1892
EDOURAD BRANLY, French. Inventor of the coherer, which was later destined
to play so large a part in the practical reception of wireless waves by Marconi.
The coherer was not named as such until later, nor was it basically conceived by
Branly, since Hughes had employed a similar device as mentioned earlier. Branly,
however, made the device as Marconi was to use it, consisting of a tube
containing loose zinc and silver filings and plugs to make contact at each end.
Since the filings would cohere (stick together) after the first spark was
received, a method of separating them for the next signal was necessary. Popoff
(Russian) conceived the idea of using the vibrator and hammer from an (for those
days) electric bell in the circuit so that, almost the instant the filings
cohered, the hammer would strike the tube and cause them to “decohere”.
1893
NIKOLA TESLA, Siberian. Suggested a means of wireless communication, which used
the earth as a conductor and created stationary electric waves on it. Invented
the Tesla Coil, which, in effect, created high frequency oscillations of a broad
nature (in reality was a broadband transmitter) but, since he made no effort to
detect them, missed an opportunity of putting it “all together” and being
the first; that was to be left up to Marconi. By 1905 Tesla had devised a means
of wireless communication from his earlier experiments, but the Marconi system
was well established at that time.
1895
- 1900
GUGLIELMO MARCONI, Italian. Considering the inventions and research of
previous years, it is with no
great
surprise we find that scientists of this era looked upon Marconi as a
non-scientific interloper full of audacity. In 1895 Marconi conducted
experiments with “Hertzian waves”, and was able to send and receive messages
over a distance of 1.25 miles (2 kilometres). He employed the coherer invented
by Branly with Popoff’s tapper for decohering after signal was received. In
fact his apparatus differed only very slightly from that of his predecessors
when he applied for and was granted his first patent in England in 1896 for
wireless telegraphy. From then on however
Marconi made rapid strides in the advancement of the art, being successful in
transmitting and receiving messages between two warships over a distance of
twelve miles (19 kilometres). In this year Marconi was successful in enlisting
the backing of a number of wealthy Englishmen, and formed the Wireless Telegraph
and Signal Company; he was made a director of this company and placed in charge
of all development work although he was but then 23 years old. In 1899, he
adapted to wireless Sir Oliver Lodge’s principles of syntony,
(tuning or resonating - narrow-banding of circuits), perfecting it and obtaining
a patent in 1900. It was a remarkable step forward in wireless transmission and
reception, since it eliminated much of the interference caused by stations
transmitting simultaneously, a problem of no mean proportions up to that time.
In 1899, Marconi, was successful in covering distances up to 74 miles (125
kilometres) with his instruments, and ship to shore stations began to install
his equipment. His activities and progress with wireless filtered through to
America, and in 1899 he was invited there by the New York Herald
which engaged him to report the New York yacht race held in October of that
year. Marconi accepted for another reason, he wanted to interest the Unites
States Navy in his equipment in the hope that it would make large purchases and
thus help commercially exploit wireless. To facilitate matters, representatives
of the British company financed and incorporated the Wireless Telegraph Company
of America, to take care of the Marconi interests in that country. Marconi then
went ahead with the transmission and reception of the yacht race results, and an
amazed
American public obtained the news as to who had won, long before the ships had
returned to port. From this angle Marconi’s efforts were thoroughly
successful, but not so with the Navy. In demonstrations, the official witnesses
were considerably impressed by the efficiency of his equipment, although in
their reports mention was made of the interference obtained when two
transmitters were operating simultaneously. Marconi, with success of his
experiments on Lodge’s syntony or tuning still fresh in his mind, specified
that this defect could be overcome. The deciding factor, however, against
Marconi’s equipment were the terms of his proposed contract which the Navy
definitely rejected. Thus for a while no further real progress was made in
wireless in the USA. Marconi, in the meantime had gone back to England to
continue with his experiments and make further rapid advancements in the art of
wireless communication. His famous Atlantic transmission of the letter “S”
(three dots) followed on December 12, 1901.
PDF Article "Greatest Of All Amateurs - Marconi" by Hiram P Maxim,
President of the ARRL,
describing his meeting with Marconi - from the September 1922 issue of QST
magazine.
1900
- 1905
REGINALD A. FESSENDEN and LEE DE FOREST, Americans. If America is to
boast outstanding contributors to the art or wireless in the early days, it is
these two gentlemen who take accreditation.
Fessenden,
while fully acquainted with Marconi’s wireless equipment – having
experimented with these devices was more interested in radiotelephony. He knew
that Marconi’s system was only adapted for damped-wave transmission and would
not tolerate superimposing on it voice or further irregular waves. Consequently
he began to experiment with continuous
wave transmission (CW, today, a term which has come mean Morse code
transmission) which led him to perfecting the arc
transmitter. However the coherer would not receive the voice impulses modulated
on an oscillating wave produced by the arc; so drawing on his electricity and
chemical training Fessenden created the electrolytic
detector, which allowed current to flow in only one direction. It consisted
of a small aluminium cup filled with a solution of acid and water, into which a
fine silver wire dipped. It was a tremendous improvement over the coherer and
increased a receiver’s efficiency considerably. Later on Fessenden conceived
the idea of employing an alternator as a continuous wave radio frequency source.
While at the time he was laughed at, his idea was later to play a very important
role in the progress of radio.
Meanwhile,
de Forest was experimenting with wireless too, and in 1901 built a system less
cumbersome and more efficient than Marconi’s. He to employed the electrolytic
detector, which caused between himself and Fessenden considerable legal conflict
that was later determined in Fessenden’s favour. De Forest secured some
financial backing and formed the American Wireless Telegraph Company. With this
company he commenced manufacturing equipment, some of which he sold to the Army.
Unfortunately the company depended on stock promotion to finance its development
work. It was soon in financial difficulties, which hampered it from getting into
the commercial communications field. In this same period, 1904 to be exact, J
AMBROSE FLEMING, English, developed the two-element (diode) “valve”
(so called because of its
characteristic of only allowing current flow in one direction) while employed by
Marconi. He remembered Edison’s experiments and the so called “Edison
effect” – since he had been a scientific adviser to the Edison Electric
Light Company of America – and hence it occurred to him that the phenomenon
could be employed to advantage as a detector of radio waves. This invention,
which Fleming called the “glow lamp
oscillation detector or oscillation
valve”, was to enjoy only a short life inasmuch as De Forest’s discovery
of the 3 element (triode) or audion tube was soon to follow.
1906
DE FOREST’S Audion. Here is
one of the greatest contributions of all to the early art of radio! It consisted
only of the insertion of a grid between the filament and plate of Fleming’s
“valve”, yet this addition of a third element so revolutionised radio that
it continued in common use for another 70 years. While the power or the ability
of the audion tube as an amplifier or oscillator had not yet been recognised,
its merit as a detector was soon
proven. Despite this invention and other meritorious work in the wireless field,
De Forest’s finances were in extremely poor shape. To obtain the necessary
capital he was forced to sell stock in his company, but somehow an unwilling
public could not be persuaded to purchase. Later on, in 1912, to obtain funds
for himself and his company, De Forest sold the rights to the Audion amplifier
to the American Telephone and Telegraph Company for a paltry sum compared to its
actual worth.
1907
First
Crystal Detector,
by G. W. PICKARD. Up to this time the most popular
detector was Fessenden’s electrolytic type; the coherer, while still
somewhat used, having been found unstable and insensitive. The Fleming
diode valve was never really popularised because of its insensitivity to
weak signals. Consequently the discovery of the crystal detector marks
another great stride in the development
of radio. Carborundum
was first used by H. C. Dunwoody, of the U.S. Army in 1906, however it was
Pickard who first used silicon to great effectiveness. He later
determined that other minerals could be used, such as galena (lead ore)
and iron pyrites. The crystal detector was extremely effective in
demodulating feeble irregular signals (both modulated CW and damped waves)
although somewhat critical in the adjustment of the “catwhisker”.
Because of its sensitivity and inexpensiveness it was the most popular of
all detectors until the advent of low cost audions, and was to a great
extent responsible for increased public interest in wireless or radio.
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