Ham Radio General Class Practice Test

How does antenna height affect the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna?

1. If the antenna is too high, the pattern becomes unpredictable

2. Antenna height has no effect on the pattern

3. If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional

4. If the antenna is less than 1/2 wavelength high, radiation off the ends of the wire is eliminated

The correct answer is: If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional

The correct answer reflects a fundamental principle regarding the performance of horizontal dipole antennas. When a horizontal dipole antenna is positioned at a height less than 1/2 wavelength above the ground, its azimuthal radiation pattern tends to be almost omnidirectional. This means that the antenna will radiate energy evenly in all horizontal directions. This occurs because, at lower heights, ground reflections and other factors create a less pronounced null in the radiation pattern. The radiation lobes spread out more evenly, effectively dispersing the signal across a broad area. This omnidirectional characteristic is advantageous in certain communication scenarios where coverage in multiple directions is desired. As an antenna increases in height, the hierarchy of lobes alters, and certain directional properties come into play, but at a lower elevation, the effects of the ground and the way signals are radiated contribute to this omnidirectional behavior. This principle is essential for operators aiming to optimize their station's coverage and communication capabilities in amateur radio activities.