wireless transmission media 
The twisted-pair cable, coaxial cable and fibre optic cable are examples of physical transmission media.
Wireless transmission medium or unguided medium is through air.


In physical transmission medium, waves are guided along a solid transmission medium. Wireless transmission medium waves are unguided and the transmission and reception are by means of antennas.

Twisted-Pair Cable 

    Two insulated copper wires that  are twisted around each other. Each connection on twisted-pair requires both wires.  
   The twisted-pair cable is generally a common form of transmission medium. It consists of two wires or conductors twisted together, each with its own plastic insulation. The twisted wires cancel out electromagnetic interference that can cause crosstalk , the noise generated by adjacent pairs

Coaxial Cable  

A cable consisting of a conducting outer metal tube that encloses and is insulated from a central conducting core, used primarily for the transmission of high-frequency signals

The coaxial cable, often referred to as ‘coax’, consists of a single copper wire surrounded by at least three layers.They are an insulating material, a woven or braided metal and a plastic outer coating.
This cable is often used as cable television (CATV) network wiring because it can be cabled over longer distances in comparison to the twisted-pair cable.

Fibre Optic Cable  

Glass fibre used for laser transmission of video, audio and/or data.
The fibre optic cable is a networking medium that uses light for data transmission.
The intensity of light is increased and decreased to represent binary one and zero.
Its core consists of dozens or hundreds of thin strands of glass or plastic which uses light to transmit signals.
Each strand, called an optical fibre, is as thin as a human hair


Wireless is a method of communication that uses electromagnetic waves rather than wire conductors to transmit data between devices.Wireless networks are telephone or computer networks that use radio frequencies and infrared waves as their carrier.
Wireless transmission can be categorised into three broad groups:
  • Radio Waves
  • Microwaves
  • Infrared
Radio Waves

There is no clear difference between radio waves and microwaves. Electromagnetic waves ranging in frequencies between 3 KHz and 1 GHz are
normally called radio waves. Waves ranging in frequencies between 1 and 300 GHz are normally called microwaves.
Radio waves are normally omnidirectional. When an antenna transmits radio waves, they are propagated in all directions. This means that the sending and receiving antennas do not have to be aligned.

The omnidirectional characteristics of radio waves make them useful for multicasting, in which there is one sender but many receivers.
Our AM and FM radio stations, cordless phones and televisions are examples of multicasting


Electronic waves with frequencies between 1 GHz to 300 GHz are normally called microwaves.
Unlike radio waves, microwaves are unidirectional, in which the sending and receiving antennas need to be aligned. Microwaves propagation is    
line-of-sight therefore towers with mounted antennas need to be in direct sight of each other.

Two types of antenna are used for microwave communications. They are the parabolic dish antenna and the horn antenna.
The parabolic dish antenna receives ingoing transmissions by reflecting the signal to a common point called the focus.
Outgoing transmissions are broadcasted through a horn antenna by deflecting signals outward in a series of narrow parallel beams.
High-frequency microwaves cannot penetrate walls. This is why receiving antennas cannot be placed inside buildings.

Infrared is used in devices such as the mouse, wireless keyboard and printers. Some manufacturers provide a special port called the IrDA port that allows a wireless keyboard to communicate with a PC. 
Infrared signals have frequencies between 300 GHz to 400 THz. They are used for short-range communication.
Infrared signals have high frequencies and cannot penetrate walls. Due to its short-range communication system, the use of an infrared communication 
system in one room will not be affected by the use of another system in the next room.
This is why using an infrared TV remote control in our home will not interfere with the  use of our neighbour’s infrared TV remote control.

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