08-07-2017, 05:05 PM
10-07-2017, 09:49 AM
Radio waves are easy to generate and are widely used for both indoor and outdoor communications because of their ability to traverse buildings and travel long distances.
The key features are :-
• Since radio transmission is omnidirectional in nature, there is no need to physically align the transmitter and receiver.
• The frequency of the radio wave determines many of the characteristics of the transmission.
• At low frequencies, waves can easily pass through obstacles. However, its power falls with an inverse-square relationship with respect to distance.
• Higher frequency waves are more prone to absorption by raindrops and are reflected by obstacles.
• Due to the long transmission range of radio waves, interference between transmissions is a problem to be addressed.
In bands VLF, LF and MF, the propagation of the waves, also called earth waves, follows the curvature of the earth. The maximum transmission ranges of these waves are on the order of a few hundred kilometers. They are used for low bandwidth transmissions, such as amplitude modulation (AM) radio broadcasting.
HF and VHF band transmissions are absorbed by the atmosphere, near the surface of the Earth. However, a portion of the radiation, called the sky wave, radiates outward and upward to the ionosphere in the upper atmosphere. The ionosphere contains ionized particles formed due to solar radiation. These ionized particles reflect the celestial waves back to Earth. A powerful wave of the sky can be reflected several times between the Earth and the ionosphere. Sky waves are used by amateur amateur operators and for military communication.
vasu k
10-12-2017, 04:09 PM
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