Abstract: In an automatic tuning system for an antenna having a single variable reactance element, the power transmitted to the antenna and the power reflected from the antenna on the feedline are sensed. The variable reactance component of the antenna is adjusted until the ratio between the transmitted and reflected power on the feedline indicates that the standing wave ratio on the feedline is at a minimum, whereupon the antenna will be tuned. The adjustment of the variable reactance component is by a stepping motor controlled by a microprocessor, which is programmed to make calculations to determine when the standing wave ratio reaches a minimum.