Extremely low frequency (ELF) is the band of radio frequencies from 3 to 30 Hz, at one time used by the US Navy and Soviet/Russian Navy to communicate with submerged submarines.
Because of the electrical conductivity of seawater, submarines are shielded from most electromagnetic communications; signals in the ELF frequency range, however, can penetrate much deeper. Two factors limit the usefulness of ELF communications channels: the low data tran...
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Extremely low frequency (ELF) is the band of radio frequencies from 3 to 30 Hz, at one time used by the US Navy and Soviet/Russian Navy to communicate with submerged submarines.
Because of the electrical conductivity of seawater, submarines are shielded from most electromagnetic communications; signals in the ELF frequency range, however, can penetrate much deeper. Two factors limit the usefulness of ELF communications channels: the low data transmission rate of a few characters per minute and, to a lesser extent, the one-way nature due to the impracticality of installing a transmitter of the required size on a submarine (transmitters need to be of exceptional size for the users to achieve successful communication). Generally ELF signals were used to order a submarine to rise to a shallow depth where it could receive some other form of communication.
One of the difficulties posed when broadcasting in the ELF frequency range is antenna size. This is because the antenna must be at least...
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