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The Q of an inductor is the measure of its quality. The more 'perfect' the inductor, the higher its Q value. Q = X_{L} / r_{i} where: Q = quality (unitless) A 'reallife' inductor can be regarded as a 'perfect' inductor connected in series with a resistance (r_{i}).
The Q of a coil is also known as the merit of a coil. A 'perfect' inductor would have a Q of infinity. Although it is possible to achieve Qs on the order of 2000 or so, most inductors have Q values that are less than 100 when used in their intended frequency ranges. The basic equation for Q shows that the Q of an inductor is proportional to its reactance:
Internal Resistance of an Inductor The internal resistance (r_{i}) of an inductor is made up mainly of the DC resistance of the wire that makes up the inductor, itself. At radio frequencies, however, the value of r_{i} is increased by significant amounts of eddy currents and RF skin effects. There is an inverse relationship between the Q of an inductor and its internal resistance:
For most practical purposes, the internal resistance of an inductor is negligible when the Q value is greater than 100 (the reactance is more than a hundred times greater than the internal resistance).


David L. Heiserman, Editor  Copyright © SweetHaven
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Revised: June 06, 2015