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![]() "Walter Maxwell" wrote Reg, I had never given much thought to the series relationship of the capacitance between turns. I had always considered them as being in parallel, thus the honeycomb, or the basket-weave configurations to minimize the interturn capacitance. Have I misconstrued the purpose of those configurations? Do I also understand you correctly that with a specified length of the solenoid, and a given diameter, the total interturn capacitance is independent of the number of turns, because the capacitance between turns adds in series to the same value regardless of the number of turns? ==================================== Walt, As I said, I was referring only to the solenoid form. Below the self-resonant frequency and for some way above it, the distributed self-capacitance is equivalent to a lumped capacitor across the ends of the coil. Coi Because capacitances between adjacent turns are in series with each other, the capacitance between turns only matters when there are only one or two turns. So, for ordinary proportioned coils, when there are more than a few turns, the self-capacitance tends to become independent of the number of turns, wire diameter and wire spacing. The wire turns can be considered to form the outside of a Faraday cage. To calculate self capacitance, consider wire spacing to be zero. When isolated in space we have the capacitance between the two fat halves of a dipole. Which is calculable from length and diameter of the coil, and is equivalent to a lumped capacitance between its ends, which may be used to calculate the self-resonant frequency. Or the self-resonant frequency can be calculated directly from dimensions and number of turns. In the past I have measured the self-resonant frequency of coils of all sorts of dimensions. From antenna loading coils, coax choke coils, to 6 feet long, 1 inch diameter, 1000 turns, 160-meter helical antennas. In all cases measurement results agree with the calculating formula within the uncertainties of the measured input data. ---- Reg. |
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