Question

Why is it not possible to use sky waves for the transmission of the tv signals? Upto what distance can a signal be transmitted using an antenna of height $'h'$?

Answer 1

The propagation of sky waves will happen only because of the reflection of the radio waves by the ionosphere. The reflection that takes place in the ionosphere reflects the waves only up to the certain critical frequency value and that wave is transparent to the wave that has higher frequency than that of the critical frequency.

Complete step by step answer:
SKIP, also called sky wave propagation, belongs to the type of radio wave propagation. The sky wave propagation basically works on the principle that the reflection that take place in the ionosphere reflects the radio waves so when the signal that is sent to the transmitter from the one point of the surface to the earth, the signal will bounce from the ionosphere and from there it will get reflected towards the surface of the earth. The process will take place, that is the waves will repeatedly bounce back towards the earth surface and it can also be received at a very far distance.
The angle at which the waves that hit the ionosphere and the surface of the earth is very small. There will be a little scattering and there will be little loss of the intensity of the signal.
The tv signals will always lie in the range of frequency of $100Mhz - 220Mhz$. The waves that have this frequency range will not get reflected in the ionosphere and hence it will get transmitted through the sky waves. The distance that a signal can be transmitted using an antenna is $\sqrt {2Rh}$.

Note:
The critical frequencies of the sky wave propagation are $30MHz$. Waves that have a frequency value that is more than the critical value will not get reflected by the ionosphere. Therefore the sky wave propagation will not be possible for the radio waves that have high frequencies.