Formula for Q of resonant circuit?
M J Dowden wrote:
I am trying to find the formula used to calculate the Q of a parallel R-L-C resonant circuit. There are a number of questions in the Amateur Extra test pool[1] that ask this and the formula that I have does not produce the correct answers. I have been using Q = (2 * Pi * f * L) / R, but the questions in section E5G of the test pool don't seem to work with that. The answers that are produced by that formula are among the "distracters," suggesting that I am making an obvious error that they expect some people to make. It's obvious that this formula for Q is not valid for a parallel RLC-Circuit. If you let R go towards infinity, by this formula, the Q goes to zero, although it should obviously be infinite, since the circuit has no losses. The correct formula is Q = R / (2*pi*f*L) = R * 2*pi*f*C 73, -- Fabian Kurz, DJ1YFK * Dresden, Germany * http://fkurz.net/ Online Log: http://dl0tud.tu-dresden.de/~dj1yfk/log.html |
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