Radio

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>.

ErnstS.Sibberson

RADIO

RADIO. 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.

BobBatchelor

Radio. Radio developed from wired and later wireless telegraph and telephone technology, and adapted its broadcasting contents from vaudeville, the phonograph, the popular press, and film.In the early 1920s, these elements combined to create a new medium.

Before 1920.

Radio developed first outside the United States. A few American experimenters sought improved point‐to‐point communication to compete with existing wired services and to transmit to ships at sea. Lee de Forest (1874–1961), the first important American wireless inventor, developed his Audion three‐element vacuum tube in 1906. But it took years to realize its ability to amplify sound and thus its wireless applications. Perhaps the first broadcast took place on Christmas Eve 1906 when Reginald Fessenden transmitted signals of his voice and recorded music near Boston. Early public attention focused on radio's lifesaving role in such disasters as the 1912 Titanic sinking. Edwin Howard Armstrong (1890–1954), another key American inventor, patented several circuits widely used in radio receivers and fought lengthy patent battles with de Forest and others. Thousands of soldiers learned to use radio during World War I, but postwar development was slowed by the cancellation of government manufacturing contracts and by the fact that the patents needed to make radios were held by competing firms. Cooperation was imperative, and the Radio Corporation of America (RCA) was founded in 1919 to coordinate American radio manufacturing through a shared patent pool. But this hard‐won legal agreement did not foresee broadcasting.

1920–1927.

The inception of service by station KDKA in East Pittsburgh on 2 November 1920 is widely accepted as the birth of regular American broadcasting. Operated by the Westinghouse Corporation to encourage purchase of its radios, the station offered a regular weekly schedule of a few hours of talk and music designed for general listening. RCA built stations (also to sell radios), as did American Telephone and Telegraph (AT&T), which perceived radio as similar to toll telephony. As public interest soared, some five hundred stations went on the air by 1922, creating a cacophony of interference. Under a 1912 Radio Act that had not foreseen broadcasting's demand, the U.S. Department of Commerce had to license all applicants. Secretary of Commerce Herbert Hoover called four radio conferences (1922–1926) to develop industry agreement on new legislation, then persuaded Congress to pass it. The resulting Radio Act of 1927 established a Federal Radio Commission (FRC) to license and regulate stations.

How to support these stations created further controversy. AT&T's New York station, WEAF, first sold time to advertisers in 1922, and eventually this became the accepted means of meeting operating costs. WEAF also first interconnected stations with telephone lines (1923) to allow program sharing, thereby creating the first experimental networks. The National Broadcasting Company (NBC) was the first company established (in 1926 by owner RCA) as a national radio network. The Columbia Broadcasting System (CBS) followed in 1927. There were then nearly seven hundred AM (amplitude modulation) stations on the air.

1928–1948.

The years before television competition marked radio's golden age. Despite the Depression of the 1930s, radio prospered as it provided free entertainment and news to anyone who owned a receiver. By the early 1930s, popular formats were well established, including half‐hour situation comedies, variety and music programs, brief daily newscasts, fifteen‐minute daytime serial dramas, and evening dramas of many kinds. Radio stars ranked in public appeal with those of film and stage. One indicator of radio's growing role came on Halloween in 1938, when a CBS adaptation of H.G. Wells's War of the Worlds, directed by and starring the young actor Orson Welles, frightened millions into believing that America was under attack by invading Martians.

Audience ratings based on telephone surveys conducted by the C.E. Hooper Company measured radio's growing appeal to advertisers. Radio's share of all advertising soared—from less than 1 percent in 1928 to a high of 15 percent in 1945 when radio profited from wartime paper shortages that limited newspapers' advertisements. Despite the networks' dominance, radio's local appeal was evident as local advertising revenue grew from 20 percent of radio income in the late 1920s to twice that two decades later. This encouraged station growth—from just over 600 AM outlets in 1930 to 765 in 1940 and 1,612 in 1948.

Meanwhile, more regional and national networks appeared. Mutual Broadcasting System began operating in 1934 based on cooperative sharing of programs among its stations. The dominance of CBS and NBC (which operated two parallel national networks) over programs and advertising led the Federal Communications Commission (FCC, created in 1934 to replace the FRC) to investigate in 1938–1941. The FCC ordered NBC to divest one network, a decision upheld by the Supreme Court in 1943. NBC's Blue network was sold and became the American Broadcasting Company in 1945.

The search for interference‐free operation eventually led to frequency modulation (FM) radio in the late 1930s. Based on a new transmission system perfected by Edwin Armstrong, the first experimental station aired in 1938. FM generally eliminated on‐air static and provided much improved sound quality over AM stations. The FCC approved commercial FM operation in 1941. Few FM stations aired before America's entry into World War II froze further expansion, but by 1948 some 460 FM stations were on the air.

1948–1980.

Network radio declined after network television's first season in 1948–1949, and stations began a difficult transition back to the role of a local, music‐based medium. Network programming disappeared by the early 1950s as audiences and advertisers moved to television. Whereas more than 90 percent of the 1,000 radio stations on the air in 1947 had been affiliated with a national network, a decade later fewer than half the 3,000 stations held network agreements, while only a quarter of 1967's 5,700 AM–FM stations were tied to any network's hourly newscasts, special events, and sports coverage.

The continued growth in the number of stations offered solid evidence of radio's successful transition to something quite different from television. A return to music‐based programming (as in radio's earliest days) was paced by “Top–40” stations that attracted youth who learned a lifelong radio habit (as adults, many would tune to “golden oldies” outlets). Although the number of FM stations declined through 1957 because of few receivers, smaller audiences, and industry focus on television and AM, FM expanded in the 1960s aided by FCC approval of stereo FM in 1961. By 1979 FM stations collectively surpassed the more numerous AM outlets in total national listening.

The FCC reserved some FM frequencies for noncommercial or educational service. From 15 such stations in 1948, what later became known as public radio grew to 162 outlets in 1960, more than 400 in 1970, and over 1,000 by 1980. National Public Radio tied many of these outlets together beginning in the early 1970s and numerous states had networks of stations. Public radio offered drama, music, in‐depth news reporting, and special programs. Audiences were small but intensely loyal.

Since 1980.

As the twentieth century ended, radio was characterized by program specialization, use of satellites for distribution of programs, and continued expansion—to some twelve thousand AM and FM stations by 2000. Fully three‐quarters of all radio listening was to FM stations. Deregulation in 1996 encouraged ownership of chains of hundreds of stations—and up to eight outlets in the largest cities. With little FCC program oversight, often strident right‐wing talk shows, conservative religious station, and other controversial formats thrived. Early in 2000, the FCC established Low Power FM (LPFM), which could in time place hundreds of mini‐stations on the air. Further change loomed with the inception of digital radio services projected early in the new century.
See also Electricity and Electrification; Mass Marketing; New Deal Era, The; Popular Culture; Public Broadcasting; Twenties, The.

Bibliography

Erik Barnouw , A Tower in Babel: A History of Broadcasting in the United States to 1933, 1966.
Erik Barnouw , The Golden Web: A History of Broadcasting in the United States, 1933–1953, 1968.
Susan J. Douglas , Inventing American Broadcasting, 1899–1922, 1987.
Christopher H. Sterling and and John Michael Kittros , Stay Tuned: A Concise History of American Broadcasting, 2d ed., 1990.
Susan Smulyan , Selling Radio: The Commercialization of American Broadcasting, 1920–1934, 1994.
Ray Barfield , Listening to Radio, 1920–1950, 1996.
Robert L. Hilliard and and Michael C. Keith , The Broadcast Century: A Biography of American Broadcasting, 2d ed., 1997.
Michele Hilmes , Radio Voices: American Broadcasting, 1922–1952, 1997.
John Dunning , On the Air: The Encyclopedia of Old‐Time Radio, 1998.
Donald G. Godfrey and and Frederic A. Leigh , Historical Dictionary of American Radio, 1998.
Christopher H. Sterling, ed. Encyclopedia of Radio, 2001.

Christopher H. Sterling

radio 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).

RADIO

An Experimental Apparatus

In 1920 radio was still in the experimental stage. Guglielmo Marconi invented wireless telegraphy in 1899. The wireless telegraph sent a series of dot and dash signals through space, using the same code invented in the 1840s by Samuel Morse. In 1906 an actual voice communication was transmitted, and wireless telephony was invented. Both forms of communication were commonly called "wireless," but in 1912 the U.S. Navy ordered that the terms radiotelegraphy and radiotelephony be employed instead. The American public rapidly accepted the change, but by 1920 the simple term radio had become the American name for the still experimental invention. The British, however, continued using the term wireless for most of the twentieth century.

Vacuum Tubes

The earliest radios were crystal sets, difficult to tune and operate. During World War I, however, developments in vacuum tubes, devices similar to light bulbs and the ancestors of the modern transistors, allowed the sending and receiving of radio signals to become much more precise and powerful.

The First Radio Station

The first commercial radio station was started by Dr. Frank Conrad, an engineer with Westinghouse in East Pittsburgh, Pennsylvania, who was working on voice-transmitting equipment for the U.S. Navy. He set up what amounted to a ham radio operation in his garage and tested the navy's equipment by talking to the Westinghouse plant some four or five miles away. In April 1920, as his transmissions became of more than research interest, he received a license to use the call letters 8XK and began communicating with a circle of radio-buff friends in the Pittsburgh area. To save his voice and his time he began playing phonograph records over the air. A local department store heard about the broadcast music and placed an advertisement in the Pittsburgh Sun hoping to sell radio receivers to those who could not make their own.

Marketing Radio

At that point Harry P. Davis, a Westinghouse vice president with a mind for marketing, foresaw that voices and music coming over the airways would appeal to the public at large, not just technically minded hobbyists. At Davis's urging Westinghouse set up Conrad in the plant with a more powerful transmitter, and on 27 October 1920 the Department of Commerce licensed the station to operate on the wavelength of 360 meters and assigned it a four-letter, nautical call sign, KDKA, as if Conrad were broadcasting from a ship. The first commercial radio station was born, and a new era had dawned.

The Radio Boom

With litigation over some twelve hundred vacuumtube patents still unresolved, additional new stations did not pop up overnight. The navy joined the chorus of those wanting an end to the patent squabbling, which was literally stopping progress, and the situation was substantially improved by agreements made in July 1921. Some legal wrangling, however, persisted for years. Nevertheless, commercial radio stations—mostly small, shoestring operations—began springing up nationwide. The second station, WEAF in New York, started to broadcast in September 1921; by the end of 1922 there were 508 stations. In April 1923 the editors of Scientific American proclaimed, "1922 will stand out in the history of radio. For it was during the past year that radio broadcasting became a regular feature of everyday life, and radio entered the average home life of the average man." In 1921, before the boom began, only $9 million worth of radio equipment was sold. In 1923 that figure had increased to some $46 million, and in 1926 the total national expenditure on radio equipment was $400 million. With this tremendous growth came the need for regulation, and in February 1927 the Federal Radio Commission was established.

The Superhet

In 1922 Edwin Armstrong made a significant scientific breakthrough for broadcasting when he invented the superheterodyne receiver. In the "superhet" the incoming signal is mixed (heterodyned) with another nearby frequency. When one frequency is subtracted from the other the resultant signal is more easily and cleanly amplified—leading to increased fidelity. The invention eventually came to be included in virtually all radio receivers. In 1922 there were already some sixty thousand households with radios. By 1933 there would be close to twenty million.

FM Radio

By 1929 Armstrong had successfully tested frequency modulation (FM), a new form of broadcasting in which the radio-wave frequency itself is varied to transmit the signal. All original radio broadcasting used amplitude modulation (AM), in which the size (amplitude) of the wave is varied to transmit the signal. FM signals are less susceptible to noise interference than AM and are less likely to overlap each other in cases of poor reception. They do, however, have to be spaced farther apart on the radio band. Because of the onset of the Depression and difficulty in convincing broadcast companies that FM radio would work, it would be another ten years before Armstrong would be able to put an FM station on the air.

Sources:

Hugh G. J. Aitken, The Continuous Wave: Technology and the American Radio, 1900-1922 (Princeton: Princeton University Press, 1985);

Gleason Archer, History of the Radio to 1926 (New York: American Historical Society, 1938);

Susan J. Douglas, Inventing American Broadcasting, 1899-1922 (Baltimore: Johns Hopkins University Press, 1987);

Thomas S. W. Lewis, "Radio Revolutionary: Edwin Armstrong's Innovations," Invention and Technology, 1 (Fall 1985);

John Liston, "Twelve Months of Radio," Scientific American, 128 (April 1923): 242, 286-287;

Paul Schubert, The Electric Word: The Rise of Radio (New York: Macmillan, 1928).

Radio

Radio is the technology that allows information to be transmitted and received over radio waves. Radio makes it possible to establish wireless two-way communication between individual pairs of transmitters/receivers and it is used for one-way broadcasts to many receivers. Radio signals can carry speech, music, or digitally encoded entertainment. Radio waves occur naturally in space or can be created by people. They are a long-wave form of electromagnetic radiation, or radiation that transmits energy through the interaction of electricity and magnetism.

The history of radio

In the nineteenth century, Scottish physicist James Clerk Maxwell (1831–1879) developed a mathematical theory proving that magnetism and electricity were related. His theory linking the two forces became known as the electromagnetic theory. He predicted that light is only one type of electromagnetic radiation and that wavelengths should exist below infrared (those situated outside the visible spectrum at the red or long-wavelength end) and above ultraviolet (situated outside the visible spectrum at the violet or short-wavelength end). In the 1880s, German physicist Heinrich Hertz (1857–1894) discovered extremely long-wavelength radio waves, proving Maxwell's theory.

Italian physicist and engineer Guglielmo Marconi (1874–1937), fascinated with Hertz's discovery of radio waves, built his first crude radio transmitter and receiver in 1895. In 1901, using his "wireless" (as radio was called then), he sent the first message via signals similar to Morse code (which uses dots and dashes for letters and numbers) across the Atlantic Ocean. In the succeeding years, other scientists improved on Marconi's invention, and it eventually became possible to send voice signals by radio waves.

Radio broadcasting as we know it today began in 1920. Station KDKA in Pittsburgh, Pennsylvania, made the announcement to the few people who owned radio receivers that Warren G. Harding had been elected president of the United States. Within a few years, many homes had radio receivers and several radio stations scheduled regular programming.

Radio waves and frequencies

Although turning on a radio produces sound, radio waves themselves cannot be "heard" and have nothing to do with sound waves. While sound waves are a vibration of the air, radio waves are electromagnetic and a part of the light spectrum. Radio waves travel at a speed of 186,282 miles (299,727 kilometers) per second—the speed of light. Radio waves travel through the air, surrounding us with vibrations that can only be detected through a radio receiver.

Radio programs begin as sound waves, which microphones change into electrical signals. From the antenna atop the radio station, the electrical signals are broadcast as electromagnetic waves. The receiver picks up the waves in the air, electrically amplifies (enlarges) them, and converts them back into sound through the speaker of the radio in your home.

Although radio waves from many stations surround us all the time, the radio does not receive them all at the same time because the stations broadcast at different frequencies. A frequency is the number of times per second that radio waves vibrate. The numbers on a radio dial represent the frequencies used by radio stations in your area. For example, if the dial is set at 96, the radio signal you hear is broadcasted at 960 kilocycles, or 960,000 cycles per second.

Words to Know

Carrier wave: Radio signal with superimposed information.

Electromagnetic radiation: Radiation that transmits energy through the interaction of electricity and magnetism.

Infrared radiation: Electromagnetic radiation of a wavelength shorter than radio waves but longer than visible light that takes the form of heat.

Modulation: Process by which a characteristic of radio waves, such as amplitude or frequency, is changed to make the waves correspond to a signal or information that is being transmitted.

Ultraviolet radiation: Electromagnetic radiation of a wavelength just shorter than the violet end of the visible light spectrum.

Wavelength: The distance between two peaks in any wave.

Modulation

A radio signal alone, without information (speech, music) added to it, is called a carrier wave. Adding information to a carrier signal is a process called modulation. The simplest modulation method is to vary the strength of the signal. The result is called amplitude modulation, or AM. The method that varies the signal's frequency is known as frequency modulation, or FM. AM radio waves are about 1,000 feet (1,600 kilometers) in wavelength, while FM radio waves are only a few feet in wavelength. Broadcasts on AM radio stations can often be heard for hundreds of miles, especially at night when electromagnetic interference is minimal. Broadcasts on FM stations do not travel such a distance, but they have better sound quality and are not affected by lightning-caused static that often plagues AM broadcasts.

[See also Electromagnetic spectrum ]

RADIO

Five Radios in Every Home

Radio continued throughout the 1980s to be the most pervasive medium in America. Ninety-nine percent of American households owned radios in the 1980s (compared to 98 percent who owned televisions), and each household had an average of 5.5 radios. Those figures do not take into account automobile radios, which had become standard equipment in most of the 5.5 million passenger cars sold each year. The American radio audience tended to be younger, better educated, and wealthier than the television audience, though Multimedia Audiences, a sampling of media choices at specified times, indicated that 91.7 percent of Americans were likely to be watching television as compared to 85.3 percent who were listening to the radio.

Local Origins

Radio and television differed significantly in the origin of their programming. The three major national television networks dominated prime-time programming, and though FCC rules stipulated that a certain amount of the broadcast day had to be reserved for locally originated programs, network shows were the meat of the television schedule. Radio programs almost always originated locally. Radio networks provided some feeds and owned a handful of stations, but radio was a medium of independent stations airing local programs. The radio listener had access to more than nine thousand stations in the United States (as compared to 1,362 television stations in 1988), though most could only be picked up by listeners within about a fifty-mile radius of the broadcast center. Those were about evenly divided between AM and FM broadcasters by 1989.

The Rise of FM

The most significant change in radio during the 1980s was in the rise of FM programming. In 1980 AM stations outnumbered FM broadcasters by about 3-2, and about nine hundred new FM stations were authorized by the FCC during the decade. Quality of signal was the reason. FM broadcasts had greater fidelity, less superfluous noise, and could be easily converted to stereophonic reception with standard equipment. AM broadcasts, on the other hand, had a built-in staticlike noise, and though the FCC authorized the production of AM stereo broadcasts in 1982, there was no standard, and stations were unwilling to commit to the expense of equipment to improve sound quality that might not meet whatever standard emerged. As a result no standard was established, and FM became the medium of choice for listeners who appreciated clearly reproduced music. Slowly AM became the home of talk radio—news, sports, and call-in programs.

Shock Radio

In notable instances FM radio acquired a rebel character. Alternative programming was far more common on FM bands, and rock music calculated to shock adults as presented by irreverent disc jockeys was a staple of progressive stations in most large markets. In 1986 Susan Baker, wife of Secretary of Treasury James A. Baker, led a group called Parents' Music Resource Center (PMRC) to lobby Congress for legislation to prohibit radio broadcast of songs, specifically popular rock 'n' roll music, with sexually explicit lyrics. The issue was broadened when listeners complained about disc jockeys whose programs featured obscene language and explicit sexual content—their programs were called shock radio. In November 1987 the FCC ruled that indecent programming was allowed, but only between the hours of mid-night and 6:00 A.M. The ruling was in keeping with a general inclination during the decade to avoid unnecessary regulation of broadcasting. In 1981 broadcasters had been freed of the fairness doctrine, which required equal airtime for political opponents; the restriction limiting commercials to no more than twenty minutes an hour had been lifted; and radio broadcasters had been relieved of many FCC reporting requirements

NPR

National Public Radio (NPR), on the other hand, brought the voice of civility to FM radio. All Things Considered and its rising-time counterpart Morning Edition won awards and attracted record audiences for public broadcasting, but the network also faced a budget crisis. In May 1983 NPR president Frank Mankiewicz announced a surprisingly large debt that had been masked by accounting errors and promptly resigned. The Corporation for Public Broadcasting, the umbrella organization that included NPR, negotiated a multimillion-dollar loan and initiated an aggressive fund-raising campaign. Beginning that year NPR may have been commercial free, but during specified weeks it gave a significant portion of its programming to pleas for donations to support operations. The tactic worked, and by the end of the decade NPR was a significant radio presence, as the most successful nationally based news radio network.

radio was the dominant sound medium of the first half of the 20th cent., and—though now less popular than television—still has a residual power in areas such as news and music. The solution to the technical problem of how to send telegraph and telephone messages without connecting cables was found in the late 19th cent. when wire-less means of communication became viable with the discovery by Hertz of electromagnetic waves. In Britain, Italian inventor Marconi developed the first wireless telegraph in 1896, sending airwave messages in Morse code over the Atlantic in 1901. The development of the thermionic valve in America by Lee de Forest and in Britain by John A. Fleming allowed speech to be turned into radio waves, and the First World War brought rapid developments in this means of transmitting messages on the airwaves.

After the war, electrical companies such as Marconi's experimented with transmitting entertainment items to the many amateur radio receivers throughout Britain. After initial attempts to ban such activities, the government decided to license the experiments, leading to the creation in 1922 of the British Broadcasting Company as a monopoly private consortium of radio companies, responsible to the postmaster-general and supported by a licence fee.

With its elevation to a corporation in 1927, the BBC set the tone for radio in Britain over the next 40 years—a paternalistic diet of information and education, with some concessions to entertainment in the form of light musical and variety items. Challenges from the more populist fare of other radio stations—Radio Luxembourg from 1933, American Forces Radio in the Second World War, and offshore pirate radio stations in the 1960s—brought gradual revision to programming policy. The biggest changes to British radio however came in the early 1970s with government legislation to permit commercial radio, under the name of Independent Local Radio (ILR). Capital and LBC in 1973 were the first of a network of stations that grew up throughout the country over the next few years, under the guidance of the Independent Broadcasting Authority (now the Radio Authority). ILR's populist fare often proved more successful than the BBC national and local radio in certain areas, and under Conservative free enterprise policy in the 1980s and 1990s, the expansion of commercial radio was cemented with licences to new national, regional, local, community, and ethnic stations. The pattern of radio consumption has been irrevocably changed, and the BBC entered the 21st cent. with fundamental questions about its position in British culture and society still unanswered.

Douglas J. Allen

radio. Broadcasting in independent Ireland began with the Dublin Broadcasting Station, generally referred to by its call sign 2RN, which began transmitting on 1 January 1926. A second station in Cork, broadcasting some local programmes along with relays of 2RN, opened in 1927 but closed again in 1930. From 6 February 1933 2RN was superseded by Radio Athlone, whose high‐powered broadcasts reached a wider geographical area. From 1937 the station was generally known as Radio Éireann, although this did not become a legal entity until the Broadcasting Act of 1960 created the Radio Éireann authority.

Widespread evasion makes the number of radio licences an inadequate guide to audience size. However, drives against unlicensed sets pushed licence numbers up from 100,000 in 1937 to 139,000 in 1938, and from 187,000 in 1947 to 261,000 in 1948. In 1961, the last year before the advent of television, 502,000 licences were issued. In 1979 the authority belatedly responded to consumer demand by launching a pop music station, 2FM. An Irish language station, Radio na Gaeltachta, began broadcasting in 1972.

In Northern Ireland, transmissions by the British Broadcasting Corporation began in 1924, and the opening of a new transmitter at Lisnagarvey near Lisburn, Co. Antrim, in 1936 permitted reception beyond the 50‐mile radius round Belfast. By 1939 124,000 licences had been issued, suggesting that perhaps half of all Northern Ireland families had a radio, compared to around one in four in the Irish Free State.

As a body under state control, 2RN and its successors played an important part in the dissemination of an official culture, notably through Irish language broadcasts, and through programmes devoted to traditional music and Gaelic games. In Northern Ireland, by contrast, efforts to promote a distinctive local culture were inhibited by intense political and public hostility to anything suggestive of an ‘Irish’ identity.

RADIO

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.

Neil Schneider

(see also: Mass Media; Mass Media and Tobacco Control; Media Advocacy )

radio Broadcasting or reception of electromagnetic radiation in the form of radio waves. A transmitter generates a radio signal of fixed frequency (the carrier wave). A microphone converts the sound to be broadcast into a varying electrical signal that combines with the carrier by means of modulation (varying the frequency or amplitude of the carrier). Frequency modulation (FM) minimizes interference and provides greater fidelity than amplitude modulation (AM). The modulated carrier wave passes to an aerial, which transmits it into the atmosphere. At the receiver, another aerial intercepts the signal, and it undergoes ‘detection’, the reverse of modulation, to retrieve the signal. Radio waves travel at the speed of light and are transmitted not only by line-of-sight (ground waves), but also by reflection from the ionosphere (sky waves). Sky waves enable long-range transmission. The ultra high frequency (UHF) and very high frequency (VHF) radio waves used to send signals for television penetrate the ionosphere with little reflection, and long-range broadcasting is made possible by means of artificial satellites. The development of radio was a truly international effort. It stems from the work of Scottish physicist James Clerk Maxwell. German physicist Heinrich Hertz devised an apparatus for the transmission and detection of radio waves. In 1895, Italian physicist Guglielmo Marconi gave a demonstration of the first wireless telegraph, and in 1901 he sent the first transatlantic message using Morse code. In 1904, English engineer Sir John Fleming invented the thermionic valve. In 1906, US physicist Lee De Forest developed the audion triode valve, which was able to detect and amplify radio waves. It remained at the heart of radio and television manufacture until the invention (1948) of the transistor.

ra·di·o / ˈrādēˌō/ • n. (pl. -os) the transmission and reception of electromagnetic waves of radio frequency, esp. those carrying sound messages: cellular phones are linked by radio rather than wires. ∎  the activity or industry of broadcasting sound programs to the public: she has written much material for radio| [as adj.] a radio station. ∎  radio programs: we used to listen to a lot of radio. ∎  an apparatus for receiving such programs: she turned on the radio. ∎  an apparatus capable of both receiving and transmitting radio messages between individuals, ships, planes, etc.: a ship-to-shore radio. ∎  [in names] a broadcasting station or channel: Monitor Radio. • v. (-oes, -oed) [intr.] communicate or send a message by radio: the pilot radioed for help. ∎  [tr.] communicate with (a person or place) by radio: we'll radio Athens right away.

343. Radio

See also 265. MEDIA .

phototelegraphy

the transmission of pictures, print, etc., by means of radio or telegraphy. —phototelegraphic, adj.

radiophony

radiotelephony. —radiophonic, adj.

radiotechnology

the science and technology of radio engineering. —radiotechnologic, radiotechnological, adj. See also 342. RADIATION .

radiotelegraphy

1. the transmitting and receiving of messages by radiotelegraph.

2. the science and technology of the radiotelegraph. —radiotelegraphic, adj.

radiotelephony

verbal communication at a distance by radio, using telephones. Also called radiophony . —radiotelephonic, adj.

telemechanics

the science of operating or controlling mechanisms by remote control, especially by radio.

radio XX. abbrev. of radiotelegraphy, -telephony; see next.

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