A variable inductor is an inductor whose inductance can be easily adjusted by changing an external variable, such as a sliding contact or variable capacitor. Variable inductors are used in radio frequency (RF) circuits to tune radios and other electronic equipment to specific frequencies. They are also used to create and shape waveforms for signal conditioning in electrical circuits.
Variable inductors typically consist of a coil of wire wound around a core of adjustable ferrite or iron. A sliding contact on the core, or a variable capacitor connected in parallel with the inductor, allows for the inductance to be altered. By changing the relative positions of the contact, or changing the capacitance of the capacitor, the amount of inductance in the circuit is changed. As the inductance increases, the frequency of the circuit decreases and vice versa. This allows the circuit to be tuned to a specific frequency with great accuracy.