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Extremely low frequency (ELF) is the band of radio frequencies from 3 to 300 Hz.ELF was used by the US Navy to communicate with submerged submarines. Because of the electrical conductivity of salt water, submarines are shielded from most electromagnetic communications. Signals in the ELF frequency range, however, can penetrate much more deeply. The low transmission rate of most ELF communications limits their use as communications channels; generally an ELF signal serves to request that a submarine surface and initiate some other form of contact. For details see: communications with submarines
One of the difficulties posed when broadcasting in the ELF frequency range is antenna size. In order to transmit internationally using ELF frequencies, an extremely large antenna is required. The US maintained two sites, in the Chequamegon National Forest , Wisconsin and the Escanaba State Forest , Michigan, until dismantling them beginning in late September 2004. Both sites used long power lines as antennae, in multiple strands ranging from 14 to 28 mileA mile is any of several units of distance, or, as physicists say, of length. Today, one mile is mainly equal to about 1609 metres on land and 1852 metres at sea and in the air, but see below for the details. Current definitions The meanings of mile thats (22.5 to 45 kilometers) long. Considerable amounts of electrical power are generated and emitted by ELF.
There have been some concerns over the possible ecologicalEcology is the branch of science that studies the distribution and abundance of living organisms, and the interactions between organisms and their environment. The environment of an organism includes both its physical habitat, which can be described as th impact of ELF signals. In 1984 a federal judge halted construction requiring more environmental and health studies. This judgement was overruled by an federal appeals court on the basis that the US Navy claimed to have spent over 25 million dollars studying the effects of the electromagnetic fields with results indicating that they were similiar to the effect produced by standard power distribution lines. The judgement was not accepted by everyone and during the time ELF was in use Wisconsin politicians such as Herb Kohl, Russ FeingoldRussell Dana Feingold (born March 2, 1953) is a member of the Democratic Party who has served in the United States Senate for the state of Wisconsin since 1992. He was born in Janesville, Wisconsin and graduated from Joseph A. Craig High School. He later and Dave ObeyDavid Ross Obey (born October 3, 1938) is an American politician. He has been a Democratic member of the United States House of Representatives since 1969, representing the Seventh Congressional District of Wisconsin. Obey was born in Okmulgee, Oklahoma a called for its closure.
Some amateur radioAmateur radio commonly called ham radio , is a hobby enjoyed by many people throughout the world; as of 2004 about 3 million worldwide, 70,000 in Germany, 5,000 in Norway, 57,000 in Canada, and 700,000 in the USA. A holder of an Amateur Radio license has aficionados record ELF (or even lower) signals from very large homemade antennas, and play them back at higher speeds in order to catch the Earth's natural fluctuations in its electromagnetic field. Increasing the speed of the magnetic tape increases the pitch, so that it is brought into the audio frequency range.
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