Sky waves are used by amateur ham radio operators and for military communication. A powerful sky wave may be reflected several times between the Earth and the ionosphere. These ionized particles reflect the sky waves back to the Earth. The ionosphere contains ionized particles formed due to the Sun's radiation. However, a portion of the radiation, called the sky wave, is radiated outward and upward to the ionosphere in the upper atmosphere. The HF and VHF band transmissions are absorbed by the atmosphere, near the Earth's surface. They are used for low bandwidth transmissions such as Amplitude Modulation (AM) radio broadcasting. The maximum transmission ranges of these waves are of the order of a few hundred kilometers. In the VLF, LF and MF bands the propagation of waves, also called as ground waves follow the curvature of the earth. The higher frequency waves are more prone to absorption by rain drops and they get reflected by obstacles.ĭue to the long transmission range of the radio waves, interference between transmissions is a problem that needs to be addressed.
However, their power falls with an inverse-squared relation with respect to the distance. The frequency of the radio wave determines many of the characteristics of the transmission.Īt low frequencies, the waves can pass through obstacles easily. Since radio transmission is Omni directional in nature, the need to physically align the transmitter and receiver does not arise. Radio waves are easy to generate and are widely used for both indoor and outdoor communications because of their ability to pass through buildings and travel long distances. In this chapter, let us go through different interesting topics such as the properties of radio waves, the propagation of radio waves and their types.
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