Which of the following describes combining speech with an RF carrier signal?
The correct answer is Modulation. Modulation is the process of combining speech (or other information) with an RF carrier signal. The carrier is a high-frequency radio wave, and modulation varies one or more of its properties (amplitude, frequency, or phase) in accordance with the information signal. For voice communications, your speech (audio signal) modulates the carrier, creating a modulated RF signal that can be transmitted. For amateur radio operators, understanding modulation is fundamental because all voice and data transmissions require modulation. Common types include AM (amplitude modulation), FM (frequency modulation), and SSB (single sideband, a form of AM). Without modulation, the carrier would contain no information.
Exam Tip
Modulation = combining information with carrier. Think 'M'odulation = 'M'ixes speech with carrier. Impedance matching transfers power, oscillation generates signals, filtering removes frequencies - none combine speech with carrier.
Memory Aid
"Modulation = Mixes information with carrier. Think 'M'odulation = 'M'ixes speech with 'M'odulated carrier. Combines audio with RF to create transmit signal."
Real-World Application
When you speak into your microphone, the audio signal modulates the RF carrier generated by your transmitter. In FM, your voice varies the carrier's frequency. In SSB, your voice varies the carrier's amplitude. This modulated signal is then amplified and transmitted. At the receiving end, the modulation is removed (demodulated) to recover your voice. Modulation is what makes radio communication possible - it puts your information onto the radio wave.
Key Concepts
Why Other Options Are Wrong
Option A (Impedance matching): Incorrect. Impedance matching ensures maximum power transfer between components. It doesn't combine speech with a carrier - it matches impedances for efficient power transfer.
Option B (Oscillation): Incorrect. Oscillation is the generation of periodic signals. It creates the carrier but doesn't combine it with speech - that's modulation's job.
Option D (Low-pass filtering): Incorrect. Low-pass filtering removes high frequencies. It filters signals but doesn't combine speech with a carrier.
题目解析
The correct answer is Modulation. Modulation is the process of combining speech (or other information) with an RF carrier signal. The carrier is a high-frequency radio wave, and modulation varies one or more of its properties (amplitude, frequency, or phase) in accordance with the information signal. For voice communications, your speech (audio signal) modulates the carrier, creating a modulated RF signal that can be transmitted. For amateur radio operators, understanding modulation is fundamental because all voice and data transmissions require modulation. Common types include AM (amplitude modulation), FM (frequency modulation), and SSB (single sideband, a form of AM). Without modulation, the carrier would contain no information.
考试技巧
Modulation = combining information with carrier. Think 'M'odulation = 'M'ixes speech with carrier. Impedance matching transfers power, oscillation generates signals, filtering removes frequencies - none combine speech with carrier.
记忆口诀
Modulation = Mixes information with carrier. Think 'M'odulation = 'M'ixes speech with 'M'odulated carrier. Combines audio with RF to create transmit signal.
实际应用示例
When you speak into your microphone, the audio signal modulates the RF carrier generated by your transmitter. In FM, your voice varies the carrier's frequency. In SSB, your voice varies the carrier's amplitude. This modulated signal is then amplified and transmitted. At the receiving end, the modulation is removed (demodulated) to recover your voice. Modulation is what makes radio communication possible - it puts your information onto the radio wave.
错误选项分析
Option A (Impedance matching): Incorrect. Impedance matching ensures maximum power transfer between components. It doesn't combine speech with a carrier - it matches impedances for efficient power transfer. Option B (Oscillation): Incorrect. Oscillation is the generation of periodic signals. It creates the carrier but doesn't combine it with speech - that's modulation's job. Option D (Low-pass filtering): Incorrect. Low-pass filtering removes high frequencies. It filters signals but doesn't combine speech with a carrier.
知识点
Modulation, RF carrier, Signal processing, Transmission methods
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.