define sky wave propogation

Hi Alka!

Sky wave propagation is a long distance communication technique. It is also known as ionospheric propagation. The frequency range used for this mode of propagation is from 3MHz -30MHz (or up to 40MHz).

In the ionosphere of the Earth’s atmosphere, there are a large number of charged particles (ions). The ionosphere is situated about 65km - 400km above the surface of the Earth. The ionization of molecules occurs due to the absorption of the ultraviolet rays and high energy radiation from the Sun. The ionosphere acts as a reflecting layer for certain range of frequencies (3MHz-30MHz). The transmitting antenna sends the EM signals of this frequency range towards the ionosphere. When the EM waves strikes the ionosphere, it is reflected back to the Earth. A receiving antenna at a remote location on the Earth receives these reflected signals.