Air Core Inductor

Coil Diameter, D= m
Winding Width, W= m (leave empty if d given instead)
OR Wire Diameter, d= m (W=d*N, tight wound coil)
Inductance, L= H
Turns, N=
Winding Width= m
Wire Spacing= m
Wire Length= m

This formula is most accurate when the coil length W is greater than 0.4*D and less than 3*D and the frequency is less than 10 MHz. Also, wire diameter is assumed to be small (under 10%) compared to diameter D. As the frequency goes above 10 MHz, parasitic capacitance causes the formula to be less accurate.

Q=X/R, where X=2*pi*f*L, R=resistance of wire. Q changes drastically as a function of frequency. At lower frequency, Q is good as only the DC resistance has an effect. As the frequency increase, Q will increase up to a point when the skin effects and the distributed capacitance begin to dominate. Then, Q will decrease till it reached zero at self resonance frequency.

Q can be increase by decreasing the windings resistance ( using heavy gauge wires), spread the windings to lower distributed capacitance and using a iron or ferrite core to wind over to increase the inductance.

© 2007 Tom Ahola