by Joseph J. Carr    McGraw-Hill     2001

The antenna is arguably one of the most important parts of the receiving and/or transmitting station (Fig. 1-1). That is what this book is all about.

Thus, most forms of ground wave propagate in the troposphere. But because certain propagation phenomena (caused mostly by weather conditions) only occur at higher altitudes, tropospheric propagation should be differentiated from other forms of ground wave.

The ionosphere is the region of earth’s atmosphere that is above the stratosphere. The peculiar feature of the ionosphere is that molecules of air gas (O2 and N) can be ionized by stripping away electrons under the influence of solar radiation and certain other sources of energy.

In the ionosphere, the air density is so low that ions can travel relatively long distances before recombining with oppositely charged ions to form electrically neutral atoms. As a result, the ionosphere remains ionized for long periods of the day—even after sunset.