Editing Low frequency (section)

==Antennas==
Since the ground waves used in this band require [[vertical polarization]], vertical antennas are used for transmission. [[Mast radiator]]s are most common, either insulated from the ground and fed at the bottom, or occasionally fed through guy-wires. [[T-antenna]]s and [[T-antenna#L-antenna|inverted L-antennas]] are used when antenna height is an issue.

LF transmitting antennas for high power transmitters require large amounts of space, and have been the cause of controversy in Europe and the United States, due to concerns about possible health hazards associated with [[electromagnetic radiation and health|human exposure to radio waves]].

===Longwave receiving antennas===
[[Image:Low cost DCF77 receiver.jpg|thumb|Low cost LF [[time signal]] [[Radio receiver design|''crystal receiver'']] using ferrite [[loop antenna]].]]
Antenna requirements for LF reception are much more modest than for transmission. Although non-resonant long wire antennas are sometimes used, ferrite [[loop antenna]]s are far more popular because of their small size.

Amateur radio operators have achieved good LF reception using [[active antenna]]s: A short whip with a built-in [[pre-amplifier]].

===Antenna heights===
Due to the long wavelengths in the band, nearly all LF antennas are [[electrically short]], shorter than one quarter of the radiated wavelength, so their low radiation resistance makes them inefficient, requiring very low resistance grounds and conductors to avoid dissipating transmitter power.
These electrically short antennas need [[loading coil]]s at the base of the antenna to bring them into resonance. Many antenna types, such as the [[umbrella antenna]] and L- and T-antenna, use capacitive top-loading (a "top hat"), in the form of a network of horizontal wires attached to the top of the vertical radiator. The [[capacitance]] improves the efficiency of the antenna by increasing the current, without increasing its height.

The height of antennas differ by usage. For some [[non-directional beacon]]s (NDBs) the height can be as low as 10&nbsp;meters, while for more powerful navigation transmitters such as [[Decca Navigator System|DECCA]], masts with a height around 100&nbsp;meters are used. [[T-antenna]]s have a height between 50–200&nbsp;meters, while mast aerials are usually taller than 150&nbsp;meters.

The height of mast antennas for [[LORAN-C]] is around 190&nbsp;meters for transmitters with radiated power below 500&nbsp;kW, and around 400&nbsp;meters for transmitters greater than {{nobr|{{gaps|1|000}} kilowatts.}} The main type of LORAN-C antenna is insulated from ground.

LF [[Longwave|(longwave) broadcasting stations]] use mast antennas with heights of more than 150&nbsp;meters or [[T-antenna|T-aerials]]. The mast antennas can be ground-fed insulated masts or upper-fed grounded masts. It is also possible to use cage antennas on grounded masts.

===Directional array antennas===
For broadcasting stations, directional antennas are often required. They consist of multiple masts, which often have the same height. Some longwave antennas consist of multiple mast antennas arranged in a circle with or without a mast antenna in the center. Such antennas focus the transmitted power toward ground and give a large zone of fade-free reception. This type of antenna is rarely used, because they are very expensive and require much space and because fading occurs on longwave much more rarely than in the medium wave range. One antenna of this kind was used by [[transmitter Orlunda]] in Sweden.