Antenna Tuner

Overview

An antenna tuner — more accurately an antenna matching unit or ATU — sits between the radio and the feedline and transforms whatever impedance the antenna presents into something close to 50 ohms. It does not make an antenna resonant, and it does not reduce loss in the feedline; it simply lets the transmitter deliver full power into a mismatched load.

Most tuners use an L-network of a variable inductor and one or two variable capacitors. Adjustment is interactive: changing the inductance changes the capacitance needed, so tuning is a matter of alternating between controls until the SWR reaches a minimum. Automatic tuners do the same search electronically.

Bands and modes

Band coverage

Modes

Safety note

Using it well

• Tune at low power first, then raise power once the match is found.
• Note the settings for each band and feed point so you can return to them.
• Keep the bypass path for antennas that are already close to 50 ohms.
• Remember that a good match at the tuner does not mean a low SWR on the feedline.