Super low frequency (SLF) is the
ITU
The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
designation for
electromagnetic wave
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
s (
radio waves) in the
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
range between 30
hertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that o ...
and 300 hertz. They have corresponding
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
s of 10,000 to 1,000 kilometers. 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
Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively. In atmospheric scien ...
(ELF), which in some contexts refers to all frequencies up to 300 hertz.
Because of the extreme difficulty of building
transmitter
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
s that can generate such long waves, frequencies in this range have been used in very few artificial communication systems. However, SLF waves can penetrate seawater to a depth of hundreds of meters. Therefore, in recent decades the U.S., Russian and Indian militaries have built huge radio transmitters using SLF frequencies to
communicate with their submarines.
The U.S. naval service is called
Seafarer
A sailor, seaman, mariner, or seafarer is a person who works aboard a watercraft as part of its crew, and may work in any one of a number of different fields that are related to the operation and maintenance of a ship.
The profession of the s ...
and operates at 76 hertz. It became operational in 1989 but was discontinued in 2004 due to advances in
VLF
Very low frequency or VLF is the ITU designation 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 a ...
communication systems. The Russian service is called
ZEVS and operates at 82 hertz. The
Indian Navy
The Indian Navy is the maritime branch of the Indian Armed Forces. The President of India is the Supreme Commander of the Indian Navy. The Chief of Naval Staff, a four-star admiral, commands the navy. As a blue-water navy, it operates si ...
has an operational ELF communication facility at the
INS Kattabomman naval base to communicate with its
Arihant class
The ''Arihant''-class ( in Sanskrit) is a class of Indian nuclear-powered ballistic missile submarines being built for the Indian Navy. They were developed under the ''Advanced Technology Vessel'' (ATV) project to design and build nuclear-po ...
and
Akula class submarines.
The requirements for receivers at SLF frequencies are less stringent than for transmitters, because the signal strength (set by atmospheric noise) is far above the noise floor of the receiver, so small, inefficient
antennas can be used.
Radio amateur
An amateur radio operator is someone who uses equipment at an amateur radio station to engage in two-way personal communications with other amateur operators on radio frequencies assigned to the amateur radio service. Amateur radio operators h ...
s have received signals in this range using simple receivers built around
personal computer
A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...
s, with coil or loop antennas connected to the PCs
sound card
A sound card (also known as an audio card) is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term ''sound card'' is also applied to external audio ...
. Signals are analysed by a software
fast Fourier transform algorithm
In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...
and converted into audible sound.
See also
*
Communication with submarines
Communication with submarines is a field within military communications that presents technical challenges and requires specialized technology. Because radio waves do not travel well through good electrical conductors like salt water, submerged s ...
References
External articles
* Tomislav Stimac, "
Definition of frequency bands (VLF, ELF... etc.)'". IK1QFK Home Page (vlf.it).
{{EMSpectrum
Radio spectrum