Much of the data below also applies to inductors in equipment, such as tank circuits.
The most common questions are:
What does the coil do? A normal physically small (physically small compared to antenna length or wavelength) loading coil or loading inductor does not replace a missing fraction of a wavelength. A physically small loading coil simply inserts a series inductive reactance that cancels capacitive antenna reactance. When a 150-ohm reactance inductor is inserted in series with a 150-ohm capacitive load (like an antenna) reactances cancel. Only the resistive parts remain.
What determines current distribution in a loading coil? Current distribution is determined by stray capacitance to the outside world and the impedance terminating the loading coil. The current in any inductor would be equal at each end except for displacement currents.Displacement currentsare “imaginary currents” that flow through a capacitance. A changingelectric fieldis tied to these currents.