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Extremely low frequency (ELF) is the ITU designation [1] for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively. [2] [3] In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz.
Extremely high frequency: 1 cm: 30 GHz 124 μeV: SHF Super high frequency: 1 dm: 3 GHz 12.4 μeV UHF Ultra high frequency: 1 m: 300 MHz: 1.24 μeV Radio waves: VHF Very high frequency: 10 m 30 MHz 124 neV: HF High frequency: 100 m 3 MHz 12.4 neV MF Medium frequency: 1 km: 300 kHz: 1.24 neV LF Low frequency: 10 km 30 kHz 124 peV: VLF Very low ...
Super low frequency: SLF: 2: 30–300 Hz 10,000–1,000 km: Communication with submarines Ultra low frequency: ULF: 3: 300–3,000 Hz 1,000–100 km: Communication with submarines, communication within mines, landline telephony, fax machines, fiber-optic communication: Very low frequency: VLF: 4: 3–30 kHz 100–10 km
This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz). Another conflicting designation which includes this frequency range is Extremely Low Frequency (ELF), which in some contexts refers to all frequencies up to 300 hertz.
Very low frequency or VLF is the ITU designation [1] for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave as the wavelengths range from one to ten myriameters (an obsolete metric unit equal to 10 kilometers).
Project Sanguine was a US Navy project proposed in 1968 for communication with submerged submarines using extremely low frequency (ELF) radio waves. The initially proposed system, hardened to survive a nuclear attack, would have required a giant antenna covering two-fifths of the state of Wisconsin.
Extremely low frequency (ELF) (< 3 kHz) and very low frequency (VLF) (3–30 kHz) signals can propagate efficiently in this waveguide. For instance, lightning strikes launch a signal called radio atmospherics , which can travel many thousands of kilometers, because they are confined between the Earth and the ionosphere.
The global electromagnetic resonance phenomenon is named after physicist Winfried Otto Schumann who predicted it mathematically in 1952. Schumann resonances are the principal background in the part of the electromagnetic spectrum [2] from 3 Hz through 60 Hz [3] and appear as distinct peaks at extremely low frequencies around 7.83 Hz (fundamental), 14.3, 20.8, 27.3, and 33.8 Hz.