Wireless telegraphy - Wikipedia
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History of telecommunication Efforts to find a way to transmit telegraph signals without wires grew out of the success of electric telegraph networks, the first instant telecommunication systems. Developed beginning in the s, a telegraph line was a person-to-person text message system consisting of multiple telegraph offices linked by an overhead wire supported on telegraph poles.
To send a message, an operator at one office would tap on a switch called a telegraph keycreating pulses of electric current which spelled out a message in Morse code. When the key was pressed, it would connect a battery to the telegraph line, sending current down the wire. At the receiving office the current pulses would operate a telegraph soundera device which would make a "click" sound when it received each pulse of current.
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The operator at the receiving station who knew Morse code would translate the clicking sounds to text and write down the message. The ground was used as the return path for current in the telegraph circuit, to avoid having to use a second overhead wire. By the s, telegraph was the standard way to send most urgent commercial, diplomatic and military messages, and industrial nations had built continentwide telegraph networks, with submarine telegraph cables allowing telegraph messages to bridge oceans.
However installing and maintaining a telegraph line linking distant stations was very expensive, and wires could not reach some locations such as ships at sea. Inventors realized if a way could be found to send electrical impulses of Morse code between separate points without a connecting wire, it could revolutionize communications.
The successful solution to this problem was the discovery of radio waves inand the development of practical radiotelegraphy transmitters and receivers by aboutdescribed in the next section.
- Wireless telegraphy
- Julio Cervera Baviera
However this was preceded by a 50 year history of ingenious but ultimately unsuccessful experiments by inventors to achieve wireless telegraphy by other means. Ground, water, and air conduction[ edit ] A number of wireless electrical signaling schemes based on the sometimes erroneous idea that electric currents could be conducted long range through water, ground, and air were investigated for telegraphy before practical radio systems became available.
The original telegraph lines used two wires between the two stations to form a complete electrical circuit or "loop".
Invención de la radio
Inhowever, Carl August von Steinheil of MunichGermanyfound that by connecting one leg of the apparatus at each station to metal plates buried in the ground, he could eliminate one wire and use a single wire for telegraphic communication.
This led to speculation that it might be possible to eliminate both wires and therefore transmit telegraph signals through the ground without any wires connecting the stations. Other attempts were made to send the electric current through bodies of water, in order to span rivers, for example. Prominent experimenters along these lines included Samuel F. Morse in the United States and James Bowman Lindsay in Great Britain, who in Augustwas able to demonstrate transmission across a mill dam at a distance of yards metres.
Tesla's experiments had led him to incorrectly conclude that he could use the entire globe of the Earth to conduct electrical energy   and his large scale application of his ideas, a high-voltage wireless power station, now called Wardenclyffe Towerlost funding and was abandoned after a few years.
Telegraphic communication using earth conductivity was eventually found to be limited to impractically short distances, as was communication conducted through water, or between trenches during World War I. Electrostatic and electromagnetic induction[ edit ] Thomas Edison's patent for a ship-to-shore wireless telegraph that used electrostatic induction Both electrostatic and electromagnetic induction were used to develop wireless telegraph systems that saw limited commercial application.
In the United States, Thomas Edisonin the mids, patented an electromagnetic induction system he called "grasshopper telegraphy", which allowed telegraphic signals to jump the short distance between a running train and telegraph wires running parallel to the tracks.
During the Great Blizzard ofthis system was used to send and receive wireless messages from trains buried in snowdrifts.
The disabled trains were able to maintain communications via their Edison induction wireless telegraph systems,  perhaps the first successful use of wireless telegraphy to send distress calls.
Edison would also help to patent a ship-to-shore communication system based on electrostatic induction. Beginning with tests across the Bristol Channel inPreece was able to telegraph across gaps of about 5 kilometres 3.
However, his induction system required extensive lengths of antenna wiresmany kilometers long, at both the sending and receiving ends. The length of those sending and receiving wires needed to be about the same length as the width of the water or land to be spanned.
For example, for Preece's station to span the English Channel from Dover, Englandto the coast of France would require sending and receiving wires of about 30 miles 48 kilometres along the two coasts. These facts made the system impractical on ships, boats, and ordinary islands, which are much smaller than Great Britain or Greenland.
Julio Cervera Baviera - Wikipedia
In addition, the relatively short distances that a practical Preece system could span meant that it had few advantages over underwater telegraph cables.
At the beginning ofCervera was working in the photoengraving industry in Barcelona. Imprisonment[ edit ] Cervera's work in Spanish Africa earned him the promotion of commander. He was released two years later.
Its purpose was to support the actions of General Macias before the Spanish public but it ended up criticizing the Puerto Rican volunteers in the Spanish Army. After Spain's defeat against the United StatesSpaniards looked for reasons to explain it.
In twenty-four hours, the people of Puerto Rico went from being fervently Spanish to enthusiastically American. They humiliated themselves, giving in to the invader as the slave bows to the powerful lord. The duel never took place, as Cervera explained his intentions in writing the pamphlet, and all parties were satisfied.
He began collaborating with Guglielmo Marconi on resolving the engineering problems of a long range wireless communication, obtaining some patents by the end of This was after Marconi established the radiotelegraphic service between the Isle of Wight and Bournemouth in Cervera thus achieved some success in this field, but his radiotelegraphic activities ceased suddenly, the reasons for which are unclear to this day.
After 8 months he became frustrated with his inability to reform the curriculum, and traveled to Europe and the United States from Maywhere he became interested in instruction via correspondence. It gave degrees for the careers of mechanical engineer, electrician, and mechanic-electrician.