Draw a schematic diagram describing the three modes of propagation of electromagnetic waves in the atmosphere. In ionospheric reflection indicate clearly which one of these achieves long distance communication.

Write an expression for the maximum line of sight distance ${\mathrm{d}}_{\mathrm{M}}$ between two antennas having height ${\mathrm{H}}_1$ and ${\mathrm{H}}_2$ above the earth's surface.

Write briefly any two factors which demonstrate the need for modulating a signal. Draw a suitable diagram to show amplitude modulation using sinusoidal signal as the modulating signal.

Which mode of wave propagation is suitable for television broadcast and satellite communication and why ? Draw a suitable diagram depicting this mode of propagation of the wave.

A TV tower is $80 \mathrm{m}$ tall. Calculate the maximum distance upto which the signal transmitted from the tower can be received.