Why cannot the (i) ground waves (ii) space waves and (iii) sky waves be sustained for long distance communication system beyond 10 MHz to 20 MHz.

Explanation

(i) In ground wave propagation, the conduction
losses due to ground are very high at higher
frequencies. (ii) The space wave propagation has
a limited line of sight distance due to curvature
of earth. (iii) At frequencies beyond 30 MHz,
the sky waves pass through the ionosphere and
are not reflected back.