Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Hhchicken1-at-aol-dot-com> Bart, >>The calc should be 0.5 *(C1+C2), Surely this would mean that two identical toroids would have the same capacitance as just one?! I'm a bit confused about this myself as I'm trying to work out the Fres of my mini coil which will use two identical stacked toroids. Thanks, Henry