Hey, you folks are good! I think you all have given me something to start with. In answer to the question of why do I want to know this stuff, I'm thinking of building a low pass filter to connect to the output of my inverter. I've been reading how the clipped square waves of the inexpensive inverters are really sinewaves with a lot of harmonic frequencies added in. If you filter out the harmonics with a low pass filter, voila, you have a sine wave. And I need a sine wave to run my microwave oven. I've been playing with this really cool downloadable filter software called "Elsie," by James Tonne (The student version is free). It is telling me my filter designs have dramatically different characteristics when the source output impedance changes just the tiniest amount. So I want to make sure I'm not too far away from reality before I actually build the filter. Thanks all for your very straightforward, concise, and practical solutions. If you see a flash on the northeastern horizon, don't worry, it's not nuclear armageddon. It's only me burning my eyebrows!