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1Sumati J. Singh
TRANSMISSION MEDIA
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Unguided
No physical conductor required
Electromagnetic waves
Air is the medium
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EM Spectrum3
Visible Light
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Infrared U V X-ray,Gamma
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Propagation Types4
Ground Very low frequency radio waves move in
all directions and follow the curvature of planet
Sky Transmitter sends high frequency waves to the
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sky, that are refracted back by Ionosphere andreceiver can catch them. This allows larger distance.
Line of sight Very high freq radio waves travelstraight. Antennas must be aligned, facing eachother. Either close or tall.
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Propagation Types5
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Radio Bands6
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Radiowaves7
Freq 3kHz 1GHz
Omni directional
Subject to interference from electrical equipments
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ene ra e u ngs, pass roug o s ac es Power reduces sharply with distance, 1/r2
High freq travel in a straight line, bounce off
obstacles, absorbed by rain Used for AM, FM, television, cellular phones,
wireless LAN
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Microwaves8
Freq 1GHz 300GHz
Unidirectional line of sight Narrowly focused antennas
Dont interfere
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More distance , taller towers VHF microwave cant penetrate walls
Band is wide, higher data rates are possible
Certain portions require govt. permissions
Bi-direction needs two frequencies
wLANs, satellite, cellular phones
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Terrestial Microwave9
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Parabolic Dish Antenna10
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Horn Antenna11
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Infrared Waves Freq 300 GHz 400 THz
Short range communication
Cannot pass through objects
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uc re uce n er erence Cheap, easy to build & no licensing
More secure
Large band Remote control, PANs, IrDA ports
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Light Waves Freq 400 THz 900 THz
Transfer data up to few kms.
Unidirectional
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p o o e ec or aser s se up on o s es
High bandwidth at very low cost
Cannot penetrate rain or thick fog
Hot sunny days, they are affected by turbulent air Connect two LANs in two buildings
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Light Wave14
Laser
Laser
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Satellite Natural/Man-made
Cover max. area of the earth
Path of revolution orbit
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c as a g m crowave repea er
Geostationary satellite 36000 km, 24 hrs 1
revolution
Transponders receive signal from one, amplify &send back to other
12-20 transponder with 36-50 GHz bandwidth
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Satellite16
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Satellite Frequencies17
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Geosynchronous Sattelite18
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