Файл:Variometer.jpg

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ОписаниеVariometer.jpg	English: A variometer, an adjustable air core inductor used in radio equipment, from a 1920 book on radio. It was widely used in radio receivers during the 1910s and 20s. Today it is mostly used in transmitter antenna tuners and matching sections for low frequency antennas, to match the transmission line to the antenna. It consists of two coils of wire with the same number of turns, connected in series. The inner coil is mounted on a vertical shaft that allows its axis to be turned with respect to the outer coil. When the inner coil's axis is parallel to the outer coil and their magnetic fields are in the same direction, their magnetic fields add, so their inductance is maximum. When the inner coil is turned so that it's axis is at an angle to the other, the mutual inductance between them is smaller so the total inductance is less. When the inner coil is turned 180° so its axis is parallel with the outer but their magnetic fields are in opposite directions, they subtract so the total field, and thus the total inductance, is very small. Thus the inductance can be continuously adjusted over a wide range.
Дата	1920
Източник	Downloaded April 30, 2013 from Elmer Eustace Bucher (1920) The Wireless Experimenter's Manual, Wireless Press, Inc., New York, p. 189, fig. 150a on Google Books
Автор	НеизвестенUnknown author

Public domain	This media file is in the public domain in the United States. This applies to U.S. works where the copyright has expired, often because its first publication occurred prior to January 1, 1929, and if not then due to lack of notice or renewal. See this page for further explanation.	United States
	This image might not be in the public domain outside of the United States; this especially applies in the countries and areas that do not apply the rule of the shorter term for US works, such as Canada, Mainland China (not Hong Kong or Macao), Germany, Mexico, and Switzerland. The creator and year of publication are essential information and must be provided. See Wikipedia:Public domain and Wikipedia:Copyrights for more details.