AWP Unit 5 Sky Wave Propagation
AWP Unit 5 Sky Wave Propagation
AWP Unit 5 Sky Wave Propagation
S.Mahendrakumar
Asst. Prof. (Sr. Gr.)
Department of ECE
Velalar College of Engineering and
Technology, Erode.
1
Content
2
Ground Wave Propagation
Disadvantages
Requires relatively high transmission
power.
Frequencies up to 2 MHz.
3
Sky Wave Propagation
4
Sky Wave Propagation
5
Ionosphere
The ionosphere is a region of Earth's upper
atmosphere, from about 50 km to 400 km.
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Ionosphere
7
Refractive Index of Ionosphere
Reflection of wave from ionosphere is through
refraction of waves.
Snells Law of refraction in the ionosphere.
n- is refractive index
i- is angle of incident
r- is angle of refraction
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The Ionosphere layers
D Layer
E Layer
Es Layer
F1 Layer
F2 - Layer
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The Ionosphere layers
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The Ionospheric Layers
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D-Layer
12
E-Layer
It is a thin layer
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F1-Layer
Average height 180km
Average thickness 20km
It combines with F2 layer at night
fc=5MHz
Its virtual height is 180km
Maximum single hop range 3,000km
Although some HF waves get reflected from
it, most of them pass through it
It affect HF waves by providing more
absorption.
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F2-Layer
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Virtual height
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The virtual height is the height from which the
radio wave appears to be reflecting.
Virtual Height > Actual Height
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Critical Frequency (fc)
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Critical Frequency (fc)
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Critical Frequency (fc)
Angle of incident i = 0
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Critical Frequency (fc)
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Critical Frequency (fc)
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Critical Angle (c)
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Critical Angle (c)
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Critical Angle (c)
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Maximum Usable Frequency
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1
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2
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Comparing Equ. 1 & 2.
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Skip Distance
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Skip Distance
The SKIP DISTANCE is the distance from the
transmitter to the point where the sky wave is
first returned to Earth.
The size of the skip distance depends on the
frequency, angle of incidence and ionization.
The minimum distance from the transmitter,
along the surface of the earth, at which a wave
above the critical frequency will be returned to
earth.
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Skip Distance
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Skip Distance
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Optimum Working Frequency (OWF)
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Optimum Working Frequency (OWF)
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Fading
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Fading
The random variation in the received signal strength
is called fading.
The main causes of fading are
Multipath propagation
Variation in ionosphere condition
Types of fading
Multipath fading
Selective fading
Interference fading
Polarization fading
Skip fading
Absorption fading
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Diversity
40
Q&A
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Multiple Choice Questions
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c
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a
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a
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b
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c
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Q&A
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