The self-capacitance of a multi-turn solenoid has little to do with
spacing between turns. Self-c depends on coil length and diameter.

The self-capacitances between adjacent turns are all in series with
each other. Resulting capacitance across coil is negligible.

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A coil 6.6" long, 6" diameter, 26.5 turns, has L = 68 uH, Q = 500 at
3.8 MHz, and self-resonant frequency = 9 MHz.
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Reg.