Antenna tuner

An antenna tuner is an impedance-matching network placed between radio equipment and an antenna. It reduces impedance mismatch at the equipment connection, improving power transfer without necessarily changing the antenna’s own resonance.

Impedance matching: The adjustment of electrical impedances to improve power transfer or reduce signal reflection between connected systems. An antenna tuner is a practical impedance-matching network between an antenna and radio equipment.
Electrical impedance: The frequency-dependent opposition that a circuit presents to alternating current, combining resistance and reactance. A tuner transforms the antenna system's impedance to suit the radio or feed line.
Antenna matching unit: A radio-frequency network that transforms an antenna-system impedance to a desired value; often another name for an antenna tuner. The name overlaps with antenna tuner, though some contexts distinguish units by placement or function.
Automatic antenna tuner: An antenna tuner that selects matching components automatically in response to a measured load. Automatic units extend tuner use to radios that retune quickly across frequencies.
Feed-line loss: The reduction of signal power as it travels along a transmission line, caused by conductor and dielectric losses. A tuner at the transmitter can leave a mismatched feed line lossy even when the radio sees a match.
Standing wave ratio: A measure of the amplitude ratio between standing waves formed by reflected and forward waves on a transmission line. Tuners are often adjusted to reduce the standing wave ratio measured at the transmitter.
Reactance: The frequency-dependent opposition to alternating current caused by capacitance or inductance, measured in ohms. Tuner capacitors and inductors supply reactance to cancel or transform a load.
Balun: A device that converts between balanced and unbalanced electrical connections, often while also transforming impedance. A balun addresses balance as well as possible impedance transformation; it is not simply a tuner.
Manual antenna tuner: An adjustable impedance-matching network whose inductors or capacitors are set by an operator. Manual controls let operators match loads across a broad range of amateur-radio bands.
Antenna efficiency: The fraction of power accepted by an antenna that is radiated rather than dissipated as heat or other losses. A tuner improves the match but cannot recover power lost in an inefficient antenna.

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