{{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 cables would have high power loss.]]
'''Radio frequency''' ('''RF''') is the oscillation rate of an alternating electric current or voltage or of a 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}}. These are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves, 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 currents that oscillate at radio frequencies ('''RF currents''') have special properties not shared by direct current or lower alternating current, such as the 50 or 60 Hz current used in electrical power distribution. * Energy from RF currents in conductors can radiate into space as electromagnetic waves (radio waves).<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 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 waves. RF current may be carried efficiently over transmission lines such as coaxial cables. {{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<br />range !! scope="col" rowspan="2" | Wavelength<br />range !! scope="col" colspan="2" | ITU designation !! scope="col" rowspan="2" | 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 Hz | >10⁵ km || || style="text-align:center" | || {{n/a}} |- ! scope="row" {{rh2|align=right}} | 3–30 Hz | 10⁵–10⁴ km|| Extremely low frequency || style="text-align:center" | ELF || {{n/a}} |- ! scope="row" {{rh2|align=right}} | 30–300 Hz | 10⁴–10³ km|| Super low frequency || style="text-align:center" | SLF || {{n/a}} |- ! scope="row" {{rh2|align=right}} | 300–3000 Hz | 10³–100 km|| Ultra low frequency || style="text-align:center" | ULF || {{n/a}} |- ! scope="row" {{rh2|align=right}} | 3–30 kHz | 100–10 km|| Very low frequency || style="text-align:center" | VLF || {{n/a}} |- ! scope="row" {{rh2|align=right}} | 30–300 kHz | 10–1 km|| Low frequency || style="text-align:center" | LF || {{n/a}} |- ! scope="row" {{rh2|align=right}} | 300 kHz – 3 MHz | 1 km – 100 m|| Medium frequency || style="text-align:center" | MF || {{n/a}} |- ! scope="row" {{rh2|align=right}} | 3–30 MHz | 100–10 m|| High frequency || style="text-align:center" | HF || style="text-align:center" | HF |- ! scope="row" {{rh2|align=right}} | 30–300 MHz | 10–1 m|| Very high frequency || style="text-align:center" | VHF || style="text-align:center" | VHF |- ! scope="row" {{rh2|align=right}} | 300 MHz – 3 GHz | 1 m – 100 mm|| Ultra high frequency || style="text-align:center" | UHF || style="text-align:center" | UHF, L, S |- ! scope="row" {{rh2|align=right}} | 3–30 GHz | 100–10 mm|| Super high frequency || style="text-align:center" | SHF || style="text-align:center" | S, C, X, Ku, K, Ka |- ! scope="row" {{rh2|align=right}} | 30–300 GHz | 10–1 mm|| Extremely high frequency || style="text-align:center" | EHF || style="text-align:center" | Ka, V, W, mm |- ! scope="row" {{rh2|align=right}} | 300 GHz – 3 THz | 1 mm – 0.1 mm|| Tremendously high frequency || style="text-align:center" | THF || {{n/a}} |- |Radio Spectrum Allocations in Canada|thumb|top|right |International Telecommunication Union ITU|thumb|top|right |}
Frequencies of 1 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 GHz and above are designated millimeter wave. More detailed 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>
Radio-frequency signal generators are commonly used as sources in RF testing and calibration setups, providing controlled oscillating signals over wide frequency ranges. In addition to commercial instrumentation, several manufacturers and engineering organizations publish technical documentation and design guides describing practical implementations of RF generators and high-frequency power systems.<ref>{{cite web |title=High-Frequency Generators Design – Practical Engineering Guide |url=https://www.rotkopf.it/documents_1/rf-design |website=Rotkopf Radiofrequency |access-date=13 March 2026}}</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 Radio waves Radio waves Category:Television terminology