TC 9-64 _________________________________________________________________________
Figure 2-Sum 4. Surface Wave Propagation
Ground waves are composed of two separate component waves: the surface
wave and the space wave.
Surface waves travel along the contour of the earth by diffraction.
Space waves can travel through the air directly to the receiving antenna or
can be reflected from the surface of the earth.
Figure 2-Sum 5. Space Wave Propagation
Sky waves, often called ionospheric waves, are radiated in an upward direction
and returned to Earth at some distant location because of refraction.
Natural horizon is the line-of-sight horizon.
Radio horizon is one-third farther than the natural horizon.
The ionosphere consists of several layers of ions, formed by the process called
ionization.
Ionization is the process of knocking electrons free from their parent atom,
thus upsetting electrical neutrality.
Recombination is the opposite of ionization; that is, the free ions combine
with positive ions, causing the positive ions to return to their original neutral
atom state.
The D layer is the lowest region of the ionosphere and refracts signals of low
frequencies back to Earth.
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