Barton & Marco, > Marco, you may want to consider making the toroid movable up and down. Malcolm > posted in a reply this week about fine tuning the resonator simply by raising > or lowering the toroid. Makes a lot of sense to me. I modeled this with E-Tesla 5.1 and tested with real parts. The amount of Fsec shift due to different toroid heights is too small to be significant on a big coil (like the Model 9J). Jeff