Radio

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This article is about science and technology. For its use in audio distribution, see Radio broadcasting. For the user device, see Radio receiver. For other uses, see Radio (disambiguation).
A variety of radio antennas on Sandia Peak near Albuquerque, New Mexico, US

Radio is the technology of communicating using radio waves.<ref name="OED">"Radio". Oxford Living Dictionaries. Oxford University Press. 2019. Archived from the original on 24 March 2019. Retrieved 26 February 2019.</ref><ref name="PCMag">"Definition of radio". Encyclopedia. PCMagazine website, Ziff-Davis. 2018. Retrieved 26 February 2019.</ref><ref name="Ellingson1">Ellingson, Steven W. (2016). Radio Systems Engineering. Cambridge University Press. pp. 1–4. ISBN 978-1316785164.</ref> Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves. They are received by another antenna connected to a radio receiver. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications.

In radio communication, used in radio and television broadcasting, cell phones, two-way radios, wireless networking, and satellite communication, among numerous other uses, radio waves are used to carry information across space from a transmitter to a receiver, by modulating the radio signal (impressing an information signal on the radio wave by varying some aspect of the wave) in the transmitter. In radar, used to locate and track objects like aircraft, ships, spacecraft and missiles, a beam of radio waves emitted by a radar transmitter reflects off the target object, and the reflected waves reveal the object's location. In radio navigation systems such as GPS and VOR, a mobile navigation instrument receives radio signals from navigational radio beacons whose position is known, and by precisely measuring the arrival time of the radio waves the receiver can calculate its position on Earth. In wireless radio remote control devices like drones, garage door openers, and keyless entry systems, radio signals transmitted from a controller device control the actions of a remote device.

The noun radio is also used to mean a broadcast radio receiver.

The existence of radio waves was first proven by German physicist Heinrich Hertz on 11 November 1886.<ref name="KIT"/> In the mid 1890s, building on techniques physicists were using to study electromagnetic waves, Guglielmo Marconi developed the first apparatus for long-distance radio communication,<ref name="ieeexplore.ieee.org">Bondyopadhyay, Prebir K. (1995) "Guglielmo Marconi – The father of long distance radio communication – An engineer's tribute", 25th European Microwave Conference: Volume 2, pp. 879–85</ref> sending a wireless Morse Code message to a recipient over a kilometer away in 1895,<ref name="1890s – 1930s: Radio">"1890s – 1930s: Radio". Elon University. Archived from the original on 8 June 2022. Retrieved 14 July 2022.</ref> and the first transatlantic signal on 12 December 1901.<ref name="IEEEatlantic">Belrose, John S. (5–7 September 1995). "Radio's First Message -- Fessenden and Marconi". Institute of Electrical and Electronics Engineers. Retrieved 6 November 2022.</ref> The first commercial radio broadcast was transmitted on 2 November 1920, when the live returns of the Harding-Cox presidential election were broadcast by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA.<ref name="History of Commercial Radio">"History of Commercial Radio". Federal Communications Commission. 23 October 2020. Archived from the original on 1 January 2022. Retrieved 14 July 2022.</ref>

The emission of radio waves is regulated by law, coordinated by the International Telecommunication Union (ITU), which allocates frequency bands in the radio spectrum for various uses.

Etymology

The word "radio" is derived from the Latin word "radius", meaning "spoke of a wheel, beam of light, ray". It was first applied to communications in 1881 when, at the suggestion of French scientist Ernest Mercadier [fr], Alexander Graham Bell adopted "radiophone" (meaning "radiated sound") as an alternate name for his photophone optical transmission system.<ref>"radio (n.)". Online Etymology Dictionary. Retrieved 13 July 2022.</ref><ref>Bell, Alexander Graham (July 1881). "Production of Sound by Radiant Energy". Popular Science Monthly. pp. 329–330. [W]e have named the apparatus for the production and reproduction of sound in this way the "photophone", because an ordinary beam of light contains the rays which are operative. To avoid in future any misunderstandings upon this point, we have decided to adopt the term "radiophone", proposed by M. Mercadier, as a general term signifying the production of sound by any form of radiant energy...</ref>

Following Heinrich Hertz's discovery of the existence of radio waves in 1886, the term "Hertzian waves" was initially used for this radiation.<ref>Manning, Trevor (2009). Microwave Radio Transmission Design Guide. Artech House. p. 2.</ref> The first practical radio communications systems, developed by Guglielmo Marconi in 1894–1895, transmitted telegraph signals by radio waves,<ref name=KIT /> so radio communication was first called "wireless telegraphy". Up until about 1910 the term "wireless telegraphy" also included a variety of other experimental systems for transmitting telegraph signals without wires, including electrostatic induction, electromagnetic induction and aquatic and earth conduction, so there was a need for a more precise term referring exclusively to electromagnetic radiation.<ref name="Maver">Maver, William Jr. (1903). American Telegraphy and Encyclopedia of the Telegraph: Systems, Apparatus, Operation. New York: Maver Publishing Co. p. 333. wireless telegraphy.</ref><ref name="Steuart">Steuart, William Mott; et al. (1906). Special Reports: Telephones and Telegraphs 1902. Washington D.C.: U.S. Bureau of the Census. pp. 118–119.</ref>

The French physicist Édouard Branly, who in 1890 developed the radio wave detecting coherer, called it in French a radio-conducteur.<ref name="earlyradiohistory.us">https://earlyradiohistory.us/sec022.htm Thomas H. White, United States Early Radio History, Section 22</ref><ref>Collins, A. Frederick (10 May 1902). "The Genesis of Wireless Telegraphy". Electrical World and Engineer. p. 811.</ref> The radio- prefix was later used to form additional descriptive compound and hyphenated words, especially in Europe. For example, in early 1898 the British publication The Practical Engineer included a reference to "the radiotelegraph" and "radiotelegraphy".<ref name="earlyradiohistory.us"/><ref>"Wireless Telegraphy". The Practical Engineer. 25 February 1898. p. 174. Dr. O. J. Lodge, who preceded Marconi in making experiments in what may be called "ray" telegraphy or radiotelegraphy by a year or two, has devised a new method of sending and receiving the messages. The reader will understand that in the radiotelegraph electric waves forming the signals of the message starting from the sending instrument and travel in all directions like rays of light from a lamp, only they are invisible.</ref>

The use of "radio" as a standalone word dates back to at least 30 December 1904, when instructions issued by the British Post Office for transmitting telegrams specified that "The word 'Radio'... is sent in the Service Instructions".<ref name="earlyradiohistory.us"/><ref>"Wireless Telegraphy", The Electrical Review (London), 20 January 1905, page 108, quoting from the British Post Office's 30 December 1904 Post Office Circular.</ref> This practice was universally adopted, and the word "radio" introduced internationally, by the 1906 Berlin Radiotelegraphic Convention, which included a Service Regulation specifying that "Radiotelegrams shall show in the preamble that the service is 'Radio'".<ref name="earlyradiohistory.us"/>

The switch to "radio" in place of "wireless" took place slowly and unevenly in the English-speaking world. Lee de Forest helped popularize the new word in the United States—in early 1907, he founded the DeForest Radio Telephone Company, and his letter in the 22 June 1907 Electrical World about the need for legal restrictions warned that "Radio chaos will certainly be the result until such stringent regulation is enforced".<ref>"Interference with Wireless Messages", Electrical World, 22 June 1907, page 1270.</ref> The United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms "wireless telegraph" and "wireless telegram", by 1912 it began to promote the use of "radio" instead. The term started to become preferred by the general public in the 1920s with the introduction of broadcasting.

History

See History of radio, Invention of radio, Timeline of radio, History of broadcasting

Electromagnetic waves were predicted by James Clerk Maxwell in his 1873 theory of electromagnetism, now called Maxwell's equations, who proposed that a coupled oscillating electric field and magnetic field could travel through space as a wave, and proposed that light consisted of electromagnetic waves of short wavelength. On 11 November 1886, German physicist Heinrich Hertz, attempting to confirm Maxwell's theory, first observed radio waves he generated using a primitive spark gap transmitter.<ref name=KIT>"125 Years Discovery of Electromagnetic Waves". Karlsruhe Institute of Technology. 16 May 2022. Archived from the original on 14 July 2022. Retrieved 14 July 2022.</ref> Experiments by Hertz and physicists Jagadish Chandra Bose, Oliver Lodge, Lord Rayleigh, and Augusto Righi, among others, showed that radio waves like light demonstrated reflection, refraction, diffraction, polarization, standing waves, and traveled at the same speed as light, confirming that both light and radio waves were electromagnetic waves, differing only in frequency.<ref>Sungook Hong (2001), Wireless: From Marconi's Black-box to the Audion, MIT Press, pp. 5–10</ref> In 1895, Guglielmo Marconi developed the first radio communication system, using a spark gap transmitter to send Morse code over long distances. By December 1901, he had transmitted across the Atlantic ocean.<ref name=KIT /><ref name="ieeexplore.ieee.org"/><ref name="1890s – 1930s: Radio"/><ref name="IEEEatlantic"/> Marconi and Karl Ferdinand Braun shared the 1909 Nobel Prize in Physics "for their contributions to the development of wireless telegraphy".<ref>"The Nobel Prize in Physics 1909". NobelPrize.org. 2023. Archived from the original on 31 July 2023. Retrieved 31 July 2023.</ref>

During radio's first two decades, called the radiotelegraphy era, the primitive damped wave radio transmitters could only transmit pulses of radio waves, not the continuous waves which were needed for audio modulation, so radio was used for person-to-person commercial, diplomatic and military text messaging. Starting around 1908 industrial countries built worldwide networks of powerful transoceanic spark transmitters to exchange telegram traffic between continents and communicate with their colonies and naval fleets. During World War 1 the development of continuous wave radio transmitters, rectifying electrolytic, and crystal radio receiver detectors enabled amplitude modulation (AM) radiotelephony to be achieved by Reginald Fessenden and others, allowing sound (audio) to be transmitted. On 2 November 1920, the first commercial radio broadcast was transmitted by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA featuring live coverage of the Harding-Cox presidential election.<ref name="History of Commercial Radio"/>

Technology

Radio waves are radiated by electric charges undergoing acceleration.<ref name="Kraus">Kraus, John D. (1988). Antennas (2nd ed.). Tata-McGraw Hill. p. 50. ISBN 0074632191.</ref><ref name="Serway">Serway, Raymond; Faughn, Jerry; Vuille, Chris (2008). College Physics, 8th Ed. Cengage Learning. p. 714. ISBN 978-0495386933.</ref> They are generated artificially by time varying electric currents, consisting of electrons flowing back and forth in a metal conductor called an antenna.<ref name="Balanis">Balanis, Constantine A. (2005). Antenna theory: Analysis and Design, 3rd Ed. John Wiley and Sons. p. 10. ISBN 978-1118585733.</ref><ref name="Ellingson2">Ellingson, Steven W. (2016). Radio Systems Engineering. Cambridge University Press. pp. 16–17. ISBN 978-1316785164.</ref>

As they travel farther from the transmitting antenna, radio waves spread out so their signal strength (intensity in watts per square meter) decreases, so radio transmissions can only be received within a limited range of the transmitter, the distance depending on the transmitter power, the antenna radiation pattern, receiver sensitivity, noise level, and presence of obstructions between transmitter and receiver. An omnidirectional antenna transmits or receives radio waves in all directions, while a directional antenna or high-gain antenna transmits radio waves in a beam in a particular direction, or receives waves from only one direction.<ref name="Visser">Visser, Hubregt J. (2012). Antenna Theory and Applications. John Wiley & Sons. ISBN 978-1119990253. Retrieved 29 August 2022.</ref><ref>Zainah Md Zain; Hamzah Ahmad; Dwi Pebrianti; Mahfuzah Mustafa; Nor Rul Hasma Abdullah; Rosdiyana Samad; Maziyah Mat Noh (2020). Proceedings of the 11th National Technical Seminar on Unmanned System Technology 2019: NUSYS'19. Springer Nature. p. 535. ISBN 978-9811552816. Extract of pp. 535–536</ref><ref>"Omnidirectional Antenna - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 5 September 2022.</ref>

Radio waves travel at the speed of light in vacuum.<ref>"Electromagnetic Radiation". NASA. Archived from the original on 23 May 2016. Retrieved 18 August 2022.</ref><ref>"How far can radio waves travel in vacuum? and light waves?". Physics Stack Exchange. July 2019. Archived from the original on 18 August 2022. Retrieved 18 August 2022.</ref>

The other types of electromagnetic waves besides radio waves, infrared, visible light, ultraviolet, X-rays and gamma rays, can also carry information and be used for communication. The wide use of radio waves for telecommunication is mainly due to their desirable propagation properties stemming from their large wavelength.<ref name="Ellingson2"/>

Radio communication

Radio communication. Information such as sound is converted by a transducer such as a microphone to an electrical signal, which modulates a radio wave produced by the transmitter. A receiver intercepts the radio wave and extracts the information-bearing modulation signal, which is converted back to a human usable form with another transducer such as a loudspeaker.
Comparison of AM and FM modulated radio waves

In radio communication systems, information is carried across space using radio waves. At the sending end, the information to be sent is converted by some type of transducer to a time-varying electrical signal called the modulation signal.<ref name="Ellingson2" /><ref name="HowStuffWorks">Brain, Marshall (7 December 2000). "How Radio Works". HowStuffWorks.com. Retrieved 11 September 2009.</ref> The modulation signal may be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal consisting of a sequence of bits representing binary data from a computer. The modulation signal is applied to a radio transmitter. In the transmitter, an electronic oscillator generates an alternating current oscillating at a radio frequency, called the carrier wave because it serves to "carry" the information through the air. The information signal is used to modulate the carrier, varying some aspect of the carrier wave, impressing the information on the carrier. Different radio systems use different modulation methods:<ref name="Faruque">Faruque, Saleh (2016). Radio Frequency Modulation Made Easy. Springer Publishing. ISBN 978-3319412023. Retrieved 29 August 2022.</ref>

Many other types of modulation are also used. In some types, a carrier wave is not transmitted but just one or both modulation sidebands.<ref>Tony Dorbuck (ed.), The Radio Amateur's Handbook, Fifty-Fifth Edition, American Radio Relay League, 1977, p. 368</ref>

The modulated carrier is amplified in the transmitter and applied to a transmitting antenna which radiates the energy as radio waves. The radio waves carry the information to the receiver location.<ref>John Avison, The World of Physics, Nelson · 2014, page 367</ref> At the receiver, the radio wave induces a tiny oscillating voltage in the receiving antenna which is a weaker replica of the current in the transmitting antenna.<ref name="Ellingson2" /><ref name="HowStuffWorks" /> This voltage is applied to the radio receiver, which amplifies the weak radio signal so it is stronger, then demodulates it, extracting the original modulation signal from the modulated carrier wave. The modulation signal is converted by a transducer back to a human-usable form: an audio signal is converted to sound waves by a loudspeaker or earphones, a video signal is converted to images by a display, while a digital signal is applied to a computer or microprocessor, which interacts with human users.<ref name="Faruque" />

The radio waves from many transmitters pass through the air simultaneously without interfering with each other because each transmitter's radio waves oscillate at a different rate, in other words, each transmitter has a different frequency, measured in hertz (Hz), kilohertz (kHz), megahertz (MHz) or gigahertz (GHz). The receiving antenna typically picks up the radio signals of many transmitters. The receiver uses tuned circuits to select the radio signal desired out of all the signals picked up by the antenna and reject the others. A tuned circuit (also called resonant circuit or tank circuit) acts like a resonator, similar to a tuning fork.<ref name="HowStuffWorks" /> It has a natural resonant frequency at which it oscillates. The resonant frequency of the receiver's tuned circuit is adjusted by the user to the frequency of the desired radio station; this is called "tuning". The oscillating radio signal from the desired station causes the tuned circuit to resonate, oscillate in sympathy, and it passes the signal on to the rest of the receiver. Radio signals at other frequencies are blocked by the tuned circuit and not passed on.<ref>C-W and A-M Radio Transmitters and Receivers, United States. Department of the Army – 1952, pp. 167–168</ref>

Bandwidth

Frequency spectrum of a typical modulated AM or FM radio signal. It consists of a component C at the carrier wave frequency <math>f_c</math> with the information (modulation) contained in two narrow bands of frequencies called sidebands (SB) just above and below the carrier frequency.

A modulated radio wave, carrying an information signal, occupies a range of frequencies. The information (modulation) in a radio signal is usually concentrated in narrow frequency bands called sidebands (SB) just above and below the carrier frequency. The width in hertz of the frequency range that the radio signal occupies, the highest frequency minus the lowest frequency, is called its bandwidth (BW).<ref name="Faruque" /><ref name="Spectrum101">"Spectrum 101" (PDF). US National Aeronautics and Space Administration (NASA). February 2016. Archived (PDF) from the original on 11 February 2017. Retrieved 2 December 2019., p. 6</ref> For any given signal-to-noise ratio, an amount of bandwidth can carry the same amount of information (data rate in bits per second) regardless of where in the radio frequency spectrum it is located, so bandwidth is a measure of information-carrying capacity. The bandwidth required by a radio transmission depends on the data rate of the information (modulation signal) being sent, and the spectral efficiency of the modulation method used; how much data it can transmit in each kilohertz of bandwidth. Different types of information signals carried by radio have different data rates. For example, a television (video) signal has a greater data rate than an audio signal.<ref name="Faruque" /><ref name="Pogorel-Girard">Pogorel, Girard; Chaduc, Jean-Marc (2010). The Radio Spectrum: Managing a Strategic Resource. Wiley). ISBN 978-0470393529. Retrieved 29 August 2022.</ref>

The radio spectrum, the total range of radio frequencies that can be used for communication in a given area, is a limited resource.<ref name="Spectrum101" /><ref name="Ellingson1" /> Each radio transmission occupies a portion of the total bandwidth available. Radio bandwidth is regarded as an economic good which has a monetary cost and is in increasing demand. In some parts of the radio spectrum, the right to use a frequency band or even a single radio channel is bought and sold for millions of dollars. So there is an incentive to employ technology to minimize the bandwidth used by radio services.<ref name="Pogorel-Girard" />

A slow transition from analog to digital radio transmission technologies began in the late 1990s.<ref>Norberg, Bob (27 November 2022). "Digital Radio Is Coming, But Analog Isn't Dead Yet". The Ledger. Archived from the original on 3 September 2022. Retrieved 3 September 2022.</ref><ref>"Analogue To Digital: Radio Slow To Tune Into Transition". Financial Express. 13 October 2005. Archived from the original on 3 September 2022. Retrieved 3 September 2022.</ref> Part of the reason for this is that digital modulation can often transmit more information (a greater data rate) in a given bandwidth than analog modulation, by using data compression algorithms, which reduce redundancy in the data to be sent, and more efficient modulation. Other reasons for the transition is that digital modulation has greater noise immunity than analog, digital signal processing chips have more power and flexibility than analog circuits, and a wide variety of types of information can be transmitted using the same digital modulation.<ref name="Faruque" />

Because it is a fixed resource which is in demand by an increasing number of users, the radio spectrum has become increasingly congested in recent decades, and the need to use it more effectively is driving many additional radio innovations such as trunked radio systems, spread spectrum (ultra-wideband) transmission, frequency reuse, dynamic spectrum management, frequency pooling, and cognitive radio.<ref name="Pogorel-Girard" />

ITU frequency bands

The ITU arbitrarily 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 times a power of ten, and each covering a decade of frequency or wavelength.<ref name="Ellingson1"/><ref name="ITU2016">"Radio Regulations, 2016 Edition" (PDF). International Telecommunication Union. 3 November 2016. Retrieved 9 November 2019. Article 2, Section 1, p.27</ref> Each of these bands has a traditional name:<ref name="Nomenclature">Nomenclature of the frequency and wavelength bands used in telecommunications (PDF) (Report). Geneva: International Telecommunications Union. 2015. ITU-R V.431-8. Retrieved 6 April 2023.</ref>

Band name Abbreviation Frequency Wavelength
Extremely
low frequency		 ELF 3–30 Hz 100,000–
10,000 km
Super
low frequency		 SLF 30–300 Hz 10,000 –
1,000 km
Ultra
low frequency		 ULF 300–
3,000 Hz		 1,000–
100 km
Very
low frequency		 VLF 3–30 kHz 100–10 km
Low
frequency		 LF 30–300 kHz 10–1 km
Medium
frequency		 MF 300–
3,000 kHz		 1,000–
100 m
Band name Abbreviation Frequency Wavelength
High
frequency		 HF 3–30 MHz 100–10 m
Very
high frequency		 VHF 30–300 MHz 10–1 m
Ultra
high frequency		 UHF 300–
3,000 MHz		 100–10 cm
Super
high frequency		 SHF 3–30 GHz 10–1 cm
Extremely
high frequency		 EHF 30–300 GHz 10–1 mm
Tremendously
high frequency		 THF 300–3,000 GHz
(0.3–3.0 THz)		 1.0–0.1 mm

It can be seen that the bandwidth, the range of frequencies, contained in each band is not equal but increases exponentially as the frequency increases; each band contains ten times the bandwidth of the preceding band.<ref>Communications-electronics Management of the Electromagnetic Spectrum (Report). Headquarters, Department of the Army. United States Department of the Army. 1973. p. 2.</ref>

The term "tremendously low frequency" (TLF) has been used for wavelengths from 1–3 Hz (300,000–100,000 km),<ref>Duncan, Christopher; Gkountouna, Olga; Mahabir, Ron (2021). "Theoretical Applications of Magnetic Fields at Tremendously Low Frequency in Remote Sensing and Electronic Activity Classification". In Arabnia, Hamid R.; Deligiannidis, Leonidas; Shouno, Hayaru; Tinetti, Fernando G.; Tran, Quoc-Nam (eds.). Advances in Computer Vision and Computational Biology. Transactions on Computational Science and Computational Intelligence. Cham: Springer International Publishing. pp. 235–247. doi:10.1007/978-3-030-71051-4_18. ISBN 978-3030710507. S2CID 238934419.</ref> but the term has not been defined by the ITU.<ref name="Nomenclature"/>

Regulation

Further information: Radio regulation and Radio communication service

The airwaves are a resource shared by many users. Two radio transmitters in the same area that attempt to transmit on the same frequency will interfere with each other, causing garbled reception, so neither transmission may be received clearly.<ref name="Spectrum101"/> Interference with radio transmissions can not only have a large economic cost, but it can also be life-threatening (for example, in the case of interference with emergency communications or air traffic control).<ref name="CISA">"Radio Frequency Interference Best Practices Guidebook - CISA - Feb. 2020" (PDF). Cybersecurity and Infrastructure Security Agency SAFECOM/National Council of Statewide Interoperability Coordinators. USDepartment of Homeland Security. Retrieved 29 August 2022.</ref><ref name="Mazar">Mazar (Madjar), Haim (2016). Radio Spectrum Management: Policies, Regulations and Techniques. Wiley. ISBN 978-1118511794. Retrieved 29 August 2022.</ref>

To prevent interference between different users, the emission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU), which allocates bands in the radio spectrum for different uses.<ref name="Spectrum101" /><ref name="Ellingson1" /> Radio transmitters must be licensed by governments, under a variety of license classes depending on use, and are restricted to certain frequencies and power levels. In some classes, such as radio and television broadcasting stations, the transmitter is given a unique identifier consisting of a string of letters and numbers called a call sign, which must be used in all transmissions.<ref name="ITU1">"ARTICLE 19 Identification of stations" (PDF). International Telecommunication Union. Retrieved 29 August 2022.</ref> In order to adjust, maintain, or internally repair radiotelephone transmitters, individuals must hold a government license, such as the general radiotelephone operator license in the US, obtained by taking a test demonstrating adequate technical and legal knowledge of safe radio operation.<ref name="FCC2">"Commercial Radio Operator Types of Licenses". Federal Communications Commission. 6 May 2016. Retrieved 29 August 2022.</ref>

Exceptions to the above rules allow the unlicensed operation by the public of low power short-range transmitters in consumer products such as cell phones, cordless phones, wireless devices, walkie-talkies, citizens band radios, wireless microphones, garage door openers, and baby monitors. In the US, these fall under Part 15 of the Federal Communications Commission (FCC) regulations. Many of these devices use the ISM bands, a series of frequency bands throughout the radio spectrum reserved for unlicensed use. Although they can be operated without a license, like all radio equipment these devices generally must be type-approved before the sale.<ref name="FCC4">Dichoso, Joe (October 9, 2007). "FCC Basics of Unlicensed Transmitters" (PDF). Federal Communications Commission. Retrieved 29 August 2022.</ref>

Applications

Below are some of the most important uses of radio, organized by function.

Broadcasting

Further information: Broadcasting

Broadcasting is the one-way transmission of information from a transmitter to receivers belonging to a public audience.<ref name="Pizzi">Pizzi, Skip; Jones, Graham (2014). A Broadcast Engineering Tutorial for Non-Engineers, 4th Ed. National Association of Broadcasters, Taylor and Francis. ISBN 978-0415733397.</ref> Since the radio waves become weaker with distance, a broadcasting station can only be received within a limited distance of its transmitter.<ref name="Witten">Witten, Alan Joel (2017). Handbook of Geophysics and Archaeology. Routledge. ISBN 978-1351564588. Retrieved 30 August 2022.</ref> Systems that broadcast from satellites can generally be received over an entire country or continent. Older terrestrial radio and television are paid for by commercial advertising or governments. In subscription systems like satellite television and satellite radio the customer pays a monthly fee. In these systems, the radio signal is encrypted and can only be decrypted by the receiver, which is controlled by the company and can be deactivated if the customer does not pay.<ref name="Bonsor">Bonsor, Kevin (26 September 2001). "How Satellite Radio Works". howstuffworks.com. HowStuffWorks. Retrieved 30 August 2022.</ref>

Broadcasting uses several parts of the radio spectrum, depending on the type of signals transmitted and the desired target audience. Longwave and medium wave signals can give reliable coverage of areas several hundred kilometers across, but have a more limited information-carrying capacity and so work best with audio signals (speech and music), and the sound quality can be degraded by radio noise from natural and artificial sources. The shortwave bands have a greater potential range but are more subject to interference by distant stations and varying atmospheric conditions that affect reception.<ref name="Gosling2">Gosling, William (1998). Radio Antennas and Propagation: Radio Engineering Fundamentals. Newnes. ISBN 978-0750637411. Retrieved 30 August 2022.</ref><ref name="Griffin">Griffin, B. Whitfield (2000). Radio-electronic Transmission Fundamentals. SciTech Publishing/Noble. ISBN 978-1884932137. Retrieved 30 August 2022.</ref>

In the very high frequency band, greater than 30 megahertz, the Earth's atmosphere has less of an effect on the range of signals, and line-of-sight propagation becomes the principal mode. These higher frequencies permit the great bandwidth required for television broadcasting. Since natural and artificial noise sources are less present at these frequencies, high-quality audio transmission is possible, using frequency modulation.<ref name="Pizzi-Jones">Pizzi, Skip; Jones, Graham (2014). A Broadcast Engineering Tutorial for Non-Engineers. CRC Press/Focal Press. ISBN 978-1317906834. Retrieved 30 August 2022.</ref><ref name="Perez">Perez, Reinaldo (2013). Handbook of Electromagnetic Compatibility. Academic Press. ISBN 978-1483288970. Retrieved 30 August 2022.</ref>

Audio: Radio broadcasting

Main article: Radio broadcasting

Radio broadcasting means transmission of audio (sound) to radio receivers belonging to a public audience. Analog audio is the earliest form of radio broadcast. AM broadcasting began around 1920. FM broadcasting was introduced in the late 1930s with improved fidelity. A broadcast radio receiver is called a radio. Most radios can receive both AM and FM.<ref>Green, Clarence R.; Bourque, Robert M. (1980). The Theory and Servicing of AM, FM, and FM Stereo Receivers. Prentice-Hall. p. 6.</ref>

1100 W AM broadcasting transmitter
Mast radiator antenna of AM radio station
Panasonic AM radio from 1964
  • AM (amplitude modulation) – in AM, the amplitude (strength) of the radio carrier wave is varied by the audio signal. AM broadcasting, the oldest broadcasting technology, is allowed in the AM broadcast bands, between 148–283 kHz in the low frequency (LF) band for longwave broadcasts and between 526–1706 kHz in the medium frequency (MF) band for medium-wave broadcasts.<ref>"Appendix C: Glossary" (PDF). Radio – Preparing for the Future (Report). London: Ofcom. October 2005. p. 2.</ref> Because waves in these bands travel as ground waves following the terrain, AM radio stations can be received beyond the horizon at hundreds of miles distance, but AM has lower fidelity than FM. Radiated power (ERP) of AM stations in the US is usually limited to a maximum of 10 kW, although a few (clear-channel stations) are allowed to transmit at 50 kW. AM stations broadcast in monaural audio; AM stereo broadcast standards exist in most countries, but the radio industry has failed to upgrade to them, due to lack of demand.<ref name=Gupta/>
FM broadcast transmitter of radio station KWNR, Las Vegas, with a power of 35 kW on 95.5 MHz
FM broadcasting antenna
AM/FM boombox radio with FM whip antenna
FM car radio's interface display
"Roberts" radio for DAB
A single DAB station transmits a 1,500 kHz bandwidth signal that carries from 9–12 channels of digital audio modulated by OFDM from which the listener can choose. Broadcasters can transmit a channel at a range of different bit rates, so different channels can have different audio quality. In different countries DAB stations broadcast in either Band III (174–240 MHz) or L band (1.452–1.492 GHz) in the UHF range, so like FM reception is limited by the visual horizon to about 40 miles (64 km).<ref>Trends in Radio Research: Diversity, innovation, and policies. Cambridge Scholars Publishing. 2018. p. 263.</ref><ref name=Hoeg-Lauterbach>Hoeg, Wolfgang; Lauterbach, Thomas (2004). Digital Audio Broadcasting: Principles and applications of digital radio. John Wiley & Sons. ISBN 978-0470871423. Retrieved 30 August 2022.</ref>
  • Digital Radio Mondiale (DRM) is a competing digital terrestrial radio standard developed mainly by broadcasters as a higher spectral efficiency replacement for legacy AM and FM broadcasting. Mondiale means "worldwide" in French and Italian; DRM was developed in 2001, and is currently supported by 23 countries, and adopted by some European and Eastern broadcasters beginning in 2003. The DRM30 mode uses the commercial broadcast bands below 30 MHz, and is intended as a replacement for standard AM broadcast on the longwave, mediumwave, and shortwave bands. The DRM+ mode uses VHF frequencies centered around the FM broadcast band, and is intended as a replacement for FM broadcasting. It is incompatible with existing radio receivers, so it requires listeners to purchase a new DRM receiver. The modulation used is a form of OFDM called COFDM in which, up to 4 carriers are transmitted on a channel formerly occupied by a single AM or FM signal, modulated by quadrature amplitude modulation (QAM).<ref name=ETSI-201-980/><ref name=Berg1/>
The DRM system is designed to be as compatible as possible with existing AM and FM radio transmitters, so that much of the equipment in existing radio stations can continue in use, augmented with DRM modulation equipment.<ref name=ETSI-201-980>DRM System Specification (PDF) (vers. 4.2.1). Geneva, CH: European Broadcasting Union. January 2021. p. 178. ETSI ES 201 980. Retrieved 19 April 2018 – via ETSI.org.</ref><ref name=Berg1>Berg, Jerome S. (2008). Broadcasting on the Short Waves: 1945 to today. McFarland. ISBN 978-0786451982. Retrieved 30 August 2022.</ref>
Volkswagen's RNS-510 receiver supports Sirius Satellite Radio.

Video: Television broadcasting

Main article: Television broadcasting

Television broadcasting is the transmission of moving images by radio, which consist of sequences of still images, which are displayed on a screen on a television receiver (a "television" or TV) along with a synchronized audio (sound) channel. Television (video) signals occupy a wider bandwidth than broadcast radio (audio) signals. Analog television, the original television technology, required 6 MHz, so the television frequency bands are divided into 6 MHz channels, now called "RF channels".<ref name="Enticknap">Enticknap, Leo Douglas Graham (2005). Moving Image Technology: From Zoetrope to Digital. Wallflower Press (Columbia University Press). ISBN 978-1904764069. Retrieved 31 August 2022.</ref>

The current television standard, introduced beginning in 2006, is a digital format called high-definition television (HDTV), which transmits pictures at higher resolution, typically 1080 pixels high by 1920 pixels wide, at a rate of 25 or 30 frames per second. Digital television (DTV) transmission systems, which replaced older analog television in a transition beginning in 2006, use image compression and high-efficiency digital modulation such as OFDM and 8VSB to transmit HDTV video within a smaller bandwidth than the old analog channels, saving scarce radio spectrum space. Therefore, each of the 6 MHz analog RF channels now carries up to 7 DTV channels – these are called "virtual channels". Digital television receivers have different behavior in the presence of poor reception or noise than analog television, called the "digital cliff" effect. Unlike analog television, in which increasingly poor reception causes the picture quality to gradually degrade, in digital television picture quality is not affected by poor reception until, at a certain point, the receiver stops working and the screen goes black.<ref name="Starks">Starks, M. (2013). The Digital Television Revolution: Origins to Outcomes. Springer. ISBN 978-1137273345. Retrieved 31 August 2022.</ref><ref name="Brice">Brice, Richard (2002). Newnes Guide to Digital TV. Newnes. ISBN 978-0750657211. Retrieved 31 August 2022.</ref>

Television studio control room, Celebro Studios, London
A television broadcasting antenna
A modern flatscreen television receiver
(left) DISH Network's Super Dish 121 mounted on a rooftop. (right) A residential tower block with TV satellite dishes used by various users

Time

Government standard frequency and time signal services operate time radio stations which continuously broadcast extremely accurate time signals produced by atomic clocks, as a reference to synchronize other clocks.<ref name="Weik">Weik, Martin H. (2000). "standard frequency and time signal". Computer Science and Communications Dictionary. Computer Science and Communications Dictionary. Springer. p. 1649. doi:10.1007/1-4020-0613-6_18062. ISBN 978-0792384250. Retrieved 1 September 2022.</ref> Examples are BPC, DCF77, JJY, MSF, RTZ, TDF, WWV, and YVTO.<ref name="RadioNavAids">Radio Aids to Navigation, Publication 117, Chapter 2, Radio Time Signals. Lighthouse Press. 2005. ISBN 978-1577855361. Retrieved 1 September 2022.</ref> One use is in radio clocks and watches, which include an automated receiver that periodically (usually weekly) receives and decodes the time signal and resets the watch's internal quartz clock to the correct time, thus allowing a small watch or desk clock to have the same accuracy as an atomic clock. Government time stations are declining in number because GPS satellites and the Internet Network Time Protocol (NTP) provide equally accurate time standards.<ref name="NPR">"What Closing A Government Radio Station Would Mean For Your Clocks". National Public Radio, Weekend Edition. Retrieved 1 September 2022.</ref>

Two-way voice communication

Main article: Two-way radio
Cellphones typical of Japan in the early 21st century.
File:Honor 50 Pro front.png
Modern smartphone
Cellular phone tower shared by antennas belonging to 3 different networks.

A two-way radio is an audio transceiver, a receiver and transmitter in the same device, used for bidirectional person-to-person voice communication with other users with similar radios. An older term for this mode of communication is radiotelephony. The radio link may be half-duplex, as in a walkie-talkie, using a single radio channel in which only one radio can transmit at a time, so different users take turns talking, pressing a "push to talk" button on their radio which switches off the receiver and switches on the transmitter. Or the radio link may be full duplex, a bidirectional link using two radio channels so both people can talk at the same time, as in a cell phone.<ref name="Frenzel">Frenzel, Louis (2017). Electronics Explained: Fundamentals for Engineers, Technicians, and Makers. Newnes. ISBN 978-0128118795. Retrieved 2 September 2022.</ref>

  • Cell phone – a portable wireless telephone that is connected to the telephone network by radio signals exchanged with a local antenna at a cellular base station (cell tower).<ref name="HowCellPhonesWork">Brain, Marshall; Tyson, Jeff; Layton, Julia (2018). "How Cell Phones Work". How Stuff Works. InfoSpace Holdings LLC. Retrieved 31 December 2018.</ref> The service area covered by the provider is divided into small geographical areas called "cells", each served by a separate base station antenna and multichannel transceiver. All the cell phones in a cell communicate with this antenna on separate frequency channels, assigned from a common pool of frequencies. The purpose of cellular organization is to conserve radio bandwidth by frequency reuse. Low power transmitters are used so the radio waves used in a cell do not travel far beyond the cell, allowing the same frequencies to be reused in geographically separated cells. When a user carrying a cellphone crosses from one cell to another, his phone is automatically "handed off" seamlessly to the new antenna and assigned new frequencies. Cellphones have a highly automated full duplex digital transceiver using OFDM modulation using two digital radio channels, each carrying one direction of the bidirectional conversation, as well as a control channel that handles dialing calls and "handing off" the phone to another cell tower. Older 2G, 3G, and 4G networks use frequencies in the UHF and low microwave range, between 700 MHz and 3 GHz. The cell phone transmitter adjusts its power output to use the minimum power necessary to communicate with the cell tower; 0.6 W when near the tower, up to 3 W when farther away. Cell tower channel transmitter power is 50 W. Current generation phones, called smartphones, have many functions besides making telephone calls, and therefore have several other radio transmitters and receivers that connect them with other networks: usually a Wi-Fi modem, a Bluetooth modem, and a GPS receiver.<ref name="Lawson">Lawson, Stephen. "Ten Ways Your Smartphone Knows Where You Are". PCWorld. Retrieved 2 September 2022.</ref><ref name=Zander>Guowang Miao; Jens Zander; Ki Won Sung; Ben Slimane (2016). Fundamentals of Mobile Data Networks. Cambridge University Press. ISBN 978-1107143210.</ref><ref>"Cellular Telephone Basics". Privateline.com. 1 January 2006. p. 2. Archived from the original on 17 April 2012. Retrieved 2 September 2022.</ref>
(left) 5G millimeter wave antenna, Germany (right) Polish 5G smartphones
  • 5G cellular network – next-generation cellular networks which began deployment in 2019. Their major advantage is much higher data rates than previous cellular networks, up to 10 Gbps; 100 times faster than the previous cellular technology, 4G LTE. The higher data rates are achieved partly by using higher frequency radio waves, in the higher microwave band 3–6 GHz, and millimeter wave band, around 28 and 39 GHz. Since these frequencies have a shorter range than previous cellphone bands, the cells will be smaller than the cells in previous cellular networks which could be many miles across. Millimeter-wave cells will only be a few blocks long, and instead of a cell base station and antenna tower, they will have many small antennas attached to utility poles and buildings.<ref name="S.Brown">Brown, Sara. "5G, explained". mitsloan.mit.edu. MIT Sloan School of Management. Retrieved 2 September 2022.</ref><ref name="Osseiran-Monserrat-Marsch">Osseiran, Afif; Monserrat, Jose F.; Marsch, Patrick (2016). 5G Mobile and Wireless Communications Technology. Cambridge University Press. ISBN 978-1107130098. Retrieved 2 September 2022.</ref>
Satellite phones, showing the large antennas needed to communicate with the satellite
  • Satellite phone (satphone) – a portable wireless telephone similar to a cell phone, connected to the telephone network through a radio link to an orbiting communications satellite instead of through cell towers. They are more expensive than cell phones; but their advantage is that, unlike a cell phone which is limited to areas covered by cell towers, satphones can be used over most or all of the geographical area of the Earth. In order for the phone to communicate with a satellite using a small omnidirectional antenna, first-generation systems use satellites in low Earth orbit, about 400–700 miles (640–1,100 km) above the surface. With an orbital period of about 100 minutes, a satellite can only be in view of a phone for about 4 – 15 minutes, so the call is "handed off" to another satellite when one passes beyond the local horizon. Therefore, large numbers of satellites, about 40 to 70, are required to ensure that at least one satellite is in view continuously from each point on Earth. Other satphone systems use satellites in geostationary orbit in which only a few satellites are needed, but these cannot be used at high latitudes because of terrestrial interference.<ref name="Chandler">Chandler, Nathan (13 February 2013). "How Satellite Phones Work". howstuffworks.com. HowStuffWorks. Retrieved 2 September 2022.</ref><ref name="TW">"Satellite Phone : Functioning/Working Of Satellite Phone". tutorialsweb.com. Tutorials Web. Retrieved 2 September 2022.</ref>
  • Cordless phone – a landline telephone in which the handset is portable and communicates with the rest of the phone by a short-range full duplex radio link, instead of being attached by a cord. Both the handset and the base station have low-power radio transceivers that handle the short-range bidirectional radio link.<ref>McComb, Gordon (October 1982). "Never Miss a Call: PS Buyer's Guide to Cordless Phones". Popular Science. pp. 84–85 – via Google Books.</ref> As of 2022, cordless phones in most nations use the DECT transmission standard.<ref>Guy, Nick (13 July 2022). "Wirecutter: The Best Cordless Phone". The New York Times. ISSN 0362-4331. Retrieved 7 September 2022.</ref>
Motorola SCR-536 from WW2, the first walkie-talkie
  • Land mobile radio system – short-range mobile or portable half-duplex radio transceivers operating in the VHF or UHF band that can be used without a license. They are often installed in vehicles, with the mobile units communicating with a dispatcher at a fixed base station. Special systems with reserved frequencies are used by first responder services; police, fire, ambulance, and emergency services, and other government services. Other systems are made for use by commercial firms such as taxi and delivery services. VHF systems use channels in the range 30–50 MHz and 150–172 MHz. UHF systems use the 450–470 MHz band and in some areas the 470–512 MHz range. In general, VHF systems have a longer range than UHF but require longer antennas. AM or FM modulation is mainly used, but digital systems such as DMR are being introduced. The radiated power is typically limited to 4 watts.<ref name="HowCellPhonesWork"/> These systems have a fairly limited range, usually 3 to 20 miles (4.8 to 32 km) depending on terrain. Repeaters installed on tall buildings, hills, or mountain peaks are often used to increase the range when it is desired to cover a larger area than line-of-sight. Examples of land mobile systems are CB, FRS, GMRS, and MURS. Modern digital systems, called trunked radio systems, have a digital channel management system using a control channel that automatically assigns frequency channels to user groups.<ref>U.S. Fire Administration (June 2016). Voice Radio Communications Guide for the Fire Service (PDF) (Report). Washington, D.C.: Federal Emergency Management Agency. pp. 33–34. Retrieved 7 September 2022.</ref>
Firefighter using modern walkie-talkie
VHF marine radio on a ship
  • Marine radio – medium-range transceivers on ships, used for ship-to-ship, ship-to-air, and ship-to-shore communication with harbormasters They use FM channels between 156 and 174 MHz in the VHF band with up to 25 watts power, giving them a range of about 60 miles (97 km). Some channels are half-duplex and some are full-duplex, to be compatible with the telephone network, to allow users to make telephone calls through a marine operator.<ref>Fletcher, Sue (2002). A Boater's Guide to VHF and GMDSS. Camden, Maine: International Marine/McGraw-Hill. ISBN 0071388028. OCLC 48674566.</ref>
  • Amateur radio – long-range half-duplex two-way radio used by hobbyists for non-commercial purposes: recreational radio contacts with other amateurs, volunteer emergency communication during disasters, contests, and experimentation. Radio amateurs must hold an amateur radio license and are given a unique callsign that must be used as an identifier in transmissions. Amateur radio is restricted to small frequency bands, the amateur radio bands, spaced throughout the radio spectrum starting at 136 kHz. Within these bands, amateurs are allowed the freedom to transmit on any frequency using a wide variety of voice modulation methods, along with other forms of communication, such as slow-scan television (SSTV), and radioteletype (RTTY). Additionally, amateurs are among the only radio operators still using Morse code radiotelegraphy.<ref>The ARRL Handbook for Radio Communications 2017 (94th ed.). Newington, Connecticut: American Radio Relay League. 2016. ISBN 978-1625950628. OCLC 961215964.</ref>

One-way voice communication

One way, unidirectional radio transmission is called simplex.

  • Baby monitor – a crib-side appliance for parents of infants that transmits the baby's sounds to a receiver carried by the parent, so they can monitor the baby while they are in other parts of the house.<ref name="HSW1">Brain, Marshall (11 February 2021). "Radio basics: Real life examples". How radio works. How Stuff Works website. Retrieved 27 August 2022.</ref> The wavebands used vary by region, but analog baby monitors generally transmit with low power in the 16, 9.3–49.9 or 900 MHz wavebands, and digital systems in the 2.4 GHz waveband.<ref>Radiofrequency Toolkit for Environmental Health Practitioners (PDF) (Report). Vancouver, British Columbia, Canada: British Columbia Centre for Disease Control/National Collaborating Centre for Environmental Health. p. 26. ISBN 978-1926933481.</ref> Many baby monitors have duplex channels so the parent can talk to the baby, and cameras to show video of the baby.<ref>"Best Baby Monitor Buying Guide". Consumer Reports. 24 April 2016. Retrieved 9 September 2022.</ref>
  • Wireless microphone – a battery-powered microphone with a short-range transmitter that is handheld or worn on a person's body which transmits its sound by radio to a nearby receiver unit connected to a sound system. Wireless microphones are used by public speakers, performers, and television personalities so they can move freely without trailing a microphone cord. Traditionally, analog models transmit in FM on unused portions of the television broadcast frequencies in the VHF and UHF bands. Some models transmit on two frequency channels for diversity reception to prevent nulls from interrupting transmission as the performer moves around.<ref>Eargle, John (2005). "Overview of Wireless Microphone Technology". The Microphone Book (2nd ed.). Oxford: Focal Press. pp. 142–151. ISBN 978-1136118067 – via Google Books.</ref> Some models use digital modulation to prevent unauthorized reception by scanner radio receivers; these operate in the 900 MHz, 2.4 GHz or 6 GHz ISM bands.<ref>Bell, Dee Ana (1 November 2012). "Avoiding Audio Problems with Wireless Microphone Systems". TV Technology. Retrieved 10 September 2022.</ref> European standards also support wireless multichannel audio systems (WMAS) that can better support the use of large numbers of wireless microphones at a single event or venue. As of 2021, U.S. regulators were considering adopting rules for WMAS.<ref>Vernon, Tom (28 August 2021). "Wireless Mic Industry Debates WMAS Technology". Radio World. Retrieved 10 September 2022.</ref>

Data communication

Further information: Data transmission, Telemetry, and Wireless
  • Wireless networking – automated radio links which transmit digital data between computers and other wireless devices using radio waves, linking the devices together transparently in a computer network. Computer networks can transmit any form of data: in addition to email and web pages, they also carry phone calls (VoIP), audio, and video content (called streaming media). Security is more of an issue for wireless networks than for wired networks since anyone nearby with a wireless modem can access the signal and attempt to log in. The radio signals of wireless networks are encrypted using WPA.<ref name="Lewis-Davis">Lewis, Barry D.; Davis, Peter T. (2004). Wireless Networks For Dummies. John Wiley & Sons. ISBN 978-0764579776. Retrieved 12 September 2022.</ref>
A laptop (with Wi-Fi module) and a typical home wireless router (on the right) connecting it to the Internet. The laptop shows its own photo
    • Wireless LAN (wireless local area network or Wi-Fi) – based on the IEEE 802.11 standards, these are the most widely used computer networks, used to implement local area networks without cables, linking computers, laptops, cell phones, video game consoles, smart TVs and printers in a home or office together, and to a wireless router connecting them to the Internet with a wire or cable connection. Wireless routers in public places like libraries, hotels and coffee shops create wireless access points (hotspots) to allow the public to access the Internet with portable devices like smartphones, tablets or laptops. Each device exchanges data using a wireless modem (wireless network interface controller), an automated microwave transmitter and receiver with an omnidirectional antenna that works in the background, exchanging data packets with the router. Wi-Fi uses channels in the 2.4 GHz and 5 GHz ISM bands with OFDM (orthogonal frequency-division multiplexing) modulation to transmit data at high rates. The transmitters in Wi-Fi modems are limited to a radiated power of 200 mW to 1 watt, depending on country. They have a maximum indoor range of about 150 ft (50 m) on 2.4 GHz and 50 ft (20 m) on 5 GHz.<ref name="Lowe" />
Neighborhood wireless WAN router on telephone pole
    • Wireless WAN (wireless wide area network, WWAN) – a variety of technologies that provide wireless internet access over a wider area than Wi-Fi networks do – from an office building to a campus to a neighborhood, or to an entire city. The most common technologies used are: cellular modems, that exchange computer data by radio with cell towers; satellite internet access; and lower frequencies in the UHF band, which have a longer range than Wi-Fi frequencies. Since WWAN networks are much more expensive and complicated to administer than Wi-Fi networks, their use so far has generally been limited to private networks operated by large corporations.<ref name="Lowe">Lowe, Doug (2020). Networking For Dummies. John Wiley & Sons. ISBN 978-1119748670. Retrieved 12 September 2022.</ref>
    • Bluetooth – a very short-range wireless interface on a portable wireless device used as a substitute for a wire or cable connection, mainly to exchange files between portable devices and connect cellphones and music players with wireless headphones. In the most widely used mode, transmission power is limited to 1 milliwatt, giving it a very short range of up to 10 m (30 feet). The system uses frequency-hopping spread spectrum transmission, in which successive data packets are transmitted in a pseudorandom order on one of 79 1 MHz Bluetooth channels between 2.4 and 2.83 GHz in the ISM band. This allows Bluetooth networks to operate in the presence of noise, other wireless devices and other Bluetooth networks using the same frequencies, since the chance of another device attempting to transmit on the same frequency at the same time as the Bluetooth modem is low. In the case of such a "collision", the Bluetooth modem just retransmits the data packet on another frequency.<ref name="Muller">Muller, Nathan J. (2002). Networking A to Z. McGraw-Hill Professional. pp. 45–47. ISBN 978-0071429139. Archived from the original on 24 June 2021. Retrieved 12 September 2022.</ref>
    • Packet radio – a long-distance peer-to-peer wireless ad-hoc network in which data packets are exchanged between computer-controlled radio modems (transmitter/receivers) called nodes, which may be separated by miles, and maybe mobile. Each node only communicates with neighboring nodes, so packets of data are passed from node to node until they reach their destination using the X.25 network protocol. Packet radio systems are used to a limited degree by commercial telecommunications companies and by the amateur radio community.<ref name="Silver">Silver, H. Ward (2008). The ARRL Extra Class License Manual for Ham Radio. American Radio Relay League. ISBN 978-0872591356. Retrieved 12 September 2022.</ref>
  • Text messaging (texting) – this is a service on cell phones, allowing a user to type a short alphanumeric message and send it to another phone number, and the text is displayed on the recipient's phone screen. It is based on the Short Message Service (SMS) which transmits using spare bandwidth on the control radio channel used by cell phones to handle background functions like dialing and cell handoffs. Due to technical limitations of the channel, text messages are limited to 160 alphanumeric characters.<ref name="Hillebrand">Hillebrand, Friedhelm (2010). Short Message Service (SMS): The Creation of Personal Global Text Messaging. John Wiley & Sons. ISBN 978-0470689936. Retrieved 12 September 2022.</ref>
Parabolic antennas of microwave relay links on tower in Australia
  • Microwave relay – a long-distance high bandwidth point-to-point digital data transmission link consisting of a microwave transmitter connected to a dish antenna that transmits a beam of microwaves to another dish antenna and receiver. Since the antennas must be in line-of-sight, distances are limited by the visual horizon to 30–40 miles (48–64 km). Microwave links are used for private business data, wide area computer networks (WANs), and by telephone companies to transmit long-distance phone calls and television signals between cities.<ref name="McGregor-Driscoll-Mcdowell">McGregor, Michael A.; Driscoll, Paul D.; Mcdowell, Walter (2016). Head's Broadcasting in America: A Survey of Electronic Media. Routledge. ISBN 978-1317347927. Retrieved 12 September 2022.</ref><ref name="EIA">Radio-Electronics-Television Manufacturers Association. Engineering Department (1955). "Microwave Relay Systems for Communications". Electronic Industries Association. Retrieved 12 September 2022.</ref>
  • Telemetry – automated one-way (simplex) transmission of measurements and operation data from a remote process or device to a receiver for monitoring. Telemetry is used for in-flight monitoring of missiles, drones, satellites, and weather balloon radiosondes, sending scientific data back to Earth from interplanetary spacecraft, communicating with electronic biomedical sensors implanted in the human body, and well logging. Multiple channels of data are often transmitted using frequency-division multiplexing or time-division multiplexing.<ref name="Bailey">Bailey, David (2003). Practical Radio Engineering and Telemetry for Industry. Elsevier. ISBN 978-0080473895. Retrieved 12 September 2022.</ref> Telemetry is starting to be used in consumer applications such as:
RFID tag from a DVD
  • Radio Frequency Identification (RFID) – identification tags containing a tiny radio transponder (receiver and transmitter) which are attached to merchandise. When it receives an interrogation pulse of radio waves from a nearby reader unit, the tag transmits back an ID number, which can be used to inventory goods. Passive tags, the most common type, have a chip powered by the radio energy received from the reader, rectified by a diode, and can be as small as a grain of rice. They are incorporated in products, clothes, railroad cars, library books, airline baggage tags and are implanted under the skin in pets and livestock (microchip implant) and even people. Privacy concerns have been addressed with tags that use encrypted signals and authenticate the reader before responding. Passive tags use 125–134 kHz, 13, 900 MHz and 2.4 and 5 GHz ISM bands and have a short range. Active tags, powered by a battery, are larger but can transmit a stronger signal, giving them a range of hundreds of meters.<ref name="Hunt-Puglia-Puglia">Hunt, V. Daniel; Puglia, Albert; Puglia, Mike (2007). RFID: A Guide to Radio Frequency Identification. John Wiley & Sons. ISBN 978-0470112243. Retrieved 12 September 2022.</ref>
  • Submarine communication – When submerged, submarines are cut off from all ordinary radio communication with their military command authorities by the conductive seawater. However radio waves of low enough frequencies, in the VLF (30 to 3 kHz) and ELF (below 3 kHz) bands are able to penetrate seawater. Navies operate large shore transmitting stations with power output in the megawatt range to transmit encrypted messages to their submarines in the world's oceans. Due to the small bandwidth, these systems cannot transmit voice, only text messages at a slow data rate. The communication channel is one-way, since the long antennas needed to transmit VLF or ELF waves cannot fit on a submarine. VLF transmitters use miles long wire antennas like umbrella antennas. A few nations use ELF transmitters operating around 80 Hz, which can communicate with submarines at lower depths. These use even larger antennas called ground dipoles, consisting of two ground (Earth) connections 23–60 km (14–37 mi) apart, linked by overhead transmission lines to a power plant transmitter.<ref name="White">White, Ryan (17 December 2021). "How do submarines communicate with the outside world?". navalpost.com. Naval Post. Retrieved 12 September 2022.</ref><ref name="NRR">"Naval Research Reviews, Vol. 27". Superintendent of Government Documents. 1974. Retrieved 12 September 2022.</ref>

Space communication

Satellite Communications Center Dubna in Russia<ref>"Ground infrastructure". Russian Satellite Communications Company.</ref>

This is radio communication between a spacecraft and an Earth-based ground station, or another spacecraft. Communication with spacecraft involves the longest transmission distances of any radio links, up to billions of kilometers for interplanetary spacecraft. In order to receive the weak signals from distant spacecraft, satellite ground stations use large parabolic "dish" antennas up to 25 metres (82 ft) in diameter and extremely sensitive receivers. High frequencies in the microwave band are used, since microwaves pass through the ionosphere without refraction, and at microwave frequencies the high-gain antennas needed to focus the radio energy into a narrow beam pointed at the receiver are small and take up a minimum of space in a satellite. Portions of the UHF, L, C, S, ku and ka band are allocated for space communication. A radio link that transmits data from the Earth's surface to a spacecraft is called an uplink, while a link that transmits data from the spacecraft to the ground is called a downlink.<ref name="NASA3">"State-of-the-Art of Small Spacecraft Technology, 9.0 - Communications". nasa.gov. National Aeronautics and Space Administration. 16 October 2021. Retrieved 11 September 2022.</ref>

Communications satellite belonging to Azerbaijan
  • Communication satellite – an artificial satellite used as a telecommunications relay to transmit data between widely separated points on Earth. These are used because the microwaves used for telecommunications travel by line of sight and so cannot propagate around the curve of the Earth. As of 1 January 2021, there were 2,224 communications satellites in Earth orbit.<ref name="UCSdatabase">"UCS Satellite Database". Union of Concerned Scientists. 1 January 2021. Retrieved 21 May 2021.</ref> Most are in geostationary orbit 22,200 miles (35,700 km) above the equator, so that the satellite appears stationary at the same point in the sky, so the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track it. In a satellite ground station a microwave transmitter and large satellite dish antenna transmit a microwave uplink beam to the satellite. The uplink signal carries many channels of telecommunications traffic, such as long-distance telephone calls, television programs, and internet signals, using a technique called frequency-division multiplexing (FDM). On the satellite, a transponder receives the signal, translates it to a different downlink frequency to avoid interfering with the uplink signal, and retransmits it down to another ground station, which may be widely separated from the first. There the downlink signal is demodulated and the telecommunications traffic it carries is sent to its local destinations through landlines. Communication satellites typically have several dozen transponders on different frequencies, which are leased by different users.<ref name="Marsten">Marsten, Richard B. (2014). Communication Satellite Systems Technology. Academic Press. ISBN 978-1483276816. Retrieved 11 September 2022.</ref>
  • Direct broadcast satellite – a geostationary communication satellite that transmits retail programming directly to receivers in subscriber's homes and vehicles on Earth, in satellite radio and TV systems. It uses a higher transmitter power than other communication satellites, to allow the signal to be received by consumers with a small unobtrusive antenna. For example, satellite television uses downlink frequencies from 12.2 to 12.7 GHz in the ku band transmitted at 100 to 250 watts, which can be received by relatively small 43–80 cm (17–31 in) satellite dishes mounted on the outside of buildings.<ref name="rfwirelessworld">"Satellite TV-Direct Broadcast Satellite System, DBS TV". rfwireless-world.com. RF Wireless World. Retrieved 11 September 2022.</ref>

Radar

Main article: Radar
Military air traffic controller on US Navy aircraft carrier monitors aircraft on radar screen

Radar is a radiolocation method used to locate and track aircraft, spacecraft, missiles, ships, vehicles, and also to map weather patterns and terrain. A radar set consists of a transmitter and receiver.<ref name="HowRadarWorks">Brain, Marshall (2020). "How radar works". How Stuff Works. Retrieved 3 September 2022.</ref><ref name="Skolnik">Skolnik, Merrill (2021). "Radar". Encyclopædia Britannica online. Encyclopædia Britannica Inc. Retrieved 3 September 2022.</ref> The transmitter emits a narrow beam of radio waves which is swept around the surrounding space. When the beam strikes a target object, radio waves are reflected back to the receiver. The direction of the beam reveals the object's location. Since radio waves travel at a constant speed close to the speed of light, by measuring the brief time delay between the outgoing pulse and the received "echo", the range to the target can be calculated. The targets are often displayed graphically on a map display called a radar screen. Doppler radar can measure a moving object's velocity, by measuring the change in frequency of the return radio waves due to the Doppler effect.<ref>"JetStream". www.noaa.gov.</ref>

Radar sets mainly use high frequencies in the microwave bands, because these frequencies create strong reflections from objects the size of vehicles and can be focused into narrow beams with compact antennas.<ref name="Skolnik" /> Parabolic (dish) antennas are widely used. In most radars the transmitting antenna also serves as the receiving antenna; this is called a monostatic radar. A radar which uses separate transmitting and receiving antennas is called a bistatic radar.<ref Name="Chernyak">Chernyak, Victor S. (1998). Fundamentals of multisite radar systems: multistatic radars and multiradar systems. CRC Press. pp. 3, 149. ISBN 9056991655.</ref>

ASR-8 airport surveillance radar antenna. It rotates once every 4.8 seconds. The rectangular antenna on top is the secondary radar.
  • Airport surveillance radar – In aviation, radar is the main tool of air traffic control. A rotating dish antenna sweeps a vertical fan-shaped beam of microwaves around the airspace and the radar set shows the location of aircraft as "blips" of light on a display called a radar screen. Airport radar operates at 2.7 – 2.9 GHz in the microwave S band. In large airports the radar image is displayed on multiple screens in an operations room called the TRACON (Terminal Radar Approach Control), where air traffic controllers direct the aircraft by radio to maintain safe aircraft separation.<ref name="FAA">"Airport Surveillance Radar". Air traffic control, technology. US Federal Aviation Administration website. 2020. Retrieved 3 September 2022.</ref>
  • Electronic countermeasures (ECM) – Military defensive electronic systems designed to degrade enemy radar effectiveness, or deceive it with false information, to prevent enemies from locating local forces. It often consists of powerful microwave transmitters that can mimic enemy radar signals to create false target indications on the enemy radar screens.<ref name="Artech-Horizon House">International Electronic Countermeasures Handbook. Artech/Horizon House. 2004. ISBN 978-1580538985. Retrieved 11 September 2022.</ref>
Rotating marine radar antenna on a ship

Radiolocation

Main article: Radiolocation

Radiolocation is a generic term covering a variety of techniques that use radio waves to find the location of objects, or for navigation.<ref name="Sharp-Yu">Sharp, Ian; Yu, Kegen (2018). Wireless Positioning: Principles and Practice, Navigation: Science and Technology. Springer. ISBN 978-9811087912. Retrieved 10 September 2022.</ref>

An early iPhone with its GPS navigation app in use.
A personal navigation assistant by Garmin, which uses GPS to give driving directions to a destination.
    • Global Positioning System (GPS) – The most widely used satellite navigation system, maintained by the US Air Force, which uses a constellation of 31 satellites in low Earth orbit. The orbits of the satellites are distributed so at any time at least four satellites are above the horizon over each point on Earth. Each satellite has an onboard atomic clock and transmits a continuous radio signal containing a precise time signal as well as its current position. Two frequencies are used, 1.2276 and 1.57542 GHz. Since the velocity of radio waves is virtually constant, the delay of the radio signal from a satellite is proportional to the distance of the receiver from the satellite. By receiving the signals from at least four satellites a GPS receiver can calculate its position on Earth by comparing the arrival time of the radio signals. Since each satellite's position is known precisely at any given time, from the delay the position of the receiver can be calculated by a microprocessor in the receiver. The position can be displayed as latitude and longitude, or as a marker on an electronic map. GPS receivers are incorporated in almost all cellphones and in vehicles such as automobiles, aircraft, and ships, and are used to guide drones, missiles, cruise missiles, and even artillery shells to their target, and handheld GPS receivers are produced for hikers and the military.<ref name="El-Rabbany">El-Rabbany, Ahmed (2002). Introduction to GPS: The Global Positioning System. Artech House. ISBN 978-1580531832. Retrieved 10 September 2022.</ref><ref name="Kiland-Silverstein Gray">Kiland, Taylor Baldwin; Silverstein Gray, Judy (15 July 2016). The Military GPS: Cutting Edge Global Positioning System. Enslow Publishing. ISBN 978-0766075184. Retrieved 10 September 2022.</ref>
  • Radio beacon – a fixed location terrestrial radio transmitter which transmits a continuous radio signal used by aircraft and ships for navigation. The locations of beacons are plotted on navigational maps used by aircraft and ships.<ref name="Deltour">Deltour, B.V. (August 1960). "A Guide To Nav-Com Equipment". Flying Magazine Aug 1960. Retrieved 10 September 2022.</ref>
    • VHF omnidirectional range (VOR) – a worldwide aircraft radio navigation system consisting of fixed ground radio beacons transmitting between 108.00 and 117.95 MHz in the very high frequency (VHF) band. An automated navigational instrument on the aircraft displays a bearing to a nearby VOR transmitter. A VOR beacon transmits two signals simultaneously on different frequencies. A directional antenna transmits a beam of radio waves that rotates like a lighthouse at a fixed rate, 30 times per second. When the directional beam is facing north, an omnidirectional antenna transmits a pulse. By measuring the difference in phase of these two signals, an aircraft can determine its bearing (or "radial") from the station accurately. By taking a bearing on two VOR beacons an aircraft can determine its position (called a "fix") to an accuracy of about 90 metres (300 ft). Most VOR beacons also have a distance measuring capability, called distance measuring equipment (DME); these are called VOR/DME's. The aircraft transmits a radio signal to the VOR/DME beacon and a transponder transmits a return signal. From the propagation delay between the transmitted and received signal the aircraft can calculate its distance from the beacon. This allows an aircraft to determine its location "fix" from only one VOR beacon. Since line-of-sight VHF frequencies are used VOR beacons have a range of about 200 miles for aircraft at cruising altitude. TACAN is a similar military radio beacon system which transmits in 962–1213 MHz, and a combined VOR and TACAN beacon is called a VORTAC. The number of VOR beacons is declining as aviation switches to the RNAV system that relies on Global Positioning System satellite navigation.<ref name="USDOD">"2008 Federal Radionavigation Plan". U.S. Department of Defense. 2009. Retrieved 10 September 2022.</ref><ref name="Martin">Martin, Swayne. "How A VOR Works". boldmethod.com. Boldmethod -Digital Aviation Content. Retrieved 10 September 2022.</ref>
    • Non-directional beacon (NDB) – Legacy fixed radio beacons used before the VOR system that transmit a simple signal in all directions for aircraft or ships to use for radio direction finding. Aircraft use automatic direction finder (ADF) receivers which use a directional antenna to determine the bearing to the beacon. By taking bearings on two beacons they can determine their position. NDBs use frequencies between 190 and 1750 kHz in the LF and MF bands which propagate beyond the horizon as ground waves or skywaves much farther than VOR beacons. They transmit a callsign consisting of one to 3 Morse code letters as an identifier.<ref name="SI">"Non-Directional Beacon (NDB)". systemsinterface.com. Systems Interface. Retrieved 10 September 2022.</ref>
EPIRB emergency locator beacon on a ship
  • Emergency locator beacon – a portable battery powered radio transmitter used in emergencies to locate airplanes, vessels, and persons in distress and in need of immediate rescue. Various types of emergency locator beacons are carried by aircraft, ships, vehicles, hikers and cross-country skiers. In the event of an emergency, such as the aircraft crashing, the ship sinking, or a hiker becoming lost, the transmitter is deployed and begins to transmit a continuous radio signal, which is used by search and rescue teams to quickly find the emergency and render aid. The latest generation Emergency Position Indicating Rescue Beacons (EPIRBs) contain a GPS receiver, and broadcast to rescue teams their exact location within 20 meters.<ref name="CBC">"How does an emergency beacon work?". cbc.ca. CBC News. Retrieved 10 September 2022.</ref>
Wildlife officer tracking radio-tagged mountain lion
  • Radio direction finding (RDF) – this is a general technique, used since the early 1900s, of using specialized radio receivers with directional antennas (RDF receivers) to determine the exact bearing of a radio signal, to determine the location of the transmitter. The location of a terrestrial transmitter can be determined by simple triangulation from bearings taken by two RDF stations separated geographically, as the point where the two bearing lines cross, this is called a "fix". Military forces use RDF to locate enemy forces by their tactical radio transmissions, counterintelligence services use it to locate clandestine transmitters used by espionage agents, and governments use it to locate unlicensed transmitters or interference sources. Older RDF receivers used rotatable loop antennas, the antenna is rotated until the radio signal strength is weakest, indicating the transmitter is in one of the antenna's two nulls. The nulls are used since they are sharper than the antenna's lobes (maxima). More modern receivers use phased array antennas which have a much greater angular resolution.<ref name="defenceweb">"An Introduction to Radio Direction Finding". defenceweb.co.za. defenceWeb. 8 January 2021. Retrieved 10 September 2022.</ref><ref name="Moell-Curlee">Moell, Joseph D.; Curlee, Thomas N. (1987). Transmitter Hunting: Radio Direction Finding Simplified. McGraw Hill Professional. ISBN 978-0830627011. Retrieved 10 September 2022.</ref>
    • Animal migration tracking – a widely used technique in wildlife biology, conservation biology, and wildlife management in which small battery-powered radio transmitters are attached to wild animals so their movements can be tracked with a directional RDF receiver. Sometimes the transmitter is implanted in the animal. The VHF band is typically used since antennas in this band are fairly compact. The receiver has a directional antenna (typically a small Yagi) which is rotated until the received signal is strongest; at this point the antenna is pointing in the direction of the animal. Sophisticated systems used in recent years use satellites to track the animal, or geolocation tags with GPS receivers which record and transmit a log of the animal's location.<ref name="Smithsonian">"Radio telemetry". Migratory Connectivity Project, Smithsonian Migratory Bird Center. Retrieved 10 September 2022.</ref>

Remote control

Main article: Radio control
US Air Force MQ-1 Predator drone flown remotely by a pilot on the ground

Radio remote control is the use of electronic control signals sent by radio waves from a transmitter to control the actions of a device at a remote location. Remote control systems may also include telemetry channels in the other direction, used to transmit real-time information on the state of the device back to the control station. Uncrewed spacecraft are an example of remote-controlled machines, controlled by commands transmitted by satellite ground stations. Most handheld remote controls used to control consumer electronics products like televisions or DVD players actually operate by infrared light rather than radio waves, so are not examples of radio remote control. A security concern with remote control systems is spoofing, in which an unauthorized person transmits an imitation of the control signal to take control of the device.<ref name="Layton">Layton, Julia (10 November 2005). "How Remote Controls Work". HowStuff Works. Retrieved 10 September 2022.</ref> Examples of radio remote control:

  • Unmanned aerial vehicle (UAV, drone) – A drone is an aircraft without an onboard pilot, flown by remote control by a pilot in another location, usually in a piloting station on the ground. They are used by the military for reconnaissance and ground attack, and more recently by the civilian world for news reporting and aerial photography. The pilot uses aircraft controls like a joystick or steering wheel, which create control signals which are transmitted to the drone by radio to control the flight surfaces and engine. A telemetry system transmits back a video image from a camera in the drone to allow the pilot to see where the aircraft is going, and data from a GPS receiver giving the real-time position of the aircraft. UAVs have sophisticated onboard automatic pilot systems that maintain stable flight and only require manual control to change directions.<ref name="Sadraey">Sadraey, Mohammad H. (2020). Design of Unmanned Aerial Systems. Wiley. ISBN 978-1119508694. Retrieved 10 September 2022.</ref>
Remote keyless entry fob for a car
  • Keyless entry system – a short-range handheld battery powered key fob transmitter, included with most modern cars, which can lock and unlock the doors of a vehicle from outside, eliminating the need to use a key. When a button is pressed, the transmitter sends a coded radio signal to a receiver in the vehicle, operating the locks. The fob must be close to the vehicle, typically within 5 to 20 meters. North America and Japan use a frequency of 315 MHz, while Europe uses 433.92 and 868 MHz. Some models can also remotely start the engine, to warm up the car. A security concern with all keyless entry systems is a replay attack, in which a thief uses a special receiver ("code grabber") to record the radio signal during opening, which can later be replayed to open the door. To prevent this, keyless systems use a rolling code system in which a pseudorandom number generator in the remote control generates a different random key each time it is used. To prevent thieves from simulating the pseudorandom generator to calculate the next key, the radio signal is also encrypted.<ref name="Smith">Smith, Craig (2016). The Car Hacker's Handbook: A Guide for the Penetration Tester. No Starch Press. ISBN 978-1593277703. Retrieved 10 September 2022.</ref>
Quadcopter, a popular remote-controlled toy

Jamming

Radio jamming is the deliberate radiation of radio signals designed to interfere with the reception of other radio signals. Jamming devices are called "signal suppressors" or "interference generators" or just jammers.<ref>"What jamming of a wireless security system is and how to resist it | Ajax Systems Blog". Ajax Systems. Retrieved 18 January 2020.</ref>

During wartime, militaries use jamming to interfere with enemies' tactical radio communication. Since radio waves can pass beyond national borders, some totalitarian countries which practice censorship use jamming to prevent their citizens from listening to broadcasts from radio stations in other countries. Jamming is usually accomplished by a powerful transmitter which generates noise on the same frequency as the target transmitter.<ref>"Remedial Electronic Counter-Countermeasures Techniques". FM 24-33 — Communications Techniques: Electronic Counter-Countermeasures (Report). Department of the Army. July 1990.</ref><ref>Varis, Tapio (1970). "The Control of Information by Jamming Radio Broadcasts". Cooperation and Conflict. 5 (3): 168–184. doi:10.1177/001083677000500303. ISSN 0010-8367. JSTOR 45083158. S2CID 145418504.</ref>

US Federal law prohibits the nonmilitary operation or sale of any type of jamming devices, including ones that interfere with GPS, cellular, Wi-Fi and police radars.<ref>"Jammer Enforcement". Federal Communications Commission. 3 March 2011. Retrieved 18 January 2020.</ref>

Scientific research

See also

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References

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General references

External links

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