Very High Frequencies

Propagation in the VHF band (30 MHz to 300 MHz) is pri­marily by line of sight (LOS) to the optical horizon, so if the antenna patterns direct most of the RF power in the hori­zontal plane, there are essentially no ionospheric effects. For earth-space propagation paths, however, the ionosphere can affect the signal adversely by refraction, diffraction, scatter­ing, or reflection. These effects can be especially important when the path traverses the equatorial, auroral, and polar ionosphere. The amplitude, phase, and polarization of the sig­nal may change measurably. These effects will be quantified in the following section.

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