36. Radio Wave Propagation.
This lesson we will discuss propagation of electromagnetic waves
in the earth's natural environment; thus, transmission using man-made
fundamental technical factors that limit, or otherwise influence,
spectrum utilization for various communications services. Even with
electromagnetic propagation is immense. Consequently this lesson is
devoted to an abbreviated introductory discussion of the earth's
propagation environment and a summary of the major modes of
propagation in natural environments.
37. The Earth's Propagation Environment.
a.The characteristics of all radio frequency transmission paths used
in connections with earth bound terminals reflect the unique nature
would not be possible without this environment, while for others it
an earth environment may not function on the moon, while others may
b. The earth's atmosphere may be the most important feature of
the propagation environment. Figure 14 is an idealized sketch of the
stratified nature of the atmosphere.
Part of the upper envelope,
known as the ionosphere, is characterized by the presence of free
gases by ultraviolet radiation and x-radiation from the sun.
Ionization is the gain or loss of electrons by an atom of a gas
Ionospheric ions are primarily positive, having lost
electrons; this results in an increased concentration of free
The various regions of the ionosphere are distinguished
night and day and is to some extent affected by solar flares and
other natural phenomena. Looking at other pertinent characteristics
of the atmosphere the troposphere contains most of the neutral gases
of the atmosphere as well as water vapor.
The temperature in the
troposphere normally decreases uniformly with height; elsewhere in
the atmosphere, it is either constant, as in parts of the
stratosphere, or increases with height, as in the ionosphere.