5. Summary. In this lesson, you learned about ground wave propagation and the influences the Earth
has on radio signals.
a. Ground waves are comprised of surface waves and space waves.
(1) Surface waves travel along the surface of the ground following the curvature of the Earth.
Ground waves should be vertically polarized to reduce the attenuation caused by an induced voltage in
the Earth.
(2) Space waves follow two paths-direct wave and ground-reflected. Space waves are
slightly refracted in the Earth's atmosphere, but suffer little ground attenuation. The direct waves and
ground-reflected waves can either reinforce or cancel each other, depending on whether or not they are
received in phase or out of phase.
b. A ground wave that is vertically polarized has is electric field perpendicular to the Earth's
surface. As a result, there is less wave energy loss than a horizontally polarized wave, the electric field
of which is parallel to the Earth's surface and, therefore, subject to absorption.
c. Ground waves suffer ground loss; their strength is attenuated as the Earth absorbs energy.
This causes the wave to tilt, the degree of which depends upon the conductivity of the surface. Poor
conducting surfaces cause high loss of energy and greater tilt. Higher frequencies also contribute to
increased tilt.
characteristics, power, time of day, and terrain.
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SS0130
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