History of radio
The history of radio had many contributors, beginning with the scientific discovery of electromagnetic radiation in the late 1800s, followed by technological development of improved devices for producing and receiving transmissions.
Radio was at first employed for "wireless telegraphy", using on-off signalling such as Morse code, initially for private point-to-point communication. The invention in the early 1900s of devices capable of audio transmissions greatly increased its utility, most prominently with the introduction of broadcasting to a widespread, non-technical, audience.
Discovery
In an 1864 presentation, published in 1865, James Clerk Maxwell proposed theories of electromagnetism and mathematical proofs demonstrating that light, radio and x-rays were all types of electromagnetic waves propagating through free space.Between 1886 and 1888, Heinrich Rudolf Hertz published the results of experiments wherein he was able to transmit electromagnetic waves through the air, proving Maxwell's electromagnetic theory.
Exploration of optical qualities
After their discovery, many scientists and inventors experimented with transmitting and detecting "Hertzian waves". Maxwell's theory showing that light and Hertzian electromagnetic waves were the same phenomenon at different wavelengths led "Maxwellian" scientists such as John Perry, Frederick Thomas Trouton and Alexander Trotter to assume they would be analogous to optical light.Following Hertz's untimely death in 1894, British physicist and writer Oliver Lodge presented a widely covered lecture on Hertzian waves at the Royal Institution on June 1 of the same year. Lodge focused on the optical qualities of the waves and demonstrated how to transmit and detect them. Lodge further expanded on Hertz's experiments showing how these new waves exhibited like light refraction, diffraction, polarization, interference and standing waves, confirming that Hertz' waves and light waves were both forms of Maxwell's electromagnetic waves. During part of the demonstration the waves were sent from the neighboring Clarendon Laboratory building, and received by an apparatus in the lecture theater.
After Lodge's demonstrations researchers pushed their experiments further down the electromagnetic spectrum towards visible light to further explore the quasioptical nature at these wavelengths. Oliver Lodge and Augusto Righi experimented with 1.5 and 12 GHz microwaves respectively, generated by small metal ball spark resonators. Russian physicist Pyotr Lebedev in 1895 conducted experiments in the 50 GHz range. Bengali Indian physicist Jagadish Chandra Bose conducted experiments at wavelengths of 60 GHz and invented waveguides, horn antennas, and semiconductor crystal detectors for use in his experiments. He would later write an essay, "Adrisya Alok" on how in November 1895 he conducted a public demonstration at the Town Hall of Kolkata, India using millimeter-range-wavelength microwaves to trigger detectors that ignited gunpowder and rang a bell at a distance.
Proposed applications
Between 1890 and 1892 physicists such as John Perry, Frederick Thomas Trouton and William Crookes proposed electromagnetic or Hertzian waves as a navigation aid or means of communication, with Crookes writing on the possibilities of wireless telegraphy based on Hertzian waves in 1892. Among physicists, what were perceived as technical limitations to using these new waves, such as delicate equipment, the need for large amounts of power to transmit over limited ranges, and their similarity to already existing optical light transmitting devices, led them to a belief that applications were very limited. The Serbian American engineer Nikola Tesla considered Hertzian waves relatively useless for long range transmission since "light" could not transmit further than the line of sight. There was speculation that this fog and stormy weather penetrating "invisible light" could be used in maritime applications such as lighthouses. The London journal The Electrician commented on Bose's achievements, saying "we may in time see the whole system of coast lighting throughout the navigable world revolutionized by an Indian Bengali scientist working single-handedly in our Presidency College Laboratory."In 1895, adapting the techniques presented in Lodge's published lectures, Russian physicist Alexander Stepanovich Popov built a lightning detector that used a coherer-based radio receiver. He presented it to the Russian Physical and Chemical Society on May 7, 1895, known as Radio Day in Russia.
Marconi and radio telegraphy
In 1894, the young Italian inventor Guglielmo Marconi began working on the idea of building long-distance wireless transmission systems based on the use of Hertzian waves, a line of inquiry that he noted other inventors did not seem to be pursuing. Marconi read through the literature and used the ideas of others who were experimenting with radio waves but did a great deal to develop devices such as portable transmitters and receiver systems that could work over long distances, turning what was essentially a laboratory experiment into a useful communication system. By August 1895, Marconi was field testing his system but even with improvements he was only able to transmit signals up to one-half mile, a distance Oliver Lodge had predicted in 1894 as the maximum transmission distance for radio waves. Marconi raised the height of his antenna and hit upon the idea of grounding his transmitter and receiver. With these improvements the system was capable of transmitting signals up to and over hills. This apparatus proved to be the first engineering-complete, commercially successful radio transmission system and Marconi went on to file British patent GB189612039A, Improvements in transmitting electrical impulses and signals and in apparatus there-for, in 1896. This patent was granted in the UK on 2 July 1897.Nautical and transatlantic transmissions
In 1897, Marconi established a radio station on the Isle of Wight, England and opened his "wireless" factory in the former silk-works at Hall Street, Chelmsford, England, in 1898, employing around 60 people.On 12 December 1901, using a kite-supported antenna for reception—signals transmitted by the company's new high-power station at Poldhu, Cornwall, Marconi transmitted a message across the Atlantic Ocean to Signal Hill in St. John's, Newfoundland.
Marconi began to build high-powered stations on both sides of the Atlantic to communicate with ships at sea. In 1904, he established a commercial service to transmit nightly news summaries to subscribing ships, which could incorporate them into their on-board newspapers. A regular transatlantic radio-telegraph service was finally begun on 17 October 1907 between Clifden, Ireland, and Glace Bay, but even after this the company struggled for many years to provide reliable communication to others.
Marconi's apparatus is also credited with saving the 700 people who survived the tragic Titanic disaster.
Audio transmission
In the late 1890s, Canadian-American inventor Reginald Fessenden came to the conclusion that he could develop a far more efficient system than the spark-gap transmitter and coherer receiver combination. To this end he worked on developing a high-speed alternator that generated "pure sine waves" and produced "a continuous train of radiant waves of substantially uniform strength", or, in modern terminology, a continuous-wave transmitter. While working for the United States Weather Bureau on Cobb Island, Maryland, Fessenden researched using this setup for audio transmissions via radio. By the fall of 1900, he successfully transmitted speech over a distance of about 1.6 kilometers, which appears to have been the first successful audio transmission using radio signals. Although successful, the sound transmitted was far too distorted to be commercially practical. According to some sources, notably Fessenden's wife Helen's biography, on Christmas Eve 1906, Reginald Fessenden used an Alexanderson alternator and rotary spark-gap transmitter to make the first radio audio 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.Around the same time American inventor Lee de Forest experimented with an arc transmitter, which unlike the discontinuous pulses produced by spark transmitters, created a steady "continuous wave" signal that could be used for amplitude modulated audio transmissions. In February 1907 he transmitted electronic telharmonium music from his laboratory station in New York City. This was followed by tests that included, in the fall, Eugenia Farrar singing "I Love You Truly". In July 1907 he made ship-to-shore transmissions by radiotelephone—race reports for the Annual Inter-Lakes Yachting Association Regatta held on Lake Erie—which were sent from the steam yacht Thelma to his assistant, Frank E. Butler, located in the Fox's Dock Pavilion on South Bass Island.
Broadcasting
The Dutch company Nederlandsche Radio-Industrie and its owner-engineer, Hanso Idzerda, made its first regular entertainment radio broadcast over station PCGG from its workshop in The Hague on 6 November 1919. The company manufactured both transmitters and receivers. Its popular program was broadcast four nights per week using narrow-band FM transmissions on 670 metres, until 1924 when the company ran into financial trouble.Regular entertainment broadcasts began in Argentina, pioneered by Enrique Telémaco Susini and his associates. At 9 pm on August 27, 1920, Sociedad Radio Argentina aired a live performance of Richard Wagner's opera Parsifal from the Coliseo Theater in downtown Buenos Aires. Only about twenty homes in the city had receivers to tune in to this program.
On 31 August 1920 the Detroit News began publicized daily news and entertainment "Detroit News Radiophone" broadcasts, originally as licensed amateur station 8MK, then later as WBL and WWJ in Detroit, Michigan.
Union College in Schenectady, New York began broadcasting on October 14, 1920, over 2ADD, an amateur station licensed to Wendell King, an African-American student at the school. Broadcasts included a series of Thursday night concerts initially heard within a radius and later for a radius.
In 1922 regular audio broadcasts for entertainment began in the UK from the Marconi Research Centre 2MT at Writtle near Chelmsford, England.