Editing High frequency (section)

{{short description|The range 3-30 MHz of the electromagnetic spectrum}}
{{for|high speed algorithmic trading|high-frequency trading}}
{{MWband
| freq = 3 to 30 [[Megahertz|MHz]]
| wave = 100 to 10 m
| bands =
}}
[[File:HighFrequency.png|thumb|HF's position in the [[electromagnetic spectrum]].]]

'''High frequency''' ('''HF''') is the [[International Telecommunication Union|ITU]] designation<ref name="1037B">{{cite book
  | title = US Federal Standard 1037B: Telecommunications, Glossary of Telecommunications Terms 
  | publisher = Office of Technology Standards, General Services Administration
  | series = 
  | volume = 
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  | date = 3 June 1991
  | location = 
  | pages = S-18
  | language = 
  | url = https://books.google.com/books?id=zYLXU4fkD34C&pg=RA15-PA18
  | archive-url= 
  | archive-date=
  | doi = 
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  | jfm =}}</ref><ref name="itu-2015-acts">{{cite conference |date=2015 |title=Final Acts WRC-15 |url=https://www.itu.int/dms_pub/itu-r/opb/act/R-ACT-WRC.12-2015-PDF-E.pdf |conference=World Radiocommunication Conference |location=Geneva, Switzerland |publisher=International Telecommunications Union |pages = 4|access-date=2025-01-12}}</ref> for the [[radio band|band]] of [[radio wave]]s with [[frequency]] between 3 and 30 [[megahertz]] (MHz). It is also known as the '''decameter band''' or '''decameter wave''' as its [[wavelength]]s range from one to ten [[decametre|decameters]] (ten to one hundred meters). Frequencies immediately below HF are denoted ''[[medium frequency]]'' (MF), while the next band of higher frequencies is known as the ''[[very high frequency]]'' (VHF) band. The HF band is a major part of the [[shortwave]] band of frequencies, so communication at these frequencies is often called ''[[shortwave radio]]''.  Because radio waves in this band can be reflected back to Earth by the [[ionosphere]] layer in the atmosphere –&nbsp;a method known as "skip" or "[[skywave]]" propagation&nbsp;– these frequencies can be used for long-distance communication across intercontinental distances and for mountainous terrains which prevent [[Line-of-sight propagation|line-of-sight]] communications.<ref name="Army Communicator">{{cite journal |last1=Harmon |first1=James V. |last2=Fiedler |first2=Ltc David M |last3=Lam |first3=Ltc Ret John R. |title=Automated HF Communications |journal=Army Communicator |date=Spring 1994 |pages=22–26 |url=https://signal.army.mil/ArmyCommunicator/1994/dfale.pdf |access-date=24 December 2018 |archive-date=23 December 2016 |archive-url=https://web.archive.org/web/20161223221533/http://www.signal.army.mil/ArmyCommunicator/1994/dfale.pdf |url-status=dead }}</ref> The band is used by international shortwave broadcasting stations (3.95–25.82&nbsp;MHz), aviation communication, government time stations, weather stations, [[amateur radio]] and [[Citizens band radio|citizens band]] services, among other uses.