Which of the following devices or circuits changes an alternating current into a varying direct current signal?
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.
Exam Tip
Rectifier = AC to DC conversion. Think 'R'ectifier 'R'emoves one direction of AC, making it DC. Transformers change voltage but stay AC, amplifiers boost signals, and reflectors are antenna parts.
Memory Aid
"Rectifier = AC to DC. Think 'R'ectifier 'R'emoves negative half of AC wave, making it DC. Uses diodes to allow current in only one direction."
Real-World Application
In your power supply, a bridge rectifier (four diodes) converts 120V AC from the wall outlet into pulsating DC. This DC is then filtered by capacitors to become smooth DC suitable for powering your transceiver. Without the rectifier, you couldn't power DC equipment from AC sources. The rectifier is the first stage in converting wall power to usable DC voltage.
Key Concepts
Why Other Options Are Wrong
Option A (Transformer): Incorrect. Transformers change AC voltage levels but don't convert AC to DC - they output AC at different voltages. Rectification requires diodes.
Option C (Amplifier): Incorrect. Amplifiers increase signal strength but don't change AC to DC - they amplify the signal in its original form (AC or DC).
Option D (Reflector): Incorrect. A reflector is an antenna element, not an electronic circuit. It doesn't convert AC to DC - it reflects radio waves.
题目解析
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.
考试技巧
Rectifier = AC to DC conversion. Think 'R'ectifier 'R'emoves one direction of AC, making it DC. Transformers change voltage but stay AC, amplifiers boost signals, and reflectors are antenna parts.
记忆口诀
Rectifier = AC to DC. Think 'R'ectifier 'R'emoves negative half of AC wave, making it DC. Uses diodes to allow current in only one direction.
实际应用示例
In your power supply, a bridge rectifier (four diodes) converts 120V AC from the wall outlet into pulsating DC. This DC is then filtered by capacitors to become smooth DC suitable for powering your transceiver. Without the rectifier, you couldn't power DC equipment from AC sources. The rectifier is the first stage in converting wall power to usable DC voltage.
错误选项分析
Option A (Transformer): Incorrect. Transformers change AC voltage levels but don't convert AC to DC - they output AC at different voltages. Rectification requires diodes. Option C (Amplifier): Incorrect. Amplifiers increase signal strength but don't change AC to DC - they amplify the signal in its original form (AC or DC). Option D (Reflector): Incorrect. A reflector is an antenna element, not an electronic circuit. It doesn't convert AC to DC - it reflects radio waves.
知识点
Rectifiers, AC to DC conversion, Power supplies, Diodes
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.