air coil

Single-layer air coil

Single-layer coils are wound on a body made of insulating material (polystyrene, pressboard). The formula presented below allows for calculating the coil's inductance with an accuracy of 5%, provided that dense winding is used, i.e., turn by turn. The principle for calculating inductance was taken from the book "Construction and Assembly of Amateur Radio Systems" by Zbigniew Faust.

Practical notes:

The coil's quality factor depends on the proportions of its dimensions and is greatest when the body diameter D is approximately twice the length of the winding. (2l).
When making a coil, wind 10% more turns than calculated. After measuring the inductance, you can always unwind a few turns if necessary, which is much easier than winding the missing turns if the measured inductance is less than required.