Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net> BTW - The much longer explanation can be found at: http://www.tpub-dot-com/neets/book2/4.htm Hi Matt, Inductors (coils) resist current "sort of" like resistors do. "Reactance" is used much like resistance to figure out such things. Xl = 2 x pi f x L Where: snip...