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radio

  ('dē-ō) pronunciation
n., pl. -os.
  1. The wireless transmission through space of electromagnetic waves in the approximate frequency range from 10 kilohertz to 300,000 megahertz.
  2. Communication of audible signals encoded in electromagnetic waves.
  3. Transmission of programs for the public by radio broadcast.
    1. An apparatus used to transmit radio signals; a transmitter.
    2. An apparatus used to receive radio signals; a receiver.
    3. A complex of equipment capable of transmitting and receiving radio signals.
    1. A station for radio transmitting.
    2. A radio broadcasting organization or network of affiliated organizations.
    3. The radio broadcasting industry.
  4. A message sent by radio.

v., -oed, -o·ing, -os.

v.tr.
  1. To transmit by radio: radio a message to headquarters.
  2. To transmit a message to by radio: radioed the spacecraft.
v.intr.

To transmit messages or a message by radio: a ship radioing for help.

[Short for RADIOTELEGRAPHY.]


 
 
How Products are Made: How is a radio made?

Background

The radio receives electromagnetic waves from the air that are sent by a radio transmitter. Electromagnetic waves are a combination of electrical and magnetic fields that overlap. The radio converts these electromagnetic waves, called a signal, into sounds that humans can hear.

Radios are a part of everyday life. Not only are they used to play music or as alarms in the morning, they are also used in cordless phones, cell phones, baby monitors, garage door openers, toys, satellites, and radar. Radios also play an important role in communications for police, fire, industry, and the military. Although there are many types of radios—clock, car, amateur (ham), stereo—all contain the same basic components.

Radios come in all shapes and sizes, from a little AM/FM "Walkman" to a highly sophisticated, multi-mode transceiver where both the transmitter and receiver are combined in one unit. The most common modes for a broadcast radio are AM (amplitude modulation) and FM (frequency modulation). Other modes used by ham radio operators, industry, and the military are CW (continuous wave using Morse code), SSB (single sideband), digital modes such as telemetry, radio teletype, and PSK (phase shift keying).

History

Guglielmo Marconi successfully sent the first radio message across the Atlantic Ocean in December 1901 from England to Newfoundland. Marconi's radio did not receive voice or music. Rather, it received buzzing sounds created by a spark gap transmitter sending a signal using Morse code.

The radio got its voice on Christmas Eve 1906. As dozens of ship and amateur radio operators listened for the evening's traffic messages, they were amazed to hear a man's voice calling "CQ, CQ" (which means calling all stations, I have messages) instead of the customary dits and dahs of Morse code. The message was transmitted by Professor Reginald Aubrey Fessenden from a small radio station in Brant Rock, Massachusetts.

In the years from 1904 to 1914, the radio went through many refinements with the invention of the diode and triode vacuum tubes. These devices enabled better transmission and reception of voice and music. Also during this time period, the radio became standard equipment on ships crossing the oceans.

The radio came of age during World War I. Military leaders recognized its value for communicating with the infantry and ships at sea. During the WWI, many advancements were made to the radio making it more powerful and compact. In 1923, Edwin Armstrong invented the superhetrodyne radio. It was a major advancement in how a radio worked. The basic principles used in the superhetrodyne radio are still in use today.

On November 2, 1920 the first commercial radio station went on the air in Pittsburgh, Pennsylvania. It was an instant success, and began the radio revolution called the "Golden Age of Radio." The Golden Age of Radio lasted from the early 1920s through the late 1940s when television brought in a whole new era. During this Golden Age, the radio evolved from a simple device in a bulky box to a complex piece of equipment housed in beautiful wooden cabinets. People would gather around the radio and listen to the latest news and radio plays. The radio occupied a similar position as today's television set.

On June 30, 1948 the transistor was successfully demonstrated at Bell Laboratories. The transistor allowed radios to become compact, with the smallest ones able to fit in a shirt pocket. In 1959, Jack Kilby and Robert Noyce received the first patent for the integrated circuit. The space program of the 1960s would bring more advances to the integrated circuit. Now, a radio could fit in the frame of eyeglasses or inside a pair of small stereo earphones. Today, the frequency dial printed on the cabinet has been replaced with light emitting diodes or liquid crystal displays.

Raw Materials

Today's radio consists of an antenna, printed circuit board, resistors, capacitors, coils and transformers, transistors, integrated circuits, and a speaker. All of these parts are housed in a plastic case.

An internal antenna consists of small-diameter insulated copper wire wound around a ferrite core. An external antenna consists of several aluminum tubes that slide within one another.

The printed circuit board consists of a copper-clad pattern cemented to a phenolic board. The copper pattern is the wiring from component to component. It replaces most of the wiring used in earlier radios.

Resistors limit the flow of electricity. They consist of a carbon film deposited on a cylindrical substrate, encased in a plastic (alkyd polyester) housing, with wire leads made of copper.

Capacitors store an electrical charge and allow alternating current to flow through an electrical circuit but prevent direct current from flowing in the same circuit. Fixed capacitors consist of two extended aluminum foil electrodes insulated by polypropylene film, housed in a plastic or ceramic housing with copper wire leads. Variable capacitors have a set of fixed aluminum plates and a set of rotating aluminum plates with an air insulator.

Coils and transformers perform similar functions. Their purpose is to insulate a circuit while transferring energy from one circuit to another. They consist of two or more sets of copper wire coils either wound on an insulator or mounted side-by-side with air as the insulator.

Transistors consist of germanium or silicon encased in a metal housing with copper wire leads. The transistor controls the flow of electricity in a circuit. Transistors replaced vacuum tubes used in earlier radios.

The integrated circuit houses thousands of resistors, capacitors, and transistors into a small and compact package called a chip. This chip is about the size of the nail on the little finger. The chip is mounted in a plastic case with aluminum tabs that allow it to be mounted to a printed circuit board.

Design

Radios consist of many specialized electronic circuits designed to perform specific tasks—radio frequency amplifier, mixer, variable frequency oscillator, intermediate frequency amplifier, detector, and audio amplifier.

The radio frequency amplifier is designed to amplify the signal from a radio broadcast transmitter. The mixer takes the radio signal and combines it with another signal produced by the radio's variable frequency oscillator to produce an intermediate frequency. The variable frequency oscillator is the tuning knob on the radio. The produced intermediate frequency is amplified by the intermediate frequency amplifier. This intermediate signal is sent to the detector which converts the radio signal to an audio signal. The audio amplifier amplifies the audio signal and sends it to the speaker or earphones.

The simplest AM/FM radio will have all of these circuits mounted on a single circuit board. Most of these circuits can be contained in a single integrated circuit. The volume control (a variable resistor), tuning knob (a variable capacitor), speaker, antenna, and batteries can be mounted either on the printed circuit board or in the radio's case.

The Manufacturing
Process

There is no single process for manufacturing a radio. The manufacturing process depends upon the design and complexity of the radio. The simplest radio has a single circuit board housed in a plastic case. The most complex radio has many circuit boards or modules housed in aluminum case.

Manufacturers purchase the basic components such as resistors, capacitors, transistors, integrated circuits, etc., from vendors and suppliers. The printed circuit boards, usually proprietary, may be manufactured in house. Many times, manufacturers will purchase complete radio modules from an vendor. Most of the manufacturing operations are performed by robots. These include the printed circuit boards and mounting of the components on the printed circuit board. Mounting of the printed circuit board and controls into the case and some soldering operations are usually done by hand.

  1. The blank printed circuit board consists of a glass epoxy resin with a thin copper film cemented to one or both sides. A light sensitive photoresist film is placed over the copper film. A mask containing the electrical circuitry is placed over the photoresist film. The photoresist film is exposed to ultraviolet light. The photoresist image is developed, transferring the image to the copper film. The unexposed areas dissolve during etching and produce a printed circuit on the board.
  2. Holes are drilled in designated locations on the printed circuit board to accept the components. Then, the board is pre-soldered by dipping it in a bath of hot solder.
  3. Smaller electronic components such as resistors, capacitors, transistors, integrated circuits, and coils are installed in their designated holes on the printed circuit board and soldered to the board. These operations can be performed by hand or by robots.
  4. Larger components such as power transformer, speaker, and antenna are mounted either on the PCB or cabinet with screws or metal spring tabs.
  5. The case that houses the radio can be made either of plastic or aluminum. Plastic cases are made from pellets that are melted and injected into a mold. Aluminum cases are stamped into shape from sheet aluminum by a metal press.
  6. External components not mounted on the printed circuit board can be the antenna, speaker, power transformer, volume, and frequency controls are mounted in the case with either screws, rivets, or plastic snaps. The printed circuit board is then mounted in the case with screws or snaps. The external components are connected and soldered to the printed circuit board with insulated wires made of copper and plastic insulation.

Quality Control

Since most of the components or a radio are manufactured by specialized vendors, the radio manufacturer must rely on those venders to produce quality parts. However, the radio manufacturer will take random samples of each component received and inspect/test them to ensure they meet the required specifications.

Random samples of the final radio assembly are also inspected to ensure quality. The overall unit is inspected for flaws—both physical and electrical. The radio is played to ensure it can select radio frequencies it's design to receive, and that the audio output is within specifications.

Byproducts/Waste

Today's environmental awareness dictates that all waste be disposed of properly. Most byproducts from the construction of a radio can be reclaimed. The etching solutions used in the printed circuit board manufacture are sent to chemical reclamation centers. Scraps from the leads of electronic components are sent to metal waste recovery centers where they are melted to create new products.

The Future

Radios are being combined with computers to connect the computer to the Internet via satellites. Eventually radios will convert from analog to digital broadcasting. Analog signals are subject to fade and interference, digital signals are not. They can produce high quality sound like that found on a CD.

Digital radios can be programmed for specific stations, types of music, news, etc. Eventually, radios will have mini-computers built in to process sounds in numerical patterns "digits" rather than an analog waveform. This will allow listeners to program their radios for favorite radio stations, music type, stock quotes, traffic information, and much more.

Where to Learn More

Books

Carter, Alden R. Radio From Marconi To The Space Age. New York: Franklin Watts, 1987.

Floyd, Thomas L. Electric Circuit Fundamentals. Columbus: Merrill Publishing Company, 1987.

The American Radio Relay League. The ARRL Handbook for Radio Amateurs. Newington, CT: ARRL, 1996.

Other

Canadian Broadcasting Company Web Page. "The Future of Digital Radio.: December 2001. <http://radioworks.cbc.ca/radio/digital-radio/drri.html>.

UC Berkley Web Page. December 2001. <http://www.cs.berkeley.edu/~gribble/cs39c/Comm/radio/radio.html>.

[Article by: Ernst S. Sibberson]


 

Communication between two or more points, employing electromagnetic waves as the transmission medium.

Radio waves transmitted continuously, with each cycle an exact duplicate of all others, indicate only that a carrier is present. The message must cause changes in the carrier which can be detected at a distant receiver. The method used for the transmission of the information is determined by the nature of the information which is to be transmitted as well as by the purpose of the communication system.

In code telegraphy the carrier is keyed on and off to form dots and dashes. The technique, often used in ship-to-shore and amateur communications, has been largely superseded in many other point-to-point services by more efficient methods.

In frequency-shift transmission the carrier frequency is shifted a fixed amount to correspond with telegraphic dots and dashes or with combinations of pulse signals identified with the characters on a typewriter. This technique is widely used in handling the large volume of public message traffic on long circuits, principally by the use of teletypewriters.

In amplitude modulation the amplitude of the earner is made to fluctuate, to conform to the fluctuations of a sound wave. This technique is used in AM broadcasting, television picture transmission, and many other services. See also Amplitude-modulation radio.

In frequency modulation the frequency of the carrier is made to fluctuate around an average axis, to correspond to the fluctuations of the modulating wave. This technique is used in FM broadcasting, television sound transmission, and microwave relaying. See also Frequency-modulation radio.

In pulse transmission the carrier is transmitted in short pulses, which change in repetition rate, width, or amplitude, or in complex groups of pulses which vary from group to succeeding group in accordance with the message information. These forms of pulse transmission are identified as pulse-code, pulse-time, pulse-position, pulse-amplitude, pulse-width, or pulse-frequency modulation. Such techniques are complex and are employed principally in microwave relay systems. See also Pulse modulation.

In radar the carrier is normally transmitted as short pulses in a narrow beam, similar to that of a searchlight When a wave pulse strikes an object, such as an aircraft, energy is reflected back to the station, which measures the round-trip time and converts it to distance. A radar can display varying reflections in a maplike presentation on a cathode-ray tube. See also Radar.

Hundreds of thousands of radio transmitters exist, each requiring a carrier at some radio frequency. To prevent interference, different carrier frequencies are used for stations whose service areas overlap and receivers are built to select only the carrier signal of the desired station. Resonant electric circuits in the receiver are adjusted, or tuned, to accept one frequency and reject others.

All nations have a sovereign right to use freely any or all parts of the radio spectrum. But a growing list of international agreements and treaties divides the spectrum and specifies sharing among nations for their mutual benefit and protection. Each nation designates its own regulatory agency. In the United States all nongovernmental radio communications are regulated by the Federal Communications Commission (FCC). See also Amateur radio; Radio broadcasting; Radio spectrum allocations.


 

(1) A transmit/receive device; a transceiver. The term may refer to the entire unit or only to the circuits that do the actual transmitting and receiving. The phrase "the device has two radios" means the unit has two transmitters or two transceivers.

(2) The transmission of electromagnetic radiation (energy) through the air or through a hollow tube called a "waveguide." Although radio is often thought of as only AM and FM radio or sometimes two-way radio, all transmission systems that propagate signals over the airwaves are called "radio," including TV, satellite, portable phones, cellphones and wireless LANs. See spectrum.

Electromagnetic Spectrum
The radio portion of the entire spectrum of radiation is from 3 kHz to 300 GHz. This huge band of frequencies has been defined by the FCC in the U.S. and governmental bodies in other countries.



 

Radio is looked at as an important tool in educating the general public about health issues. In particular, it is believed that properly developed community radio can encourage community-driven problem solving. At the government level, radio has been used to advise the public on issues such as new health standards and seasonal food warnings.

Examples of radio's role in education and public health awareness are numerous. Sound Partners—a program run by the Benton Foundation—provides grants to public radio stations interested in developing community-oriented educational content for the good of public health. Many talk-radio stations and public broadcasters feature special call-in medical programming and general health information. Public addresses via radio, such as President Clinton's radio talk on May 6, 2000, on food safety, and the radio dissemination of automotive product recalls by the United States National Highway Traffic Safety Administration, also exhibit the effectiveness of radio as a means of informing the public.

While the above services are good for the general public, physicians need to be educated in a different manner. Internet radio involves broadcasting audio content on the Internet so it can be heard anywhere in the world through a computer or WebTV unit. Examples of Internet radio delivery systems include RealNetwork's RealPlayer and Microsoft's Windows Media Player.

Internet radio is important for the public health and medical community because it creates an opportunity for high-quality interactive distance learning and education without geographic limitations. For example, in a normal educational setting doctors would need to go to a special class or conference to educate themselves. Internet radio can provide doctors with an alternative to the traditional continuing education setting.

(SEE ALSO: Mass Media; Mass Media and Tobacco Control; Media Advocacy)

— NEIL SCHNEIDER



 

Radio is the basis of the 20th-century communications revolution. It first became a possibility when the English physicist Michael Faraday demonstrated in 1831 that an electrical current could produce a magnetic field. In 1864, James C. Maxwell, a professor of experimental physics at Cambridge, proved mathematically that electrical disturbances could be detected at considerable distances. In 1888, a German, Heinrich Hertz, demonstrated that Maxwell's prediction was true for transmissions over short distances. The Italian physicist Guglielmo Marconi then perfected a radio system that in 1901 transmitted Morse code over the Atlantic Ocean from England to Newfoundland. The Royal Navy was an enthusiastic customer of the company Marconi formed to develop radio communications. Similarly, the German armed forces were among the first buyers of AEG and Siemens radio equipment. This new type of technology was well known but still cumbersome at the beginning of WW I.

The western front became a trench war, fought at close range, which made visual signalling perilous. Although field wireless sets were available in small numbers, they were heavy and imperfect. The open spark gap radio and the crystal receiver could not be fine-tuned in the transmission-glutted combat zone. Telephone and telegraph were used as the backbone communications systems, and trench warfare exacted a heavy toll on signal personnel who installed and repaired the lines. As radio was developed, the ability of the enemy to eavesdrop on radio messages (such as before Tannenberg in 1914) brought about the development of codes and ciphers. Efforts were also made to use radiotelegraph and radiotelephone between aircraft and ground headquarters. The closing stages of the war saw many planes equipped with voice radio, which proved of particular value for the control of artillery fire, but it was never wholly satisfactory or reliable.

Two inventions in the 1920s transformed not only military communications but also strategy and tactics. The first was the short-wave transmitter, which could be used to communicate at great distances but was small enough to fit into an aircraft or tank. The second was the cipher machine, beginning with the German Enigma and later with the American SIGABA, and the British TYPEX, which could be operated by minimally trained personnel, yet were (falsely) considered invulnerable to eavesdropping. During the inter-war period, smaller, more robust radio sets, some with crystal tuning, were developed. This meant that vehicles and aircraft could be equipped with radios, giving both the army and air force true mobile radio communications. It was quickly appreciated that voice radio was the only realistic way to control large numbers of personnel and vehicles. Higher frequencies were developed which improved reception. The armoured warfare of WW II would have been impossible without the installation of lightweight and reliable radios in the majority of fighting vehicles.

Military communications in WW II benefited from pre-war integration of civil communications systems. Radio relay, developed out of a requirement for mobility, became one of the outstanding developments of WW II. It was first used by the Germans and later used by the British at their headquarters in Normandy and London. Radio relay, telephone, and teletypewriter circuits spanned the English Channel for the Normandy invasion and later furnished important communications after the Allied breakout from the beachhead. Short-wave radio allowed tactics such as submarine wolf packs, massive bombing raids, and co-ordinated blitzkrieg attacks. Frequency-Modulated (FM) radio was used for local communication, such as between ships in convoy. The need for command control took priority over the risk of interception. Push-button crystal-controlled FM radios provided relatively static and interference-free communications for combat units at the tactical level.

Electronic communications proliferated in the late 20th century. After WW II, innovations such as replacing tubes with transistors and wires by printed circuits, drastically reduced the amount of power the receiver needed to operate and allowed for components to be miniaturized. Two-way mobile radio communications on a large scale revolutionized warfare, allowing for mobile operations co-ordinated over large areas. Technology today has revolutionized the means in which military units communicate with each other. Many of today's combat net radios have been enhanced to carry data in addition to voice. Military trunk systems today are the equivalent to a telephone network that can be moved around the battlefield, providing voice, fax, or data/email links.

Increases in the mobility of armies on land, at sea, or in the air as well as growing demands, as far as the quantity and quality of information transfers are concerned, forced the introduction of automated equipment for the conveyance of messages. Satellites have contributed to the development of sophisticated signal systems. Information technology is advancing at a breakneck pace in a worldwide market place, driven not by military requirements but by the industrial and consumer sectors.

— Danny M. Johnson

 

Electromagnetic radiation of lower frequency (hence longer wavelength) than visible light or infrared radiation, and consisting of the range of frequencies used for navigation signals, AM and FM broadcasting, television transmissions, cell-phone communications, and various forms of radar. For radio transmission, information is imparted to a carrier wave by varying (modulating) its amplitude, frequency, or duration. The technology of radio arose from the work of Michael Faraday, James Clerk Maxwell, Heinrich Hertz, Guglielmo Marconi, and others, and improvement followed the development of the vacuum tube, the electronic-tube oscillator, the tuned circuit, and other components. Later innovations have included the replacement of tubes by transistors and of wires by printed circuits. See also radio and radar astronomy.

For more information on radio, visit Britannica.com.

 

The Information Age began with the invention of the Telegraph and Telephone. These innovations led directly to the next important technological break-through—the arrival of commercial radio. Almost immediately, radio focused on listeners as consumers and the developing consumer culture, which would be replicated later with television, motion pictures, and most recently, the Internet. Radio transformed people's lives, changing the way living space was arranged, shaping family dynamics and leisure time, and reinforcing the ideals of the growing consumer culture.

Throughout its history, radio has not only been a driving force in American popular culture, but has basically provided the soundtrack for people's lives. Despite the all-encompassing influence of television, movies, and the Internet, radio remains at the core of the public's being. While some listeners tune in for music (spanning the spectrum from classic rock to rap) and others for talk (politics, sports, culture, and religion), radio continues to be a central component in shaping lives—musically, spiritually, politically, and culturally.

Early Days

Radio pioneers built on the success of telegraph and telephone inventors to conduct experiments with wire-based and wireless radio. Heinrich Hertz and Guglielmo Marconi carried out groundbreaking work. In 1901, Marconi gained international fame by sending a message across the Atlantic Ocean via wireless telephony. Early triumphs spurred greater advances. By the 1910s, Lee De Forest broadcast music and voice from his lab in New York. Early advocates championed the use of radio as an emergency device, citing how it was used when the Titanic sank in 1912 or during World War I (1914–1918).

In November 1920, Pittsburgh's station KDKA initiated America's first radio broadcast. Operated by the Westinghouse Corporation, KDKA was set up to en-courage radio sales. Other large companies followed suit, including the Radio Corporation of America (RCA) and the phone company AT&T. Within two years, more than 500 stations were clogging the airwaves. The federal government stepped in to regulate radio stations with the Radio Act of 1927, which established the Federal Radio Commission to license stations. The need for regulating the entire telecommunications industry later led President Franklin D. Roosevelt to support the Communications Act of 1934, which established the Federal Communications Commission (FCC).

Radio stations first sold advertising in 1922 at New York station WEAF. In 1926 and 1927, NBC (NBC-Red and NBC-Blue) and CBS were founded as national radio stations, although there were 700 other stations on the air at the time. Along with the Mutual Broadcasting System (MBS), these stations controlled the airwaves for most of radio's heyday. Since RCA owned both NBC stations, it was ordered by the FCC to divest one. In 1943, NBC-Blue became ABC.

Golden Age

The period leading up to the introduction of television is considered radio's Golden Age. Radio transformed people's lives from the late 1920s to late 1940s by providing news and entertainment to anyone who could afford a receiver. Specific audience-friendly programming was introduced to lure listeners, from half-hour sitcoms to daytime dramas and music programs. Radio had a grip on the nation's psyche, as seen on Halloween 1938 when Orson Welles narrated a dramatization of the book War of the Worlds by H. G. Wells. A panic ensued when listeners believed the news that invaders from Mars were attacking the world, despite many disclaimers that were run throughout the broadcast.

The national networks solidified their hold during the Golden Age. Local stations lost their monopolistic control over programming and as network affiliates, were contractually obliged to play the shows emanating from the larger stations. The networks delivered more sophisticated programs and made national stars of performers such as Will Rogers and Freeman Gosden and Charles Correll, better known as Amos 'n' Andy, the most popular show in America by 1929. The networks played an important cultural role, since they delivered the same programming nationwide. Radio helped promote national values and attitudes, making radio one of the few threads that tied the entire nation together. By the late 1940s, more than 90 percent of the homes in the nation had at least one radio and Americans spent more leisure time listening to the radio than doing anything else other than sleeping.

As radio developed, the kind of programs it offered changed as well. Action series, such as The Shadow and The Green Hornet, helped define how people thought about law enforcement. The medium endorsed a hero culture to listeners, from broadcasting the heroic efforts of baseball's Babe Ruth to the intergalactic exploits of Flash Gordon.

Radio had a tremendous impact on politics and journalism. President Franklin D. Roosevelt used the radio to mobilize support for his New Deal programs in "fireside chats" with the American people. As World War II (1939– 1945) loomed, the president used the radio to stoke the public's patriotic fever. Once the war began, correspondents, such as Edward R. Murrow, Walter Cronkite, and Eric Sevareid, delivered reports from the European front-lines, forever changing reporting and in essence inventing broadcast journalism.

During World War II, most people experienced the war most forcefully through radio. In addition to the breaking news, presidential reports, and reports from the frontlines, celebrities used radio to pitch for war bonds and plead for scrap metal drives and other resources. Paper shortages during wartime limited the influence of newspapers. Radio stations stepped into this void and provided a mix of news, reports, and patriotic messages that listeners craved.

Advertisers realized the power of radio and poured money into commercials. In 1928, radio garnered less than 1 percent of all advertising. By 1945, however, radio commanded 15 percent. In 1948, sponsors spent more than $400 million on radio advertising. The financial growth of radio was mimicked by the expansion of stations themselves. In 1930 there were 600 amplitude modulation (AM) stations. A decade later, the figure jumped to 765. But by 1948, it more than doubled to 1,612.

Radio in the Television Age

Frequency modulation (FM) radio developed in the late 1930s, when E. Howard Armstrong searched for a way to broadcast without the static common on AM dials. The AM dial also became overcrowded during radio's Golden Age. Inventors looked for an alternative to mainstream radio, which coincided with the anticommercialism of the 1960s.

The decade's youth culture helped spur the growth of FM stations. Listeners were antitelevision and anticonformity and could find a similar rebelliousness in the songs and programs on FM radio. Progressive rock stations took root in San Francisco, Los Angeles, New York, and Boston, eliminating advertising jingles and the antics of AM disc jockeys.

Gradually, the FM dial went through the same commercial transformation that occurred with AM. Initially, the networks started exerting their influence on FM, attempting to maintain a delicate balance between commercialism and FM's underground roots. By the end of the 1970s, however, the demand for profits and fall of the counterculture movement made FM radio look just like its AM predecessor, with the large networks squeezing out the remnants of the underground heritage. Revenues at FM stations, under $20 million in 1964, hit $284 million a decade later. There were more than 2,300 stations on air in 1972, but 3,700 by 1976. In 1977, FM revenues topped $543 million, but programming was done by committee and depended on computerization. An assembly line mentality took hold and the same rotations of hit songs were played over and over.

Modern Radio

Modern radio is far removed from its origins. At one time, pioneering entrepreneurs influenced radio and introduced diversity into programming. At the end of the twentieth century, corporate conglomerates governed the industry and a general uniformity had befallen radio. Despite the homogeneity of modern radio, however, its influence is still strong. By 2000, there were more than 12,000 AM and FM stations broadcast, with much of the programming distributed by satellite networks.

The cookie-cutter mentality at most radio stations from the 1980s onward led to the rise of talk radio, from National Public Radio (NPR) to political and sportsoriented shows. Talk radio opened the airwaves to a variety of voices and made celebrities of hosts like Howard Stern, Rush Limbaugh, and Diane Rehm. Stern, in particular, gained notoriety as a "shock jock." His show is syndicated via satellite nationwide and features racy bits and an in-your-face attitude that launched a slew of imitators. The number of stations with all-talk or news and talk format topped 850 in 1994, and talk radio placed second among popular formats, with country music at the top.

The domination of the radio industry by large corporations was helped by the passage of the Telecommunications Act of 1996, which eliminated restrictions on radio ownership. Before, companies could only own two stations in any single market and 28 nationwide. All this changed after the Telecom Act passed. For example, as of 2002, Clear Channel Radio was the largest operator of radio stations in the United States with more than 1,350 stations and reaching 110 million listeners every week. Clear Channel also syndicated more than 100 programs to 7,800 stations, including Rush Limbaugh, sports talk leader Jim Rome, and Casey Kasem. Nearly half (625) of Clear Channel's radio stations were purchased in the 1999 Jacor acquisition.

The Telecom Act pushed radio acquisitions into overdrive. The feeding frenzy, driven by an influx of Wall Street money, enabled a handful of conglomerates to take control of the industry. Although radio is now more profitable, critics rebuke the conglomerates for forcing staid, automated music and formats on listeners, as well as for the elimination of countless radio jobs. Regardless of its shortcomings, however, radio continues to attract listeners and frames the way people think about music, sports, politics, and culture. In 2001, there were nearly 13,000 stations in the United States, which reached 77 percent of the people over 12 years old every day and 95 percent of consumers weekly.

Bibliography

Barnouw, Erik. A History of Broadcasting in the United States. 3 Vols. New York: Oxford University Press, 1966–1970.

Douglas, Susan J. Listening In: Radio and the American Imagination, from Amos 'n' Andy and Edward R. Murrow to Wolfman Jack and Howard Stern. New York: Times Books, 1999.

Keith, Michael C. Talking Radio: An Oral History of American Radio in the Television Age. Armonk, N.Y.: M.E. Sharpe, 2000.

MacDonald, J. Fred. Don't Touch That Dial! Radio Programming in American Life, 1920–1960. Chicago: Nelson-Hall, 1979.

 
transmission or reception of electromagnetic radiation in the radio frequency range. The term is commonly applied also to the equipment used, especially to the radio receiver.

Uses of Radio Waves

The prime purpose of radio is to convey information from one place to another through the intervening media (i.e., air, space, nonconducting materials) without wires. Besides being used for transmitting sound and television signals, radio is used for the transmission of data in coded form. In the form of radar it is used also for sending out signals and picking up their reflections from objects in their path. Long-range radio signals enable astronauts to communicate with the earth from the moon and carry information from space probes as they travel to distant planets (see space exploration). For navigation of ships and aircraft the radio range, radio compass (or direction finder), and radio time signals are widely used. Radio signals sent from global positioning satellites can also be used by special receivers for a precise indication of position (see navigation satellite). Digital radio, both satellite and terrestrial, provides improved audio clarity and volume. Various remote-control devices, including rocket and artificial satellite operations systems and automatic valves in pipelines, are activated by radio signals. The development of the transistor and other microelectronic devices (see microelectronics) led to the development of portable transmitters and receivers. Cellular and cordless telephones are actually radio transceivers. Many telephone calls routinely are relayed by radio rather than by wires; some are sent via radio to relay satellites. Some celestial bodies and interstellar gases emit relatively strong radio waves that are observed with radio telescopes composed of very sensitive receivers and large directional antennas (see radio astronomy).

Transmission and Reception of Radio Waves

For the propagation and interception of radio waves, a transmitter and receiver are employed. A radio wave acts as a carrier of information-bearing signals; the information may be encoded directly on the wave by periodically interrupting its transmission (as in dot-and-dash telegraphy) or impressed on it by a process called modulation. The actual information in a modulated signal is contained in its sidebands, or frequencies added to the carrier wave, rather than in the carrier wave itself. The two most common types of modulation used in radio are amplitude modulation (AM) and frequency modulation (FM). Frequency modulation minimizes noise and provides greater fidelity than amplitude modulation, which is the older method of broadcasting. Both AM and FM are analog transmission systems, that is, they process sounds into continuously varying patterns of electrical signals which resemble sound waves. Digital radio uses a transmission system in which the signals propagate as discrete voltage pulses, that is, as patterns of numbers; before transmission, an analog audio signal is converted into a digital signal, which may be transmitted in the AM or FM frequency range. A digital radio broadcast offers compact-disc-quality reception and reproduction on the FM band and FM-quality reception and reproduction on the AM band.

In its most common form, radio is used for the transmission of sounds (voice and music) and pictures (television). The sounds and images are converted into electrical signals by a microphone (sounds) or video camera (images), amplified, and used to modulate a carrier wave that has been generated by an oscillator circuit in a transmitter. The modulated carrier is also amplified, then applied to an antenna that converts the electrical signals to electromagnetic waves for radiation into space. Such waves radiate at the speed of light and are transmitted not only by line of sight but also by deflection from the ionosphere.

Receiving antennas intercept part of this radiation, change it back to the form of electrical signals, and feed it to a receiver. The most efficient and most common circuit for radio-frequency selection and amplification used in radio receivers is the superheterodyne. In that system, incoming signals are mixed with a signal from a local oscillator to produce intermediate frequencies (IF) that are equal to the arithmetical sum and difference of the incoming and local frequencies. One of those frequencies is applied to an amplifier. Because the IF amplifier operates at a single frequency, namely the intermediate frequency, it can be built for optimum selectivity and gain. The tuning control on a radio receiver adjusts the local oscillator frequency. If the incoming signals are above the threshold of sensitivity of the receiver and if the receiver is tuned to the frequency of the signal, it will amplify the signal and feed it to circuits that demodulate it, i.e., separate the signal wave itself from the carrier wave.

There are certain differences between AM and FM receivers. In an AM transmission the carrier wave is constant in frequency and varies in amplitude (strength) according to the sounds present at the microphone; in FM the carrier is constant in amplitude and varies in frequency. Because the noise that affects radio signals is partly, but not completely, manifested in amplitude variations, wideband FM receivers are inherently less sensitive to noise. In an FM receiver, the limiter and discriminator stages are circuits that respond solely to changes in frequency. The other stages of the FM receiver are similar to those of the AM receiver but require more care in design and assembly to make full use of FM's advantages. FM is also used in television sound systems. In both radio and television receivers, once the basic signals have been separated from the carrier wave they are fed to a loudspeaker or a display device (usually a cathode-ray tube), where they are converted into sound and visual images, respectively.

Development of Radio Technology

Radio is based on the studies of James Clerk Maxwell, who developed the mathematical theory of electromagnetic waves, and Heinrich Hertz, who devised an apparatus for generating and detecting them. Guglielmo Marconi, recognizing the possibility of using these waves for a wireless communication system, gave a demonstration (1895) of the wireless telegraph, using Hertz's spark coil as a transmitter and Edouard Branly's coherer (a radio detector in which the conductance between two conductors is improved by the passage of a high-frequency current) as the first radio receiver. The effective operating distance of this system increased as the equipment was improved, and in 1901, Marconi succeeded in sending the letter S across the Atlantic Ocean using Morse code. In 1904, Sir John A. Fleming developed the first vacuum electron tube, which was able to detect radio waves electronically. Two years later, Lee de Forest invented the audion, a type of triode, or three-element tube, which not only detected radio waves but also amplified them.

Radio telephony—the transmission of music and speech—also began in 1906 with the work of Reginald Fessiden and Ernst F. W. Alexanderson, but it was not until Edwin H. Armstrong patented (1913) the circuit for the regenerative receiver that long-range radio reception became practicable. The major developments in radio initially were for ship-to-shore communications. Following the establishment (1920) of station KDKA at Pittsburgh, Pa., the first commercial broadcasting station in the United States, technical improvements in the industry increased, as did radio's popularity. In 1926 the first broadcasting network was formed, ushering in the golden age of radio. Generally credited with creating the first modern broadband FM system, Armstrong built and operated the first FM radio station, KE2XCC, in 1938 at Alpine, N.J. The least expensive form of entertainment during the Great Depression, the radio receiver became a standard household fixture, particularly in the United States. Subsequent research gave rise to countless technical improvements and to such applications as radio facsimile, radar, and television. The latter changed radio programming drastically, and the 1940s and 50s witnessed the migration of the most popular comedy and drama shows from radio to television. Radio programming became mostly music and news and, to a lesser extent, talk shows. The turn of the century saw a potential rebirth for radio as mobile digital radio entered the market with a satellite-based subscription service in Europe (1998) and in the United States (2000). Two years later, a land-based digital radio subscription service was inaugurated in the United States.

Radios that combine transmitters and receivers are now widely used for communications. Police and military forces and various businesses commonly use such radios to maintain contact with dispersed individuals or groups. Citizens band (CB) radios, two-way radios operating at frequencies near 27 megahertz, most typically used in vehicles for communication while traveling, became popular in the 1970s. Cellular telephones, despite the name, are another popular form of radio used for communication.

Bibliography

See A. and W. Marcus, Elements of Radio (6th ed. 1973); D. L. Schilling, Principles of Communications Systems (2d ed. 1986).


 
Essay: The development of radio

It is often argued that science and technology develop independently and that new technologies only rarely are directly derived from scientific developments. There are enough examples of recent technological developments, such as the transistor or the laser, to contradict this. The development of radio communications is an early example of the direct application of physics.

It was an international collaboration. The theoretical basis of radio waves was laid by British physicist James Clerk Maxwell, who gave a thorough mathematical description of electromagnetic waves in 1873. Maxwell showed that light is an electromagnetic wave, but that electromagnetic waves with a much longer wavelength than that of light--now known as radio waves--also exist. Ten years later Irish physicist George Francis Fitzgerald suggested the way in which such waves could be produced. German physicist Heinrich Hertz was the first to deliberately produce such waves, showing that they are reflected and refracted in the same way as light.

In 1887 Hertz started his experiments, creating radio waves by producing sparks with a high-voltage induction coil, a device not very different from the coil that delivers the high-voltage pulses to the spark plugs in an automobile engine. As "receiver" he used two small spheres attached to the ends of an open loop of wire. When he brought the loop in the beam of electromagnetic radiation produced by the spark generator, he observed small sparks that jumped between the two spheres.

The coherer, invented independently a half-dozen years later by British physicist Oliver Lodge and French scientist Edouard Branley, was a more sensitive detector for radio waves than the receiving loop of Hertz. It consisted of a small tube filled with iron filings connected to electric wires at each end. In the presence of an electromagnetic wave, the iron filings line up (as Lodge expressed it, become "coherent") and the coherer starts conducting electricity. Branley could detect radio waves produced by a spark generator up to a distance of 30 m (100 ft), and Lodge was able to double that feat.

Guglielmo Marconi is generally credited as the inventor of radio communication as such, although transmitters and receivers had been built before him by other experimentalists. In 1894, when reading about the electromagnetic waves discovered by Heinrich Hertz, Marconi realized that the waves could be used for the transmission of signals in the same way as electric wires.

Marconi started experimenting with radio waves with the help of the physicist Augusto Righi. Lacking formal training in physics, Marconi proceeded empirically. He used a transmitter consisting of a high-voltage coil and a spark gap connected to an antenna circuit. The receiver consisted of a coil connected to a coherer, which conducts electricity when a radio signal is present. From the beginning Marconi concentrated on producing useful effects, such as ringing a bell from a distance. Marconi also went somewhat further than the physicists by experimenting with antennas, for which a physical theory was still nonexistent. By connecting an antenna and an earth conductor (ground) to the transmitter and receiver, Marconi was able to transmit radio signals over increasing distances. He experimented with different kinds of antennas and soon succeeded in transmitting signals over 2.4 km (1.5 mi).

Marconi tried first to interest the Italian government in his experiments. But the government showed no interest, so Marconi moved to England to continue his experiments there. In England he successfully applied for a patent for his system of radio transmission, and in 1897, with the help of wealthy relatives, he set up the Wireless Telegraph and Signal Company.

By trying different types of antennas and increasing the power of the transmitter, Marconi pushed signals to carry over much larger distances--reaching 240 km (150 mi) in 1900 and across the Atlantic Ocean in 1901.

The British army and navy became Marconi's first customers, buying systems developed by his company. By 1900 Marconi founded a subsidiary that leased radio communication systems, including radio operators, to ships and shore stations.

Mainly under the impetus of Marconi, radio communication systems developed quickly. The early transmitters were all of the spark-generator type, producing electromagnetic radiation in a pulselike manner. Such transmitters produced radiation in a wide spectrum, with the consequence that nearby transmitters easily interfered with each other. Although tuned circuits, introduced by Oliver Lodge and by Marconi, were an improvement, the greatest breakthrough in radio communication was the vacuum-tube oscillator. Such an oscillator could produce a continuous radio wave occupying only a narrow frequency range.

Canadian inventor Reginald Aubrey Fessenden was producing voice transmission as early as 1904 and soon was making experimental voice broadcasts that could be received all up and down the Atlantic coast of the United States. The introduction of the vacuum tube in 1913 also made possible a better way to modulate radio waves. Radio receivers using vacuum tubes were much more sensitive because the high-frequency signals as well as audio signals were amplified. Fessenden and other inventors, such as the American Edwin H. Armstrong, soon produced much more powerful transmitters and improved receivers based on vacuum tubes, although some early programs continued to use spark-generated signals until the early 1920s.

 
Word Tutor: radio
pronunciation

IN BRIEF: A way of sending sounds through space by changing them into electric waves.

pronunciation For you can look at things while talking or with a radio going full blast, but you can see only when the chatter stops. — Frederick Franck

 
Wikipedia: radio
Amateur Radio Station with multiple Receivers and Transceivers
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Amateur Radio Station with multiple Receivers and Transceivers


Radio is the wireless transmission of signals, by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. It does not require a medium of transport. Information is carried by systematically changing (modulating) some property of the radiated waves, such as their amplitude or their frequency. When radio waves pass an electrical conductor, the oscillating fields induce an alternating current in the conductor. This can be detected and transformed into sound or other signals that carry information.

The word 'radio' is used to describe this phenomenon, and radio transmissions are classed as radio frequency emissions.

Etymology

Originally, radio or radioteleography was called 'wireless telegraphy', which was shortened to 'wireless'. The prefix radio- in the sense of wireless transmission was first recorded in the word radioconductor, coined by the French physicist Edouard Branly in 1897 and based on the verb to radiate (in Latin "radius" means "spoke of a wheel, beam of light, ray"). 'Radio' as a noun is said to have been coined by advertising expert Waldo Warren (White 1944). The word appears in a 1907 article by Lee de Forest, was adopted by the United States Navy in 1912 and became common by the time of the first commercial broadcasts in the United States in the 1920s. (The noun 'broadcasting' itself came from an agricultural term, meaning 'scattering seeds'.) The term was then adopted by other languages in Europe and Asia, although British Commonwealth countries retained the term 'wireless' until the mid-20th century. In Japanese, the term 'wireless' is the basis for the term 'radio wave' although the term for the device that listens to radio waves is literally 'device for receiving sounds'.

In recent years the term 'wireless' has gained renewed popularity through the rapid growth of short range networking, e.g., WLAN ('Wireless Local Area Network'), WiFi and Bluetooth as well as mobile telephony, e.g., GSM and UMTS. Today, the term 'radio' often refers to the actual transceiver device or chip, whereas 'wireless' refers to the system and/or method used for radio communication. Hence one talks about radio transceivers and Radio Frequency Identification (RFID), but about wireless devices and wireless sensor networks.

Invention

Further information: Invention of radio

Although invention was long attributed to Guglielmo Marconi, the identity of the original inventor of radio, at the time called wireless telegraphy, is contentious[1]. Development from a laboratory demonstration to commercial utility spanned several decades and required the efforts of many practitioners. The controversy over who invented the radio, with the benefit of hindsight, can be broken down as follows:

  • In 1891, Nikola Tesla began wireless research. He developed means to reliably produce radio frequencies, publicly demonstrated the principles of radio, and transmitted long-distance signals.
  • Between 1893 and 1894, Roberto Landell de Moura, a Brazilian priest and scientist, conducted experiments. He did not publicise his achievement until 1900 but later obtained Brazilian patent.
  • Alexander Stepanovich Popov, in 1894, built his first radio receiver, which contained a coherer but actually coherer was first demonstrated by J.C. Bose. Popov demonstrated the coherer, further refined as a lightning detector, to the Russian Physical and Chemical Society on May 7, 1895.
  • In 1894, Guglielmo Marconi read about Hertz's and Tesla's work on wireless telegraphy, and began his own experiments.
  • By 1897 Nikola Tesla had successfully conducted experiments, and obtained a U.S. patent for his invention of "wireless transmission of data" (i.e. radio) in 1897 and 1900.[1]
  • In December of 1901 Guglielmo Marconi used J.C. Bose's inventions to receive the radio signal in his first transatlantic radio communication over a distance of 2000 miles from Poldhu, UK, to St. Johns, Newfoundland. Marconi was celebrated worldwide for this achievement, but the fact that the radio patent was already registered by Tesla in 1900, as well as the fact the receiver was invented by Bose was not well known. Soon after the patent is given to Marconi. He even received the Nobel Prize.
  • In 1943, the U.S. Supreme Court acknowledged that Marconi's work wasn't original, and the patent ownership is given back to Nikola Tesla. However, Tesla died shortly before the decision was announced.[2]

History

For more details on this topic, see History of radio.
Tesla demonstrating wireless transmissions during his high frequency and potential lecture of 1891. After continued research, Tesla gave the fundamentals of radio in 1893.
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Tesla demonstrating wireless transmissions during his high frequency and potential lecture of 1891. After continued research, Tesla gave the fundamentals of radio in 1893.

In 1893, in St. Louis, Missouri, Tesla made devices for his experiments with electricity. Addressing the Franklin Institute in Philadelphia and the National Electric Light Association, he described and demonstrated in detail the principles of his wireless work. [3] The descriptions contained all the elements that were later incorporated into radio systems before the development of the vacuum tube. He initially experimented with magnetic receivers, unlike the coherers (detecting devices consisting of tubes filled with iron filings which had been invented by Temistocle Calzecchi-Onesti at Fermo in Italy in 1884) used by Guglielmo Marconi and other early experimenters. [4].

In 1894 Alexander Stepanovich Popov built his first radio receiver, which contained a coherer. Further refined as a lightning detector, it was presented to the Russian Physical and Chemical Society on May 7, 1895.

The first public demonstration of wireless telegraphy took place in the lecture theatre of the Oxford University Museum of Natural History on August 14, 1894, carried out by Professor Oliver Lodge and Alexander Muirhead. During the demonstration a radio signal was sent from the neighbouring Clarendon laboratory building, and received by apparatus in the lecture theatre.

In 1896, Marconi was awarded the British patent 12039, Improvements in transmitting electrical impulses and signals and in apparatus there-for, for radio. In 1897 he established the world's first radio station on the Isle of Wight, England. Marconi opened the world's first "wireless" factory in Hall Street, Chelmsford, England in 1898, employing around 50 people.

The next great invention was the vacuum tube detector, invented by Westinghouse engineers. On Christmas Eve, 1906, Reginald Fessenden used a synchronous rotary-spark transmitter for the first radio program broadcast, from Brant Rock, Massachusetts. Ships at sea heard a broadcast that included Fessenden playing O Holy Night on the violin and reading a passage from the Bible. The first radio news program was broadcast August 31, 1920 by station 8MK in Detroit, Michigan. The first college radio station, 2ADD, renamed WRUC in 1940, began broadcasting October 14, 1920 from Union College, Schenectady, New York. At 9 pm on August 27, 1920, Sociedad Radio Argentina aired a live performance of Richard Wagner's Parsifal opera from the Coliseo Theater in downtown Buenos Aires, only about twenty homes in the city had a receiver to tune in. The first regular entertainment broadcasts commenced in 1922 from the Marconi Research Centre at Writtle, near Chelmsford, England.

One of the first developments in the early 20th century (1900-1959) was that aircraft used commercial AM radio stations for navigation. This continued until the early 1960s when VOR systems finally became widespread (though AM stations are still marked on U.S. aviation charts). In the early 1930s, single sideband and frequency modulation were invented by amateur radio operators. By the end of the decade, they were established commercial modes. Radio was used to transmit pictures visible as television as early as the 1920s. Commercial television transmissions started in North America and Europe in the 1940s. In 1954, Regency introduced a pocket transistor radio, the TR-1, powered by a "standard 22.5 V Battery".

In 1960, Sony introduced its first transistorized radio, small enough to fit in a vest pocket, and able to be powered by a small battery. It was durable, because there were no tubes to burn out. Over the next 20 years, transistors replaced tubes almost completely except for very high-power uses. By 1963 color television was being regularly transmitted commercially, and the first (radio) communication satellite, TELSTAR, was launched. In the late 1960s, the U.S. long-distance telephone network began to convert to a digital network, employing digital radios for many of its links. In the 1970s, LORAN became the premier radio navigation system. Soon, the U.S. Navy experimented with satellite navigation, culminating in the invention and launch of the GPS constellation in 1987. In the early 1990s, amateur radio experimenters began to use personal computers with audio cards to process radio signals. In 1994, the U.S. Army and DARPA launched an aggressive, successful project to construct a software radio that could become a different radio on the fly by changing software. Digital transmissions began to be applied to broadcasting in the late 1990s.

Uses of radio

Early uses were maritime, for sending telegraphic messages using Morse code between ships and land. The earliest users included the Japanese Navy scouting the Russian fleet during the Battle of Tsushima in 1905. One of the most memorable uses of marine telegraphy was during the sinking of the RMS Titanic in 1912, including communications between operators on the sinking ship and nearby vessels, and communications to shore stations listing the survivors. The first radio couldn't transmit sound or speech and was called the "wireless telegraph"

Radio was used to pass on orders and communications between armies and navies on both sides in World War I; Germany used radio communications for diplomatic messages once its submarine cables were cut by the British. The United States passed on President Woodrow Wilson's Fourteen Points to Germany via radio during the war. Broadcasting began from San Jose in 1909[5], and became feasible in the 1920s, with the widespread introduction of radio receivers, particularly in Europe and the United States. Besides broadcasting, point-to-point broadcasting, including telephone messages and relays of radio programs, became widespread in the 1920s and 1930s. Another use of radio in the pre-war years was the development of detecting and locating aircraft and ships by the use of radar (RAdio Detection And Ranging).

Today, radio takes many forms, including wireless networks and mobile communications of all types, as well as radio broadcasting. Before the advent of television, commercial radio broadcasts included not only news and music, but dramas, comedies, variety shows, and many other forms of entertainment. Radio was unique among methods of dramatic presentation in that it used only sound. For more, see radio programming.

Audio

A Fisher 500 AM/FM hi-fi receiver from 1959.
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A Fisher 500 AM/FM hi-fi receiver from 1959.

AM broadcast radio sends music and voice in the Medium Frequency (MF—0.300 MHz to 3 MHz) radio spectrum. AM radio uses amplitude modulation, in which the amplitude of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone while the transmitted frequency remains unchanged. Transmissions are affected by static and interference because lightning and other sources of radio that are transmitting at the same frequency add their amplitudes to the original transmitted amplitude. The most wattage an AM radio station is allowed to use is 50,000 watts and the only stations that emit signals this powerful were grandfathered in; these include WJR and CKLW.

FM broadcast radio sends music and voice with higher fidelity than AM radio. In frequency modulation, amplitude variation at the microphone causes the transmitter frequency to fluctuate. Because the audio signal modulates the frequency and not the amplitude, an FM signal is not subject to static and interference in the same way as AM signals. FM is transmitted in the Very High Frequency (VHF—30 MHz to 300 MHz) radio spectrum. VHF radio waves act more like light, traveling in straight lines, hence the reception range is generally limited to about 50-100 miles. During unusual upper atmospheric conditions, FM signals are occasionally reflected back towards the Earth by the ionosphere, resulting in Long distance FM reception. FM receivers are subject to the capture effect, which causes the radio to only receive the strongest signal when multiple signals appear on the same frequency. FM receivers are relatively immune to lightning and spark interference.

FM Sub-carrier services are sec