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COHERER DEMONSTRATION BOARD, 1920's
The first radio transmissions were made using a spark transmitter and a receiver known as a “Coherer”.
In 1890 Edouard Branley found that if high frequency oscillating currents were passed through a series of metal fillings in a glass tube, the fillings tended to coherer and become more conducting.
Without the influence of the radio frequency currents, the fillings passed very little current.
Later this arrangement gave place to a device called a crystal detector
The coherer was a primitive form of radio signal detector used in the late nineteenth and early twentieth centuries, consisting of a capsule of metal filings in the space between two electrodes.
It was a key enabling technology for radio, and was the first device used to detect radio signals in practical spark gap transmitter wireless telegraphy. Its operation is based upon the large resistance offered to the passage of electric current by loose metal filings being decreased under the influence of radio frequency alternating current.
The coherer became the basis for radio reception around 1900, and remained in widespread use for about ten years. The coherer saw commercial use again in the mid 20th century in a few primitive radio-controlled toys that used spark-gap transmitter controllers.
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- In the mid 50's I ran across the device called Coherer. My Boss C. Edward Atkins Engineering Director of Tung-Sol Electric asked me if I knew what it was and than educated me on the device. He had found a Toy remote car that worked using that device. To change direction a clapper would hit the device so that it would be energized for the next command. Never ran across a coherer again.
.......... Bob Ziolkowski, Apopka FL, 2nd of January 2015
- " Dear Sirs,
I am an italian physics teacher and my hobby is to study old instruments. Without in any way diminishing the merits of Branly, I would like to inform you about an inaccuracy on the “Coherer Demonstration Board, 1920’s” web page. It gives credit to Branly for the invention of the Coherer, however, it has been proven that it was invented by Temistocle Calzecchi Onesti in 1884. The proofs are his scientific articles, published on the journal "Nuovo Cimento" (s. 3, XVI ; XVII ; XIX .
You can see also:
H.G.J. Aitken, "Syntony And Spark The Origins of Radio", p. 285. Princeton University Press 1985: "The coherer principle was, however, discovered almost simultaneously by Porfessor Calzecchi Onesti of Fermo, Italy, and it may be that Marconi's knowledge of the device came from that source rather than from Branly".
V.J. Phillips, "Early radio wave detectors", Chapter 3 Coherers, pp. 18 – 19. Peter Peregrinus LTD 1980.
I hope you will find this information helpful,
.......... Fabio Panfili, Montegiorgio (FM), Italy, 26th of June 2014
- Professor Jim Al-Khalili demonstrated this Coherer working on his TV series “Shock & Awe the Story of Electricity” it was shown in Episode 3 “Revelations and Revolutions”
Trevor Cass accompanied several of our artefacts to Cambridge University and helped set them up prior to them being filmed.
This item must have intrigued the producers of Harry Hill’s TV Burp as it appeared on his “TV Highlight of the Week”.
Not bad for a small, independent, voluntary run museum.
.......... Rosie Hourihane, Throckenholt, 12th of March 2012