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For mobile operation on the HF ham radio bands you will often see a high Q antenna with its shortened length. It will have a loading coil and perhaps a disk, spoke, or swirled looking capacitance hat. Sometimes these mobile antennas have a motorized movable tap on a large loading coil so that the number of turns used by the antenna changes commensurately with the desired operating frequency. This way the narrow bandwidth is overcome by the ability to dynamically tune the antenna. These motorized tuning antennas are called screwdriver antennas. There are manually tunable versions which require adjustment or chaing of the matching component.