Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> Yes, there is a correct height. It depends on the dia. of your sec coil. Please advise on your sec coil dia and then I can advise you as to best height. Set the toroid at 1.5 x toroid minor dia. This is the height as measured from the last turn to the bottom of the toroid. A piece of PVC waterpipe makes a good spacer. Dr. Resonance