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प्रश्न
What is space wave propagation? Which systems of communication use space waves? What is 'radio horizon' of a transmitting antenna of height h? Why is space wave propagation suitable for frequencies above 40 MHz?
उत्तर
Space Wave propagation is a type of communication method in which the radio waves from the transmitting antenna reaches the receiving antenna directly through space.
Space Wave propagation is used in
(i) Line of sight communication
(ii) Satellite communication
If transmitting antenna is at a height
\[h_T\], then the distance to the horizon
\[d_T\] is given as \[d_T = \sqrt{2R h_T}\]
\[d_T\] is called radio horizon of the transmitting antenna.
Frequency signals above 40 MHz are absorbed by the surface of earth and therefore they cannot travel along the surface of earth which is required in ground wave propagation. Also, frequencies above 40 MHz cannot be reflected by ionosphere, hence their propagation cannot be like sky wave propagation. Hence, this is the reason why space wave propagation is suitable for frequencies above 40 MHz.
As transmission of signals of frequencies above 40 MHz is achieved through space wave propagation. space wave communication is essentially limited to line of sight.Above 40 MHz frequency signals can not be sent by the sky wave or ground wave so we use the space wave
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