Space Communication PPT Physics Class 12

 Page 1


Space Communication
This Chapter includes: 
1. Space Communication
2. Power Density, Attenuation
3. Range of Electromagnetic Waves
4. Ground Wave Propagation
5. Sky Wave Propagation
6. Space Wave Propagation
7. TV Transmission and Height of TV Antenna
8. Satellite Communication
9. Remote Sensing Satellites
Page 2


Space Communication
This Chapter includes: 
1. Space Communication
2. Power Density, Attenuation
3. Range of Electromagnetic Waves
4. Ground Wave Propagation
5. Sky Wave Propagation
6. Space Wave Propagation
7. TV Transmission and Height of TV Antenna
8. Satellite Communication
9. Remote Sensing Satellites
Space Communication:
Space Communication means free space communication. 
A free space does not have solid particles or ionised particles and it has no 
gravitational or other fields of its own.  When the frequency of transmitted 
wave is very high the actual space is considered nearly  a free space.
Power Density:
Power density is radiated power per unit area and is inversely proportional 
to the square of distance from the source.  
Antenna:
Antenna is a device which acts as an emitter of electromagnetic waves and 
it also acts as a first receiver of energy.
Attenuation:
Attenuation is the loss of power of radiation due to absorption of energy in 
space and power density goes on decreasing as the electromagnetic waves 
go away from their source.  
It is proportional to the square of the distance travelled and is generally 
measured in decibel (dB).
Page 3


Space Communication
This Chapter includes: 
1. Space Communication
2. Power Density, Attenuation
3. Range of Electromagnetic Waves
4. Ground Wave Propagation
5. Sky Wave Propagation
6. Space Wave Propagation
7. TV Transmission and Height of TV Antenna
8. Satellite Communication
9. Remote Sensing Satellites
Space Communication:
Space Communication means free space communication. 
A free space does not have solid particles or ionised particles and it has no 
gravitational or other fields of its own.  When the frequency of transmitted 
wave is very high the actual space is considered nearly  a free space.
Power Density:
Power density is radiated power per unit area and is inversely proportional 
to the square of distance from the source.  
Antenna:
Antenna is a device which acts as an emitter of electromagnetic waves and 
it also acts as a first receiver of energy.
Attenuation:
Attenuation is the loss of power of radiation due to absorption of energy in 
space and power density goes on decreasing as the electromagnetic waves 
go away from their source.  
It is proportional to the square of the distance travelled and is generally 
measured in decibel (dB).
S. 
No.
Name of the frequency 
range (Band)
Short 
Form
Frequency Range
1 Very Low Frequency VLF 3 kHz to 30 kHz
2 Low Frequency LF 30 kHz to 300 kHz
3 Medium Frequency or 
Medium Wave
MF or 
MW
300 kHz to 3 MHz
4 High Frequency  or Short 
Wave
HF or 
SW
3 MHz to 30 MHz
5 Very High Frequency VHF 30 MHz to 300 MHz
6 Ultra High Frequency UHF 300 MHz to 3,000 MHz
7 Super High Frequency or 
Micro Waves
SHF 3,000 MHz to 30,000 
MHz (3 GHz to 30 GHz)
8 Extremely High Frequency EHF 30 GHz to 300 GHz
Range of Electromagnetic Waves:
Page 4


Space Communication
This Chapter includes: 
1. Space Communication
2. Power Density, Attenuation
3. Range of Electromagnetic Waves
4. Ground Wave Propagation
5. Sky Wave Propagation
6. Space Wave Propagation
7. TV Transmission and Height of TV Antenna
8. Satellite Communication
9. Remote Sensing Satellites
Space Communication:
Space Communication means free space communication. 
A free space does not have solid particles or ionised particles and it has no 
gravitational or other fields of its own.  When the frequency of transmitted 
wave is very high the actual space is considered nearly  a free space.
Power Density:
Power density is radiated power per unit area and is inversely proportional 
to the square of distance from the source.  
Antenna:
Antenna is a device which acts as an emitter of electromagnetic waves and 
it also acts as a first receiver of energy.
Attenuation:
Attenuation is the loss of power of radiation due to absorption of energy in 
space and power density goes on decreasing as the electromagnetic waves 
go away from their source.  
It is proportional to the square of the distance travelled and is generally 
measured in decibel (dB).
S. 
No.
Name of the frequency 
range (Band)
Short 
Form
Frequency Range
1 Very Low Frequency VLF 3 kHz to 30 kHz
2 Low Frequency LF 30 kHz to 300 kHz
3 Medium Frequency or 
Medium Wave
MF or 
MW
300 kHz to 3 MHz
4 High Frequency  or Short 
Wave
HF or 
SW
3 MHz to 30 MHz
5 Very High Frequency VHF 30 MHz to 300 MHz
6 Ultra High Frequency UHF 300 MHz to 3,000 MHz
7 Super High Frequency or 
Micro Waves
SHF 3,000 MHz to 30,000 
MHz (3 GHz to 30 GHz)
8 Extremely High Frequency EHF 30 GHz to 300 GHz
Range of Electromagnetic Waves:
Depending on the frequency, radio waves and micro waves travel in space in 
different ways depending on the behaviour of these waves w.r.t. the earth 
and the atmosphere.  They are:
1. Ground wave propagation
2. Sky (or ionospheric) wave propagation
3. Space (or tropospheric) wave propagation
1. Ground wave propagation: (AM Radio waves)
In ground wave propagation, the radio waves (AM)  travel along the surface 
of the earth. These waves are called ground waves or surface waves.
In fact, these waves are not confined to surface of the earth but are guided 
along the earth’s surface and they follow the curvature of the earth.
The energy of the radio waves decreases as they travel over the surface of 
the earth due to the conductivity and permittivity of the earth’s surface.
Attenuation increases with the increase in frequency.
Therefore, the ground waves are limited to frequency of 1.5 MHz (1500 kHZ) 
or wavelength of 200 m.
Propagation of Electromagnetic Waves:
Page 5


Space Communication
This Chapter includes: 
1. Space Communication
2. Power Density, Attenuation
3. Range of Electromagnetic Waves
4. Ground Wave Propagation
5. Sky Wave Propagation
6. Space Wave Propagation
7. TV Transmission and Height of TV Antenna
8. Satellite Communication
9. Remote Sensing Satellites
Space Communication:
Space Communication means free space communication. 
A free space does not have solid particles or ionised particles and it has no 
gravitational or other fields of its own.  When the frequency of transmitted 
wave is very high the actual space is considered nearly  a free space.
Power Density:
Power density is radiated power per unit area and is inversely proportional 
to the square of distance from the source.  
Antenna:
Antenna is a device which acts as an emitter of electromagnetic waves and 
it also acts as a first receiver of energy.
Attenuation:
Attenuation is the loss of power of radiation due to absorption of energy in 
space and power density goes on decreasing as the electromagnetic waves 
go away from their source.  
It is proportional to the square of the distance travelled and is generally 
measured in decibel (dB).
S. 
No.
Name of the frequency 
range (Band)
Short 
Form
Frequency Range
1 Very Low Frequency VLF 3 kHz to 30 kHz
2 Low Frequency LF 30 kHz to 300 kHz
3 Medium Frequency or 
Medium Wave
MF or 
MW
300 kHz to 3 MHz
4 High Frequency  or Short 
Wave
HF or 
SW
3 MHz to 30 MHz
5 Very High Frequency VHF 30 MHz to 300 MHz
6 Ultra High Frequency UHF 300 MHz to 3,000 MHz
7 Super High Frequency or 
Micro Waves
SHF 3,000 MHz to 30,000 
MHz (3 GHz to 30 GHz)
8 Extremely High Frequency EHF 30 GHz to 300 GHz
Range of Electromagnetic Waves:
Depending on the frequency, radio waves and micro waves travel in space in 
different ways depending on the behaviour of these waves w.r.t. the earth 
and the atmosphere.  They are:
1. Ground wave propagation
2. Sky (or ionospheric) wave propagation
3. Space (or tropospheric) wave propagation
1. Ground wave propagation: (AM Radio waves)
In ground wave propagation, the radio waves (AM)  travel along the surface 
of the earth. These waves are called ground waves or surface waves.
In fact, these waves are not confined to surface of the earth but are guided 
along the earth’s surface and they follow the curvature of the earth.
The energy of the radio waves decreases as they travel over the surface of 
the earth due to the conductivity and permittivity of the earth’s surface.
Attenuation increases with the increase in frequency.
Therefore, the ground waves are limited to frequency of 1.5 MHz (1500 kHZ) 
or wavelength of 200 m.
Propagation of Electromagnetic Waves:
Earth
Ground waves progress along the surface of the earth and must be vertically 
polarised to prevent from short-circuiting the electric component.
A wave induces currents in the earth over which it passes and thus loses 
some energy by absorption.  This is made up by energy diffracted downward 
from the upper portions of the wavefront.
Another way of attenuation is due 
to diffraction and gradual tilting 
of the wavefront.  
The increasing tilt of the 
wavefront causes greater short-
circuiting of electric field 
components of the wave.  
Eventually, at some distance from 
the antenna, the wave “lies down 
and dies”.
The maximum range of a 
transmitter depends on its 
frequency as well as its power.
In MF band, the range can not be 
increased only by increasing its 
power because propagation is 
definitely limited by its tilt.
Direction of 
propagation of wave
T
Successive 
Wavefronts
?
? – Angle of 
diffraction
N