__________________________________________________________ Radio Wave Propagation
The E layer is present during the daylight hours, refracts signals as high as
20 megahertz back to Earth; and is used for communications up to 1500 miles.
The F layer is divided into the F1 and F2 layers during the day but combine
at night to form one layer. This layer is responsible for high frequency, long-
The critical frequency is the maximum frequency that a radio wave can be
transmitted vertically and still be refracted back to Earth.
Figure 2-Sum 7. Frequency Versus Refraction and Distance