Q.The frequency range of 30 MHz to 400 GHz is used for :

A space wave travels in a straight line directly from a transmitting antenna to a receiving antenna, and it is the mode responsible for line-of-sight (LOS) communication, television broadcast, microwave links, and satellite communication. Above roughly 40 MHz, communication is confined essentially to line-of-sight paths, which lets antennas be built comparatively small and mounted well above ground level. Because earth's curvature blocks a straight-line path beyond a certain distance, a receiver situated beyond the horizon needs a tall enough antenna to intercept the wave. For a transmitting antenna of height $h_T$, its radio horizon is $d_T = \sqrt{2Rh_T}$, wh …