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When used in the context of antenna construction, radial wires are physical objects: Wires running away from the base of the antenna, used to augment or replace the conductivity of the ground near the base of the antenna. The radial wires either may run above the surface of the earth (elevated radials), on the surface (on ground radials), or ...
Buried in the ground under the antenna is an enormous radial ground system, which forms the bottom 'plate' of the capacitor with the overhead top load. The antenna must be very large at the VLF frequencies used; the supporting masts are 250–300 metres (820–980 ft) high, and the topload is about 1,900 metres (6,200 ft) in diameter.
It consists of a network of radial copper wires suspended above the ground, connected to the transmitter feedline ground. It is suspended about 8 feet above ground, so technicians can get access to the helix house at the foot of the tower. Antenna used in Lodge-Muirhead wireless system around 1900, the first counterpoise.
Base-fed mast radiator antennas shorter than about .16 wavelength are not used, [147] as the radiation resistance at that length is around 10 ohms, 5 times the typical resistance of a buried radial ground system, 2 ohms, so in an Earth-grounded antenna over 20% of the transmitter power would be wasted in the ground resistance.
Omnidirectional radiation patterns are produced by the simplest practical antennas, monopole and dipole antennas, consisting of one or two straight rod conductors on a common axis. Antenna gain (G) is defined as antenna efficiency (e) multiplied by antenna directivity (D) which is expressed mathematically as: =.
In most antennas, the radiation from the different parts of the antenna interferes at some angles; the radiation pattern of the antenna can be considered an interference pattern. This results in minimum or zero radiation at certain angles where the radio waves from the different parts arrive out of phase , and local maxima of radiation at other ...
Types of antenna often mounted on mast radiators are: fiberglass whip antennas for land mobile radio systems for taxi and delivery services, dish antennas for microwave relay links carrying commercial telecommunications and internet data, FM radio broadcasting antennas consisting of collinear bays of twisted dipole elements, and cellular base ...
One of the first radomes. The radome (top) covers the H2S radar system rotating antenna (bottom) on a Halifax bomber. A radome is often used to prevent ice and freezing rain from accumulating on antennas. In the case of a spinning radar parabolic antenna, the radome also protects the antenna from debris and rotational irregularities due to wind ...