Very low frequency in the context of Longwave

Aldra is an island in Lurøy Municipality in Nordland county, Norway. It is located just off the mainland coast, north of the village of Haugland and west of Brattland. The island is separated from the mainland by the Aldersundet strait. The islands of Stigen and Lurøya lie to the west. The village of Aldra lies on the southeastern side of the island.

Aldra island is used as a VLF-transmission site. An antenna, spanning the fjord to Brattland, was used as part of the OMEGA Navigation System until 1997. That antenna was dismantled in 2002.

Electron precipitation (also called energetic electron precipitation or EEP) is an atmospheric phenomenon that occurs when previously trapped electrons enter the Earth's atmosphere, thus creating communications interferences and other disturbances. Electrons trapped by Earth's magnetic field spiral around field lines to form the Van Allen radiation belt. The electrons are from the solar wind and may remain trapped above Earth for an indefinite period of time (in some cases years). When broadband very low frequency (VLF) waves propagate the radiation belts, the electrons exit the radiation belt and "precipitate" (or travel) into the ionosphere (a region of Earth's atmosphere) where the electrons will collide with ions. Electron precipitation is regularly linked to ozone depletion. It is often caused by lightning strikes.

OMEGA was the first global-range radio navigation system, operated by the United States in cooperation with six partner nations. It was a hyperbolic navigation system, enabling ships and aircraft to determine their position by receiving very low frequency (VLF) radio signals in the range 10 to 14 kHz, transmitted by a global network of eight fixed terrestrial radio beacons, using a navigation receiver unit. It became operational around 1971 and was shut down in 1997 in favour of the Global Positioning System.

The Ohio class of nuclear-powered submarines includes the United States Navy's 14 ballistic missile submarines (SSBNs) and its 4 cruise missile submarines (SSGNs). Each displacing 18,750 tons submerged, the Ohio-class boats are the largest submarines ever built for the U.S. Navy and are capable of carrying 24 Trident II ballistic missiles or 22 tubes with 7 BGM-109 Tomahawk cruise missiles apiece. They are also the third-largest submarines ever built, behind the Russian Navy's Soviet era 48,000-ton Typhoon class, the last of which was retired in 2023, and 24,000-ton Borei class.

Like their predecessors the Benjamin Franklin and Lafayette classes, the Ohio-class SSBNs are part of the United States' nuclear-deterrent triad, along with U.S. Air Force strategic bombers and intercontinental ballistic missiles. The 14 SSBNs together carry about half of U.S. active strategic thermonuclear warheads. Although the Trident missiles have no preset targets when the submarines go on patrol, they can be given targets quickly, from the United States Strategic Command based in Nebraska, using secure and constant radio communications links, including very low frequency systems.

A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The current from the transmitter is applied, or for receiving antennas the output signal voltage to the receiver is taken, between the monopole and the ground plane. One side of the feedline to the transmitter or receiver is connected to the lower end of the monopole element, and the other side is connected to the ground plane, which may be the Earth. This contrasts with a dipole antenna which consists of two identical rod conductors, with the current from the transmitter applied between the two halves of the antenna. The monopole antenna is related mathematically to the dipole. The vertical monopole is an omnidirectional antenna with a low gain of 2 - 5 dBi, and radiates most of its power in horizontal directions or low elevation angles. Common types of monopole antenna are the whip, rubber ducky, umbrella, inverted-L and T-antenna, inverted-F, folded unipole antenna, mast radiator, and ground plane antennas.

The monopole is usually used as a resonant antenna; the rod functions as an open resonator for radio waves, oscillating with standing waves of voltage and current along its length. Therefore the length of the antenna is determined by the wavelength of the radio waves it is used with. The most common form is the quarter-wave monopole, in which the antenna is approximately one quarter of the wavelength of the radio waves. It is said to be the most widely used antenna in the world. Monopoles shorter than one-quarter wavelength, called electrically short monopoles, are also widely used since they are more compact. Monopoles five-eights (5/8 = 0.625) of a wavelength long are also common, because at this length a monopole radiates a maximum amount of its power in horizontal directions. A capacitively loaded or top-loaded monopole is a monopole antenna with horizontal conductors such as wires or screens insulated from ground attached to the top of the monopole element, to increase radiated power. Large top-loaded monopoles, the T and inverted L antennas and umbrella antenna are used as transmitting antennas at longer wavelengths, in the LF and VLF bands.