radio wave
n.
An electromagnetic wave within the range of radio frequencies.
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For more information on radio wave, visit Britannica.com.
Waves at the end of the electromagnetic spectrum with the lowest frequency (less than 300 megahertz) and the longest wavelength (from a few feet to many miles). Because of their low frequency, radio waves carry very little energy compared to other electromagnetic waves. (See Planck's constant.)
| ITU Radio Band Numbers
4 5 6 7 8 9 10 11 12 |
| ITU Radio Band Symbols
VLF LF MF HF VHF UHF SHF EHF |
| NATO Radio bands |
| IEEE Radar bands |
Radio waves are electromagnetic waves occurring on the radio frequency portion of the electromagnetic spectrum. A common use is to transport information through the atmosphere or outer space without wires. Radio waves are distinguished from other kinds of electromagnetic waves by their wavelength, a relatively long wavelength in the electromagnetic spectrum.
Radio waves are usually produced by electric current alternating at radio frequency flowing in a special purpose conductor, called an antenna. Antenna dimensions must generally be comparable to wavelength to work efficiently. Very long waves are not practical because of the enormous antennas needed to produce them, although they are sometimes produced by lightning. Radio waves are also produced by cosmic phenomena in deep space. Actually, any kind of reciprocating motion of electric charges or magnets can produce radio waves if it is fast enough. Although very impractical, even a person waving a charged stick very fast can produce faint radio waves.
Propagation is a term that describes the travel of electromagnetic waves, there being three principle main modes of propagation. The first is a straight line travel: the manner that radio waves travel through deep space (ignoring the slight deviations caused by gravity under the theory of relativity). A second way is skip, which is bouncing between the surface of the earth and the ionosphere. Frequencies between 3 MHz and 30 MHz are most reliable for this kind of propagation, called High Frequency. The third way is to hug the surface of the earth as it curves around. Radio waves of very low frequency most often travel this way.
Radio waves were first predicted by mathematical work done in 1865 by James Clerk Maxwell. Maxwell noticed wave-like properties of light and similarities in electrical and magnetic observations and proposed equations that described light waves and radio waves as waves of electromagnetism that travel in space. In 1887 Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory. Many inventions followed making practical use of radio waves to transfer information through space.
Italian engineer Guglielmo Marconi is generally credited with inventing radio. In 1895 he transmitted a signal 2.4 kilometres in the grounds of his father's property. He patented the first 'wireless telegraphy' system in 1896.
Radio waves are divided up into bands by frequency (and corresponding wavelength) as shown in the radio frequency spectrum table below.
| Band name | Abbr | ITU band | Frequency and Wavelength |
Example uses |
|---|---|---|---|---|
| < 3 Hz > 100,000 km |
||||
| Extremely low frequency | ELF | 1 | 3–30 Hz 100,000 km – 10,000 km |
Communication with submarines |
| Super low frequency | SLF | 2 | 30–300 Hz 10,000 km – 1000 km |
Communication with submarines |
| Ultra low frequency | ULF | 3 | 300–3000 Hz 1000 km – 100 km |
Communication within mines |
| Very low frequency | VLF | 4 | 3–30 kHz 100 km – 10 km |
Submarine communication, avalanche beacons, wireless heart rate monitors, geophysics |
| Low frequency | LF | 5 | 30–300 kHz 10 km – 1 km |
Navigation, time signals, AM longwave broadcasting |
| Medium frequency | MF | 6 | 300–3000 kHz 1 km – 100 m |
AM (Medium-wave) broadcasts |
| High frequency | HF | 7 | 3–30 MHz 100 m – 10 m |
Shortwave broadcasts, amateur radio and over-the-horizon aviation communications |
| Very high frequency | VHF | 8 | 30–300 MHz 10 m – 1 m |
FM, television broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications |
| Ultra high frequency | UHF | 9 | 300–3000 MHz 1 m – 100 mm |
television broadcasts, microwave ovens, mobile phones, wireless LAN, Bluetooth, GPS and Two-Way Radios such as FRS and GMRS Radios |
| Super high frequency | SHF | 10 | 3–30 GHz 100 mm – 10 mm |
microwave devices, wireless LAN, most modern Radars |
| Extremely high frequency | EHF | 11 | 30–300 GHz 10 mm – 1 mm |
Radio astronomy, high-speed microwave radio relay |
| Above 300 GHz < 1 mm |
Notes
Broadcast Frequencies:
For more information see the NTIA frequency allocation chart: http://www.ntia.doc.gov/osmhome/allochrt.html
The range of allowed frequencies vary between countries. These are just some of the more common bands, often collectively termed shortwave. The article amateur radio contains another list.
| Band | Frequency range |
|---|---|
| 160 m | 1.8 to 2.0 MHz |
| 80 m | 3.5 to 4.0 MHz |
| 60 m | 5.3 to 5.4 MHz |
| 40 m | 7 to 7.3 MHz |
| 30 m | 10.1 to 10.15 MHz |
| 20 m | 14 to 14.35 MHz |
| 15 m | 21 to 21.45 MHz |
| 12 m | 24.89 to 24.99 MHz |
| 10 m | 28.0 to 29.7 MHz |
| 6 m | 50 to 54 MHz |
| 2 m | 144 to 148 MHz |
| 70 cm | 430 to 440 MHz |
| 33 cm | 902 to 928 MHz |
| 23 cm | 1240 to 1300 MHz |
| Band | Frequency range | Origin of name |
|---|---|---|
| HF band | 3 to 30 MHz | High Frequency |
| VHF band | 30 to 300 MHz | Very High Frequency |
| UHF band | 300 to 3000 MHz | Ultra High Frequency
Frequencies from 216 to 450 MHz were sometimes called P-band: Previous, since early British Radar used this band but later switched to higher frequencies. |
| L band | 1 to 2 GHz | Long wave |
| S band | 2 to 4 GHz | Short wave |
| C band | 4 to 8 GHz | Compromise between S and X |
| X band | 8 to 12 GHz | Used in WW II for fire control, X for cross (as in crosshair) |
| Ku band | 12 to 18 GHz | Kurz-under |
| K band | 18 to 26 GHz | German Kurz (short) |
| Ka band | 26 to 40 GHz | Kurz-above |
| V band | 40 to 75 GHz | |
| W band | 75 to 111 GHz | W follows V in the alphabet |
| Band | Frequency range |
|---|---|
| A band | 0 to 0.25 GHz |
| B band | 0.25 to 0.5 GHz |
| C band | 0.5 to 1.0 GHz |
| D band | 1 to 2 GHz |
| E band | 2 to 3 GHz |
| F band | 3 to 4 GHz |
| G band | 4 to 6 GHz |
| H band | 6 to 8 GHz |
| I band | 8 to 10 GHz |
| J band | 10 to 20 GHz |
| K band | 20 to 40 GHz |
| L band | 40 to 60 GHz |
| M band | 60 to 100 GHz |
| Radio spectrum | ||||||||||
| ELF | SLF | ULF | VLF | LF | MF | HF | VHF | UHF | SHF | EHF |
| 3 Hz | 30 Hz | 300 Hz | 3 kHz | 30 kHz | 300 kHz | 3 MHz | 30 MHz | 300 MHz | 3 GHz | 30 GHz |
| 30 Hz | 300 Hz | 3 kHz | 30 kHz | 300 kHz | 3 MHz | 30 MHz | 300 MHz | 3 GHz | 30 GHz | 300 GHz |
| The Electromagnetic Spectrum | |
|---|---|
| (Sorted by wavelength, short to long) Gamma ray • X-ray • Ultraviolet • Visible spectrum • Infrared • Terahertz radiation • Microwave • Radio waves |
|
| Visible (optical) spectrum | Violet • Blue • Green • Yellow • Orange • Red |
| Microwave spectrum | W band • V band • Ka band • K band • Ku band • X band • C band • S band • L band |
| Radio spectrum | EHF • SHF • UHF • VHF • HF • MF • LF • VLF • ULF • SLF • ELF |
| Wavelength designations | Microwave • Shortwave • Mediumwave • Longwave |
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
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