Radio wave propagation

Radio waves are used in long distance communication as carrier waves. Radio waves are mixed with the signal which is to be transmitted. This process is known as modulation. Radio waves are electromagnetic radiations. Radio waves always travel in straight paths in free space. Radio waves require very small time to travel and gets reflected if there is any object in their path. If there is any density change in the medium of travelling, radio waves undergo refraction. Radio waves can be produced by passing high frequency alternating current through an antenna. There exist three methods by which radio waves propagates through space. They are ground wave propagation (or surface wave propagation), sky wave propagation and space wave propagation. In ground wave propagation, transmitting and receiving antennas of radio waves are located very close to the surface of the earth. Ground wave propagation is used for medium-wave radio broadcasting. When radio waves travel in ionosphere, it is known as sky wave propagation. Space wave propagation or line-of-sight communication is used for VHF and UHF bands. This method is used in TV transmissions.