loading coil

A loading coil is an inductance added to an antenna or transmission line to enhance performance in communications technology. These coils are inserted into tuned electrical circuits to boost their inductance.12

In telephone lines, loading coils are placed at intervals, sometimes as close as one mile apart. They counteract the effects of capacitance, bringing the line's impedance closer to pure resistance. For radio antennas that are too short to be resonant at their intended frequency, a loading coil can be added in series to help them approach resonance. This is common in automobile radios, where short whip antennas are used for broadcast frequencies. Some telephone and telegraph cables also feature continuous loading, achieved by wrapping them with a spiral of magnetic material.1