What is the primary effect of extremely short rise or fall time on a CW signal?
The correct answer is C: The generation of key clicks. The primary effect of extremely short rise or fall time on a CW signal is the generation of key clicks - unwanted wide-bandwidth noise that sounds like clicks on adjacent frequencies.
When a CW signal has very short rise/fall times (sharp transitions), it creates a square-wave-like keying waveform with rapid transitions. These rapid transitions contain high-frequency components that extend far beyond the desired signal bandwidth, creating key clicks. Key clicks are heard as clicking or popping sounds on frequencies adjacent to your signal. They're caused by the wide spectral content of the sharp transitions. Longer rise/fall times create smoother transitions and eliminate key clicks by keeping the bandwidth narrow.
Exam Tip
Short rise/fall time = Key clicks. Remember: Extremely short rise or fall time on CW signals generates key clicks - wide-bandwidth noise that interferes with adjacent frequencies. Longer rise/fall times eliminate key clicks.
Memory Aid
"**S**hort **R**ise/**F**all = **K**ey **C**licks (think 'SRF = KC')"
Real-World Application
You're sending CW with very sharp keying (short rise/fall times). Operators on adjacent frequencies complain about key clicks - clicking sounds interfering with their signals. The sharp transitions create wide-bandwidth noise. You increase the rise/fall times (gentler transitions), and the key clicks disappear. Your signal is now clean and doesn't interfere with adjacent frequencies.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. While key clicks make signals harder to copy, the primary effect of short rise/fall time is the generation of key clicks themselves, not just making copying more difficult.
Option B: Incorrect. While short rise/fall times create harmonics, the primary problem is key clicks - the wide-bandwidth noise that interferes with adjacent frequencies.
Option D: Incorrect. Short rise/fall times don't make signals harder to tune. The primary problem is key clicks interfering with other operators.
题目解析
The correct answer is C: The generation of key clicks. The primary effect of extremely short rise or fall time on a CW signal is the generation of key clicks - unwanted wide-bandwidth noise that sounds like clicks on adjacent frequencies. When a CW signal has very short rise/fall times (sharp transitions), it creates a square-wave-like keying waveform with rapid transitions. These rapid transitions contain high-frequency components that extend far beyond the desired signal bandwidth, creating key clicks. Key clicks are heard as clicking or popping sounds on frequencies adjacent to your signal. They're caused by the wide spectral content of the sharp transitions. Longer rise/fall times create smoother transitions and eliminate key clicks by keeping the bandwidth narrow.
考试技巧
Short rise/fall time = Key clicks. Remember: Extremely short rise or fall time on CW signals generates key clicks - wide-bandwidth noise that interferes with adjacent frequencies. Longer rise/fall times eliminate key clicks.
记忆口诀
**S**hort **R**ise/**F**all = **K**ey **C**licks (think 'SRF = KC')
实际应用示例
You're sending CW with very sharp keying (short rise/fall times). Operators on adjacent frequencies complain about key clicks - clicking sounds interfering with their signals. The sharp transitions create wide-bandwidth noise. You increase the rise/fall times (gentler transitions), and the key clicks disappear. Your signal is now clean and doesn't interfere with adjacent frequencies.
错误选项分析
Option A: Incorrect. While key clicks make signals harder to copy, the primary effect of short rise/fall time is the generation of key clicks themselves, not just making copying more difficult. Option B: Incorrect. While short rise/fall times create harmonics, the primary problem is key clicks - the wide-bandwidth noise that interferes with adjacent frequencies. Option D: Incorrect. Short rise/fall times don't make signals harder to tune. The primary problem is key clicks interfering with other operators.
知识点
Key clicks, Rise and fall time, CW keying, Bandwidth
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.