Transmission Medium

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Transmission Medium

A communication channel is called a medium. There are two types of media: 

Guided (Wired) Media : 

Guided Media is a communication medium which allows the data to get guided along it i.e. physical connection is need. 
Examples : Twisted P

• Twisted Pair Cable 
• A twisted pair consists of two conductors (copper), each with its own plastic insulation, twisted together. 
• One of the wires is used to carry signals to receiver, and the other is used only as a ground reference. 
• A signal is usually carried as the difference in voltage between the two wires in the pair. This provides better immunity to external noise because the noise tends to affect both wire the same, leaving the differential voltage unchanged. 
• Frequency range for twisted pair cable is 100Hz to 5MHz. 
• Coaxial Cable 
• Coaxial cable carries signals of higher frequency range than those in twisted pair cable. 
• It has a central core conductor of solid or standard wire (usually copper) enclosed in an insulating sheath, which is in turn encased in an outer conductor of metal foil.
• The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes the circuit. This outer conductor is also enclosed in an insulating sheath and the whole cable is protected by a plastic cover. 
• Optical Fiber 
• Optical fiber is a thin, flexible medium capable of guiding an optical ray. Optical fiber cable has a cylindrical shape and consists of three sections: core, cladding and jacket.

Unguided (Wireless) Media : 

The wireless media is called unguided media. Unguided media transports electromagnetic wave without using a physical conductor. This type of communication is called wireless communication. Signals are normally broadcasted through air and thus are available to anyone who has a device (antenna) capable to receive them. Unguided signals can travel from source to destination in several ways. 

• Radio Transmission : 
• Basic idea is to transmit signal in the form of radio waves. Radiowaves have frequencies between 3 kHz and 1 GHz. Radiowaves can broadcast omnidirectionally or directionally. Various kinds of antennas are used to broadcast these signals.
•  Omnidirectional i.e. all directions
• Radio waves can penetrate through walls
• Used TV broadcasting and F.M radio broadcasting 
• Applications:
• Cellular communication
• Wireless LAN
• Satellite communication
• Microwave transmission
• The microwave transmission uses higher frequency range than radio frequency as a result, they produce better throughput and performance. Microwave are basically electromagnetic waves having frequency range between 1 GHz and 300 GHz
• Microwaves are unidirectional.
• Microwaves propagation is a line of sight propagation. 
• Cannot penetrate through walls. 
• Applications: 
• In cellular phones
• In satellite networks
• Wireless LAN
• Satellite Transmission
• A satellite is simply a repeater. It consists of several transponders each of which listens to some portion of the spectrum, amplifies the incoming signal and the rebroadcasts it at another frequency to avoid interference with the incoming signal.
• Satellite communication system consists of ground stations for transmitting and receiving signals and a communication satellite in the space. The range of frequencies used for transmission of signals from ground station to the satellite is uplink frequency and those used for transmission of signals from satellites to ground station is downlink frequency. Uplink and downlink frequencies are different to avoid interference. 
• Satellite are three types which are given bellow
• Low Earth Orbit (LEO)
• Medium Earth Orbit (MEO)
• Geostationary Earth Orbit (GLO)