The idea of wireless communication predates the discovery of "radio" with experiments in "wireless telegraphy" via inductive and capacitive induction and transmission through the ground, water, and even train tracks from the 1830s on. James Clerk Maxwell showed in theoretical and mathematical form in 1864 that electromagnetic waves could propagate through free space.
It is likely that the first intentional transmission of a signal by means of electromagnetic waves was performed in an experiment by David Edward Hughes around 1880, although this was considered to be induction at the time. In 1888 Heinrich Rudolf Hertz was able to conclusively prove transmitted airborne electromagnetic waves in an experiment confirming Maxwell's theory of electromagnetism.
After the discovery of these "Hertzian waves" (it would take almost 20 years for the term "radio" to be universally adopted for this type of electromagnetic radiation) many scientists and inventors experimented with wireless transmission, some trying to develop a system of communication, some intentionally using these new Hertzian waves, some not. Maxwell's theory showing that light and Hertzian electromagnetic waves were the same phenomenon at different wavelengths led "Maxwellian" scientist such as John Perry, Frederick Thomas Trouton and Alexander Trotter to assume they would be analogous to optical signaling and the Serbian American engineer Nikola Tesla to consider them relatively useless for communication since "light" could not transmit further than line of sight. In 1892 the physicist William Crookes wrote on the possibilities of wireless telegraphy based on Hertzian waves and in 1893 Tesla proposed a system for transmitting intelligence and wireless power using the earth as the medium. Others, such as Amos Dolbear,
Sir Oliver Lodge, Reginald Fessenden, and Alexander Popov were involved in the development of components and theory involved with the transmission and reception of airborne electromagnetic waves for their own theoretical work or as a potential means of communication.
Over several years starting in 1894 the Italian inventor Guglielmo Marconi built the first complete, commercially successful wireless telegraphy system based on airborne Hertzian waves (radio transmission). Marconi demonstrated application of radio in military and marine communications and started a company for the development and propagation of radio communication services and equipment.
Between 1886 and 1888 Heinrich Rudolf Hertz published the results of his experiments where he was able to transmit electromagnetic waves (radio waves) through the air, proving Maxwell's electromagnetic theory. Early on after their discovery, radio waves were referred to as "Hertzian waves".
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.
After learning of Hertz demonstrations of wireless transmission, inventor Nikola Tesla began developing his own system based on Hertz and Maxwell's ideas, primarily as a means of wireless lighting and power distribution. Tesla, concluding that Hertz had not demonstrated airborne electromagnetic waves (radio transmission), went on to develop a system based on what he thought was the primary conductor, the earth. In 1893 demonstrations of his ideas, in St. Louis, Missouri and at the Franklin Institute in Philadelphia, Tesla proposed this wireless power technology could also incorporate a system for the telecommunication of information.
In a lecture on the work of Hertz, shortly after his death, Professor Oliver Lodge and Alexander Muirhead demonstrated wireless signaling using Hertzian (radio) waves in the lecture theater of the Oxford University Museum of Natural History on August 14, 1894.
During the demonstration a radio signal was sent from the neighboring Clarendon Laboratory building, and received by apparatus in the lecture theater.
Building on the work of Lodge, the Indian Bengali physicist Jagadish Chandra Bose ignited gunpowder and rang a bell at a distance using millimeter range wavelength microwaves in a November 1894 public demonstration at the Town Hall of Kolkata. Bose wrote in a Bengali essay, Adrisya Alok (Invisible Light), "The invisible light can easily pass through brick walls, buildings etc. Therefore, messages can be transmitted by means of it without the mediation of wires."
Bose’s first scientific paper, "On polarisation of electric rays by double-refracting crystals" was communicated to the Asiatic Society of Bengal in May 1895. His second paper was communicated to the Royal Society of London by Lord Rayleigh in October 1895. In December 1895, the London journal The Electrician (Vol. 36) published Bose’s paper, "On a new electro-polariscope". At that time, the word 'coherer', coined by Lodge, was used in the English-speaking world for Hertzian wave receivers or detectors. The Electrician readily commented on Bose’s coherer. (December 1895). The Englishman (18 January 1896) quoted from the Electrician and commented as follows: "Should Professor Bose succeed in perfecting and patenting his ‘Coherer’, we may in time see the whole system of coast lighting throughout the navigable world revolutionised by an Indian Bengali scientist working single handed in our Presidency College Laboratory." Bose planned to "perfect his coherer", but never thought of patenting it.
In 1895, conducting experiments along the lines of Hertz's research, Alexander Stepanovich Popov built his first radio receiver, which contained a coherer. Further refined as a lightning detector, it was presented to the Russian Physical and Chemical Society on May 7, 1895.
A depiction of Popov's lightning detector was printed in the Journal of the Russian Physical and Chemical Society the same year (publication of the minutes 15/201 of this session — December issue of the journal RPCS[24]). An earlier description of the device was given by Dmitry Aleksandrovich Lachinov in July 1895 in the 2nd edition of his course "Fundamentals of Meteorology and climatology" — the first in Russia. Popov's receiver was created on the improved basis of Lodge's receiver, and originally intended for reproduction of its experiments.
In 1894 the young Italian inventor Guglielmo Marconi began working on the idea of building a commercial wireless telegraphy system based on the use of Hertzian waves (radio 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 2 miles (3.2 km) and over hills. Marconi's experimental apparatus proved to be the first engineering-complete, commercially successful radio transmission system. Marconi’s apparatus is also credited with saving the 700 people who survived the tragic Titanic disaster.
No comments