Radio frequency explained
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 to around . 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
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
See main article: Radio spectrum.
The radio spectrum of frequencies is divided into bands with conventional names designated by the International Telecommunication Union (ITU):
| Wavelength
range | ITU designation | IEEE bands |
|---|
| Full name | Abbreviation[5] |
|---|
| Below 3 Hz | >10⁵ km | | | |
|---|
| 3–30 Hz | 10⁵–10⁴ km | | | |
|---|
| 30–300 Hz | 10⁴–10³ km | | | |
|---|
| 300–3000 Hz | 10³–100 km | | | |
|---|
| 3–30 kHz | 100–10 km | | | |
|---|
| 30–300 kHz | 10–1 km | | | |
|---|
| 300 kHz – 3 MHz | 1 km – 100 m | | | |
|---|
| 3–30 MHz | 100–10 m | | | HF |
|---|
| 30–300 MHz | 10–1 m | | | VHF |
|---|
| 300 MHz – 3 GHz | 1 m – 100 mm | | | UHF, L, S |
|---|
| 3–30 GHz | 100–10 mm | | | S, C, X, Ku, K, Ka |
|---|
| 30–300 GHz | 10–1 mm | | | Ka, V, W, mm |
|---|
| 300 GHz – 3 THz | 1 mm – 0.1 mm | | | |
|---|
| | |
Frequencies of 1 GHz and above are conventionally called microwave,[6] 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[7] and the EU/NATO frequency designations.[8]
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.[9]
Mechanical oscillations
While RF usually refers to electrical oscillations, mechanical RF systems are not uncommon: see mechanical filter and RF MEMS.
See also
External links
Notes and References
- Web site: Jessica Scarpati . What is radio frequency (RF, rf)? . SearchNetworking . 29 January 2021 . en.
- Book: Service . United States Flight Standards . Airframe and Powerplant Mechanics: Airframe Handbook . 1976 . Department of Transportation, Federal Aviation Administration, Flight Standards Service . 520 . en.
- Book: Curtis, Thomas Stanley
. 1916 . High Frequency Apparatus: Its construction and practical application . Everyday Mechanics Company . US . 6 . electric shock pain..
- Book: Mieny, C.J.
. 2005 . Principles of Surgical Patient Care . 2nd . 136 . New Africa Books . 9781869280055 .
- Book: Modern Electronic Communication. 2008. 978-0132251136. Jeffrey S. Beasley. 9th. Gary M. Miller . 4–5.
- Book: Kumar . Sanjay . Shukla . Saurabh . Concepts and Applications of Microwave Engineering . PHI Learning Pvt. Ltd . 2014 . 3 . 978-8120349353 .
- https://standards.ieee.org/ieee/521/768/ IEEE Std 521-2002 Standard Letter Designations for Radar-Frequency Bands
- Book: Leonid A. Belov. Sergey M. Smolskiy. Victor N. Kochemasov. Handbook of RF, Microwave, and Millimeter-Wave Components. 2012. Artech House. 978-1-60807-209-5. 27–28.
- Web site: RF Radio Frequency Signal Generator » Electronics Notes . www.electronics-notes.com . 29 January 2021.
