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COMMUNICATION is an operation which is used to convey a message from one place to another place. The main objective of the COMMUNICATION SYSTEMS in aircrafts is to provide an uninterrupted contact with the other aircrafts and the air traffic control. Radio communication plays a vital role in safe and effective operation of aircraft on ground as well as in air. It helps in the transfer of information between pilots, ATC controller and crew members or the passengers.
NAVIGATION is the art and science of getting from point "A" to point "B" in the least possible time without losing your way. The main objective of the NAVIGATIONAL SYSTEMS in the aircraft is to provide the exact location of the aircraft when it is in the air. The navigational systems also provides information in which direction the flight should fly and the current position in which it is flying.
NOTE: These systems are classified according to their operation, purpose and nature. But all the systems are interlinked with one another and all the systems have their equal importance for the aircraft’s safety from the time of take-off till the time of landing.
RADIO WAVE PROPAGATION
ELECTROMAGNETIC RADIATION is the main key factor behind the operations of the Communication Systems.
Any power escaping into the free space on a purpose is said to be RADIATED. This radiation propagating in space with a definite energy and frequency is known as Electromagnetic Radiation.
The wave consisting of two oscillating fields (E and H) mutually perpendicular to each other and to the direction of propagation is known as a Electromagnetic Wave. The E field will be parallel to the wire from which it is transmitted while H field will be perpendicular. Now let’s make our discussion only to the RADIO WAVES.
2) GROUND WAVE PROPAGATION: These are the waves which travel along the surface of the earth. But these waves are effected by mainly two factors.
DIFFRACTION: It is the phenomenon which results in radio waves that normally travel in a straight line to bend around an obstacle.The rate of diffraction is inversely proportional to the frequency.
SURFACE ATTENUATION: The magnetic field (H) of the wave cuts the earth surface causing current flow. The power for these currents is taken from the wave due to which there is a rapid decrease in the energy of the wave causing power degradation for the wave. The energy of the wave is transferred from the wave to the earth (law of conservation of energy) due to which attenuation occurs. And is proportional to the EM wave’s FREQUENCY
3) SKY WAVE PROPAGATION: The propagation of these waves is done by the waves which are received by the receiver due to the reflection and refraction of the waves from the layer know as Ionosphere.
The ionosphere is the region of the upper atmosphere where the Sun’s ultraviolet radiation can ionize oxygen molecules to create a positive ion and a free electron.
All the EM waves obey the laws of reflection and refraction. So due to this when an EM wave is transmitted into the atmosphere. There will be a change in the Electron Density above the earth surface due to which there forms a layers of low Electron Density and high Electron Density due to which bending of the EM wave occurs.
As this bending occurs continuously, there occurs a stage where the transmitted EM wave is reflected back to the atmosphere. Which is a principle of REFRACTION