What is a relay?
The correct answer is A: An electrically-controlled switch. A relay is an electrically-controlled switch that uses an electromagnet to open or close one or more sets of contacts. When current flows through the relay's coil, it creates a magnetic field that moves an armature, which opens or closes the switch contacts. This allows a small control current to switch much larger currents or voltages. For amateur radio operators, relays are commonly used for TR (transmit/receive) switching, antenna switching, power control, and remote control functions. Relays provide electrical isolation between the control circuit and the switched circuit, making them ideal for safety and control applications. Understanding relays is essential for troubleshooting switching functions and designing control circuits.
Exam Tip
Relay = electrically-controlled switch. Think 'R'elay = 'R'emote switch controlled by electricity. It's a switch, not an amplifier or transistor. The key word is 'switch.'
Memory Aid
"Relay = Remote switch controlled by electricity. Think 'R'elay = 'R'emote 'E'lectrical 'L'ever (switch). Electromagnet controls the switch."
Real-World Application
In your station's antenna switch box, a relay might switch between your main antenna and a backup antenna. A small control signal (perhaps from your transceiver's PTT line) energizes the relay coil, which moves contacts to connect the desired antenna. This allows automatic antenna switching without manual cable changes. The relay isolates the control circuit from the RF circuit, preventing interference.
Key Concepts
Why Other Options Are Wrong
Option B (A current controlled amplifier): Incorrect. While relays are controlled by current, they don't amplify signals - they simply switch circuits on or off. Amplifiers increase signal strength, which relays don't do.
Option C (An inverting amplifier): Incorrect. An inverting amplifier is an op-amp circuit that inverts the signal phase. Relays are switches, not amplifiers, and don't process signals.
Option D (A pass transistor): Incorrect. A pass transistor is a transistor used to control current flow, not an electromagnetic switch. Relays use electromagnets, not semiconductors.
题目解析
The correct answer is A: An electrically-controlled switch. A relay is an electrically-controlled switch that uses an electromagnet to open or close one or more sets of contacts. When current flows through the relay's coil, it creates a magnetic field that moves an armature, which opens or closes the switch contacts. This allows a small control current to switch much larger currents or voltages. For amateur radio operators, relays are commonly used for TR (transmit/receive) switching, antenna switching, power control, and remote control functions. Relays provide electrical isolation between the control circuit and the switched circuit, making them ideal for safety and control applications. Understanding relays is essential for troubleshooting switching functions and designing control circuits.
考试技巧
Relay = electrically-controlled switch. Think 'R'elay = 'R'emote switch controlled by electricity. It's a switch, not an amplifier or transistor. The key word is 'switch.'
记忆口诀
Relay = Remote switch controlled by electricity. Think 'R'elay = 'R'emote 'E'lectrical 'L'ever (switch). Electromagnet controls the switch.
实际应用示例
In your station's antenna switch box, a relay might switch between your main antenna and a backup antenna. A small control signal (perhaps from your transceiver's PTT line) energizes the relay coil, which moves contacts to connect the desired antenna. This allows automatic antenna switching without manual cable changes. The relay isolates the control circuit from the RF circuit, preventing interference.
错误选项分析
Option B (A current controlled amplifier): Incorrect. While relays are controlled by current, they don't amplify signals - they simply switch circuits on or off. Amplifiers increase signal strength, which relays don't do. Option C (An inverting amplifier): Incorrect. An inverting amplifier is an op-amp circuit that inverts the signal phase. Relays are switches, not amplifiers, and don't process signals. Option D (A pass transistor): Incorrect. A pass transistor is a transistor used to control current flow, not an electromagnetic switch. Relays use electromagnets, not semiconductors.
知识点
Relays, Electrically-controlled switches, Electromagnetic switching, Control circuits
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.