Fichier:Variometer.jpg

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Description

DescriptionVariometer.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.
Date	1920
Source	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
Auteur	Auteur inconnuUnknown author

Public domain	Ce document est dans le domaine public aux États-Unis. Ceci s'applique aux travaux des États-Unis où le copyright a expiré, souvent parce que sa première publication s'est produite avant le 1^er janvier 1929. Voir cette page pour davantage d'explication.	United States
	Cette image peut ne pas être dans le domaine public en dehors des États-Unis (ceci s'applique particulièrement au Canada, en Chine (pas Hong Kong, Macao, ni Taïwan), en Allemagne ou en Suisse). Le créateur et l'année de la publication sont l'information essentielle et doivent être fournis.