What factors affect the bandwidth of a transmitted CW signal?
The correct answer is C: Keying speed and shape factor (rise and fall time). The factors that affect the bandwidth of a transmitted CW signal are keying speed (how fast you're sending) and shape factor (the rise and fall time of the keying waveform). These determine how fast the signal transitions and thus the bandwidth.
Faster keying speed means shorter dots and dashes, creating more rapid transitions and wider bandwidth. Slower rise/fall times (gentler transitions) create narrower bandwidth, while faster rise/fall times (sharper transitions) create wider bandwidth. The shape factor (rise and fall time) is particularly important - very short rise/fall times create key clicks (wide bandwidth), while longer rise/fall times keep bandwidth narrow. IF bandwidth and Q affect receiver performance but don't directly affect transmitted signal bandwidth.
Exam Tip
CW bandwidth factors = Keying speed and shape factor. Remember: Transmitted CW bandwidth is affected by keying speed (WPM) and shape factor (rise/fall time). Faster keying and shorter rise/fall times increase bandwidth.
Memory Aid
"**C**W **B**andwidth = **K**eying **S**peed + **S**hape **F**actor (think 'CB = KS+SF')"
Real-World Application
You're sending CW at 20 WPM with very short rise/fall times (sharp keying). This creates wide bandwidth and key clicks. To reduce bandwidth, you slow down the keying speed or increase the rise/fall times (gentler transitions). The keying speed and waveform shape directly determine your transmitted signal bandwidth.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. IF bandwidth and Q affect receiver performance, not the transmitted CW signal bandwidth. The transmitted bandwidth is determined by the keying characteristics.
Option B: Incorrect. Modulation index and output power don't affect CW bandwidth. CW is on/off keying, not amplitude or frequency modulation.
Option D: Incorrect. Not all options are correct. Only keying speed and shape factor affect transmitted CW bandwidth.
题目解析
The correct answer is C: Keying speed and shape factor (rise and fall time). The factors that affect the bandwidth of a transmitted CW signal are keying speed (how fast you're sending) and shape factor (the rise and fall time of the keying waveform). These determine how fast the signal transitions and thus the bandwidth. Faster keying speed means shorter dots and dashes, creating more rapid transitions and wider bandwidth. Slower rise/fall times (gentler transitions) create narrower bandwidth, while faster rise/fall times (sharper transitions) create wider bandwidth. The shape factor (rise and fall time) is particularly important - very short rise/fall times create key clicks (wide bandwidth), while longer rise/fall times keep bandwidth narrow. IF bandwidth and Q affect receiver performance but don't directly affect transmitted signal bandwidth.
考试技巧
CW bandwidth factors = Keying speed and shape factor. Remember: Transmitted CW bandwidth is affected by keying speed (WPM) and shape factor (rise/fall time). Faster keying and shorter rise/fall times increase bandwidth.
记忆口诀
**C**W **B**andwidth = **K**eying **S**peed + **S**hape **F**actor (think 'CB = KS+SF')
实际应用示例
You're sending CW at 20 WPM with very short rise/fall times (sharp keying). This creates wide bandwidth and key clicks. To reduce bandwidth, you slow down the keying speed or increase the rise/fall times (gentler transitions). The keying speed and waveform shape directly determine your transmitted signal bandwidth.
错误选项分析
Option A: Incorrect. IF bandwidth and Q affect receiver performance, not the transmitted CW signal bandwidth. The transmitted bandwidth is determined by the keying characteristics. Option B: Incorrect. Modulation index and output power don't affect CW bandwidth. CW is on/off keying, not amplitude or frequency modulation. Option D: Incorrect. Not all options are correct. Only keying speed and shape factor affect transmitted CW bandwidth.
知识点
CW bandwidth, Keying speed, Shape factor, Rise and fall time
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.