Table 3. Characteristics of the ionosphere.
The longer exposure of the ionosphere to the sun in the summer causes a greater degree of
ionization during the night and day. Therefore, higher frequencies may be used for summer
Remember, however, that the actual number of layers, their heights above the earth, and the
relative intensity of ionization present will vary. They vary from hour to hour, from day to day,
from month to month, and from year to year.
There are three distinct paths that a radio wave may take to reach the receiving antenna.
The direct and reflected paths are shown in Figure 1-7. They are purposely exaggerated to
enable the reader to clearly grasp the differences.
The direct path goes directly from the transmitting to the receiving antenna. The reflected
path bounces off the ionosphere or the surface of the earth at the same angle at which it
arrives and continues to the receiving antenna (angle incidence=angle of arrival). The
refracted path is the path caused by the bending of the waves in the same manner light
waves are bent when seen through water.