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The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).[1]

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## Limits

The frequency boundaries of the radio spectrum are a matter of convention in physics and are somewhat arbitrary. Since radio waves are the lowest frequency category of electromagnetic waves, there is no lower limit to the frequency of radio waves.[4] Radio waves are defined by the ITU as: "electromagnetic waves of frequencies arbitrarily lower than 3000 GHz, propagated in space without artificial guide".[5] At the high frequency end the radio spectrum is bounded by the infrared band. The boundary between radio waves and infrared waves is defined at different frequencies in different scientific fields. The terahertz band, from 300 gigahertz to 3 terahertz, can be considered either as microwaves or infrared. It is the highest band categorized as radio waves by the International Telecommunication Union.[4] but spectroscopic scientists consider these frequencies part of the far infrared and mid infrared bands.

The highest frequencies useful for radio communication are limited by the absorption of microwave energy by the atmosphere.[6] As frequency increases above 30 GHz (the beginning of the millimeter wave band), atmospheric gases absorb increasing amounts of power, so the power in a beam of radio waves decreases exponentially with distance from the transmitting antenna. At 30 GHz, useful communication is limited to about 1 km, but as frequency increases the range at which the waves can be received decreases. In the terahertz band above 300 GHz, the radio waves are attenuated to zero within a few meters due to the absorption of electromagnetic radiation by the atmosphere (mainly due to ozone, water vapor and carbon dioxide), which is so great that it is essentially opaque to electromagnetic emissions, until it becomes transparent again near the infrared and in the visible light ranges.[7][8]

## Bands

A radio band is a small frequency band (a contiguous section of the range of the radio spectrum) in which channels are usually used or set aside for the same purpose. To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated in bands. For example, broadcasting, mobile radio, or navigation devices, will be allocated in non-overlapping ranges of frequencies.

### Band plan

For each radio band, the ITU has a band plan (or frequency plan) which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility of transmitters and receivers.[9]

Each frequency plan defines the frequency range to be included, how channels are to be defined, and what will be carried on those channels. Typical definitions set forth in a frequency plan are:

### ITU

The actual authorized frequency bands are defined by the ITU[10] and the local regulating agencies like the US Federal Communications Commission (FCC) [11] and voluntary best practices help avoid interference.[12]

As a matter of convention, the ITU divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten (10n) metres, with corresponding frequency of 3×108−n hertz, and each covering a decade of frequency or wavelength. Each of these bands has a traditional name. For example, the term high frequency (HF) designates the wavelength range from 100 to 10 metres, corresponding to a frequency range of 3 to 30 MHz. This is just a symbol and is not related to allocation; the ITU further divides each band into subbands allocated to different services. Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque, until it becomes transparent again in the near-infrared and optical window frequency ranges.

These ITU radio bands are defined in the ITU Radio Regulations. Article 2, provision No. 2.1 states that "the radio spectrum shall be subdivided into nine frequency bands, which shall be designated by progressive whole numbers in accordance with the following table".[13]

The table originated with a recommendation of the fourth CCIR meeting, held in Bucharest in 1937, and was approved by the International Radio Conference held at Atlantic City, NJ in 1947. The idea to give each band a number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band limits in Hz, originated with B. C. Fleming-Williams, who suggested it in a letter to the editor of Wireless Engineer in 1942. For example, the approximate geometric mean of band 7 is 10 MHz, or 107 Hz.[14]

The band name "tremendously low frequency" (TLF) has been used for frequencies from 1–3 Hz (wavelengths from 300,000–100,000 km),[15] but the term has not been defined by the ITU.[16]

Band name Abbreviation ITU band number Frequency and wavelength Example uses
Extremely low frequency ELF 1 3–30 Hz
100,000–10,000 km
Communication with submarines
Super low frequency SLF 2 30–300 Hz
10,000–1,000 km
Communication with submarines
Ultra low frequency ULF 3 300–3,000 Hz
1,000–100 km
Communication with submarines, communication within mines, landline telephony, fax machines, fiber-optic communication
Very low frequency VLF 4 3–30 kHz
100–10 km
Navigation, time signals, communication with submarines, landline telephony, wireless heart rate monitors, geophysics
Low frequency LF 5 30–300 kHz
10–1 km
Medium frequency MF 6 300–3,000 kHz
1,000–100 m
AM (medium-wave) broadcasts, amateur radio, avalanche beacons, magnetic resonance imaging, positron emission tomography, electrical telegraph, wireless telegraphy, radioteletype, dial-up internet.
High frequency HF 7 3–30 MHz
100–10 m
Shortwave broadcasts, citizens band radio, amateur radio, over-the-horizon aviation communications, RFID, over-the-horizon radar, automatic link establishment (ALE) / near-vertical incidence skywave (NVIS) radio communications, marine and mobile radio telephony, CT scan, magnetic resonance imaging, positron emission tomography, ultrasound, cordless phones.
Very high frequency VHF 8 30–300 MHz
10–1 m
FM broadcasts, television broadcasts, cable television broadcasting, radars, line-of-sight ground-to-aircraft, aircraft-to-aircraft communications, emergency locator beacon homing signal, radioteletype, land mobile and maritime mobile communications, amateur radio, police, fire and emergency medical services broadcasts, weather radio, CT scan, magnetic resonance imaging, positron emission tomography, ultrasound, cordless phones.
Ultra high frequency UHF 9 300–3,000 MHz
100–10 cm
Super high frequency SHF 10 3–30 GHz
10–1 cm
Radio astronomy, microwave devices/communications, wireless LAN, DSRC, most modern radars, communications satellites, cable and satellite television broadcasting, DBS, amateur radio, satellite broadcasting, communication satellites, weather satellites, satellite radio, cordless phones, internet, satellite phones (S band).
Extremely high frequency EHF 11 30–300 GHz
10–1 mm
Radio astronomy, satellite broadcasting, communication satellites, weather satellites, high-frequency microwave radio relay, microwave remote sensing, directed-energy weapon, millimeter wave scanner, Wireless Lan 802.11ad, internet.
Terahertz or tremendously high frequency THF 12 300–3,000 GHz
1–0.1 mm
Experimental medical imaging to replace X-rays, ultrafast molecular dynamics, condensed-matter physics, terahertz time-domain spectroscopy, terahertz computing/communications, remote sensing

Frequency bands in the microwave range are designated by letters. This convention began around World War II with military designations for frequencies used in radar, which was the first application of microwaves. Unfortunately, there are several incompatible naming systems for microwave bands, and even within a given system the exact frequency range designated by a letter may vary somewhat between different application areas. One widely used standard is the IEEE radar bands established by the US Institute of Electrical and Electronics Engineers.

Radar-frequency bands according to IEEE standard[17]
Band
designation
Frequency range Explanation of meaning of letters
HF 0.003 to 0.03 GHz High frequency[18]
VHF 0.03 to 0.3 GHz Very high frequency[18]
UHF 0.3 to 1 GHz Ultra-high frequency[18]
L 1 to 2 GHz Long wave
S 2 to 4 GHz Short wave
C 4 to 8 GHz Compromise between S and X
X 8 to 12 GHz Used in World War II for fire control, X for cross (as in crosshair). Exotic.[19]
Ku 12 to 18 GHz Kurz-under
K 18 to 27 GHz German: Kurz (short)
Ka 27 to 40 GHz Kurz-above
V 40 to 75 GHz
W 75 to 110 GHz W follows V in the alphabet[citation needed]
mm or G 110 to 300 GHz[note 1] Millimeter[17]
1. ^ The designation mm is also used to refer to the range from 30 to 300 GHz.[17]

### EU, NATO, US ECM frequency designations

band
designation
New nomenclature Old nomenclature
Band Frequency (MHz) Band Frequency (MHz)
A 0 – 250 I 100 – 150 Band I
47 – 68 MHz (TV)
Band II
87.5 – 108 MHz (FM)
G 150 – 225 Band III
174 – 230 MHz (TV)
B 250 – 500 P 225 – 390
C 500 – 1 000 L 390 – 1 550 Band IV
470 – 582 MHz (TV)
Band V
582 – 862 MHz (TV)
D 1 000 – 2 000 S 1 550 – 3 900
E 2 000 – 3 000
F 3 000 – 4 000
G 4 000 – 6 000 C 3 900 – 6 200
H 6 000 – 8 000 X 6 200 – 10 900
I 8 000 – 10 000
J 10 000 – 20 000 Ku 10 900 – 20 000
K 20 000 – 40 000 Ka 20 000 – 36 000
L 40 000 – 60 000 Q 36 000 – 46 000
V 46 000 – 56 000
M 60 000 – 100 000 W 56 000 – 100 000
US Military/SACLANT
N 100 000 – 200 000
O 100 000 – 200 000

### Waveguide frequency bands

Band Frequency range [22]
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 18.0 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
E band 60 to 90 GHz
W band 75 to 110 GHz
F band 90 to 140 GHz
D band 110 to 170 GHz
Y band 325 to 500 GHz

### Comparison of radio band designation standards

The frequencies from 1–3 Hz (wavelengths from 300,000–100,000 km) have been known by the band name "tremendously low frequency" (TLF) ,[23] but the term has not been defined by the ITU.[24]

Frequency IEEE[17] EU,
NATO,
US ECM
ITU
no. abbr.
A
3 Hz 1 ELF
30 Hz 2 SLF
300 Hz 3 ULF
3 kHz 4 VLF
30 kHz 5 LF
300 kHz 6 MF
3 MHz HF 7 HF
30 MHz VHF 8 VHF
250 MHz B
300 MHz UHF 9 UHF
500 MHz C
1 GHz L D
2 GHz S E
3 GHz F 10 SHF
4 GHz C G
6 GHz H
8 GHz X I
10 GHz J
12 GHz Ku
18 GHz K
20 GHz K
27 GHz Ka
30 GHz 11 EHF
40 GHz V L
60 GHz M
75 GHz W
100 GHz
110 GHz mm
300 GHz 12 THF
3 THz

## Applications

Designations for television and FM radio broadcast frequencies vary between countries, see Television channel frequencies and FM broadcast band. Since VHF and UHF frequencies are desirable for many uses in urban areas, in North America some parts of the former television broadcasting band have been reassigned to cellular phone and various land mobile communications systems. Even within the allocation still dedicated to television, TV-band devices use channels without local broadcasters.

The Apex band in the United States was a pre-WWII allocation for VHF audio broadcasting; it was made obsolete after the introduction of FM broadcasting.

### Air band

Airband refers to VHF frequencies 108 to 137 MHz, used for navigation and voice communication with aircraft. Trans-oceanic aircraft also carry HF radio and satellite transceivers.

### Marine band

The greatest incentive for development of radio was the need to communicate with ships out of visual range of shore. From the very early days of radio, large oceangoing vessels carried powerful long-wave and medium-wave transmitters. High-frequency allocations are still designated for ships, although satellite systems have taken over some of the safety applications previously served by 500 kHz and other frequencies. 2182 kHz is a medium-wave frequency still used for marine emergency communication.

Marine VHF radio is used in coastal waters and relatively short-range communication between vessels and to shore stations. Radios are channelized, with different channels used for different purposes; marine Channel 16 is used for calling and emergencies.

Amateur radio frequency allocations vary around the world. Several bands are common for amateurs worldwide, usually in the HF part of the spectrum. Other bands are national or regional allocations only due to differing allocations for other services, especially in the VHF and UHF parts of the radio spectrum.

### Citizens' band and personal radio services

Citizens' band radio is allocated in many countries, using channelized radios in the upper HF part of the spectrum (around 27 MHz). It is used for personal, small business and hobby purposes. Other frequency allocations are used for similar services in different jurisdictions, for example UHF CB is allocated in Australia. A wide range of personal radio services exist around the world, usually emphasizing short-range communication between individuals or for small businesses, simplified license requirements or in some countries covered by a class license, and usually FM transceivers using around 1 watt or less.

### Industrial, scientific, medical

The ISM bands were initially reserved for non-communications uses of RF energy, such as microwave ovens, radio-frequency heating, and similar purposes. However, in recent years the largest use of these bands has been by short-range low-power communications systems, since users do not have to hold a radio operator's license. Cordless telephones, wireless computer networks, Bluetooth devices, and garage door openers all use the ISM bands. ISM devices do not have regulatory protection against interference from other users of the band.

### Land mobile bands

Bands of frequencies, especially in the VHF and UHF parts of the spectrum, are allocated for communication between fixed base stations and land mobile vehicle-mounted or portable transceivers. In the United States these services are informally known as business band radio. See also Professional mobile radio.

Police radio and other public safety services such as fire departments and ambulances are generally found in the VHF and UHF parts of the spectrum. Trunking systems are often used to make most efficient use of the limited number of frequencies available.

The demand for mobile telephone service has led to large blocks of radio spectrum allocated to cellular frequencies.

Reliable radio control uses bands dedicated to the purpose. Radio-controlled toys may use portions of unlicensed spectrum in the 27 MHz or 49 MHz bands, but more costly aircraft, boat, or land vehicle models use dedicated radio control frequencies near 72 MHz to avoid interference by unlicensed uses. The 21st century has seen a move to 2.4 GHz spread spectrum RC control systems.

Licensed amateur radio operators use portions of the 6-meter band in North America. Industrial remote control of cranes or railway locomotives use assigned frequencies that vary by area.

Radar applications use relatively high power pulse transmitters and sensitive receivers, so radar is operated on bands not used for other purposes. Most radar bands are in the microwave part of the spectrum, although certain important applications for meteorology make use of powerful transmitters in the UHF band.

## Notes

1. ^ ITU Radio Regulations – Article 1, Definitions of Radio Services, Article 1.2 Administration: Any governmental department or service responsible for discharging the obligations undertaken in the Constitution of the International Telecommunication Union, in the Convention of the International Telecommunication Union and in the Administrative Regulations (CS 1002)
2. ^ International Telecommunication Union's Radio Regulations, Edition of 2020.
3. ^ Colin Robinson (2003). Competition and regulation in utility markets. Edward Elgar Publishing. p. 175. ISBN 978-1-84376-230-0. Archived from the original on 2022-04-07. Retrieved 2020-11-02.
4. ^ a b Radio waves are defined by the ITU as: "electromagnetic waves of frequencies arbitrarily lower than 3000 GHz, propagated in space without artificial guide", Radio Regulations, 2020 Edition. International Telecommunication Union. Archived from the original on 2022-02-18. Retrieved 2022-02-18.
5. ^ Radio Regulations, 2020 Edition. International Telecommunication Union. Archived from the original on 2022-02-18. Retrieved 2022-02-18.
6. Gosling, William (2000). Radio Spectrum Conservation: Radio Engineering Fundamentals. Newnes. pp. 11–14. ISBN 9780750637404. Archived from the original on 2022-04-07. Retrieved 2019-11-25.
7. ^ Coutaz, Jean-Louis; Garet, Frederic; Wallace, Vincent P. (2018). Principles of Terahertz Time-Domain Spectroscopy: An Introductory Textbook. CRC Press. p. 18. ISBN 9781351356367. Archived from the original on 2023-02-21. Retrieved 2021-05-20.
8. ^ Siegel, Peter (2002). "Studying the Energy of the Universe". Education materials. NASA website. Archived from the original on 20 June 2021. Retrieved 19 May 2021.
9. ^ See detail of bands: [1] Archived 2014-07-03 at the Wayback Machine
10. ^ Frequency Plans
11. ^ For the authorized frequency bands for amateur radio use see: Authorized frequency bands
12. ^ US ARRL Amateur Radio Bands and power limits Graphical Frequency Allocations
13. ^ ITU Radio Regulations, Volume 1, Article 2; Edition of 2020. Available online at "Article 2.1: Frequency and wavelength bands" (PDF). Radio Regulations 2016 Edition. International Telecommunication Union. 1 January 2017. Archived from the original on 18 February 2022. Retrieved 18 February 2020.
14. ^ Booth, C. F. (1949). "Nomenclature of Frequencies". The Post Office Electrical Engineers' Journal. 42 (1): 47–48.
15. ^ Duncan, Christopher; Gkountouna, Olga; Mahabir, Ron (2021). Arabnia, Hamid R.; Deligiannidis, Leonidas; Shouno, Hayaru; Tinetti, Fernando G.; Tran, Quoc-Nam (eds.). "Theoretical Applications of Magnetic Fields at Tremendously Low Frequency in Remote Sensing and Electronic Activity Classification". Transactions on Computational Science and Computational Intelligence. Cham: Springer International Publishing: 235–247. doi:10.1007/978-3-030-71051-4_18. ISBN 978-3-030-71050-7.
16. ^ "Nomenclature of the frequency and wavelength bands used in telecommunications" (PDF). International Telecommunications Union. Geneva, Switzerland: International Telecommunications Union. 2015. Retrieved 7 April 2023.
17. ^ a b c Table 2 in [17]
18. ^ a b Norman Friedman (2006). The Naval Institute Guide to World Naval Weapon Systems. Naval Institute Press. pp. xiii. ISBN 978-1-55750-262-9. Archived from the original on 2023-02-21. Retrieved 2016-10-13.
19. ^ Leonid A. Belov; Sergey M. Smolskiy; Victor N. Kochemasov (2012). Handbook of RF, Microwave, and Millimeter-Wave Components. Artech House. pp. 27–28. ISBN 978-1-60807-209-5.
20. ^ NATO Allied Radio Frequency Agency (ARFA) HANDBOOK – VOLUME I; PART IV – APPENDICES, ... G-2, ... NOMENCLATURE OF THE FREQUENCY AND WAVELENGTH BANDS USED IN RADIOCOMMUNCATION.
21. ^ "www.microwaves101.com "Waveguide frequency bands and interior dimensions"". Archived from the original on 2008-02-08. Retrieved 2009-11-16.
22. ^ Duncan, Christopher; Gkountouna, Olga; Mahabir, Ron (2021). Arabnia, Hamid R.; Deligiannidis, Leonidas; Shouno, Hayaru; Tinetti, Fernando G.; Tran, Quoc-Nam (eds.). "Theoretical Applications of Magnetic Fields at Tremendously Low Frequency in Remote Sensing and Electronic Activity Classification". Transactions on Computational Science and Computational Intelligence. Cham: Springer International Publishing: 235–247. doi:10.1007/978-3-030-71051-4_18. ISBN 978-3-030-71050-7.
23. ^ "Nomenclature of the frequency and wavelength bands used in telecommunications" (PDF). International Telecommunications Union. Geneva, Switzerland: International Telecommunications Union. 2015. Retrieved 7 April 2023.

## References

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