7 Scientists of the Early Radio Development
History of radio is a big story and here we'll try to focus on the early radio development, focusing on scientists who did first experiments and made wireless transmission possible. So without further ado, here are the "7 kings" of that period.
It was sometime between 1886 and 1888 when Heinrich Rudolf Hertz studied Maxwell's theory, conducting experiments that eventually helped him engineer a method of detecting spark-gap radio waves by observing that another unpowered spark-gap, acting as an antenna, would absorb the radio energy and convert it back into an electric spark. Hertz published his results in a series of papers and again in complete book form in 1893.
This scientist was able to have some control over the frequencies of the radiated waves by altering the inductance and capacitance of his transmitting and receiving antennas. Using a corner reflector and a parabolic reflector, he managed to demonstrate that radio behaved the same as light, discovering that the electromagnetic equations could be reformulated into a partial differential equation called the wave equation.
Hertz did not devise a system for practical utilization of radio, as he seemed uninterested in the useful importance of his experiments.
In 1890, Édouard Branly demonstrated what he later called the "radio-conductor," which Lodge in 1893 named the coherer, the first sensitive device for detecting radio waves. He discovered that loose metal filings, which in a normal state have a high electrical resistance, lose this resistance in the presence of electric oscillations and become conductors of electricity. Moreover, Branly also found that when the filings had once cohered they retained their low resistance until shaken apart, for instance, by tapping on the tube. Unfortunately, the coherer was not sensitive enough to be used reliably as radio developed.
Around July 1891, Nikola Tesla developed various alternator apparatus that produced 15,000 cycles per second. A year later, he delivered a lecture called "Experiments with Alternate Currents of High Potential and High Frequency" before the Institution of Electrical Engineers of London, in which he suggested that messages could be transmitted without wires. He repeated this presentation at the Royal Institution and at the Société Française de Physique in Paris.
Tesla proposed that sending over the wire current vibrations of very high frequencies at enormous distance without affecting greatly the character of the vibrations and that telephony could be rendered practicable across the Atlantic.
There are seven elements in the complete oscillation-producing appliance, including the induction coil transformer or source of electromotive force, condenser, discharger or spark balls, arc quenching inductances, oscillation transformer, adjustable inductance for varying the period, and the controller or key in the primary circuit of the coil or transformer.
This apparatus in a typical form is generally called a Tesla apparatus for the production of high frequency electric currents.
In 1893, at St. Louis, Missouri, Tesla gave a public demonstration, "On Light and Other High Frequency Phenomena", of wireless communication. The lecture apparatus he used contained all the elements that were incorporated into radio systems before the development of the "oscillation valve", the early vacuum tube. However, the high-frequency phenomena which Tesla first developed and displayed had scientific rather than practical interest.
Tesla also developed sensitive electromagnetic receivers, that were unlike the less responsive coherers later used by other early experimenters.
Brazilian priest and scientist Roberto Landell de Moura began studying physics and electricity during his studies in Rome. When he returned to Brazil, he conducted experiments in wireless in Campinas and São Paulo (1892-1893), eventually reaching a distance of approximately 8 km. The points of transmission and reception were the Alto de Santana and Paulista Avenue in the downtown sector. One year after the experiment in public, he received his first patent from the Brazilian government which was described as "equipment for the purpose of phonetic transmissions through space, land and water elements at a distance with or without the use of wires."
Later on, he left Brazil for the United States with the intent of patenting the machine there. In spite of great difficulties, three patents were finally awarded: "The Wave Transmitter" (October 11, 1904) which is the precursor of today's radio transceiver; "The Wireless Telephone" and the "Wireless Telegraph", both dated November 22, 1904.
Sir Oliver Lodge was one of the first investigators to notice and measure stationary waves on wires produced by direct coupling (resonance) with the coatings of a Leyden jar. Two years after Tesla's high potential and high frequency lecture and five years after Hertz's signals, he performed transmission on August 14, 1894, which is a year before Marconi's initial experiments.
In August 1898, Lodge got U.S. Patent 609,154, "Electric Telegraphy", that made wireless signals using Ruhmkorff coils or Tesla coils for the transmitter and a Branly coherer for the detector. This patent was utilizing the concept of "syntonic" tuning. In 1912 Lodge sold the patent to Marconi.
Indian physicist Jagadish Chandra Bose demonstrated publicly the use of radio waves in Calcutta in November 1894. He ignited gunpowder and rang a bell at a distance using electromagnetic waves, proving that communication signals can be sent without wires. However, Bose did not commercially exploit this achievement.
In 1899, Bose announced the development of an "iron-mercury-iron coherer with telephone detector" in a paper presented at the Royal Society, London. Later he received U.S. Patent 755,840 titled "Detector for electrical disturbances" (1904) for a specific electromagnetic receiver.
Ferdinand Braun's major contributions were the introduction of a closed tuned circuit in the generating part of the transmitter, and its separation from the radiating part (the antenna) by means of inductive coupling, and later on the usage of crystals for receiving purposes.
In 1899, he would apply for the patents, Electro telegraphy by means of condensers and induction colls and Wireless electro transmission of signals over surfaces. Then on August 6, 1901, he would apply for Means for Tuning and Adjusting Electric Circuits.
By 1904, the closed circuit system of wireless telegraphy, connected with the name of Braun, was well known and generally adopted in principle.