topic 8 - transmission media (unguided)

7/29/2019 Topic 8 - Transmission Media (Unguided)

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1Sumati J. Singh

TRANSMISSION MEDIA

Unguided Media1/29/2013


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Unguided

No physical conductor required

Electromagnetic waves

Air is the medium

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1/29/2013Sumati J. Singh


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EM Spectrum3

Visible Light


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


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


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


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


topic 8 - transmission media (unguided)

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