The correct answer is Rectifier. A rectifier is a circuit or device that changes alternating current (AC) into varying direct current (DC). Rectifiers use diodes to allow current flow in only one direction, converting the bidirectional AC waveform into a unidirectional DC waveform (though it still varies in amplitude, requiring filtering to become smooth DC). For amateur radio operators, rectifiers are essential components in power supplies, converting AC wall power into DC for radio equipment. Understanding rectification is fundamental to power supply design and troubleshooting. Rectifiers can be half-wave (one diode), full-wave (two diodes), or bridge (four diodes), with bridge rectifiers being most common in modern equipment.