Types of Communication Media

Communication media
The transmission channel in the system provides connection between
transmitter and receiver. The input and output are analog waveforms. This
portion of channel is often called modulation channel.
Types of communication media:
1) Cable media: The waves are guided along a solid medium such as copper
twisted wire.
2) Broadcast media: The waves are guided along atmosphere and outer space.
Fig: Communication media
i) Twisted Pair: It is the least expensive and most widely used medium. In this
cabling the wires are twisted together in pairs. Each pair consists of a wire used
for positive data signal and another wire used for negative data signal. The
Wires are 180 degrees out of phase with each other.
Advantages:
a) Shielded twisted pair wires are less susceptible to electrical interference.
b) This twisted pair wires can carry data at a faster speed.
Disadvantages:
a) It is more difficult to connect to a terminating block.
b) It will require direct p2p(peer to peer) connections.
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ii) Coaxial Cables: It consists of two conductors. The inner conductor is held
inside an insulator with the other conductor woven around it providing a shield.
An insulating protective coating called a jacket covers the outer conductor.
Advantages:
a) Greater bandwidth: Compared to twisted pair, coaxial provides greater
bandwidth system wide, it supports a mixed range of services i.e. voice, data,
video, multimedia etc.
b) Coaxial cable shielding reduces noise and crosstalk.
Disadvantages:
a) Susceptible to damage from lightening strikes.
b) High installation costs in the local environment.
iii) Fiber optic cables: It consists of thin glass fibers that can carry information
at frequencies in the visible light spectrum.
The typical optical fiber consists of a very narrow strand of glass called the
core. Around the core a concentric layer of glass called the cladding. Cladding
has a protective coating of plastic called jacket. Optical fiber works on internal
total reflection principle, the light pulses are kept within the fiber, propagating
towards the far end with the speed of light.
Advantages:
a) Large capacity due to bandwidth
b) No corrosion
c) Smaller and lighter than copper wire
Disadvantages:
a) It will break if bend it too much
b) Difficult to splice
iv) Microwave Transmission: Microwave link can be one hop, consisting of
one pair of antennas spaced as one or two kilometres apart or can be a
backbone, including multiple hops, spanning several thousand kilometres. This
transmission is relatively inexpensive as compared to fiber optics system. This
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system permit data transmission rates of about 16 giga bits per second
(giga=109
).
Advantages:
a) No cabling needed between sites
b) Wide bandwidth
Disadvantages:
a) Microwaves travel in a straight line, if the towers are too far apart, repeaters
are needed periodically.
v) Satelite Transmission: The major breakthrough in the communication is the
satellite transmission. It relayed by satelite, starts with a transmitting antenna
located with an uplink facility. Uplink satelite dishes are very large, as much as
9 to 12 meters in diameter. The increased diameter results in more accurate
aiming and increased signal strength at the satelite. The uplink dish is pointed
toward a specific satelite and the uplinked signals are transmitted with in a
specific frequency range, so as to be received by one of the transponders tuned
to that frequency range. The transponder ‘retransmits’ the signals back to earth
but at a different frequency band (typically C-band (4 – 8 GHz) or Ku-band (12
-18 GHz) or both). The leg of the signal path from the satelite to the receiving
earth station is called downlink.
vi) Radio Transmission:
Radio waves frequency Range: 10 KHz and 1GHz.
 These waves are easy to generate.
 They can travel long distances.
 They can penetrate buildings easily so they are widely used for
communications both indoors and outdoors.
 These waves are Omni directional (can travel in all directions) so that the
transmitter and receiver do not have to be carefully aligned physically.
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Advantages:
a) Can cover larger area and can penetrate walls.
b) Current radio based products offer higher transmission rates (10 Mbit/s).
Disadvantages:
a) It is only permitted to certain frequency bands.
b) Shielding is not simple.
vii) Infrared wave Transmission: Infrared light is red light not visible to
human eyes. Unguided infrared light (wave) are widely used for short range
communication. The remote control used in TV, VCR, Stereos etc, all use
infrared communication.
Advantages:
a) These waves need low power requirements and relatively directional.
b) Low circuitry costs and these waves are easy to build.
Disadvantages:
a) Infrared waves do not pass through solid objects well.
b) Performance drops off with longer distances.
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Types of Communication Media

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Types of Communication Media