Considering the secondary of a tesla coil as a long antenna wire can I modify the resonant frequency of the secondary , between some limits of course, mounting a variable cap between the bottom end and the ground? I saw in some physics manual a schema for an old radio, but I am not sure that will work for emission too, or for tesla coils. I have in my mind to use a variable air or oil filled capacitor in the ground connection. The presence of the cap will build some high voltage on its armatures and get breakdown? It is feasible? I would be able to modify the sec and primary frequency both, easier than changing the toroid height or dimensions.