Hi All. Can anyone advise me here, please. I am building a 10.5-inch diameter TC. The height of the secondary winding is 42-inches and the resonance is 78khz. The problem is that I want to make the primary coil a helical coil, but I don't want to end up over-coupling it. So, can anyone advise me on the physical dimension I need to make the primary coil? Paul M.