Heinrich Hertz

German physicist Heinrich Hertz (1857-1894) was the first to verify the predictions of James Clerk Maxwell, made in 1873, regarding the existence of electromagnetic waves. Using a tuned spark gap transmitter and a tuned spark gap detector located a few meters away, he verified in 1887 that electromagnetic waves produced by the transmitter when it sparked caused sparks to appear in the spark gap of the receiver. Hertz also determined that electromagnetic waves could be reflected by metallic objects (the basis of RADAR) and that nonconductors allow the passage of radio waves. He is also credited with the discovery of the photoelectric effect, which is the basis of electronic image transmission.

Hertz' pioneering role has been recognized in the adoption of his name as the electrical unit for the frequency of an electic or electromagnetic wave. A Hertz (Hz) is one cycle per second. A megahertz (mHz)is 1,000,000 cycles per second, and falls right in the middle of the AM radio band.

Guglielmo Marconi

Guglielmo Marconi (1874-1937) is often called the father of radio. Inspired by the experiments of Heinrich Hertz, in 1894 he successfully began experimenting with wireless telegraphy using spark transmitters. While unsuccessful in persuading the Italian government to adopt his system, he was able to receive English patents in 1896. Shortly thereafter he received financing and formed his own wireless telegraph company. In 1901 he succeeded in transmitting signals across the Atlantic Ocean between Cornwall, England and St. Johns, Newfoundland. Marconi eventually received the Nobel Prize for physics for his accomplishments. Upon his death in Rome in 1937, all the radio stations throughout the world observed a two-minute period of silence in his honor.

Marconi was able to establish a successful commercial wireless telegraph service that served the United States and Europe, and he received patents for radio technology in the US and abroad. However, in 1943 the US Supreme Court invalidated one of Marconi's patents in favor of Nikolai Tesla, who was a contemporary and equally involved in developing wireless technology.

Valdemar Poulsen

Danish engineer and inventor Valdemar Poulsen (1869-1942) is best known for the invention of magnetic recording, but also invented the arc radio transmitter in 1903. He was able to demonstrate voice transmission in 1904. Poulsen's arc burned in a pure hydrogen atmosphere within a strong magnetic field, which created continuous radio waves with practical efficiency and less radio noise than the spark transmitter. Poulsen had a laboratory in Palo Alto, CA in the pre-WWI years, and teamed up with Federal Telegraph Company to produce commercial versions of his transmitter, some generating as much as 500 kilowatts of power. Such transmitters required water cooling and were inefficient, but saw service with the US Navy during WWI. 1,000,000 watt models were produced near the end of the war for use by the Signal Corps.

John Fleming

An electrical engineer, Sir John Ambrose Fleming (1849 - 1945) invented the first electronic tube in 1904. His two element diode, or thermionic valve, allowed current to flow only in one direction through the device. It was used to detect radio signals, and in larger versions, to convert alternating current power to direct current for powering electric equipment. Prior to his invention, a crude form of semiconductor diode was used in crystal radio sets to detect radio signals.

Reginald Fessenden

A Canadian-born electrical engineer and physicist, Reginald Aubrey Fessenden (1866-1932) transmitted the first voice message by radio. On Dec 25, 1906, his signal, transmitted from Brant ROck, MA, was received by ships on the Atlantic Ocean. He employed a high frequency alternator rotating at 20,000 RPM to generate a 50 kilohertz carrier wave. Audio modulation was provided by a water-cooled carbon microphone attached in-line between the alternator output and the transmitting antenna.

Fessenden had other significant radio inventions to his credit, including heterodyne radio reception, and the radio compass. He eventually held over 500 patents, including one for the invention of the sonic depth finder.

Charles Herrold

Charles Herrold (1875 - 1948) was born in Fulton, IL, a Mississippi river community located on the Iowa/Illinois border. William Herrold, his father, operated a grain elevator and mill. Mary Elizabeth, his mother, taught school and gave Bible lectures. In 1888 the family moved to San Jose, residing on a peach and apricot farm.

Herrold showed an early inventive streak, constructing telescopes, microscopes and photographic equipment while still in high school. Beginning at Stanford University as an Astronomy major, he switched to physics and electricity when the Astronomy professor resigned. He completed only three years of college due to health problems.

In 1899 Herrold moved to San Francisco, devoting his time to the creation of numerous inventions of a mechanical and electrical nature. Increasingly interested in radio, he eventually became Chief Engineer of the National Wireless Telegraph and Telephone Company of San Francisco. The 1906 earthquake, which destroyed Herrold's home and workshop, ended his first career. He subsequently moved to Stockton, becoming a teacher at Heald's College of Mining and Engineering. But he also began to experiment with radio technology, investigating how radio could be used to provide entertainment to families at home.

Successful as a teacher, Herrold returned to San Jose in 1908 and founded the Herrold College of Wireless and Engineering. The tuition fees supported Herrold's inventive drive, and he was soon deeply engaged in experimental broadcasts. Scheduled programming began in 1912 and extended through 1917 until WWI forced cessation of broadcasting. Records borrowed from a local store were used to provide musical content. Herrold set up crystal radio sets at local stores so that people could hear his broadcasts and learn about "wireless" at first hand. The broadcasts could be heard several hundred miles away. They were a popular demonstration at the 1915 Panama-Pacific International Exhibition in San Francisco.

Herrold devised a totally mechanical radio transmitter using a mechanically driven spark gap to generate the radio waves. His "Arc Fone" used a set of six arcs immersed in alcohol for cooling and contolled quenching and fired in sequence. The 500 DC voltage required was taken from San Jose's trolley system. A water cooled carbon microphone (also a Herrold invention) was used to modulate the radio waves generated by the rapidly firing spark gaps. A second Arc Fone station was established at the Fairmont Hotel in San Francisco for to support experimental 2-way radio transmissions.

Herrold's work was pre-empted after WWI by the advent of the vacuum tube transmitter and the arrival of hundreds of new broadcasting stations. He eventually constructed his own vacuum tube transmitter, operating it as station KQW. After changing hands several times, this station eventually became San Francisco's KCBS.

Herrold retired from the broadcasting business in 1925, and spent the next 10 years as a consultant. His contributions were largely overlooked until he was "rediscovered" in 1958 by a journalism professor researching material for a class project.

Lee DeForest

DeForest (1873-1961) invented the grid-controlled vacuum tube in 1906, adding a "grid" control element to Fleming's diode, thus permitting electronic amplification of electric signals. Small changes in an electric signal applied to the grid element of his "Audion" could control large currents flowing bewteen other elements of the vacuum tube, much as a small motion of a faucet valve handle can greatly change water flow. His invention, patented in 1907, was a key element in the growth of many industries, including broadcasting, telephony, motion pictures, medical instrumentation and others. DeForest is also credited with inventing an early process to add sound to movie films. He was a prolific inventor, receiving over 180 patents during his lifetime.

Edwin Armstrong

Born in New York City and an EE graduate of Columbia University, Edwin H. Armstrong (1890-1954) invented and patented FM (frequency modulation)as a method of radio transmission superior to AM (amplitude modulation) in its ability to transmit sound by radio with high fidelity. This development is an outstanding example of a revolutionary improvement created by one man in the face of constant professional criticism (which was erroneous and unfounded). Beginning his work in 1924, by 1933 Armstrong was able to demonstrate advantages of FM transmission over AM transmission. The first FM broadcast for public consumption was made in 1935 from a private home in Yonkers, NY.

Armstrong later constructed a transmitting station and antenna tower in Alpine, NJ and began transmitting programs transmitted by wire from WQXR to Alpine. Armstrong invented, tested and promoted FM despite learned commentary from "experts" at Bell Laboratories, Telefunken and other organizations, all of whom stated that FM had no advantages over AM. After trying to interest RCA in FM and receiving only rejection, Armstrong became the leading proponent and promoter of FM. When RCA finally awoke to the value of what they had rejected, RCA offered Armstrong a million dollars for the rights to FM. Armstrong refused, and from that point on, RCA fought a bitter legal and technical battle to develop an FM system that did not infringe upon Armstrong's patents. Disillusioned and discouraged by the long fight with RCA, Armstrong committed suicide in 1954, ironically just before a series of legal decisions that validated his patent claims and sustaining his infringement suits against RCA.

Armstrong also invented other radio technological landmarks, including the Regenerative Circuit, and the Superheterodyne Circuit.

Nikolai Tesla

A controversial person during his life and after his death, Nikolai Tesla (1856-1943) made significant contributions to radio technology, some of which were not fully acknowledged until after his death. Tesla was a scientific genius, but completely outclassed as a business man. His inventions include AC power, AC electric motors, high frequency induction transformer and the radio, a claim only recently sustained in patent law.

Born in Serbia, Tesla emigrated to the US in 1888, where (after working briefly for Thomas Edison) he sold the rights to the alternating current generator, motor and transformer to Westinghouse in 1889. The Westinghouse battle into the power systems market using AC technology precipitated a mammoth battle between Edison, a proponent of DC (direct current) and Westinghouse. AC power generation and distribution proved more flexible and economical than DC and eventually made DC power systems nearly obsolete.

Tesla, who maintained his own laboratory, experimented with any notion that crossed his mind. He experimented with lighting, x-rays, electrical resonance, remote control, broadcast power and man-made lightning. In 1900, Tesla began construction of a radio broadcasting station, but the project was never completed do to financing problems and other difficulties. In 1943, the US Supreme Court invalidated a 1904 patent filed by Marconi, giving rise to recognition of Tesla as the actual inventor of radio based on patents obtained by Tesla in 1900 for the transmission of energy by wireless (radio). Tesla is also credited with formulating many of the concepts used in later inventions, including flourescent lighting, the automotive ignition coil, rotary engines and turbines, radar and television.

Something of a cult has grown up around Tesla's name and memory, perhaps because he was given to making claims to capabilities that didn't always pan out or were not effective in practice. These include a "death ray", worldwide broadcast power, and interplanetary communication. His work was often distorted and sensationalized by the press reports of his time. Many of Tesla's "outlandish" ideas finally were realised, but not always in the manner he predicted.

Tesla's work received recognition in the scientific community as his name became the electical unit for magnetic field flux density-the number of flux lines per square meter.

David Sarnoff

David Sarnoff started his communications career as office boy for Marconi Wireless Telegraph Company of America in 1906. Promoted rapidly to telegraph operator and then to a series of management positions within Marconi, he developed an interest in radio broadcasting and began efforts to establish broadcasting stations beginning in 1915. He became Commercial Manager for Marconi in 1917, shortly before Marconi's American organization was acquired by GE and reincorporated as Radio Corporation of America (RCA).

Under Sarnoff's influence, RCA began to manufacture radios, and their sale became the chief source of RCA profits. With these profits, Sarnoff hoped to establish a nationwide radio broadcasting network, whose principal elements were to be "entertainment, information and education." Sarnoff became General Manager of RCA in 1921 and Executive Vice-President in 1929. In 1930 he became President of RCA. In 1928, a share of RCA stock could be purchased for about $85. By 1929, just before the onset of the Depression, RCA stock was $500 per share.

Sarnoff didn't always get it right. In 1955 he observed that "Television will never be a medium of entertainment."

William S. Paley

William S. Paley was the son of a wealthy cigar manufacturer. Although he had no previous experience in broadcasting, he effectively combined two minor networks in 1928 to found the Columbia Broadcasting System. Since Paley had no experience in the industry, he was unhampered by the "business-as-usual" syndrome and introduced many innovations in the way networks operated. Under his leadership, CBS was considerably more attuned to the desires of the listeners than was competitor NBC.

	This page last updated: February 19, 2003 Original content: Copyright © 2000, 2001, 2002, 2003 Museum of American Heritage Trademarks are the property of their owners