Ground dipole
Encyclopedia
A Ground dipole, or Ground antenna, is a special type of antenna
which consists of two electrode
s positioned in the ground.
Ground dipole antennas are usually used for transmitting and receiving on the ELF
and VLF
bands. The antenna consists of two electrodes, planted in the ground at some distance from each other. Radio signal currents
are sent along wires to the electrodes. The current flows in a loop, around the above-ground wires and through the Earth
(where conductive), forming a large conducting loop, which radiates electromagnetic waves.
For very long waves, a ground dipole works most effectively when the loop is as large as possible. This is best achieved by feeders built as overhead lines and where the ground between the electrodes has little conductivity. Although the ground dipole seems to be a good antenna as it requires no tall towers and its loop covers a large area with respect to the wire used, the size (with respect to the frequency being used) is still very small, and due to its large size, total resistance is relatively high, giving very low efficiency (<1%). It is also affected by lightning
, as voltage gradients induced by lightning can result in dangerously high voltages on the leads.
Ground dipole antennas are popular among amateur radio
enthusiasts. By connecting the electrodes to the analog input of a PC
soundcard, one can easily receive ELF signals by using FFT
software. One must keep in mind that this setup is very sensitive to nearby lightning strikes which can destroy the soundcard input and should therefore be equipped with adequate protection and isolation circuitry.
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
which consists of two electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
s positioned in the ground.
Ground dipole antennas are usually used for transmitting and receiving on the ELF
Extremely low frequency
Extremely low frequency is a term used to describe radiation frequencies from 3 to 300 Hz. In atmosphere science, an alternative definition is usually given, from 3 Hz to 3 kHz...
and VLF
Very low frequency
225px|thumb|right|A VLF receiving antenna at [[Palmer Station]], Antarctica, operated by Stanford UniversityVery low frequency or VLF refers to radio frequencies in the range of 3 kHz to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals...
bands. The antenna consists of two electrodes, planted in the ground at some distance from each other. Radio signal currents
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
are sent along wires to the electrodes. The current flows in a loop, around the above-ground wires and through the Earth
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
(where conductive), forming a large conducting loop, which radiates electromagnetic waves.
For very long waves, a ground dipole works most effectively when the loop is as large as possible. This is best achieved by feeders built as overhead lines and where the ground between the electrodes has little conductivity. Although the ground dipole seems to be a good antenna as it requires no tall towers and its loop covers a large area with respect to the wire used, the size (with respect to the frequency being used) is still very small, and due to its large size, total resistance is relatively high, giving very low efficiency (<1%). It is also affected by lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
, as voltage gradients induced by lightning can result in dangerously high voltages on the leads.
Ground dipole antennas are popular among amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
enthusiasts. By connecting the electrodes to the analog input of a PC
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
soundcard, one can easily receive ELF signals by using FFT
Fast Fourier transform
A fast Fourier transform is an efficient algorithm to compute the discrete Fourier transform and its inverse. "The FFT has been called the most important numerical algorithm of our lifetime ." There are many distinct FFT algorithms involving a wide range of mathematics, from simple...
software. One must keep in mind that this setup is very sensitive to nearby lightning strikes which can destroy the soundcard input and should therefore be equipped with adequate protection and isolation circuitry.