Question

The ground wave eventually disappears, as one moves away from the transmitter, because of :

• A. interference from the sky wave
• B. loss of line of signal condition
• C. maximum single - hop distance limitation
• D. diffraction effect causing tilting of the wave

Answer 1

The correct option is D diffraction effect causing tilting of the wave

In ground wave transmission, the intensity of the signal falls with distance due to its absorption by the ground. So, ground wave propagation cannot take place up to very large distance. If the energy of the signal is increased by increasing the frequency of the carrier wave, then there is corresponding increase in absorption of signal by the ground. This is made up by energy diffracted downward from the upper portions of the wavefront.
There is another way in which the surface wave is attenuated. Because of diffraction, the wavefront gradually tilts over, as shown in the figure. As the wave propagates over the Earth, it tilts over more and more. The increasing tilts cause greater short-circuiting of the electric field components of the wave. Eventually, at some distance (in wavelengths) from the antenna, as partly determined by the type of surface over which the ground wave propagates, the wave "lies down and dies".