![]() ![]() It is observed that the ionosphere reflects radio waves that have a frequency of 3 MHz-30 MHz.Similarly, the highest frequency of transmitted signals, above which the ionosphere does not reflect the signals, is called critical frequency. This angle is also called the angle of radiation, and it is the maximum angle of the radio waves originating from the earth with a horizontal imaginary line, above which the ionosphere does not reflect the signals. In skywave propagation, we depend on the reflection of the signal from the ionosphere.The disappearance of signals for a short time due to variations in the height and density of ionization of the ionosphere is called fading. Activities on the surface of Earth, variation in thickness of layers E and F with respect to seasons, and other such variable properties of the medium make skywave propagation the least reliable. ![]() This can happen multiple times before reaching the receiving antenna. The radio waves originating from any station on earth will undergo total internal reflection while returning to earth. The refractive index of the ionosphere decreases from one layer to another with respect to the height. The D layer is closest to the surface of the earth, the E layer lies above the D layer, and the F layer is at the topmost position above the E layer. The ionosphere consists of multiple layers, such as the D layer, the E layer, and the F layer. It is also called ionosphere propagation. In the case of skywave propagation, the radio waves follow the path passing through the sky (i.e., after reflection from the ionosphere). ![]()
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