Radio waves were detected after a prediction of the existence of electromagnetic waves in 1862 by James Clerk Maxwell. Maxwell had competed development of the 4 coupled equations of electromagnetism, including encompassing a term for electromagnetic induction found in the work of Michael Faraday in 1831. Maxwell predicted electromagnetic waves as a solution of these equations. Detecting their existence required ingenuity with knowledge of electromagnetic properties.
Heinrich Hertz of Germany discovered radio waves in 1888. He showed the spark of an induction coil set up oscillations in an open circuit, and the energy of the sources were were sent out to ring detectors as electric waves. He was surprised when he found the electric field fell off not as the inverse of distance-squared (as electrostatic sources had been found to fall off), but more slower. The actual falloff was later shown to vary directly as the inverse of distance, which is characteristic for electromagnetic sources.
The spark gap transmitter became the initial way of generating radio waves, which would create waves over a broad range of frequencies. Hertz had tuned the spark gap transmission with the induction coil, and transmitters were further developed for tuning the waves excited to a fundamental & a large number of harmonics. The discovery of the waves soon attracted many experimentalists to study their properties and for their use is distance communication.
In 1890, Edouard Branly (France) showed metal filings in a tube cohered from electric waves. This tube was namrf the "Branly coherer". Then in 1895, Alexander Popoff constructed receiver with the coherer to study atmospheric electricity in lightning. using detector connected with an aerial & the Earth. This receiver was improved later into a practical receptor by Sir Oliver Lodge by adding a decoherer, which tapped the coherer after each reception to dislodge the clumped fillings.
In 1896, William Marconi (Italy), connecting aerial to one side, & spark gap & ground to the other. He used an induction coil to energize the spark gap, and a telegraph key to break the current into signals. He then added a Morse register to prints dots & dashes & a Popoff receptor. This setup was the 1st wireless telegraphy (which he patented), & became the generator for wireless telegrams.
In 1898 the German physicist Braun invented an improvement over the spark-gap transmitter of Marconi, by separating the spark gap to a primary circuit, whereas tuning of the oscillator was done in a secondary winding. An induction coil connected the low-voltage primary with a high-voltage secondary.
Experiments by Nikolaus Tesla in the 1890's demonstrated radio waves and devices, his patents including the Tesla coil. In 1898 he demonstrated a radio-controlled boat. In 1900 he was given patents for an electrical transmitter, then challenger Marconi in court for Marconi's transatlantic transmission in 1901. The courts upheld Tesla in 1903, reversed to Marconi in 1904, then restored Tesla's prior patents ruling in 1943.
In 1899, Frederick Collins, noting the earlier discovery by Firth & Rogers (England) that direct current arc light transforms part of its energy to electric oscillations, connected the arc lamp with an aerial & ground. He used a microphone transmitter to modulate the oscillations so set up. For receiving Collins used a pill-box detector (which had been devised by Sir Oliver Lodge), and connected it with an Ericcson telephone receiver. This was the 1st wireless telephone, and it was improved later by Collins setting up the oscillations with his rotating oscillation arc. He as given a patent on this in 1906.
Fessenden was interested in following up Marconi's work to build instead a CW (continuous wave) transmitter. He invented the rotary spark-gap transmitter in 1902, which set up continuous oscillations for a few seconds, but soon realized the spark-gap transmitter was incapable of transmitting good voice & music. It was only capable of producing waves up to 60 Hz, which was the fastest cycle motors could create. He went another route & came up with the HF alernator, which by 1906 could be used for CW transmission up to 100 kHz.
In 1904, J,C. Bose received a patent for the 1st crystal detector for radio waves, which is solid-state. Shortly thereafter. J.A. Fleming invented the vacuum tube, in particular the diode, which could rectify AC cuurent to produce DC current. The galena crystal in Bose's invention could also effectively serve as a diode.
In 1906, G.W. Pickard invented the silicon crystal detector, in which he connected a fine pointed wire (a "cat's whisker") in contact with the crystal to enhance rectification. Soon the Branly detector had been replaced by the crystal detector.
In 1906, Lee deForest invented the "audion", which was the 1st triode vacuum tube. It could amplify a weak signal in addition to rectifying it. However, it took virtually 10 years of perfection of the vacuum tube for it to compete with crystal detector. It was found over time to not only be a useful detector, by also if energized by direct current at hi voltage it would setup sustained oscillations for wireless telegraphy & wireless telephony.
It took 10 years for vacuum tube to compete with crystal radio sets, but in about 15 years, crystal radio sets were being replaced commercially by receivers with audions, relegating crystal receivers to hobyists. The crystal radio can demodulate AM signals, but not FM signals (which did not come along till the latter 1930's).
Up to 1912 there were no regulations on radio signals, so interference was prevalent. In 1912, the 1st international agreement was reached to regulate it by assigning call letters to broadcasters.
The earliest radio station was started in San Jose in 1909 by engineer Charles Herrold with a 15-watt transmitter, sending out music and news. In 1921 it was assigned the call letters KQW, and in 1949 it was bought out by CBS, becoming KCBS of San Francisco.
World War I broke out in Europe in 1914, and in it airplanes, ships, and troops were kept in contact with radio. That year a relay system across the U.S. was begun by Hiram Percy Maxim & Clarence Tuska, In 1915 they started the Amateur Radio Relay League (ARRL) with its monthly magazine QST. By 1917 they had completed the relay system all the way across the country.
On their monitoring in WWI the Germans discovered whistler radio transmissions on their receivers, which occurred at or below 30 kHz and sounded like a descending whistle, or in some casses 2-3 descending whistles. They generally thought it was Allied code, and intensely monitored to try to discover its origins. When the war was over, it was clear the Allies had no such code, and radio scientists continued to monitor it to find its origin. By 1953 it was established by physicist L.R.O. Storey of Sweden that they were a naturally occurring transmission propagating on Earth's magnetic field lines created by lightning strokes.
In 1917 it was likely the U.S. was going to enter the war, & the Secretary of the Navy Josephus Daniels ordered a shutdown of all radio transmission, so that only the Navy could send them out. Secretary Daniels tried to continue that monopoly after the war was over, giving the Navy permanent control of all radio transmission in the US. However he was vociferously opposed by Maxim & Tuska, who and wired all hams in ARRL on the issue. When Secretary Daniels introduced a bill into the Senate for approval of that monopoly, Maxim & Tuska helped get a bill into the House restoring free transmission. They finally won out on restoring free transmission, and the ban was lifted in 1919.
With the return of radio to all amateur operators it flourished. They advanced vacuum-tube technology and explored short-wave trasmission. By discovering the reflection off the ionosphere they made worldwide communication possible.
Companies were also developing for radio. There were several separate patents issued for elements of a radio: the diode, the triode, the grid, etc. David Sarnoff in 1919 formed a consortium to buy up patents to make a complete radio. This company so-formed was named RCA, and it survived up until 1986. They marketed the 1st superheterodyne recever in 1924, which had been invented in 1918 by Edwin Armstrong..
KDKA became one of the 1st commercial stations licensed. Then in early 1922, in a protection for the development of commercial radio, amateur radio stations were explicitly banned from making entertainment broadcasts. A system was also agreed on for stopping stations from infringing on each other's wavelength. By 1923 networks were started to form.
In 1925 the International Amateur Radio Union was formed in Paris. In 1926 the ARRL put out its 1st Handbook. This has been consistently updated & re-released over the years, & is the most comprehensive radio engineering handbook in the world.
It was the Radio Act of 1927 and the Communications Act of 1934 that addressed (mostly commercial) radio issues that had been brewing for well over a decade, and established modern broadcasting regulations. The latter Act replaced the earlier Federal Radio Commission by the FCC.
In 1930, the radio engineer who had invented the superheterodyne receiver submitted a new patent to the Patent & Trademark office. Within 10 years, his invention would come to revolutionize high-frequency radio.
COMING SOON -- The Development of Very High Frequency Radio
"ARRL at 100: A Century of Ham Radio" at http://www.youtube.com/watch?v=jerSTUDql7s&feature=youtu.be
"Bose, Jagadish Chandra", online at http://en.wikipedia.org/wiki/Jagadish_Chandra_Bose .
"Coherer", online at http://en.wikipedia.org/wiki/Coherer.
Collins, Frederick, Radio Amateur's Handbook (1922).
"Crystal Radio", online at http://en.wikipedia.org/wiki/Crystal_radio .
Hawker, J P, Radio and Television (Hart, 1966).
Hertz, Heinrich, & Daniel E. Jones, Electric Waves (MacMillan, New York, 1893).
"RCA", online at http://en.wikipedia.org/wiki/RCA .
Schulberg, Pete "Radio Advertising." (NTC Business Books, 1989)
"Tesla, Nikola", online at http://en.wikipedia.org/wiki/Nikola_Tesla .
CW -- Fessenden transmitter
John S. Belrose, "Fessenden and the Early History of Radio Science," The Radioscientist, Volume 5, #3, September, 1994 online at http://www.ieee.ca/millennium/radio/radio_radioscientist.html
Discovering the Radio Faraday's work 1865 -- James Clerk Maxwell (England) developed 4 coupled eqs for E & M Solution -- predicted new E&M waves [REF] Heinrich Hertz & Daniel E. Jones, Electric Waves (MacMillan, New York, 1893). 1888 -- Heinrich Hertz (Germany) discovered radio waves -- showed spark of an induction coil set up oscillations in an open circuit, & energy of sources sent out to ring detectors as electric waves. Surprised when found fell off not as 1/r**2 (as electrostatic sources had been found to fall off), but more slower. The actual falloff was later shown as 1/r, which is characteristic for electromagnetic sources. [REF] Frederick Collins, Radio Amateur's Handbook (1922). 1890 -- Edward Branly (France) show metal filings in tube cohered from electric waves. 1895 -- Alexander Popoff constructed receiver to study atmospheric electricity, using detector connected with an aerial & the Earth. Improved upon by Sir Oliver Lodge. HOW? 1896 -- William Marconi (Italy), connecting aerial to one side, & spark gap & ground to the other, used an induction coil to energize the spark gap, & telegraph key to break J into signals. Added Morse register to prints dots & dashes & Popoff receptor -- 1st wireless telegraphy. 1899 -- Frederick Collins, noting discovery by Firth & Rogers (England) in 1803 that direct current arc light transforms part of its E to electric oscillations, connected the arc lamp with an aerial & ground. He used a microphone transmitter to modulate the oscillations so set up. For receiving he used a pill-box detector (devised by Sir Oliver Lodge), and connected it with an Ericcson telephone receiver -- 1st wireless telephone. Improved later setting up oscillations with his rotating oscillation arc. electrolytic detector soon replaced by crystal detector 1905 -- J.A. Fleming invented vacuum tube, took 10 years of perfection for it to compete with crystal detector. Found was not only detector, by if energized by direct J at hi V would setup sustained oscillations for wireless telegraphy & wireless telephony. World War I: -- Airplanes, ships, troops kept in contact with radio. -- Whistlers discovered by Germans -- thought it was Allied?? code.