There are different ways to propagate signals over large distances. These ways are called modes such as ground or surface wave propagation, ionospheric propagation, tropospheric propagation, satellite wave propagation, etc. Ionospheric propagation utilizes the layers of the ionosphere to reflect waves of specific frequency bands. It manages this feat with understanding the layers of the ionosphere namely: D, E, and F layers.
D-layer is the lowest known ionized region of the ionosphere. Sunlight strikes the atoms in this layer and break them up into ions, however, they recombine quickly, thus the ionization level is directly proportional to the amount of sunlight it receives. With this in mind, levels increase from sunrise to peaks at local noon and decrease to nothingness at sunset. It is not particularly effective with high-frequency waves but can still provide ducting to very low frequencies for worldwide communication. Only drawbacks are the necessity of large antennas and high power transmitters.
E-layer is the region above the D-layer and the lowest portion of the ionosphere useful for long distance communication. Its ionization is largely influenced by cosmic rays such as ultraviolet radiation, solar x-rays and meteor burst radiation. It also depends on the sun angle above the horizon (that is, the relative position of the sun). It starts to increase after sunrise, peaking at noon, and drops quickly after sundown and zeroes at midnight. It can accommodate a little of medium frequency surface waves and some high-frequency waves during daytime. F layer is the real layer that represents ionospheric propagation. In this layer, ions recombine more slowly and thus the effect of sun angle does not develop as fast. Furthermore, this layer can accommodate reflection even during nighttime. During daytime, F layer is divided into two layers but combine to one after sunset.
Posted 2010-12-14 and updated on Dec 14, 2010 7:50am by crisd