View source for Radio frequency

{{short description|Electromagnetic frequencies ranging from 3 kHz to 300 GHz}}
{{about|the generic oscillation|the radiation|radio wave|the spectrum|radio spectrum|the electronics|radio-frequency engineering}}
{{redirect|RF}}
[[Image:F-Stecker und Kabel.jpg|thumb|Radio-frequency electrical currents are usually carried by specially-designed [[transmission line]] such as [[coaxial cable]], as ordinary [[electrical cable]]s would have high power loss.]]

'''Radio frequency''' ('''RF''') is the [[oscillation]] rate of an [[Alternating current|alternating electric current]] or [[voltage]] or of a [[Magnetic field|magnetic]], electric or [[electromagnetic field]] or mechanical system in the [[frequency]]<ref name="Scarpati">{{cite web |author=Jessica Scarpati |title=What is radio frequency (RF, rf)? |url=https://searchnetworking.techtarget.com/definition/radio-frequency |website=SearchNetworking |access-date=29 January 2021 |language=en}}</ref> range from around {{val|20|ul=kHz}} to around {{val|300|ul=GHz}}. This is roughly between the upper limit of [[audio frequencies]] that humans can hear (though these are not electromagnetic) and the lower limit of [[infrared]] frequencies, and also encompasses the [[microwave]] range.  These are the frequencies at which energy from an oscillating current can radiate off a conductor into space as [[radio wave]]s, so they are used in [[radio]] technology, among other uses.  Different sources specify different upper and lower bounds for the frequency range.

== Electric current {{anchor|Current}} ==
[[Image:Energy is among us.jpg|thumb|Boy allowing the arc from a [[Tesla coil]] to strike his hand. Coming in contact with radio frequency arcs as shown here is extremely dangerous and can result in electrocution.]]

[[Electric current]]s that oscillate at radio frequencies ('''RF currents''') have special properties not shared by [[direct current]] or lower [[audio frequency]] [[alternating current]], such as the 50 or 60&nbsp;Hz current used in [[electrical power distribution]].
* Energy from RF currents in conductors can radiate into space as [[electromagnetic wave]]s ([[radio wave]]s).<ref>{{cite book |last1=Service |first1=United States Flight Standards |title=Airframe and Powerplant Mechanics: Airframe Handbook |date=1976 |publisher=Department of Transportation, Federal Aviation Administration, Flight Standards Service |page=520 |url=https://books.google.com/books?id=CqZTAAAAMAAJ |language=en}}</ref>  This is the basis of [[radio]] technology.
* RF current does not penetrate deeply into electrical conductors but tends to flow along their surfaces; this is known as the [[skin effect]].
* RF currents applied to the body often do not cause the painful sensation and muscular contraction of [[electric shock]] that lower frequency currents produce.<ref name="Curtis">
{{cite book
  | last = Curtis  | first = Thomas Stanley
  | year = 1916
  | title = High Frequency Apparatus: Its construction and practical application
  | publisher = Everyday Mechanics Company
  | location = US
  | pages = [https://archive.org/details/highfrequencyap00curtgoog/page/n27 6]
  | url = https://archive.org/details/highfrequencyap00curtgoog
  | quote = electric shock pain.
}}
</ref><ref name="Mieny">
{{cite book
  | last = Mieny  | first = C.J.
  | year = 2005
  | title = Principles of Surgical Patient Care
  | edition = 2nd
  | pages = 136
  | publisher = New Africa Books
  | isbn = 9781869280055
  | url = https://books.google.com/books?id=TSxQ6ZzovgkC&q=%22electric+shock%22+pain+%22high+frequency&pg=PA136
}}
</ref> This is because the current changes direction too quickly to trigger [[depolarization]] of nerve membranes. However, this does not mean RF currents are harmless; they can cause internal injury as well as serious superficial burns called [[Radiation burn|RF burns]].
* RF current can [[ionize]] air, creating a conductive path through it. This property is exploited by "high frequency" units used in electric [[arc welding]], which use currents at higher frequencies than power distribution uses.
* Another property is the ability to appear to flow through paths that contain insulating material, like the [[dielectric]] insulator of a [[capacitor]]. This is because [[capacitive reactance]] in a circuit decreases with increasing frequency.
* In contrast, RF current can be blocked by a coil of wire, or even a single turn or bend in a wire. This is because the [[inductive reactance]] of a circuit increases with increasing frequency.
* When conducted by an ordinary electric cable, RF current has a tendency to reflect from discontinuities in the cable, such as connectors, and travel back down the cable toward the source, causing a condition called [[standing wave]]s. RF current may be carried efficiently over [[transmission line]]s such as [[coaxial cable]]s.
{{breakafterimages}}

==Frequency bands==
{{main|Radio spectrum}}

The [[radio spectrum]] of frequencies is divided into bands with conventional names designated by the [[International Telecommunication Union]] (ITU):
:{| class="wikitable" style="text-align:right"
|-
! scope="col" rowspan="2" | [[Frequency range|Frequency<br />range]] !! scope="col" rowspan="2" | [[Wavelength]]<br />range !! scope="col" colspan="2" | [[ITU]] designation !! scope="col" rowspan="2" | [[Radio spectrum#IEEE|IEEE bands]]<ref name="IEEE Std 521" />
|-
! scope="col" | Full name
! scope="col" | Abbreviation<ref name="beasley">{{cite book|title=Modern Electronic Communication|year=2008|isbn=978-0132251136|author=Jeffrey S. Beasley|edition=9th|author2=Gary M. Miller |pages=4–5}}</ref>
|-
! scope="row" {{rh2|align=right}} | Below 3&nbsp;Hz
| >10<sup>5</sup>&nbsp;km || || style="text-align:center" | || {{n/a}}
|-
! scope="row" {{rh2|align=right}} | 3–30&nbsp;Hz
| 10<sup>5</sup>–10<sup>4</sup>&nbsp;km|| [[Extremely low frequency]] || style="text-align:center" | [[Extremely low frequency|ELF]] || {{n/a}}
|-
! scope="row" {{rh2|align=right}} | 30–300&nbsp;Hz
| 10<sup>4</sup>–10<sup>3</sup>&nbsp;km|| [[Super low frequency]] || style="text-align:center" | [[Super low frequency|SLF]] || {{n/a}}
|-
! scope="row" {{rh2|align=right}} | 300–3000&nbsp;Hz
|  10<sup>3</sup>–100&nbsp;km|| [[Ultra low frequency]] || style="text-align:center" | [[Ultra low frequency|ULF]] || {{n/a}}
|-
! scope="row" {{rh2|align=right}} | 3–30&nbsp;kHz
| 100–10&nbsp;km|| [[Very low frequency]] || style="text-align:center" | [[VLF]] || {{n/a}}
|-
! scope="row" {{rh2|align=right}} | 30–300&nbsp;kHz
| 10–1&nbsp;km|| [[Low frequency]] || style="text-align:center" | [[Low frequency|LF]] || {{n/a}}
|-
! scope="row" {{rh2|align=right}} | 300&nbsp;kHz – 3&nbsp;MHz
| 1&nbsp;km – 100 m|| [[Medium frequency]] || style="text-align:center" | [[Medium frequency|MF]] || {{n/a}}
|-
! scope="row" {{rh2|align=right}} | 3–30&nbsp;MHz
| 100–10&nbsp;m|| [[High frequency]] || style="text-align:center" | [[High frequency|HF]]  || style="text-align:center" | [[High frequency|HF]]
|-
! scope="row" {{rh2|align=right}} | 30–300&nbsp;MHz
| 10–1&nbsp;m|| [[Very high frequency]] || style="text-align:center" | [[VHF]] || style="text-align:center" | [[VHF]]
|-
! scope="row" {{rh2|align=right}} | 300&nbsp;MHz – 3&nbsp;GHz
| 1 m – 100&nbsp;mm|| [[Ultra high frequency]] || style="text-align:center" | [[UHF]] || style="text-align:center" | [[UHF]], [[L band|L]], [[S band|S]]
|-
! scope="row" {{rh2|align=right}} | 3–30&nbsp;GHz
| 100–10&nbsp;mm|| [[Super high frequency]] || style="text-align:center" | [[Super high frequency|SHF]] || style="text-align:center" | [[S band|S]], [[C band (IEEE)|C]], [[X band|X]], [[Ku band|Ku]], [[K band (IEEE)|K]], [[Ka band|Ka]]
|-
! scope="row" {{rh2|align=right}} | 30–300&nbsp;GHz
| 10–1&nbsp;mm|| [[Extremely high frequency]] || style="text-align:center" | [[Extremely high frequency|EHF]] || style="text-align:center" | [[Ka band|Ka]], [[V band|V]], [[W band|W]], [[Millimetre band|mm]]
|-
! scope="row" {{rh2|align=right}} | 300&nbsp;GHz – 3&nbsp;THz
|  1&nbsp;mm – 0.1&nbsp;mm|| [[Tremendously high frequency]] || style="text-align:center" | [[Tremendously high frequency|THF]] || {{n/a}}
|-
|[[File:Spectrum.pdf|Radio Spectrum Allocations in Canada|thumb|top|right]]
|[[File:International Telecommunication Union ITU.png|International Telecommunication Union ITU|thumb|top|right]]
|}



Frequencies of 1&nbsp;GHz and above are conventionally called [[microwave]],<ref name="Kumar">{{cite book
 | last1  = Kumar
 | first1 = Sanjay
 | last2  = Shukla
 | first2 = Saurabh
 | title  = Concepts and Applications of Microwave Engineering
 | publisher = PHI Learning Pvt. Ltd
 | date   = 2014
 | pages  = 3
 | url    = https://books.google.com/books?id=GY9eBAAAQBAJ&q=microwave&pg=PA3
 | isbn   = 978-8120349353
 }}</ref> while frequencies of 30&nbsp;GHz and above are designated [[millimeter wave]].
More detailed [[radio spectrum|band designations]] are given by the standard [[IEEE]] letter- band frequency designations<ref name="IEEE Std 521">[https://standards.ieee.org/ieee/521/768/ IEEE Std 521-2002 ''Standard Letter Designations for Radar-Frequency Bands''], [[Institute of Electrical and Electronics Engineers]], 2002. ([https://www.nap.edu/read/21774/chapter/10#235 Convenience copy] at National Academies Press.)</ref> and the  EU/NATO frequency designations.<ref name="BelovSmolskiy2012">{{cite book|author1=Leonid A. Belov|author2=Sergey M. Smolskiy|author3=Victor N. Kochemasov|title=Handbook of RF, Microwave, and Millimeter-Wave Components|url=https://books.google.com/books?id=bHhYjINB6KMC&pg=PA28|year=2012|publisher=Artech House|isbn=978-1-60807-209-5|pages=27–28}}</ref>

==Applications==
{{see also|Applications of radio|Radio spectrum#Applications}}
Radio has many practical applications, which include broadcasting, voice communication, data communication, radar, radiolocation,  medical treatments, and remote control.

==Measurement==
Test apparatus for radio frequencies can include standard instruments at the lower end of the range, but at higher frequencies, the test equipment becomes more specialized.<ref>{{cite web |title=RF Radio Frequency Signal Generator » Electronics Notes |url=https://www.electronics-notes.com/articles/test-methods/signal-generators/rf-radio-frequency-signal-generator.php |website=www.electronics-notes.com |access-date=29 January 2021}}</ref>{{citation needed|date=July 2017}}<ref>{{Citation |title=Measure a DUT's input power using a directional coupler and power sensor |author1=Siamack Ghadimi|publisher=EDN|date=2021}}</ref>

==Mechanical oscillations==
While RF usually refers to electrical oscillations, mechanical RF systems are not uncommon: see [[mechanical filter]] and [[RF MEMS]].

==See also==
{{div col begin|colwidth=15em}}
* [[Amplitude modulation]] (AM)
* [[Bandwidth (signal processing)]]
* [[Electromagnetic interference]]
* [[Electromagnetic radiation]]
* [[Electromagnetic spectrum]]
* [[EMF measurement]]
* [[Frequency allocation]]
* [[Frequency modulation]] (FM)
* [[Plastic welding]]
* [[Pulsed electromagnetic field therapy]]
* [[Radio astronomy]]
* [[Spectrum management]]
* [[Waveguide (radio frequency)]]
{{div col end}}

==References==
{{reflist}}

==External links==
* [https://ieee.li/pdf/viewgraphs/analog-rf-emc-considerations-pwb-design.pdf Analog, RF and EMC Considerations in Printed Wiring Board (PWB) Design]
* [http://www.vlf.it/frequency/bands.html Definition of frequency bands (VLF, ELF ... etc.) IK1QFK Home Page (vlf.it)]
* [http://www.sengpielaudio.com/calculator-wavelength.htm Radio, light, and sound waves, conversion between wavelength and frequency] {{Webarchive|url=https://web.archive.org/web/20120311050010/http://www.sengpielaudio.com/calculator-wavelength.htm |date=2012-03-11 }}
* [http://www.sunmantechnology.com/resources_gls_rfts.html RF Terms Glossary] {{Webarchive|url=https://web.archive.org/web/20080820005518/http://www.sunmantechnology.com/resources_gls_rfts.html |date=2008-08-20 }}

{{radio spectrum}}
{{EMSpectrum}}
{{Telecommunications}}
{{Analogue TV transmitter topics}}

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{{DEFAULTSORT:Radio Frequency}}
[[Category:Radio spectrum]]
[[Category:Radio technology|Radio waves]]
[[Category:Waves|Radio waves]]
[[Category:Television terminology]]