Editing Low frequency (section)

==Uses==
===Radio broadcasting===
{{main | Longwave}}
[[AM broadcasting]] is authorized in the [[longwave]] band on frequencies between 148.5 and 283.5&nbsp;kHz in Europe and parts of Asia.

===Standard time signals===
{{further|Radio clock#List of radio time signal stations}}
[[File:Atomic clock.jpg|thumb|200px|{{center|An LF [[radio clock]]}}]]
In Europe and Japan, many low-cost consumer devices have since the late 1980s contained [[radio clock]]s with an LF receiver for these signals. Since these frequencies propagate by [[ground wave]] only, the precision of time signals is not affected by varying propagation paths between the transmitter, the ionosphere, and the receiver. In the United States, such devices became feasible for the mass market only after the output power of [[WWVB]] was increased in 1997 and 1999.

[[JJY]] transmitting broadcast on the exact same frequency, and has a similar [[timecode]].

===Military===
{{further|Communication with submarines}}
Radio signals below 50&nbsp;kHz are capable of penetrating ocean depths to approximately {{convert|200|metres|feet}}; the longer the wavelength, the deeper they go. The British, German, Indian, Russian, Swedish, United States,<ref>
{{cite web
 | title=Very Low Frequency (VLF)
 | year = 1998
 | department = United States Nuclear Forces
 | website = fas.org
 | url=http://www.fas.org/nuke/guide/usa/c3i/vlf.htm
 | access-date = 2008-01-09  | url-status=live
 | archive-url=https://web.archive.org/web/20071227165518/http://www.fas.org/nuke/guide/usa/c3i/vlf.htm
 | archive-date = 2007-12-27
}}
</ref>
and possibly other [[navy|navies]] communicate with [[submarine]]s on these frequencies.

In addition, [[Royal Navy]] nuclear submarines carrying ballistic missiles are allegedly under standing orders to monitor the [[BBC Radio 4]] transmission on 198&nbsp;kHz in waters near the UK. It is rumoured that they are to construe a sudden halt in transmission, particularly of the morning news programme [[Today (BBC Radio 4)|''Today'']], as an indicator that the UK is under attack, whereafter their [[Letters of last resort|sealed orders]] take effect.<ref>
{{cite episode
 | title=The Human Button
 | series = [[Today (BBC Radio 4)|Today]]
 | air-date=2008-12-02
 | network=[[BBC]]
 | station=[[BBC Radio 4]]
 | url=http://www.bbc.co.uk/programmes/b00fq2sy
 | access-date=2011-08-06 | url-status=live
 | archive-url=https://web.archive.org/web/20110203232901/http://www.bbc.co.uk/programmes/b00fq2sy
 | archive-date=2011-02-03 | df = dmy-all
}}
</ref>

The United States has four LF stations maintaining contact with its submarine force: [[Aguada, Puerto Rico]], [[Naval Air Station Keflavik|Keflavik, Iceland]], [[Awase Airfield|Awase, Okinawa]], and [[Naval Air Station Sigonella|Sigonella, Italy]], using AN/FRT-95 solid state transmitters.

In the U.S., the [[Ground Wave Emergency Network]] or GWEN operated between 150 and 175&nbsp;kHz, until replaced by satellite communications systems in 1999. GWEN was a land based military radio communications system which could survive and continue to operate even in the case of a nuclear attack.

===Experimental and amateur===
The 2007&nbsp;[[World Radiocommunication Conference]] (WRC-07) made a worldwide amateur radio allocation in this band. An international 2.1&nbsp;kHz allocation, the [[2200-meter band|{{nobr|{{gaps|2|200}} meter band}}]] (135.7–137.9&nbsp;kHz) is available to [[amateur radio]] operators in several countries in Europe,<ref>
{{cite report
 |title=ERC {{nobr|Recommendation 62-01 E}}
 |year=1997
 |section=Use of the band 135.7–137.8&nbsp;kHz by the Amateur Service
 |id={{nobr|ERC Rec 62-01 E}}
 |publisher=[[European Conference of Postal and Telecommunications Administrations]] (CEPT)
 |place=Mainz, DE
}}
</ref>
New Zealand, Canada, US,<ref name=ARRL-bandchart>
{{cite AV media
 |title   = Regulatory Band Chart
 |date    = 2017-09-22
 |edition = 11×17″ color
 |medium  = chart / graphic
 |publisher = [[American Radio Relay League]]
 |place   = Newington, CT
 |url     = http://www.arrl.org/files/file/Regulatory/Band%20Chart/Band%20Chart%20-%2011X17%20Color.pdf
 |access-date  = 2020-11-26 |url-status=live
 |archive-url  = https://web.archive.org/web/20201111222535/http://www.arrl.org/files/file/Regulatory/Band%20Chart/Band%20Chart%20-%2011X17%20Color.pdf
 |archive-date = 2020-11-11  |df = dmy-all
}}
</ref>
and French overseas dependencies.

The world record distance for a two-way contact is over 10,000&nbsp;km from near [[Vladivostok]] to [[New Zealand]].<ref name=ZLUA0>
{{cite news
 |title = QSO ZL / UA0 on 136&nbsp;kHz
 |department = The World of LF
 |website = wireless.org.uk
 |url = http://www.wireless.org.uk/newspic92.htm
 |access-date = 2006-06-01   |url-status=live
 |archive-url = https://web.archive.org/web/20070929025210/http://www.wireless.org.uk/newspic92.htm
 |archive-date = 2007-09-29
}}
</ref>
As well as conventional [[Morse code]] many operators use very slow computer-controlled Morse code (so-called [[QRP operation#QRSS|"QRSS"]]) or specialized digital communications modes.

The UK allocated a 2.8&nbsp;kHz sliver of spectrum from 71.6&nbsp;kHz to 74.4&nbsp;kHz beginning in April&nbsp;1996 to UK amateurs who applied for a Notice of Variation to use the band on a noninterference basis with a maximum output power of 1&nbsp;Watt&nbsp;[[effective radiated power|ERP]]. This was withdrawn on 30&nbsp;June 2003 after a number of extensions in favor of the cross-European standard 136&nbsp;kHz band.<ref name=ofcom>
{{cite press release
 |title=UK Spectrum Strategy 2002
 |date=16 September 2016
 |publisher=[[Ofcom]]
 |url=http://www.ofcom.org.uk/static/archive/ra/topics/spectrum-strat/future/strat02/strategy02app_a.doc
 |access-date=5 June 2006 |url-status=live
 |archive-url=https://web.archive.org/web/20070930031406/http://www.ofcom.org.uk/static/archive/ra/topics/spectrum-strat/future/strat02/strategy02app_a.doc
 |archive-date=30 September 2007
}}
</ref>
Very slow Morse Code from G3AQC in the UK was received {{convert|3275|mi|km}} away, across the [[Atlantic Ocean]], by W1TAG in the US on 21-22&nbsp;November 2001 on 72.401&nbsp;kHz.{{efn|
Low-frequency experimenter Lawrence "Laurie" Mayhead, G3AQC, has added another LF accomplishment to his list – trans-Atlantic reception of his 73&nbsp;kHz signal. [...] Mayhead reports that on the night of 21-22&nbsp;November, his signal on 72.401&nbsp;kHz was received in the US. "I managed to transmit a full call sign to John Andrews, W1TAG, in Holden, Massachusetts", he said. Mayhead was using dual-frequency CW – or DFCW – featuring elements that are two minutes long; Andrews detected his signal using ARGO {{nobr|DSP software. — [[ARRL]] Nov 2001<ref>
{{cite news
 |title      = G3AQC's signal spans the Atlantic on 73&nbsp;kHz!
 |date       = 30 November 2001
 |periodical = The ARRL Letter
 |publisher  = [[American Radio Relay League]]
 |place      = Newington, CT
 |url = http://www.arrl.org/arrlletter?issue=2001-11-30
 |access-date = 12 January 2014  |url-status = live
 |archive-url=https://web.archive.org/web/20140112215834/http://www.arrl.org/arrlletter?issue=2001-11-30
 |archive-date=12 January 2014
}}
</ref>}}
}}

In the United States, there is an exemption within FCC Part&nbsp;15 regulations permitting unlicensed transmissions in the frequency range of 160–190&nbsp;kHz. Longwave radio hobbyists refer to this as the '[[LowFER]]' band, and experimenters, and their transmitters are called '[[LowFER]]s'. This frequency range between 160&nbsp;kHz and 190&nbsp;kHz is also referred to as the {{nobr|{{gaps|1|750}} meter}} band. Requirements<ref>
{{cite report
 |title = Part&nbsp;15 — Radio frequency devices
 |section = § 15.217 Operation in the band 160–190 kHz ({{nobr|47 CFR 15.217}})
 |series = The Electronic Code of Federal Regulations
 |website = ecfr.gov
 |id = {{nobr|47 CFR 15.217}} ({{nobr|47 CFR 15.206}})
 |url = http://www.ecfr.gov/cgi-bin/text-idx?SID=ea364b89f317550d594a9315deca6022&mc=true&node=pt47.1.15&rgn=div5#se47.1.15_1209
 | access-date = 17 March 2024
}}{{failed verification |date=March 2024}} Cited section {{nobr|47 CFR 15.206}} not present / removed: section id §15.205 skips to §15.207&nbsp;.
</ref> include:
* The total input power to the final radio frequency stage (exclusive of filament or heater power) shall not exceed one watt.
* The total length of the transmission line, antenna, and ground lead (if used) shall not exceed 15 meters.
* All emissions below 160&nbsp;kHz or above 190&nbsp;kHz shall be attenuated at least 20&nbsp;dB below the level of the unmodulated carrier.
* As an alternative to these requirements, a field strength of 2400/F(kHz)&nbsp;microvolts/meter (measured at a distance of 300 meters) may be used (as described in 47CFR15.209).
* In all cases, operation may not cause harmful interference to licensed services.
Many experimenters in this band are amateur radio operators.<ref>
{{cite web
 |title = Part&nbsp;15 — Rado frequency devices
 |series = Federal Register 
 |url = http://www.ecfr.gov/cgi-bin/text-idx?SID=7f66d50bc733c74f45ff68ec5dda7d93&node=47:1.0.1.1.16&rgn=div5#47:1.0.1.1.16.3
 |access-date=2014-07-21  |url-status=live
 |archive-url=https://web.archive.org/web/20140726053324/http://www.ecfr.gov/cgi-bin/text-idx?SID=7f66d50bc733c74f45ff68ec5dda7d93&node=47:1.0.1.1.16&rgn=div5#47:1.0.1.1.16.3
 |archive-date=2014-07-26
}}
</ref>

===Meteorological information broadcasts===
{{Expand section|date=June 2008}}
A regular service transmitting [[radioteletype|RTTY]] marine meteorological information in [[SYNOP]] code on LF is the German Meteorological Service ([[Deutscher Wetterdienst]] or [http://www.dwd.de DWD]). The DWD operates station DDH47 on 147.3&nbsp;kHz using standard ITA-2 alphabet with a transmission speed of 50&nbsp;[[baud]] and FSK modulation with 85&nbsp;Hz shift.<ref>
{{cite web
 |title = DWD Sendeplan
 |access-date = 2008-01-08  |url-status = dead
 |url = http://www.dwd.de/de/wir/Geschaeftsfelder/Seeschifffahrt/Sendeplaene/Sendeplaene.htm
 |archive-url = https://archive.today/20120730093823/http://www.dwd.de/de/wir/Geschaeftsfelder/Seeschifffahrt/Sendeplaene/Sendeplaene.htm
 |archive-date = 2012-07-30
}}
</ref>

===Radio navigation signals===
{{Expand section|date=June 2008}}
In parts of the world where there is no longwave broadcasting service, [[Non-directional beacon]]s used for aeronavigation operate on 190–300&nbsp;kHz (and beyond into the MW band). In Europe, Asia and Africa, the NDB allocation starts on 283.5&nbsp;kHz.

The [[LORAN]]-C radio navigation system operated on 100&nbsp;kHz.

In the past, the [[Decca Navigator System]] operated between 70&nbsp;kHz and 129&nbsp;kHz. The last Decca chains were closed down in 2000.

[[Differential GPS]] telemetry transmitters operate between 283.5 and 325&nbsp;kHz.<ref>
{{cite report
 |first = Alan (G4TMV) |last = Gale
 |year = 2011
 |title = World DGPS database for DXers
 |version = 4.6
 |url = http://www.ndblist.info/datamodes/worldDGPSfreqorder.pdf
 |access-date = 2008-01-14   |url-status = dead   |via = ndblist.info
 |archive-url = https://web.archive.org/web/20110721225343/http://www.ndblist.info/datamodes/worldDGPSfreqorder.pdf
 |archive-date = 2011-07-21
}}
</ref>

The commercial "[[Datatrak]]" radio navigation system operates on a number of frequencies, varying by country, between 120–148&nbsp;kHz.

===Other applications===
Some radio frequency identification ([[RFID]]) tags utilize LF. These tags are commonly known as LFIDs or LowFIDs (low frequency identification). The LF RFID tags are [[near field and far field|near-field]] devices, interacting with the [[resonant inductive coupling|inductive near field]], rather than with radiated waves (radio waves) that are the only part of the electromagnetic field that persists into the far field. As such, they are technically ''not'' radio devices nor radio antennas, even though they do operate at radio frequencies, and are ''called'' "antennas" in the RFID trade, but not in [[radio engineering]]. It is more proper, and technically more informative to think of them as secondary coils of very loosely coupled [[transformer]]s.