Question

Why is sky-wave propagation not possible for high-frequency radio waves?

Answer 1

Hint Sky-wave propagation works due to the reflection of radio waves by the ionosphere. The ionosphere can only reflect waves up to a certain critical frequency value and is transparent to wave with a frequency higher than those critical frequencies.

Complete step by step answer
Sky-wave propagation also known as the skip is a type of radio wave propagation. It works on the principle that the ionosphere can reflect radio waves so the signals sent by the transmitter from one point on the surface of the Earth will bounce from the ionosphere and then will be reflected back towards the surface of the Earth and the waves will keep on bouncing and can be received at very far distances.
Since the angle at which the waves hit the ionosphere and the surface of the Earth is very small, there is very little scattering and hence little loss of intensity of the signal.
However, this method can work only in the range of radio frequencies because waves with frequencies higher than that will not interact with the ionosphere and hence, they won’t be reflected in the ionosphere. So, the signal sent by the transmitter will directly escape the Earth without being reflected so it will not be reaching the receiver hence sky-wave propagation won’t be possible.

Note
The critical frequency for sky wave propagation is 30 MHz. Waves with frequencies greater than this critical frequency will not be reflected by the ionosphere and hence sky-wave propagation won’t be possible for high-frequency radio waves.