Which of the following describes a signal in the time domain?
The correct answer is B: Amplitude at different times. A signal described in the time domain shows amplitude at different times. The time domain representation plots signal amplitude (voltage, current, or power) versus time.
Time domain analysis shows how a signal changes over time - you see the waveform shape, amplitude variations, timing, and transient behavior. This is the most intuitive way to view signals - like looking at an oscilloscope display. The time domain is complementary to the frequency domain (which shows amplitude at different frequencies). Both representations contain the same information, just viewed from different perspectives. Time domain is useful for understanding signal timing, pulse shapes, and transient behavior.
Exam Tip
Time domain = Amplitude vs time. Remember: Time domain representation shows amplitude at different times. This is like an oscilloscope display - voltage or current plotted against time.
Memory Aid
"**T**ime **D**omain = **A**mplitude **T**ime (think 'TD = AT' = Amplitude Time)"
Real-World Application
You're viewing a signal on an oscilloscope. The display shows voltage amplitude on the vertical axis and time on the horizontal axis. This is time domain representation - you see how the signal's amplitude changes over time. If it's a sine wave, you see the amplitude rising and falling in a sinusoidal pattern over time.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Power at intervals of phase describes phase domain analysis, not time domain. Time domain shows amplitude vs time, not power vs phase.
Option C: Incorrect. Frequency at different times describes frequency modulation or chirp signals, but time domain representation shows amplitude at different times, not frequency.
Option D: Incorrect. Discrete impulses in time order describes a specific type of signal (impulse train), not the general definition of time domain representation.
题目解析
The correct answer is B: Amplitude at different times. A signal described in the time domain shows amplitude at different times. The time domain representation plots signal amplitude (voltage, current, or power) versus time. Time domain analysis shows how a signal changes over time - you see the waveform shape, amplitude variations, timing, and transient behavior. This is the most intuitive way to view signals - like looking at an oscilloscope display. The time domain is complementary to the frequency domain (which shows amplitude at different frequencies). Both representations contain the same information, just viewed from different perspectives. Time domain is useful for understanding signal timing, pulse shapes, and transient behavior.
考试技巧
Time domain = Amplitude vs time. Remember: Time domain representation shows amplitude at different times. This is like an oscilloscope display - voltage or current plotted against time.
记忆口诀
**T**ime **D**omain = **A**mplitude **T**ime (think 'TD = AT' = Amplitude Time)
实际应用示例
You're viewing a signal on an oscilloscope. The display shows voltage amplitude on the vertical axis and time on the horizontal axis. This is time domain representation - you see how the signal's amplitude changes over time. If it's a sine wave, you see the amplitude rising and falling in a sinusoidal pattern over time.
错误选项分析
Option A: Incorrect. Power at intervals of phase describes phase domain analysis, not time domain. Time domain shows amplitude vs time, not power vs phase. Option C: Incorrect. Frequency at different times describes frequency modulation or chirp signals, but time domain representation shows amplitude at different times, not frequency. Option D: Incorrect. Discrete impulses in time order describes a specific type of signal (impulse train), not the general definition of time domain representation.
知识点
Time domain, Amplitude vs time, Signal representation, Waveform analysis
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.