Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!mimsy!cvl!umd5!cgs From: cgs@umd5 (Chris Sylvain) Newsgroups: sci.electronics Subject: Re: Tesla Coil - broadcast power Message-ID: <1405@umd5> Date: Wed, 24-Dec-86 00:09:21 EST Article-I.D.: umd5.1405 Posted: Wed Dec 24 00:09:21 1986 Date-Received: Wed, 24-Dec-86 04:00:44 EST References: <4815@reed.UUCP> <823@A60.UUCP> <824@A60.UUCP> <904@sfsup.UUCP> <553@rpics.RPI.EDU> <162@ndmath.UUCP> Reply-To: cgs@umd5.umd.edu (Chris Sylvain) Organization: University of Maryland, College Park Lines: 57 Keywords: inductor "Q" In article <162@ndmath.UUCP> milo@ndmath.UUCP (Greg Corson) writes: > >I have been told that the "Q" of each coil should be as high as possible, how >would you calculate it in this situation? > There's two "flavors" of Q: Loaded and Unloaded. Unloaded Q is determined by the series resistance present in both inductors and capacitors. This series resistance dissipates energy in the circuit, and affects the "sharpness" of the response peak of a resonant LC circuit. "Most diagrams of resonant circuits show only inductance and capacitance; no resistance is indicated. Nevertheless, resistance is always present. At frequencies up to about 30 MHz this resistance is mostly in the wire of the coil. At higher frequencies energy loss in the capacitor also becomes a factor. *This energy loss is equivalent to resistance* [emphasis mine]. When maximum sharpness or selectivity is needed, the objective of design is to reduce the inherent resistance to the lowest possible value. The value of the reactance of either the inductor or capacitor at the resonant frequency of a series-resonant circuit, divided by the series resistance in the circuit, is called the Q (quality factor) of the circuit, or: _Q= X/R_ where: Q= quality factor X= reactance in ohms of either the inductor or capacitor R= series resistance in ohms" (1) Q can be used to determine the voltage across the LC circuit: _V= Q*E_ where: E= the voltage being applied to the circuit. _Loaded_ Q: "However, when the circuit delivers energy to a load (as in the case of the resonant circuits used in transmitters) the energy consumed in the circuit itself is negligible compared with that consumed by the load." "The Q of a parallel resonant circuit loaded by a resistive impedance is: _Q= R/X_ where: R= parallel load resistance in ohms X= reactance in ohms." "The effective Q of a circuit loaded by a parallel resistance becomes higher when the reactances are decreased. A circuit loaded with a relatively low resistance (a few thousand ohms [!!!]) must have low-reactance elements (large capacitance and small inductance) to have a reasonably high Q." (2) (50/75 ohms is relatively low to me !) The reactance in ohms of an inductor is: _2 * PI * f * L_ where: PI= famous constant f= frequency of interest L= value of inductor in Henries I hope this helps... --- (1) & (2) _The ARRL Handbook for the Radio Amateur_ pps. 2-32 & 2-34 reprinted and edited somewhat without permission... -- --==---==---==-- .. The jaws that bite, the claws that catch! .. ARPA: cgs@umd5.UMD.EDU BITNET: cgs%umd5@umd2 UUCP: ..!seismo!umd5.umd.edu!cgs