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The coherer was the first device used to detect radio signals in wireless telegraphy. Its operation is based upon the large resistance offered to the passage of electric current by loose metal filings, which decreases under the influence of radio frequency alternating current. The coherer became the basis for radio reception, and remained in widespread use for about ten years. Wireless is an old-fashioned term for a radio receiver, referring to its use as a wireless telegraph; now the term is used to describe modern wireless connections such as in cellular networks and wireless broadband Internet. ...
It has been suggested that Electrical telegraph be merged into this article or section. ...
Wiktionary has related dictionary definitions, such as: resistance Resistance may refer to: Antibiotic resistance, the ability of a microorganism to withstand the effects of an antibiotic Disease resistance, in immunology; see also disease resistance in fruit and vegetables Resistance, in physics, a force that tends to oppose motion Friction, the...
Electric current is the flow of electric charge. ...
Rough plot of Earths atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves. ...
City lights viewed in a motion blurred exposure. ...
History
Temistocle Calzecchi-Onesti is thought to have performed the first experiments with a predecessor of the coherer in 1884. The invention of the device is usually credited to Edouard Branly. Branly is best known for his researches concerning radio-conductors, and the coherer. He began his studies in this field in 1890, being led to undertake them by observing the anomalous change in the resistance of thin metallic films when exposed to electric sparks. Platinum deposited upon glass was first employed. The effect was at first attributed to the influence of the ultraviolet light of the spark. The variations in the resistance of metals in a finely divided state were even more striking, and they were shown by Branly to be due to the action of the electrical, or Hertzian, waves of which the spark was the source. The further developments from these experiments led to the coherer. Later this simple device was employed by Oliver Lodge in his researches and formed an important part of Guglielmo Marconi's successful system of wireless telegraphy. Temistocle Calzecchi Onesti (b. ...
Eugène Édouard Désiré Branly (23 October 1844 - 24 March 1940) was a French physicist. ...
Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ...
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Guglielmo Marconi Guglielmo Marchese Marconi, GCVO (25 April 1874 – 20 July 1937) was an Italian electrical engineer and Nobel laureate of partially Irish descent, known for the development of a practical wireless telegraphy system commonly known as the radio. Marconi was President of the Accademia dItalia and a member...
Description The coherer is based around the effect that had been known since the 1850s; that small particles of dust or even metal filings stick together or cohere when an electric field is present. Image File history File links Coherer. ...
Image File history File links Coherer. ...
In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ...
It is a glass tube filled with sharply cut silver and nickel shavings. Silver electrodes make contact with the shavings on both ends. One electrode is connected to the antenna and the other to ground. A series combination of a battery and a telegraph sounder is also attached to the two electrodes. When the signal from a spark gap transmitter is received, the shavings tend to cling to each other, reducing the resistance of the coherer. The battery supplies more current, and the telegraph sounder is actuated, giving an audible click. More often a pair of headphones replaced the telegraph sounder, being much more sensitive to weak signals. General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Atomic mass 107. ...
General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic Atomic mass 58. ...
An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. ...
In biology, antenna (plural: antennae) refers to the sensing organs of several arthropods. ...
The word ground has several meanings: The surface of the Earth Soil, a mixture of sand and organic material present on the surface of the Earth Ground (electricity), in electrical engineering, something that is connected to the Earth or at the voltage defined as zero (in the US, called ground...
This article or section does not cite its references or sources. ...
A Telegraph Sounder is a device which produces an audible sound when connected to an operating electrical telegraph. ...
The spark gap transmitter was the first practical way to send radio signals. ...
Wiktionary has related dictionary definitions, such as: resistance Resistance may refer to: Antibiotic resistance, the ability of a microorganism to withstand the effects of an antibiotic Disease resistance, in immunology; see also disease resistance in fruit and vegetables Resistance, in physics, a force that tends to oppose motion Friction, the...
 A radio reciver with a coherer detector. The problem of the filings continuing to cling together after the removal of the RF energy was solved by tapping the coherer with a small mallet attached to the sounder after the arrival of each signal shaking up the filings and raising the resistance of the coherer to the original value. This is referred to as 'decohering' the device and was subject to much innovation during the life of this component. Tesla's, for example had the tube rotating continuously along its axis, following each successive activation. Image File history File links Cohererrx. ...
Image File history File links Cohererrx. ...
RF may be: RF is the IATA code for Florida West International Airways Rf or RF may stand for: Radio frequency, a term in broadcasting. ...
Tesla can refer to: Scientist and inventor Nikola Tesla The tesla, an SI unit named after Nikola Tesla. ...
Development One innovation was the development of the mercury coherer. This device consisted of a small metallic cup containing a pool of mercury on which has a very thin insulating film of oil over it; above the surface a small iron disc is suspended. By means of an adjusting screw the lower edge of the disc is made to touch the oil-covered mercury with a pressure small enough not to puncture the film of oil. The action of detection occurs when the signal breaks down the insulating film of oil, allowing the cell conduct operating the receiving instrument wired in parallel. This form of coherer is self-restoring and needs no decohering. General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery white Atomic mass 200. ...
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Natural olive oil Synthetic motor oil Oil, in a general sense, is a chemical compound that is not miscible with water, and is in a liquid state at ambient temperatures. ...
General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ...
Limitations of coherers Although the coherer was satisfactory for responding to the "on-off keying" characteristic of an early spark gap transmitter, they cannot follow the complex waveforms of audio broadcasting. This can only be accomplished by the crystal detectors. On-off keying (OOK) is a type of modulation that represents digital data as the presence or absence of a carrier wave. ...
The spark gap transmitter was the first practical way to send radio signals. ...
The Cats Whisker is the tiny wire that connects to the detector in a crystal radio. ...
See also A detector is a device that recovers information of interest contained in a modulated wave. ...
In radio terminology, a receiver is an electronic circuit that receives a radio signal from an antenna and decodes the signal for use as sound, pictures, navigational-position information, etc. ...
This is a list of communications, computers, electronic circuits, fiberoptics, microelectronics, medical electronics, reliablity, and semiconductors. ...
External links - "The Coherer". World of Wireless, Virtual radiomuseum.
- "Coherer / Receiver". Marconi Calling Company.
- Slaby, Adolphus, "The New Telegraphy, Recent experiments in telegraphy with sparks.". The Century Magazine. April, 1898. (Earlyradiohistory.us)
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