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radio wave

 
Dictionary: radio wave
 

n.

An electromagnetic wave within the range of radio frequencies.


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Radio waves lie at the low-frequency end of the electromagnetic spectrum. They are primarily used …
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Radio waves lie at the low-frequency end of the electromagnetic spectrum. They are primarily used … (credit: © Merriam-Webster Inc.)
Wave from the portion of the electromagnetic spectrum at lower frequencies than microwaves. The wavelengths of radio waves range from thousands of metres to around 30 cm. These correspond to frequencies as low as 3 Hz and as high as 1 gigahertz (109 Hz). Radio-wave communications signals travel through the air in a straight line, reflect off of clouds or layers of the ionosphere, or are relayed by satellites in space. They are used in standard broadcast radio and television, short-wave radio, navigation and air-traffic control, cellular telephony, and even remote-controlled toys.

For more information on radio wave, visit Britannica.com.

 
Science Dictionary: radio waves
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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.)

  • Radio waves can pass through the atmosphere and therefore are very useful for communication. Commercial, short-wave, and citizens' band radio are broadcast with radio waves, as is television.
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    Wikipedia: Radio waves
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    ITU Radio Band Numbers

    edit

    Radio waves are electromagnetic waves occurring on the radio frequency portion of the electromagnetic spectrum.

    Diagram of the electric (E) and magnetic (H) fields of Radio Waves emanating from a radio transmitting antenna (small dark vertical line in the center). The E and H fields are perpendicular as implied by the phase diagram in the lower right.

    Contents

    Discovery and utilization

    Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves.

    Radio waves were first predicted by mathematical work done in 1865 by James Clerk Maxwell. Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. He then 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 the use of radio waves to transfer information through space.

    Nikola Tesla and Guglielmo Marconi are credited with inventing systems to allow radio waves to be used for communication.[1][2]

    Radio portion of the electromagnetic spectrum

    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 in air
    Example uses
    subHertz subHz 0 < 3 Hz
    > 100,000 km
    Natural and man-made electromagnetic waves millihertz, microhertz, nanohertz from earth, ionosphere, sun, planets, etc
    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, RFID
    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, RFID
    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. Land Mobile and Maritime Mobile 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 Land Mobile, 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-frequency microwave radio relay
    Terahertz THz 300–30,000 GHz
    1 mm – 90 um
    Terahertz imaging - a potential replacement for x-rays in some medical applications, ultrafast molecular dynamics, Condensed-matter physics, Terahertz time-domain spectroscopy, terahertz computing/communications

    Notes

    • Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.
    • The ELF, SLF, ULF, and VLF bands overlap the AF (audio frequency) spectrum, which is approximately 20–20,000 Hz. However, sounds are transmitted by atmospheric compression and expansion, and not by electromagnetic energy.
    • The SHF and EHF bands are sometimes not considered to be a part of the radio spectrum, forming their own microwave spectrum.

    Named frequency bands

    General

    Broadcast Frequencies:

    • Longwave AM Radio = 148.5 - 283.5 kHz (LF)
    • Mediumwave AM Radio = 530 kHz - 1710 kHz (MF)
    • Shortwave AM Radio = 3 MHz - 30 MHz (HF)
    • TV Band I (Channels 2 - 6) = 54 MHz - 88 MHz (VHF)
    • FM Radio Band II = 88 MHz - 108 MHz (VHF)
    • TV Band III (Channels 7 - 13) = 174 MHz - 216 MHz (VHF)
    • TV Bands IV & V (Channels 14 - 69) = 470 MHz - 806 MHz (UHF) [1]

    For more information see the NTIA frequency allocation chart: http://www.ntia.doc.gov/osmhome/allochrt.html

    Amateur radio frequencies

    The range of allowed amateur radio frequencies vary between countries. The article Amateur radio frequency allocations lists frequencies allocated for amateur radio use.

    IEEE US

    Per IEEE Std 521-2002. Reaffirmed standard of 1984; originally dates back to World War II.

    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 1000 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 27 GHz German Kurz (short)
    Ka band 27 to 40 GHz Kurz-above
    V band 40 to 75 GHz
    W band 75 to 110 GHz W follows V in the alphabet
    mm band 110 to 300 GHz

    EU, NATO, US ECM frequency designations

    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

    Waveguide frequency bands

    Band Frequency range [3]
    R band 1.70 to 2.60 GHz
    D band 2.20 to 3.30 GHz
    S band 2.60 to 3.95 GHz
    E band 3.30 to 4.90 GHz
    G band 3.95 to 5.85 GHz
    F band 4.90 to 7.05 GHz
    C band 5.85 to 8.20 GHz
    H band 7.05 to 10.10 GHz
    X band 8.2 to 12.4 GHz
    Ku band 12.4 to 18.0 GHz
    K band 15.0 to 26.5 GHz
    Ka band 26.5 to 40.0 GHz
    Q band 33 to 50 GHz
    U band 40 to 60 GHz
    V band 50 to 75 GHz
    W band 75 to 110 GHz
    Y band 325 to 500 GHz

    References

    See also

    References


     
     

     

    Copyrights:

    Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
    Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
    Science Dictionary. The New Dictionary of Cultural Literacy, Third Edition Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin. All rights reserved.  Read more
    Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Radio waves" Read more

     

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