...under perpetual construction.

A variometer consists usually of two coaxial coils, connected in series, where the coils relative position can be varied in some way. If `L _{1}` and

For two coaxial coils, like the ones in the picture, the mutual inductance is at maximum when they are also

If the two concentrical coils are rotated, so that their axes are not parallel any more, the mutual inductance decreases, reaching zero (almost) when the angle is

If the two coaxial coils are moved along their axis instead (

The form below computes the main parameters for the two types of variometer described above. The self-inductances are calculated using the formulas in

These formulas agree very well with the results of some electromagnetic simulations I have done, see the page for details.

References:

[1] |
R. Lundin, "A Handbook Formula for the Inductance of a Single-Layer Circular Coil," Proc. IEEE, vol. 73, no. 9, pp. 1428-1429, Sep. 1985. |

[2] |
F.E. Terman, "Radio Engineers' Handbook," London, McGraw-Hill, 1st ed., Sep. 1950. |