Editing Longwave (section)

==Non-broadcast use==
===Non-directional beacons===
{{Main|Non-directional beacon}}

[[Non-directional beacon]]s transmit continuously for the benefit of [[radio direction finder]]s in marine and aeronautical navigation.  They identify themselves by a [[callsign]] in [[Morse code]].  They can occupy any frequency in the range 190–1750&nbsp;kHz.  In North America, they occupy 190–535&nbsp;kHz.  In ITU Region 1 the lower limit is 280&nbsp;kHz.

===Time signals===
There are institutional broadcast stations in the range that transmit coded time signals to radio clocks. For example:
*[[WWVB]] in [[Colorado]], United States, on 60&nbsp;kHz, 70 kW [[Effective radiated power|ERP]]
*[[DCF77]] in [[Frankfurt]], [[Germany]], on 77.5&nbsp;kHz, 50 kW
*[[JJY]] in Japan, on 40 & 60&nbsp;kHz, 50 kW
*[[RBU_(radio_station)|RBU]] 66.66&nbsp;kHz in [[Taldom transmitter]], Russia, 10 kW
*[[BPC (time signal)|BPC]] in [[Shangqiu]], [[China]], 68.5&nbsp;kHz, 90 kW
*[[Time from NPL|MSF]] time and 60&nbsp;kHz frequency standard transmitted from [[Anthorn radio station|Anthorn]] in the UK, 17 kW ERP.
*[[ALS162_time_signal|ALS162]] from [[Allouis]], [[France]], on 162&nbsp;kHz, 800 kW

[[Radio clock|Radio-controlled clocks]] receive their time calibration signals with built-in long-wave receivers. They use long-wave, rather than [[shortwave|short-wave]] or [[mediumwave|medium-wave]], because long-wave signals from the transmitter to the receiver always travel along the same direct path across the surface of the [[Earth]], so the time delay correction for the signal travel time from the transmitting station to the receiver is always the same for any one receiving location.

Longwaves travel by [[groundwave]]s that hug the surface of the Earth, unlike [[mediumwave]]s and [[shortwave radio|shortwaves]]. Those higher-frequency signals do not follow the surface of the [[Earth]] beyond a few kilometers, but can travel as [[skywave]]s, '[[refraction|bouncing]]' off different layers of the [[ionosphere]] at different times of day. These different [[radio propagation|propagation]] paths can make the time lag different for every signal received. The delay between when the long-wave signal was sent from the [[transmitter]] (when the coded time was correct) and when the signal is received by the clock (when the coded time is slightly late) depends on the overland distance between the clock and the transmitter and the [[speed of light#In a medium|speed of light through the air]], which is also very nearly constant. Since the time lag is essentially the same, a single constant shift forward from the time coded in the signal can compensate for all long-wave signals received at any one location from the same time signal station.

===Submarine communication===
The militaries of the United Kingdom, Russian Federation, United States, Germany, India and Sweden use frequencies below 50&nbsp;kHz to communicate with submerged [[submarine]]s.

===Amateur radio===
In the ITU Radio Regulations the band 135.7–137.8&nbsp;kHz is allocated (on a secondary basis) to [[Amateur radio]] worldwide, subject to a power limit of 1 watt EIRP. Many countries' regulators license amateurs to use it.

===LowFER===
In North America during the 1970s, the frequencies 167, 179, and 191&nbsp;kHz were assigned to the short-lived [[Public Emergency Radio of the United States]].

Nowadays, in the United States, [[Part 15]] of FCC regulations allow unlicensed use of the 160–190&nbsp;kHz band a transmitter / amplifier output power to the antenna of at most 1&nbsp;watt, with an antenna at most 15&nbsp;meters (49&nbsp;feet) high; this is called [[LowFER|Low Frequency Experimental Radio]] (LowFER). The 190–435&nbsp;kHz band is used for [[Non-directional beacon|navigational beacons]].

Frequencies from 472–479&nbsp;kHz are available to licensed amateurs as the new [[630-meter band|630&nbsp;m band]], part of the now-defunct [[500 kHz|maritime band]], but this is often considered a [[medium wave]] sub-band.

===Historic===
Swedish station SAQ, located at the [[Varberg Radio Station]] facility in Grimeton, is the last remaining operational [[Alexanderson alternator]] long-wave transmitter. Although the station ended regular service in 1996, it has been maintained as a [[World Heritage Site]], and makes at least two demonstration transmissions yearly, on 17.2&nbsp;kHz.<ref>[http://alexander.n.se/in-english/saq-transmission SAQ Transmission.] {{webarchive|url=http://archive.wikiwix.com/cache/20150407073704/http://alexander.n.se/in-english/saq-transmission |date=7 April 2015 }} Radiostation Grimeton SAQ. Retrieved 5 April 2015.</ref>