Radio frequency

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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[1] range from around 20 kHz to around 300 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

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).[2] 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.[3][4] 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.

Frequency bands

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The radio spectrum of frequencies is divided into bands with conventional names designated by the International Telecommunication Union (ITU):

Frequency
range		 Wavelength
range		 ITU designation IEEE bands[5]
Full name Abbreviation[6]
scope="row" Template:Rh2 | Below 3 Hz >10⁵ km Template:Screen reader-only
scope="row" Template:Rh2 | 3–30 Hz 10⁵–10⁴ km Extremely low frequency ELF Template:Screen reader-only
scope="row" Template:Rh2 | 30–300 Hz 10⁴–10³ km Super low frequency SLF Template:Screen reader-only
scope="row" Template:Rh2 | 300–3000 Hz 10³–100 km Ultra low frequency ULF Template:Screen reader-only
scope="row" Template:Rh2 | 3–30 kHz 100–10 km Very low frequency VLF Template:Screen reader-only
scope="row" Template:Rh2 | 30–300 kHz 10–1 km Low frequency LF Template:Screen reader-only
scope="row" Template:Rh2 | 300 kHz – 3 MHz 1 km – 100 m Medium frequency MF Template:Screen reader-only
scope="row" Template:Rh2 | 3–30 MHz 100–10 m High frequency HF HF
scope="row" Template:Rh2 | 30–300 MHz 10–1 m Very high frequency VHF VHF
scope="row" Template:Rh2 | 300 MHz – 3 GHz 1 m – 100 mm Ultra high frequency UHF UHF, L, S
scope="row" Template:Rh2 | 3–30 GHz 100–10 mm Super high frequency SHF S, C, X, Ku, K, Ka
scope="row" Template:Rh2 | 30–300 GHz 10–1 mm Extremely high frequency EHF Ka, V, W, mm
scope="row" Template:Rh2 | 300 GHz – 3 THz 1 mm – 0.1 mm Tremendously high frequency THF Template:Screen reader-only
Radio Spectrum Allocations in Canada
International Telecommunication Union ITU


Frequencies of 1 GHz and above are conventionally called microwave,[7] 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[5] and the EU/NATO frequency designations.[8]

Applications

Script error: No such module "Labelled list hatnote". 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.[9][citation needed][10]

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.[11]

Mechanical oscillations

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

See also

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References

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  1. ^ Page Module:Citation/CS1/styles.css has no content.Jessica Scarpati. "What is radio frequency (RF, rf)?". SearchNetworking. Retrieved 29 January 2021.
  2. ^ Page Module:Citation/CS1/styles.css has no content.Service, United States Flight Standards (1976). Airframe and Powerplant Mechanics: Airframe Handbook. Department of Transportation, Federal Aviation Administration, Flight Standards Service. p. 520.
  3. ^ Page Module:Citation/CS1/styles.css has no content.Curtis, Thomas Stanley (1916). High Frequency Apparatus: Its construction and practical application. US: Everyday Mechanics Company. pp. 6. electric shock pain.
  4. ^ Page Module:Citation/CS1/styles.css has no content.Mieny, C.J. (2005). Principles of Surgical Patient Care (2nd ed.). New Africa Books. p. 136. ISBN 9781869280055.
  5. ^ a b IEEE Std 521-2002 Standard Letter Designations for Radar-Frequency Bands, Institute of Electrical and Electronics Engineers, 2002. (Convenience copy at National Academies Press.)
  6. ^ Page Module:Citation/CS1/styles.css has no content.Jeffrey S. Beasley; Gary M. Miller (2008). Modern Electronic Communication (9th ed.). pp. 4–5. ISBN 978-0132251136.
  7. ^ Page Module:Citation/CS1/styles.css has no content.Kumar, Sanjay; Shukla, Saurabh (2014). Concepts and Applications of Microwave Engineering. PHI Learning Pvt. Ltd. p. 3. ISBN 978-8120349353.
  8. ^ Page Module:Citation/CS1/styles.css has no content.Leonid A. Belov; Sergey M. Smolskiy; Victor N. Kochemasov (2012). Handbook of RF, Microwave, and Millimeter-Wave Components. Artech House. pp. 27–28. ISBN 978-1-60807-209-5.
  9. ^ Page Module:Citation/CS1/styles.css has no content."RF Radio Frequency Signal Generator » Electronics Notes". www.electronics-notes.com. Retrieved 29 January 2021.
  10. ^ Page Module:Citation/CS1/styles.css has no content.Siamack Ghadimi (2021), Measure a DUT's input power using a directional coupler and power sensor, EDN
  11. ^ Page Module:Citation/CS1/styles.css has no content."High-Frequency Generators Design – Practical Engineering Guide". Rotkopf Radiofrequency. Retrieved 13 March 2026.

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