RADIO WAVES

(Redirected from Radio wave)
'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.

Contents

What Makes Radio Waves?

Propagation of radio waves

Historical Discovery

Radio Portion of the Electromagnetic Wave Spectrum

Named frequency bands

General

Amateur radio frequencies

IEEE US

EU, NATO, US ECM Frequency Designations

References

See also

References

What Makes Radio Waves?

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 of 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.

Historical Discovery

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 Portion of the Electromagnetic Wave Spectrum

Radio waves and 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'

★ 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 = 530kHz - 1710kHz (MF)

★ TV Band I (Channels 2 - 6) = 54MHz - 88MHz (VHF)

★ FM Radio Band II = 88MHz - 108MHz (VHF)

★ TV Band III (Channels 7 - 13) = 174MHz - 216MHz (VHF)

★ TV Bands IV & V (Channels 14 - 69) = 470MHz - 806MHz (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 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

IEEE US

Band	Frequency range	Origin of name
HF band	3 to 30 MHz	'H'igh 'F'requency
VHF band	30 to 300 MHz	'V'ery 'H'igh 'F'requency
UHF band	300 to 3000 MHz	'U'ltra 'H'igh 'F'requencyFrequencies from 216 to 450 MHz were sometimes called P-band: 'P'revious, since early British Radar used this band but later switched to higher frequencies.
L band	1 to 2 GHz	'L'ong wave
S band	2 to 4 GHz	'S'hort wave
C band	4 to 8 GHz	'C'ompromise 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	'K'urz-'u'nder
K band	18 to 26 GHz	German 'K'urz (short)
Ka band	26 to 40 GHz	'K'urz-'a'bove
V band	40 to 75 GHz
W band	75 to 111 GHz	'W' follows V in the alphabet

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

References

★ ITU-R Recommendation V.431: Nomenclature of the frequency and wavelength bands used in telecommunications. International Telecommunication Union, Geneva.

★ ANSI/IEEE Standard: Letter designations for radar-frequency bands.

★ AFR 55-44/AR 105-86/OPNAVINST 3430.9A/MCO 3430.1, 27 October 1964 superseded by AFR 55-44/AR 105-86/OPNAVINST 3430.1A/MCO 3430.1A, 6 December 1978: Performing Electronic Countermeasures in the United States and Canada, Attachment 1,ECM Frequency Authorizations.

See also

★ Radio propagation

★ Frequency allocation

★ Radio astronomy

★ Radio electronics

References

★ James Clerk Maxwell, "A Dynamical Theory of the Electromagnetic Field", ''Philosophical Transactions of the Royal Society of London'' '155', 459-512 (1865).

★ href="Heinrich_Hertz">Heinrich Hertz, "Electric waves: being researches on the propagation of electric action with finite velocity through space". Cornell University Library Historical Monographs Collection. {Reprinted by} Cornell University Library Digital Collections