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Radio
Radio
frequency (RF) is any of the electromagnetic wave frequencies that lie in the range extending from around 7004200000000000000♠20 kHz to 7011300000000000000♠300 GHz, roughly the frequencies used in radio communication.[1] The term does not have an official definition, and different sources specify slightly different upper and lower bounds for the frequency range. RF usually refers to electrical rather than mechanical oscillations. However, mechanical RF systems do exist (see mechanical filter and RF MEMS). Although radio frequency is a rate of oscillation, the term "radio frequency" or its abbreviation "RF" are used as a synonym for radio – i.e., to describe the use of wireless communication, as opposed to communication via electric wires. Examples include:

Radio-frequency identification ISO/IEC 14443-2 Radio
Radio
frequency power and signal interface[2]

Contents

1 Special
Special
properties of RF current 2 Radio
Radio
communication 3 Frequency
Frequency
bands 4 In medicine 5 Effects on the human body

5.1 Extremely low frequency
Extremely low frequency
RF 5.2 Microwaves 5.3 General RF exposure

6 As a weapon 7 Measurement 8 See also 9 References 10 External links

Special
Special
properties of RF current[edit] Electric currents that oscillate at radio frequencies 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 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 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. Therefore, RF current must be carried by specialized types of cable called transmission line.

Radio
Radio
communication[edit] To receive radio signals an antenna must be used. However, since the antenna will pick up thousands of radio signals at a time, a radio tuner is necessary to tune into a particular frequency (or frequency range).[5] This is typically done via a resonator – in its simplest form, a circuit with a capacitor and an inductor form a tuned circuit. The resonator amplifies oscillations within a particular frequency band, while reducing oscillations at other frequencies outside the band. Another method to isolate a particular radio frequency is by oversampling (which gets a wide range of frequencies) and picking out the frequencies of interest, as done in software defined radio. The distance over which radio communications is useful depends significantly on things other than wavelength, such as transmitter power, receiver quality, type, size, and height of antenna, mode of transmission, noise, and interfering signals. Ground waves, tropospheric scatter and skywaves can all achieve greater ranges than line-of-sight propagation. The study of radio propagation allows estimates of useful range to be made. Frequency
Frequency
bands[edit] Main article: Radio
Radio
spectrum The radio spectrum of frequencies is divided into bands with conventional names designated by the International Telecommunications Union (ITU):

Frequency Wavelength Designation Abbreviation[6] IEEE bands[7]

3–30 Hz 105–104 km Extremely low frequency ELF -

30–300 Hz 104–103 km Super low frequency SLF -

300–3000 Hz 103–100 km Ultra low frequency ULF -

3–30 kHz 100–10 km Very low frequency VLF -

30–300 kHz 10–1 km Low frequency LF -

300 kHz – 3 MHz 1 km – 100 m Medium frequency MF -

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 -

Frequencies of 1 GHz and above are conventionally called microwave,[8] while frequencies of 300 GHz and above are designated millimeter wave. More detailed band designations are given by the standard IEEE letter- band frequency designations[7] and the EU/NATO frequency designations.[9] In medicine[edit] Radio
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] Magnetic resonance imaging
Magnetic resonance imaging
(MRI) uses radio frequency waves to generate images of the human body.[12] Radio
Radio
frequencies at non-ablation energy levels are sometimes used as a form of cosmetic treatment that can tighten skin, reduce fat (lipolysis), or promote healing.[13] RF diathermy is a medical treatment that uses RF induced heat as a form of physical or occupational therapy and in surgical procedures. It is commonly used for muscle relaxation. It is also a method of heating tissue electromagnetically for therapeutic purposes in medicine. Diathermy
Diathermy
is used in physical therapy and occupational therapy to deliver moderate heat directly to pathologic lesions in the deeper tissues of the body. Surgically, the extreme heat that can be produced by diathermy may be used to destroy neoplasms, warts, and infected tissues, and to cauterize blood vessels to prevent excessive bleeding. The technique is particularly valuable in neurosurgery and surgery of the eye. Diathermy
Diathermy
equipment typically operates in the short-wave radio frequency (range 1–100 MHz) or microwave energy (range 434–915 MHz). Pulsed electromagnetic field therapy
Pulsed electromagnetic field therapy
(PEMF) is a medical treatment that purportedly helps to heal bone tissue reported in a recent NASA study. This method usually employs electromagnetic radiation of different frequencies - ranging from static magnetic fields, through extremely low frequencies (ELF) to higher radio frequencies (RF) administered in pulses. Effects on the human body[edit] Extremely low frequency
Extremely low frequency
RF[edit] High-power extremely low-frequency RF with electric field levels in the low kV/m range is known to induce perceivable currents within the human body that create an annoying tingling sensation. These currents will typically flow to ground through a body contact surface such as the feet, or arc to ground where the body is well insulated.[14][15] Microwaves[edit] Main article: Microwave
Microwave
burn Microwave
Microwave
exposure at low-power levels below the Specific absorption rate set by government regulatory bodies are considered harmless non-ionizing radiation and have no effect on the human body. However, levels above the Specific absorption rate set by the U.S. Federal Communications Commission are considered potentially harmful (see Mobile phone radiation and health). Long-term human exposure to high-levels of microwaves is recognized to cause cataracts according to experimental animal studies and epidemiological studies. The mechanism is unclear but may include changes in heat sensitive enzymes that normally protect cell proteins in the lens. Another mechanism that has been advanced is direct damage to the lens from pressure waves induced in the aqueous humor. High-power exposure to microwave RF is known to create a range of effects from lower to higher power levels, ranging from unpleasant burning sensation on the skin and microwave auditory effect, to extreme pain at the mid-range, to physical burning and blistering of skin and internals at high power levels (see microwave burn). General RF exposure[edit] The 1999 revision of Canadian Safety Code 6 recommended electric field limits of 100 kV/m for pulsed EMF to prevent air breakdown and spark discharges, mentioning rationale related to auditory effect and energy-induced unconsciousness in rats.[16] The pulsed EMF limit was removed in later revisions, however.[17] For health effects see electromagnetic radiation and health. For high-power RF (electromagnetic, not electrical) exposure see radiation burn. For low-power RF exposure see radiation-induced cancer. As a weapon[edit] See also: Directed energy weapons §  Microwave
Microwave
weapons A heat ray is an RF harassment device that makes use of microwave radio frequencies to create an unpleasant heating effect in the upper layer of the skin. A publicly known heat ray weapon called the Active Denial System was developed by the US military as an experimental weapon to deny the enemy access to an area. A death ray is a weapon that delivers heat ray electromagnetic energy at levels that injure human tissue. The inventor of the death ray, Harry Grindell Matthews, claims to have lost sight in his left eye while developing his death ray weapon based on a primitive microwave magnetron from the 1920s (note that a typical microwave oven induces a tissue damaging cooking effect inside the oven at about 2 kV/m). Measurement[edit]

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Since radio frequency radiation has both an electric and a magnetic component, it is often convenient to express intensity of radiation field in terms of units specific to each component. The unit volts per meter (V/m) is used for the electric component, and the unit amperes per meter (A/m) is used for the magnetic component. One can speak of an electromagnetic field, and these units are used to provide information about the levels of electric and magnetic field strength at a measurement location. Another commonly used unit for characterizing an RF electromagnetic field is power density. Power density is most accurately used when the point of measurement is far enough away from the RF emitter to be located in what is referred to as the far field zone of the radiation pattern.[18] In closer proximity to the transmitter, i.e., in the "near field" zone, the physical relationships between the electric and magnetic components of the field can be complex, and it is best to use the field strength units discussed above. Power density is measured in terms of power per unit area, for example, milliwatts per square centimeter (mW/cm²). When speaking of frequencies in the microwave range and higher, power density is usually used to express intensity since exposures that might occur would likely be in the far field zone. See also[edit]

Amplitude modulation
Amplitude modulation
("AM") Electromagnetic Interference Electromagnetic radiation Electromagnetic spectrum EMF measurement Frequency
Frequency
allocation Frequency
Frequency
bandwidth Frequency
Frequency
modulation ("FM") Plastic welding Pulsed electromagnetic field therapy Spectrum management

References[edit]

^ "Definition of RADIO FREQUENCY". Merriam-Webster. Encyclopædia Britannica. n.d. Retrieved 6 August 2015.  ^ "ISO/IEC 14443-2:2001 Identification cards — Contactless integrated circuit(s) cards — Proximity cards — Part 2: Radio frequency power and signal interface". Iso.org. 2010-08-19. Retrieved 2011-11-08.  ^ Curtis, Thomas Stanley (1916). High Frequency
Frequency
Apparatus: Its Construction and Practical Application. USA: Everyday Mechanics Company. p. 6.  ^ Mieny, C. J. (2003). Principles of Surgical Patient Care (2nd ed.). New Africa Books. p. 136. ISBN 9781869280055.  ^ Brain, Marshall (2000-12-07). "How Radio
Radio
Works". HowStuffWorks.com. Retrieved 2009-09-11.  ^ Jeffrey S. Beasley; Gary M. Miller (2008). Modern Electronic Communication (9th ed.). pp. 4–5. ISBN 978-0132251136.  ^ a b IEEE Std 521-2002 Standard Letter Designations for Radar- Frequency
Frequency
Bands, Institute of Electrical and Electronics Engineers, 2002. ^ Kumar, Sanjay; Shukla, Saurabh (2014). Concepts and Applications of Microwave
Microwave
Engineering. PHI Learning Pvt. Ltd. p. 3. ISBN 8120349350.  ^ 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.  ^ 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.  ^ Bethge, K. (2004-04-27). Medical Applications of Nuclear Physics. Springer Science & Business Media. ISBN 9783540208051.  ^ "Noninvasive Radio
Radio
Frequency
Frequency
for Skin Tightening and Body Contouring, Frontline Medical Communications, 2013" (PDF). skinandallergynews.com. Retrieved 16 March 2018.  ^ Limits of Human Exposure to Radiofrequency Electromagnetic Fields in the Frequency
Frequency
Range from 3 kHz to 300 GHz, Canada Safety Code 6, page 63 ^ Extremely Low Frequency
Frequency
Fields Environmental Health Criteria Monograph No.238, chapter 5, page 121, WHO ^ Limits of Human Exposure to Radiofrequency Electromagnetic Fields in the Frequency
Frequency
Range from 3 kHz to 300 GHz, Canada Safety Code 6, page 62 ^ http://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/radio_guide-lignes_direct/index-eng.php Safety Code 6: Health Canada's Radiofrequency Exposure Guidelines - Environmental and Workplace Health - Health Canada ^ Broadcasters, National Association of (1996). Antenna & Tower Regulation Handbook. NAB, Science and Technology Department. ISBN 9780893242367. 

External links[edit]

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

v t e

Radio
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

v t e

Electromagnetic spectrum

Gamma rays X-rays Ultraviolet Visible Infrared Terahertz radiation Microwave Radio

← higher frequencies       longer wavelengths →

Visible (optical)

Violet Blue Green Yellow Orange Red

Microwaves

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

Radio

EHF SHF UHF VHF HF MF LF VLF ULF SLF ELF

Wavelength
Wavelength
types

Microwave Shortwave Medium wave Longwave

v t e

Telecommunications

History

Beacon Broadcasting Cable protection system Cable TV Communications satellite Computer network Drums Electrical telegraph Fax Heliographs Hydraulic telegraph Internet Mass media Mobile phone Optical telecommunication Optical telegraphy Pager Photophone Prepay mobile phone Radio Radiotelephone Satellite communications Semaphore Smartphone Smoke signals Telecommunications history Telautograph Telegraphy Teleprinter
Teleprinter
(teletype) Telephone The Telephone Cases Television Timeline of communication technology Undersea telegraph line Videoconferencing Videophone Videotelephony Whistled language

Pioneers

Edwin Howard Armstrong John Logie Baird Paul Baran Alexander Graham Bell Tim Berners-Lee Jagadish Chandra Bose Vint Cerf Claude Chappe Donald Davies Lee de Forest Philo Farnsworth Reginald Fessenden Elisha Gray Erna Schneider Hoover Charles K. Kao Hedy Lamarr Innocenzo Manzetti Guglielmo Marconi Antonio Meucci Radia Perlman Alexander Stepanovich Popov Johann Philipp Reis Nikola Tesla Camille Tissot Alfred Vail Charles Wheatstone Vladimir K. Zworykin

Transmission media

Coaxial cable Fiber-optic communication

Optical fiber

Free-space optical communication Molecular communication Radio
Radio
waves Transmission line

Network topology and switching

Links Nodes Terminal node Network switching (circuit packet) Telephone exchange

Multiplexing

Space-division Frequency-division Time-division Polarization-division Orbital angular-momentum Code-division

Networks

ARPANET BITNET Cellular network Computer CYCLADES Ethernet FidoNet Internet ISDN LAN Mobile NGN NPL network Public Switched Telephone Radio Telecommunications equipment Television Telex WAN Wireless World Wide Web

Category Portal

v t e

Analog television
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
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
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
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

Frequencies & Bands

Frequency
Frequency
offset Microwave
Microwave
transmission Television channel frequencies UHF VHF

Propagation

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

Testing

Distortionmeter Field strength meter Vectorscope VIT signals Zero reference pulse

Artifacts

Dot crawl Ghosting Hanover bars Sparklies

Authority control

GND: 4160130-0 N

.