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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 Hertzdemonstrated 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 Teslaand Guglielmo Marconiare 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 spectrumtable below.

Band name Abbr ITUband Frequency
and
Wavelength in air
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 longwavebroadcasting, 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
Shortwavebroadcasts, amateur radioand over-the-horizon aviation communications, RFID
Very high frequency VHF 8 30-300 MHz
10 m - 1 m
FM, televisionbroadcasts 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
televisionbroadcasts, microwaveovens, mobile phones, wireless LAN, Bluetooth, GPSand Two-Way Radios such as Land Mobile, FRS and GMRS Radios
Super high frequency SHF 10 3-30 GHz
100 mm - 10 mm
microwavedevices, 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

  • 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 infraredand 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://learnhub.com/redirect?u=http%3A%2F%2Fwww.ntia.doc.gov%2Fosmhome%2Fallochrt.html

Amateur radio frequencies

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

IEEE US

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

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 Britishradarused 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 IIfor fire control, X for cross (as in crosshair)
Ku band 12 to 18 GHz Kurz-under
K band 18 to 27 GHz GermanKurz (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

[edit]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

[edit]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

  1. vishal1991 saidMon, 23 Mar 2009 03:14:40 -0000 ( Link )

    for more information go to the following url:
    http://en.wikipedia.org/wiki/Radio_waves

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