Calculators

Everything here was derived while building, and most of it exists in no other tool. Where a calculator overlaps something published, its page says so.

One page here is not a calculator. Coil geometry stopped computing: JavaTC does the whole geometry at once and a second set of numbers beside it is noise. What the page still carries is what JavaTC does not, which is where Wheeler's forms stop being right and what a tapped primary does to a published set of figures.

Every one of them opens on the same coil, and so does every interactive figure in the articles. That is deliberate. It is the machine whose numbers are known all the way down: the primary counted turn by turn, the tank measured rather than assumed, the frequencies taken off it. Somebody else's build publishes what its builder chose to publish, and the figures a calculator actually needs are usually among the ones left out.

For the whole coil geometry at once, primary and secondary together, use JavaTC. It is Barton B. Anderson's, with Paul Nicholson, Phil Slawinski and Matt Lewis named on it, and it is what this field has checked against itself for years. Nothing here replaces it: these ten answer questions it does not ask.

Its coupling figure is an estimate, not a measurement. It asks for the ground radius, the wall radius and the ceiling, so it is not blind to the room, but nearby metal and walls throw it off anyway and it cannot know what is standing beside your coil. Two builds on the record show the size of it. BrOdin wound a secondary to JavaTC's 0.185 and got massive racing sparks at 2000 A, and brought the coupling down until they stopped. On another coil Uspring read the builder's file at 0.134 and suggested dropping the secondary; the builder lowered it and the topload by 2 cm and reported 0.172, a quarter more coupling out of two centimetres. Take the printed number to start with, then measure the coil you built.

How to measure it. Sweep impedance across the tank with the secondary standing where it will stand and no power anywhere. You get three readings: two dips, which are the two poles, and a peak between them, which is the secondary's own resonance. Three readings against two unknowns, and the pole equations invert to give you both the coupling and the primary's frequency, measured on the coil as it is rather than computed from its dimensions. The inversion, the algebra and the bench note are on the two poles, and what the answer then buys you is on coupling.