The Physics Factbook
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website
|National Research Council. An Evaluation of the US Navy's ELF Submarine Communications Ecological Monitoring Program. Washington, DC: National Academy Press, 1997.||"The frequency is shifted between 72 Hz and 80 Hz (with a center of 76 Hz) depending on whether a code of "one" or "zero"is to be transmitted"||72 & 80 Hz
76 Hz mean
|Lehtoranta, V & Romero, R. Reception of Submarine Communication Systems. 22 November 1999.||"Frequencies are 76 Hz for the US System and 82 Hz in the Russian system"||76 Hz (US)
82 Hz (Russia)
|Bannister, Peter & Fraser-Smith, Antony. Reception of ELF Signals at Antipodal Distances.||"Wisconsin Transmitter Facility/ Michigan Transmitter Facility dual antenna transmitting system, which typically operates at a center frequency of 76 Hz"||76 Hz|
|Aldridge, Bob. Project ELF: Extremely Low Frequency Signals to Submarines. 18 February 2001.||"US ELF transmitters operate at 76 cycles per second (Hz)"||76 Hz|
|The Navy's ELF System. High Frequency Active Auroral Research Program (HAARP). 11 September 1997.||"The transmitter facility in Michigan uses about six acres of land and the one in Wisconsin about two acres. The operating frequency is 76 Hz."||76 Hz|
A wave is disturbance that propagates through either some material medium or space. Waves can be classified into two groups. Mechanical waves are waves that travel though a medium. Electromagnetic waves are waves that can travel though space. Examples of electromagnetic waves include microwaves, infrared waves, light rays, ultraviolet waves, x-rays, gamma rays and radio waves.
Extremely Low Frequencies (ELF) transmissions are electromagnetic waves used mainly for naval strategic communications. In general, the frequency of ELF waves range from 3 Hz to 3000 Hz. This particular range is important to the US Navy because of its capability in providing a communication system for submerged submarines during covert operations. In addition, the sea water's high electrical conductivity prevents the detection of submarines and it's communication with the world above which uses normal radio transmissions. The lower the frequency of the ELF transmissions, the deeper the signal can travel in sea water, thereby decreasing the chances of submarines being detected by enemies. The Navvy's ELF Communications System uses a frequency-modulation principle called minimum shift keying. In this type of modulation, the frequency is shifted between 72 Hz and 80 Hz with a center of 76 Hz.
Our military currently operates an ELF system with two transmitting antennas, each located in Michigan and Wisconsin. The ELF antenna in Wisconsin is located in Chequamegon National Forest and consists of 28 miles of antenna cable. The ELF antenna in Michigan is located in Escanaba State Forest and consists of 56 miles of antenna cable. The antennas are able to generate ELFs as low as 10,000 feet deep below sea level and at an altitude of 80 kilometers. By targeting the supercharged portion of the ionosphere over the Arctic, scientists are hoping to create a virtual transmitter in space that would allow the Navy to communicate with submarines worldwide. Many controversies have developed over the presence of these huge transmitting antennas in Michigan and Wisconsin. Many argue that signals are damaging the ionosphere. In 1984 Wisconsin sued the Federal government charging that the Navy had covered up the risks of electromagnetic pollution. Wisconsin had won the case, but the Pentagon claimed national security considerations and got the decision thrown out.
Lisa Wu -- 2001
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