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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 NRead More
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