Figure 1-3. Horizontal wave polarization.
Wavelength, frequency, and polarization are all essential elements of the actual wave and are
factors which affect the radio wave propagation. The simplest form of propagation is through
space. Radio waves tend to travel in straight lines unless they are acted on by some force.
They can be reflected off the surface of any sharply defined object such as the earth's
surface. The radio waves can also meet other obstructions or objects that will scatter or
reflect the signal. They can be reflected, refracted, or diffracted.
Radio waves are reflected similar to light waves traveling at the same speed. Although light
waves can be seen, radio waves must be detected by electronic equipment. Figure 1-4
illustrates how radio waves are reflected off the ionosphere.
Refraction can best be illustrated by a pencil held obliquely so that a portion of it is beneath
the surface of some water (Figure 1-5). From most viewpoints, the pencil will have the
appearance of being bent at the point where it enters the water. This effect is because light
waves travel more slowly in water than air.
Diffraction of a radio wave is the phenomena of bending the wave around a solid object. The
lower the frequency or the longer the wavelength, the greater the bending of the wave.
Therefore, radio waves are more readily diffracted than light waves. Sound waves are more
readily diffracted than radio waves. This illustrates why sound waves can be heard around
the corner of a large building.
IT0302
1-4
Previous Page
