In radio communication, a ground dipole, also referred to as an earth dipole antenna, transmission line antenna, and in technical literature as a horizontal electric dipole (HED), is a huge, specialized type of radio antenna that radiates extremely low frequency (ELF) electromagnetic waves. It is the only type of transmitting antenna that can radiate practical amounts of power in the ELF frequency range of 3 Hz to 3 kHz. A ground dipole consists of two ground electrodes buried in the earth, separated by tens to hundreds of kilometers, linked by overhead transmission lines to a power plant transmitter located between them. Alternating current electricity flows in a giant loop between the electrodes through the ground, radiating ELF waves, so the ground is part of the antenna. To be most effective, ground dipoles must be located over certain types of underground rock formations. The idea was proposed by U.S. Dept. of Defense physicist Nicholas Christofilos in 1959.
Although small ground dipoles have been used for years as sensors in geological and geophysical research, their only use as antennas has been in a few military ELF transmitter facilities to communicate with submerged submarines. Besides small research and experimental antennas, three full-scale ground dipole installations are known to have been constructed; two by the U.S. Navy at Republic, Michigan and Clam Lake, Wisconsin, and one by the Russian Navy on the Kola peninsula near Murmansk, Russia. The U.S. facilities were used between 1985 and 2004 but are now decommissioned.
Other articles related to "ground dipole":
... Ground dipoles are not needed for reception of ELF signals ... The requirements for receiving antennas at ELF frequencies are less stringent than transmitting antennas, because the signal to noise ratio in ELF receivers is dominated by the large atmospheric noise in the band ...
Famous quotes containing the word ground:
“Our children do not want models of perfection, neither do they want us to be buddies, friends, or confidants who never rise above their own levels of maturity and experience. We need to walk that middle ground between perfection and peerage, between intense meddling and apathythe middle ground where our values, standards, and expectations can be shared with our children.”
—Neil Kurshan (20th century)