Q.The frequency range of 3 MHz to 30 MHz is used for

Sky-wave propagation lets radio signals travel over very long distances - well beyond the horizon - by bouncing off the ionosphere, a region of the upper atmosphere (roughly 65 km to 400 km up) that is rich in ions produced when air molecules absorb ultraviolet and other high-energy solar radiation. Because ionisation is low near the ground (radiation already absorbed higher up) and low at extreme heights (too few molecules left to ionise), it peaks at an intermediate altitude, spread across named layers - D, E, F1 and F2 - each affecting different frequency bands differently. The ionosphere reflects a specific band of roughly 3-40 MHz back do …