Q.Explain ground wave propagation.

Modes of Radio Wave Propagation

A radio signal launched from a transmitting antenna can reach a receiver by three distinct routes. Which route dominates depends almost entirely on the frequency of the wave.

Ground (surface) wave

The wave glides along the surface of the Earth, following its curvature because the ground guides it. It works well only at low frequencies (up to about 2 MHz) — higher frequencies are absorbed rapidly by the ground. This is how medium-wave (AM) broadcast signals travel over short-to-moderate distances.

Sky wave

Waves in the HF range (about 3–30 MHz) are sent upward, and the ionosphere (ionised upper atmosphere) reflects them back to Earth. By bouncing between the ionosphere and the ground, a shortwave signal can reach far beyond the horizon — this enables long-distance and international broadcasting.

Space (line-of-sight) wave

Above about 30 MHz the ionosphere no longer reflects waves — they punch straight through it. Such VHF/UHF signals therefore travel in a straight line from transmitter to receiver, used for TV, FM radio, and satellite communication. The range is limited by the horizon. For a transmitting antenna of height $h_T$, …