File:Hertz first oscillator.png

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Captions

Captions

Heinrich Hertz's first radio transmitter, 1886

Summary

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Description
English: The first spark gap oscillator built by German scientist Heinrich Hertz around 1886, the first radio transmitter, with which Hertz discovered radio waves. It consists of two 1 meter copper wires, supported on wax insulators, with a 7.5 mm spark gap between the inner ends, with 30 cm zinc balls on the outer ends. He used different sized balls to change the capacitance, in order to change the frequency. It functioned as a half wave dipole antenna. An induction coil (not shown) applied a high voltage of about 20,000 volts between the two sides, creating sparks across the gap between the small balls at center. The sparks caused oscillating standing waves of radio current in the antenna at its resonant frequency, radiating radio waves. The frequency of the waves was approximately 50 MHz, about the frequency of modern television broadcasting transmitters.

Caption: "The First Oscillator of Hertz. Two copper wires, each 1 metre in length, supported on rods of sealing wax. The large spheres are of sheet zinc, and are 30 centimetres in diameter. Base 260 x 7.5 centimetres"
Date
Source Retrieved December 30, 2014 from Rollo Appleyard, "Pioneers of Electrical Communication 5: Heinrich Rudolf Hertz" in Electrical Communication magazine, International Standard Electric Corp., New York, Vol. 6, No. 2, October 1927, p. 66, fig. 3 on http://www.americanradiohistory.com
Author Rollo Appleyard
Permission
(Reusing this file)		 This 1927 issue of Electrical Communication magazine would have the copyright renewed in 1955. 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 1954, 1955, and 1956 show no renewal entries for Electrical Communication. Therefore the magazine's copyright was not renewed and it is in the public domain.

Licensing

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Public domain
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.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.

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