File:Marconi's first radio transmitter.jpg
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This is a file from the Wikimedia Commons. The description on its description page there is shown below.
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Summary
| Description |
English: Recreation of the first radio transmitter with a monopole antenna, built by Guglielmo Marconi in August 1895 during his development of radio communication. It was a spark-gap transmitter which generated radio waves by an electric spark between two electrodes of a Righi spark gap (left, on table). The high voltage to produce the spark was generated by an induction coil (center) powered by a battery (on floor). A telegraph key (right, on table) in the primary circuit allowed the operator to switch the transmitter on and off rapidly, producing pulses of radio waves which spelled out text messages in Morse code. The unique feature of this transmitter is that it includes Marconi's invention of a monopole antenna. Marconi found that by connecting one side of the transmitter to an elevated copper sheet "capacity area" (top) and the other side to ground (earth), he could transmit longer distances than when using the previous dipole antennas invented by Hertz. This crucial innovation reduced the frequency of the radio waves, and radiated vertically polarized waves which had a greater range. With it Marconi achieved the first radio transmissions of practical distance, about 3 1/2 miles. |
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| Source | Retrieved January 28, 2016 from Guglielmo Marconi, "Looking back over thirty years of radio", Radio Broadcast magazine, Doubleday, Page, and Co., New York, Vol. 10, No. 1, November 1926, p. 31 on http://www.americanradiohistory.com |
| Author | Guglielmo Marconi |
| Permission (Reusing this file) |
This 1926 issue of Radio Broadcast magazine would have the copyright renewed in 1954. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. Search of the Renewals for Periodicals for 1953, 1954, and 1955 show no renewal entries for Radio Broadcast. Therefore the copyright was not renewed and it is in the public domain. |
Licensing
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This work is in the public domain because it was published in the United States between 1929 and 1963, and although there may or may not have been a copyright notice, the copyright was not renewed. For further explanation, see Commons:Hirtle chart and the copyright renewal logs.
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This work is in the public domain in its country of origin and other countries and areas where the copyright term is the author's life plus 70 years or fewer.  You must also include a United States public domain tag to indicate why this work is in the public domain in the United States.
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| This file has been identified as being free of known restrictions under copyright law, including all related and neighboring rights. | |
| Annotations | This image is annotated: View the annotations at Commons |
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| Date/Time | Dimensions | User | Comment | |
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| current | 09:34, 20 April 2016 | 924 × 1,372 (419 KB) | Wdwd | higher resulotion |
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