Which of the following is used to convert a signal from one frequency to another?
The correct answer is Mixer. A mixer is a circuit used to convert a signal from one frequency to another by combining two input signals to produce sum and difference frequencies. This frequency conversion (also called heterodyning) is fundamental to superheterodyne receivers, which convert incoming RF signals to intermediate frequencies (IF) for easier processing. Mixers are also used in transmitters to generate output frequencies and in transverters to convert between bands. For amateur radio operators, understanding mixers is essential because virtually all modern receivers use superheterodyne architecture with mixers for frequency conversion. The mixer combines the RF signal with a local oscillator signal to produce the desired output frequency.
Exam Tip
Mixer = frequency conversion. Think 'M'ixer = 'M'ixes two frequencies to create new ones. Phase splitters change phase, inverters reverse polarity, amplifiers boost signals - none change frequency.
Memory Aid
"Mixer = Mixes frequencies to convert. Think 'M'ixer = 'M'ixes two signals to create new frequencies. Combines RF and LO to produce IF."
Real-World Application
In your receiver, a mixer combines the incoming 146.52 MHz signal with a 135.52 MHz local oscillator signal to produce an 11 MHz intermediate frequency (146.52 - 135.52 = 11 MHz). This IF signal is easier to filter and amplify than the original RF frequency. The mixer is what makes frequency conversion possible, allowing receivers to tune across bands while using fixed-frequency IF stages.
Key Concepts
Why Other Options Are Wrong
Option A (Phase splitter): Incorrect. A phase splitter divides a signal into two signals with different phases (typically 0° and 180°). It doesn't change frequency - it only changes phase relationships.
Option C (Inverter): Incorrect. An inverter reverses signal polarity or inverts logic states. It doesn't change frequency - it only inverts the signal.
Option D (Amplifier): Incorrect. An amplifier increases signal strength but doesn't change frequency. It amplifies the signal at its original frequency.
题目解析
The correct answer is Mixer. A mixer is a circuit used to convert a signal from one frequency to another by combining two input signals to produce sum and difference frequencies. This frequency conversion (also called heterodyning) is fundamental to superheterodyne receivers, which convert incoming RF signals to intermediate frequencies (IF) for easier processing. Mixers are also used in transmitters to generate output frequencies and in transverters to convert between bands. For amateur radio operators, understanding mixers is essential because virtually all modern receivers use superheterodyne architecture with mixers for frequency conversion. The mixer combines the RF signal with a local oscillator signal to produce the desired output frequency.
考试技巧
Mixer = frequency conversion. Think 'M'ixer = 'M'ixes two frequencies to create new ones. Phase splitters change phase, inverters reverse polarity, amplifiers boost signals - none change frequency.
记忆口诀
Mixer = Mixes frequencies to convert. Think 'M'ixer = 'M'ixes two signals to create new frequencies. Combines RF and LO to produce IF.
实际应用示例
In your receiver, a mixer combines the incoming 146.52 MHz signal with a 135.52 MHz local oscillator signal to produce an 11 MHz intermediate frequency (146.52 - 135.52 = 11 MHz). This IF signal is easier to filter and amplify than the original RF frequency. The mixer is what makes frequency conversion possible, allowing receivers to tune across bands while using fixed-frequency IF stages.
错误选项分析
Option A (Phase splitter): Incorrect. A phase splitter divides a signal into two signals with different phases (typically 0° and 180°). It doesn't change frequency - it only changes phase relationships. Option C (Inverter): Incorrect. An inverter reverses signal polarity or inverts logic states. It doesn't change frequency - it only inverts the signal. Option D (Amplifier): Incorrect. An amplifier increases signal strength but doesn't change frequency. It amplifies the signal at its original frequency.
知识点
Mixers, Frequency conversion, Heterodyning, Superheterodyne receivers
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.