Counterpoise (ground system)

Counterpoise (ground system)

A counterpoise is a type of electrical ground that is not connected to earth. It is used in radio antenna systems when a normal earth ground cannot be used because of high soil resistance[1] It consists of a network of wires or cables (or a metal screen) running parallel to the ground, suspended from a few centimetres to several metres above the ground (or lying on the surface). The counterpoise functions as one plate of a large capacitor, with the conductive layers of the earth acting as the other.

Contents

Uses

Counterpoises are typically used in antenna systems where a good earth ground is not available. Monopole antennas used at low frequencies, such as the mast radiator antennas used for AM broadcasting, require the radio transmitter to be electrically connected to the earth under the antenna; this is called a ground. The ground must have a low electrical resistance, because any resistance in the ground connection will dissipate power from the transmitter. Low-resistance grounds for radio transmitters are normally constructed of a network of cables buried in the earth. However, in areas with dry, sandy or rocky soil the ground has a high resistance; a low-resistance ground connection cannot be made. In these cases, a counterpoise is used instead. Since the radio frequency alternating currents from the transmitter can pass through a capacitor, the counterpoise functions as a low-resistance ground connection. A common design for a counterpoise is a series of radial wires close to the ground extending from the base of the antenna in all directions, connected together at the centre.

The size of the counterpoise used for radio work depends on the wavelength of the transmit frequency. With a monopole antenna the counterpoise functions as a ground plane, reflecting the radio waves radiated downward by the antenna. To perform adequately, the counterpoise should extend at least one-quarter wavelength from the antenna tower in all directions. In designing a counterpoise for an AM radio station, for example, AM broadcast-band radio waves are a maximum of 1857 feet (566 m) long. Therefore, the counterpoise should extend 464 feet (141 m) from the tower to make a circle 928 feet (283 m) in diameter. Counterpoises are also used in high-voltage systems, such as lightning rods and Tesla coils.

See also

References

  1. ^ Cebik, L. B. (December 31, 2009). "Counterpoise? On the Use and Abuse of a Word". antenneX. http://www.antennex.com/shack/Dec06/cps.html. Retrieved 25 September 2010. 

External links


Wikimedia Foundation. 2010.

Игры ⚽ Нужен реферат?

Look at other dictionaries:

  • Counterpoise — For the electrical concept, see Counterpoise (ground system). Counterpoise is an alternative review journal based in Gainesville, Florida (USA). It was founded in 1997 by Charles Willett, as a project of the AIP Task Force[1] of the American… …   Wikipedia

  • counterpoise — /kown teuhr poyz /, n., v., counterpoised, counterpoising. n. 1. a counterbalancing weight. 2. any equal and opposing power or force. 3. the state of being in equilibrium; balance. 4. Radio. a network of wires or other conductors connected to the …   Universalium

  • Lightning protection system — A lightning protection system is a system that protects a structure from damage due to lightning strikes, either through safely conducting the strike to the ground, or preventing the structure from being struck. Most lightning protection systems… …   Wikipedia

  • Lightning rod — A lightning rod (USA) or lightning conductor (UK) is a single component in a lightning protection system. In addition to rods placed at regular intervals on the highest portions of a structure, a lightning protection system typically includes a… …   Wikipedia

  • military technology — Introduction       range of weapons, equipment, structures, and vehicles used specifically for the purpose of fighting. It includes the knowledge required to construct such technology, to employ it in combat, and to repair and replenish it.… …   Universalium

  • VHF omnidirectional range — This article is about the radio navigation aid. For other uses, see Vor. D VOR (Doppler VOR) ground station, co located with DME …   Wikipedia

  • Antenna (radio) — Whip antenna on car …   Wikipedia

  • Europe, history of — Introduction       history of European peoples and cultures from prehistoric times to the present. Europe is a more ambiguous term than most geographic expressions. Its etymology is doubtful, as is the physical extent of the area it designates.… …   Universalium

  • France — /frans, frahns/; Fr. /frddahonns/, n. 1. Anatole /ann nann tawl /, (Jacques Anatole Thibault), 1844 1924, French novelist and essayist: Nobel prize 1921. 2. a republic in W Europe. 58,470,421; 212,736 sq. mi. (550,985 sq. km). Cap.: Paris. 3.… …   Universalium

  • literature — /lit euhr euh cheuhr, choor , li treuh /, n. 1. writings in which expression and form, in connection with ideas of permanent and universal interest, are characteristic or essential features, as poetry, novels, history, biography, and essays. 2.… …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”