terrestrial propagation

7/25/2019 Terrestrial Propagation

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Terrestrial Propagation


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Terrestrial Waves- electromagnetic waves

traveling within Earths

atmosphere.

Terrestrial Radio

Communication

- communication between two ormore points on Earth.


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General Classifcation oRadio waves

Ground

Waves

Space

Waves

Sky

Waves


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AtmosphericLayer


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Ground Waves/ SurfaceWaves Propagation

Travel around the curvature of the earth, sometimes right around the

globe

tili!es fre"uencies belo# $% range

Propagates best over a good conductor &sea#ater' and highest

attenuation is over (ungle areas)

Progress along the surface of the earth and must be vertically polari!ed

to prevent short circuiting the electric component)

Wave induces current to the ground* some of its energy is lost due to

absorption)

With enough po#er transmitted, #ave front could propagate around the

+arth

Travel around the curvature of the earth, sometimes right around the

globe

tili!es fre"uencies belo# $% range

Propagates best over a good conductor &sea#ater' and highest

attenuation is over (ungle areas)

Progress along the surface of the earth and must be vertically polari!ed

to prevent short circuiting the electric component)

Wave induces current to the ground* some of its energy is lost due to

absorption)

With enough po#er transmitted, #ave front could propagate around the

+arth


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Ground Waves/ SurfaceWaves Propagation


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Space Waves/Tropospheric Propagation

Travel in the troposphere* the portion of the atmosphere closest to

the ground)

tili!es fre"uencies above $% range

nclude both direct and ground-reflected #aves.

irect #aves / Line of Sight 0 travels in straight line bet#een

the transmit and receive antenna

- limited by the curvature of +arth

Ground-reflected #aves - reflected by earth1s surface as they

propagate bet#een transmit and receive antenna


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Space Waves/Tropospheric Propagation


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Sky Waves/ onosphericPropagation

The #ave strikes the ionosphere and is refracted back to the

ground)

tili!es fre"uencies in the $% range and sometimes fre"uencies

(ust above or belo# it)

onosphere is a region in the earth1s atmosphere #here the air

pressure is so lo# that the free electrons and ions can move

about for some time #ithout getting close enough to recombine

into neutral atoms) t absorbs large "ualities of radiant energy

from the sun, becoming heated and ioni!ed) oni!ation is the

result of the bombardment of the sun1s rays by a variety of #ave

from heat and light to cosmic rays) 2ost important ioni!ing agents

are ultraviolet, alpha, beta and gamma rays coming from the sun,

cosmic rays and meteors)


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onospheric

Layers


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Sky Waves/ onosphericPropagation


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-Layer

The lo#est, e3isting at an average height

of 45 km, #ith an average thickness of 65

kmLeast important layer in $% propagation7eflects some 8L% and L% #aves and

absorbs 2% and $% #aves to a certain

e3tent


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+-Layer

+3isting at about 655km in height, #ith

thickness of 9:km

isappears at night)Aid 2% surface propagation a little and

reflects some $% #aves in daytimeThis layer is also kno#n as KENELLY-

HEAVISIDE LAYER


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+s Layer/

SporadicThin layer of very high ioni!ation density,

sometimes making an appearance #ith the

+ layer)When it occurs, it often persists during the

night)


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%-Layer

+3istataheightof6;5kmindaytimeand combines#iththe%9layeratnight)ts

daytimethicknessisabout95km2ain+ffectistoprovidemoreabsorption

for$%#aves

!

la"er

Themostimportantreflectingmediumfor$%radio#aves)

Appro3imatethicknessis955kmanditsheightrangesfrom9:5to

terrestrial propagation

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