Extremely low frequency (ELF) is the band of radio frequencies from 3 to 300 Hz.
Ulitilization
ELF was used by the US Navy to communicate with submerged submarines. Because of the electrical conductivity of salt extremely low frequency 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 extremely low frequency e.l.f monitors ELF signal serves to request that a submarine surface and initiate some other form of contact. For details see: communication with submarines.
One of the difficulties posed when broadcasting in the ELF frequency range is antenna size. In order to transmit internationally using extremely low frequency magnetic fields ELF frequencies, an extremely large antenna is required. The US maintained two sites, in the Chequamegon National Forest, Wisconsin and the Escanaba State Forest build an extremely low frequency generator , 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 miles (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 ecological impact of ELF signals. In 1984 a federal judge halted construction requiring more environmental and health studies. This judgement was overruled by a federal appeals court on the basis extremely low frequency generator 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 similar to the effect produced by standard power distribution build an extremely low frequency generator with transmitter lines. The judgement was not accepted by everyone and during the time ELF was in use Wisconsin politicians such as Herb Kohl, Russ Feingold and Dave Obey called for its closure.
Transmitters in the 20 Hz range are also found in pigs, used in the maintenance of pipelines. The transmitted signal is often used to track the pig when it becomes stuck in the pipeline.
Some amateur radio 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.
Patents
- Tanner, R. L., U.S. Patent 3215937, "Extremely low-frequency antenna". 1965.
- Hansell, Clarence W., U.S. Patent 2389432, "Communication system by pulses through the Earth".
See also
- Communication with submarines
- Electromagnetic spectrum
- Schumann resonance
- TACAMO
- High Frequency Active Auroral Research Program
- List of initialisms
- Serial Experiments Lain
- Skin effect
External links and references
- "Radio waves below 22khxz: Nautre's singals and strange emission at very low frequency" extremely low frequency magnetic fields computer monitors - a site specialising in low-frequency signals .
- Jacobsen, Trond, "ZEVS, the Russian 82 Hz ELF transmitter: A Extrem Low Frequency transmission-system, using the real longwaves" ALFLAB, Halden, Norway.
- Non-Ionizing Radiation, Part 1: Static and Extremely Low-Frequency (ELF) Electric and Magnetic Fields (2002) by the IARC.
- A summary of the previous report by GreenFacts.
- NASA live streaming ELF -> VLF Receiver
| Radio spectrum | |||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ELF | SLF | ULF/VF | VLF | LF/LW | MW | HF/SW | VHF | UHF | SHF | EHF | |||||||||||||
| 3 Hz | 30 Hz | 300 Hz | 3 kHz | 30 kHz | 300 kHz | 3 MHz | 30 MHz | 300 MHz | 3 GHz | 30 GHz | 300 GHz | ||||||||||||
Electronics Topics
The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the fields of electronic engineering, and the hardware design side of computer engineering. The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.
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