Radio
History, Wikipedia
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.
The meaning and usage of the word
"radio" has developed in parallel with developments within the field
of communications and can be seen to have three distinct phases:
electromagnetic waves and experimentation; wireless communication and technical
development; and radio broadcasting and
commercialization.
In an 1864 presentation, published in 1865, James
Clerk Maxwell proposed
his theories and mathematical proofs on electromagnetism that showed that light and other
phenomena were all types of electromagnetic waves propagating through free space.
In 1886–88 Heinrich
Rudolf Hertz conducted
a series of experiments that proved the existence of Maxwell's electromagnetic
waves, using a frequency in what would later be called the radio spectrum.
Many individuals—inventors, engineers, developers and businessmen—constructed
systems based on their own understanding of these and other phenomena, some
predating Maxwell and Hertz's discoveries. Thus "wireless telegraphy"
and radio wave-based systems can be attributed to multiple
"inventors".
Development from a laboratory
demonstration to a commercial entity spanned several decades and required the
efforts of many practitioners.
In 1878, David E. Hughes noticed that sparks could be heard
in a telephone receiver when experimenting with his carbon microphone. He
developed this carbon-based detector further and eventually could detect
signals over a few hundred yards. He demonstrated his discovery to the Royal Society in 1880, but was told it was
merely induction, and therefore abandoned further research.
Thomas Edison came across the electromagnetic
phenomenon while experimenting with a telegraph at Menlo
Park. He noted an
unexplained transmission effect while experimenting with a telegraph. He referred to this as etheric force in an announcement on November 28,
1875. Elihu Thomson published
his findings on Edison's new "force", again attributing it to
induction, an explanation that Edison accepted. Edison would go on the next
year to take out U.S. Patent 465,971 on a system of electrical wireless
communication between ships based on electrostatic
coupling using the
water and elevated terminals. Although this was not a radio system the Marconi Company would purchase the rights in 1903
to protect them legally from lawsuits.
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 polarization 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 revolutionized 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. 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.
In 1896, Marconi was awarded British
patent 12039,
Improvements
in transmitting electrical impulses and signals and in apparatus there-for, the first patent ever issued for a
Hertzian wave (radio wave) base wireless telegraphic system.
In 1897, he established a radio station
on the Isle of Wight, England. Marconi opened his
"wireless" factory in the former silk-works
at Hall Street, Chelmsford, England in 1898, employing around 60 people.
Shortly after the 1900s, Marconi held the patent rights for radio. Marconi
would go on to win the Nobel Prize in Physics in 1909 and be more
successful than any other inventor in his ability to commercialize radio and its
associated equipment into a global business. In the US some of his
subsequent patented refinements (but not his original radio patent) would be
overturned in a 1935 court case (upheld by the US Supreme Court in 1943).
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