Radio frequency

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 range from around 20 kHz to around 300 GHz. This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies;[1][2] these are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves. Different sources specify different upper and lower bounds for the frequency range.

Electric current

Electric currents that oscillate at radio frequencies (RF currents) have special properties not shared by direct current or alternating current of lower frequencies.

Energy from RF currents in conductors can radiate into space as electromagnetic waves (radio waves). 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 easily 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
Main article: Radio spectrum

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

Frequency range	Wavelength range	ITU designation		IEEE bands^[5]
Frequency range	Wavelength range	Full name	Abbreviation^[6]	IEEE bands^[5]
Below 3 Hz	>10⁵ km	Tremendously low frequency^[7]	TLF	N/A
3–30 Hz	10⁵–10⁴ km	Extremely low frequency	ELF	N/A
30–300 Hz	10⁴–10³ km	Super low frequency	SLF	N/A
300–3000 Hz	10³–100 km	Ultra low frequency	ULF	N/A
3–30 kHz	100–10 km	Very low frequency	VLF	N/A
30–300 kHz	10–1 km	Low frequency	LF	N/A
300 kHz – 3 MHz	1 km – 100 m	Medium frequency	MF	N/A
3–30 MHz	100–10 m	High frequency	HF	HF
30–300 MHz	10–1 m	Very high frequency	VHF	VHF
300 MHz – 3 GHz	1 m – 10 cm	Ultra high frequency	UHF	UHF, L, S
3–30 GHz	10–1 cm	Super high frequency	SHF	S, C, X, Ku, K, Ka
30–300 GHz	1 cm – 1 mm	Extremely high frequency	EHF	Ka, V, W, mm
300 GHz – 3 THz	1 mm – 0.1 mm	Tremendously high frequency	THF	N/A

Frequencies of 1 GHz and above are conventionally called microwave,[8] 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.[9]
Applications
Communications

Radio frequencies are used in communication devices such as transmitters, receivers, computers, televisions, and mobile phones, to name a few. Radio frequencies are also applied in carrier current systems including telephony and control circuits. The MOS integrated circuit is the technology behind the current proliferation of radio frequency wireless telecommunications devices such as cellphones.
Medicine
Main article: Medical applications of radio frequency

Radio frequency (RF) energy, in the form of radiating waves or electrical currents, has been used in medical treatments for over 75 years,[10] generally for minimally invasive surgeries using radiofrequency ablation including the treatment of sleep apnea.[11]
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.
Mechanical oscillations

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

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
Spectrum management

References

J. A. Fleming, The Principles of Electric Wave Telegraphy and Telephony, London: Longmans, Green & Co., 1919, p. 364
A. A. Ghirardi, Radio Physics Course, 2nd ed. New York: Rinehart Books, 1932, p. 249
Curtis, Thomas Stanley (1916). High Frequency Apparatus: Its Construction and Practical Application. USA: Everyday Mechanics Company. pp. 6. "electric shock pain."
Mieny, C. J. (2005). Principles of Surgical Patient Care (2nd ed.). New Africa Books. p. 136. ISBN 9781869280055.
IEEE Std 521-2002 Standard Letter Designations for Radar-Frequency Bands Archived 2013-12-21 at the Wayback Machine, Institute of Electrical and Electronics Engineers, 2002. (Convenience copy at National Academies Press.)
Jeffrey S. Beasley; Gary M. Miller (2008). Modern Electronic Communication (9th ed.). pp. 4–5. ISBN 978-0132251136.
Tremendously low frequency (TLF) (Electromagnetic radiation, frequency below 3 Hz)
Kumar, Sanjay; Shukla, Saurabh (2014). Concepts and Applications of Microwave Engineering. PHI Learning Pvt. Ltd. p. 3. ISBN 978-8120349353.
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.
Ruey J. Sung & Michael R. Lauer (2000). Fundamental approaches to the management of cardiac arrhythmias. Springer. p. 153. ISBN 978-0-7923-6559-4. Archived from the original on 2015-09-05.

Melvin A. Shiffman; Sid J. Mirrafati; Samuel M. Lam; Chelso G. Cueteaux (2007). Simplified Facial Rejuvenation. Springer. p. 157. ISBN 978-3-540-71096-7.

External links

Definition of frequency bands (VLF, ELF … etc.) IK1QFK Home Page (vlf.it)
Radio, light, and sound waves, conversion between wavelength and frequency
RF Terms Glossary

Radio spectrum (ITU)

ELF
3 Hz/100 Mm
30 Hz/10 Mm

SLF
30 Hz/10 Mm
300 Hz/1 Mm

ULF
300 Hz/1 Mm
3 kHz/100 km

VLF
3 kHz/100 km
30 kHz/10 km

LF
30 kHz/10 km
300 kHz/1 km

MF
300 kHz/1 km
3 MHz/100 m

HF
3 MHz/100 m
30 MHz/10 m

VHF
30 MHz/10 m
300 MHz/1 m

UHF
300 MHz/1 m
3 GHz/100 mm

SHF
3 GHz/100 mm
30 GHz/10 mm

EHF
30 GHz/10 mm
300 GHz/1 mm

THF
300 GHz/1 mm
3 THz/0.1 mm

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Electromagnetic spectrum

Gamma rays X-rays Ultraviolet Visible Infrared Microwave Radio
Frequency vs. wave length.svg
← higher frequencies longer wavelengths →

X-rays

soft X-ray hard X-ray

Ultraviolet

Extreme ultraviolet Vacuum ultraviolet Lyman-alpha FUV MUV NUV UVC UVB UVA

Visible (optical)

Violet Blue Cyan Green Yellow Orange Red

Infrared

NIR SWIR MWIR LWIR FIR

Microwaves

W band V band Q band Ka band K band Ku band X band C band S band L band

Radio

THF EHF SHF UHF VHF HF MF LF VLF ULF SLF ELF

Wavelength types

Microwave Shortwave Medium wave Longwave

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Telecommunications
History

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Pioneers

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Transmission
media

Coaxial cable Fiber-optic communication
optical fiber Free-space optical communication Molecular communication Radio waves
wireless Transmission line
data transmission circuit telecommunication circuit

Network topology
and switching

Bandwidth Links Nodes
terminal Network switching
circuit packet Telephone exchange

Multiplexing

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Concepts

Communication protocols Computer network Data transmission Store and forward Telecommunications equipment

Types of network

Cellular network Ethernet ISDN LAN Mobile NGN Public Switched Telephone Radio Television Telex UUCP WAN Wireless network

Notable networks

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Locations (by regions)

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Category Category List-Class article Outline Portal Portal Commons page Commons

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Analog television broadcasting topics
Systems

180-line 405-line (System A) 441-line 525-line (System J, System M) 625-line (System B, System C, System D, System G, System H, System I, System K, System L, System N) 819-line ( System E , System F )

Color systems

NTSC PAL PAL-M PAL-S PALplus SECAM

Video

Back porch and front porch Black level Blanking level Chrominance Chrominance subcarrier Colorburst Color killer Color TV Composite video Frame (video) Horizontal scan rate Horizontal blanking interval Luma Nominal analogue blanking Overscan Raster scan Safe area Television lines Vertical blanking interval White clipper

Sound

Multichannel television sound NICAM Sound-in-Syncs Zweikanalton

Modulation

Frequency modulation Quadrature amplitude modulation Vestigial sideband modulation (VSB)

Transmission

Amplifiers Antenna (radio) Broadcast transmitter/Transmitter station Cavity amplifier Differential gain Differential phase Diplexer Dipole antenna Dummy load Frequency mixer Intercarrier method Intermediate frequency Output power of an analog TV transmitter Pre-emphasis Residual carrier Split sound system Superheterodyne transmitter Television receive-only Direct-broadcast satellite television Television transmitter Terrestrial television Transposer Digital television transition

Frequencies & Bands

Frequency offset Microwave transmission Television channel frequencies UHF VHF

Propagation

Beam tilt Distortion Earth bulge Field strength in free space Noise (electronics) Null fill Path loss Radiation pattern Skew Television interference

Testing

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