Question

What is sky wave communication? Why is this mode of propagation restricted to the frequencies only upto few MHz?

Answer 1

Ionospheric reflection of radio waves, back towards the earth, is known as sky wave communication. The ionospheric layers act as a reflector for a certian range of frequencies (3-30 MHz). Electromagnetic waves of frequencies higher than 30MHz (or few up to 40 MHz) penetrate the ionosphere and escape.