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File:Inverted-L antenna with counterpoise.jpg

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Summary

Description
English: Wire radio transmitting antenna built by radio amateur William D. Reynolds, 9ZAF, of Denver, Colorado, USA around 1920, which was also the initial transmitting site for broadcasting station KLZ, first licensed March 10, 1922. It is an elaborate inverted-L antenna, which was widely used on the longwave radio bands popular during the early 20th century.

It consists of ten 90 ft. parallel horizontal wires suspended like a "clothesline" between two 80 ft towers. Two 6-strand vertical "cage" conductors feed the antenna at the near end, joining together to a single cage, which drops down to the transmitter. The vertical "cage" line is the radiating element, functioning as an electrically short monopole antenna. The horizontal cables serve as a capacitive top-load, to increase the current in the vertical driven element, increasing radiated power. Using "cage" line made of a cylindrical array of parallel wires rather than a single wire reduces the resistance, which is important at low frequencies, where radiation resistance is so low that a large portion of the transmitter power can be wasted in ohmic resistance of the antenna or ground. Cage line also has higher capacitance to ground, increasing current in the antenna and output power. Cage line is also used for the two outer conductors of the horizontal top-load because they have more capacitance to ground and carry more current than the inner conductors.

The second grid of horizontal wires, lower down on the antenna, is a counterpoise that serves as the ground for the transmitter. The other side of the transmitter's output is connected to it. It functions as a large capacitor plate, with the conductive layers in the Earth serving as the other plate, allowing the RF current from the transmitter to pass into the ground. Counterpoises often work better than physical grounds at low frequencies, when the soil has high resistance.
Deutsch: Eindrucksvolle Amateurfunkantenne aus den 1920er-Jahren. Der vordere und hintere Gittermast dient dem mechanischen Aufbau und ist ohne elektrische Funktion. Die eigentliche Antenne vom Typ „Inverted-L“ („Umgedrehtes L“) besteht aus dem Y-förmigen Reusenleiter (vorn) und der an einen riesigen Wäscheständer erinnernden Dachkapazität (oben, Flattop capacitive load). Die unteren Wäscheleinen“ (knapp oberhalb des Hausdachs) bilden das Gegengewicht zur Antenne.
Date Prior to September 1922
Source Downloaded April 23, 2013 from QST magazine, American Radio Relay League, Hartford, Conn., Vol. 6, No. 6, January 1923, p. 62 on Google Books
Author Unknown authorUnknown author

Licensing

Public domain
This work is in the public domain in the United States because it was published (or registered with the U.S. Copyright Office) before January 1, 1929.

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Note: This tag should not be used for sound recordings.PD-1923Public domain in the United States//commons.wikimedia.org/wiki/File:Inverted-L_antenna_with_counterpoise.jpg
Annotations
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Captions

Inverted L amateur radio antenna built by William Reynolds, Denver Colorado around 1920

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Date/TimeThumbnailDimensionsUserComment
current14:53, 30 September 2020Thumbnail for version as of 14:53, 30 September 2020376 × 592 (53 KB)HohumUpload colourised images separately
04:43, 22 June 2020Thumbnail for version as of 04:43, 22 June 2020376 × 592 (58 KB)F1jmmColorisation
17:10, 26 April 2013Thumbnail for version as of 17:10, 26 April 2013376 × 592 (53 KB)ChetvornoUser created page with UploadWizard

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