What is indicated on a waterfall display by one or more vertical lines on either side of a data mode or RTTY signal?
The correct answer is D: Overmodulation. What is indicated on a waterfall display by one or more vertical lines on either side of a data mode or RTTY signal is overmodulation. Overmodulation causes the signal to extend beyond its intended bandwidth, creating vertical lines (spurious emissions) on the waterfall. For amateur radio operators, this is a visual indicator of overmodulation. Understanding this helps when operating digital modes.
Exam Tip
Waterfall vertical lines beside data/RTTY = overmodulation. Think 'V'ertical 'L'ines = 'V'ery 'L'arge modulation (overmodulation). Overmodulation causes signal to extend beyond intended bandwidth, creating vertical lines. Not long path, not backscatter, not insufficient modulation - just overmodulation.
Memory Aid
"Waterfall vertical lines beside data/RTTY = overmodulation. Think 'V'ertical 'L'ines = 'V'ery 'L'arge modulation. Overmodulation causes signal to extend beyond intended bandwidth, creating vertical lines. Visual indicator of overmodulation."
Real-World Application
A waterfall display shows a data mode signal. Vertical lines appear on either side of the signal. These lines indicate overmodulation - the signal is extending beyond its intended bandwidth, creating spurious emissions. This is a visual indicator that modulation levels are too high. Overmodulation is the cause.
Key Concepts
Why Other Options Are Wrong
Option A (Long path propagation): Incorrect. Long path propagation doesn't create vertical lines - it affects signal strength, not bandwidth. Long path isn't the cause.
Option B (Backscatter propagation): Incorrect. Backscatter propagation doesn't create vertical lines - it affects signal characteristics, not bandwidth. Backscatter isn't the cause.
Option C (Insufficient modulation): Incorrect. Insufficient modulation would make the signal weaker, not create vertical lines - overmodulation creates the lines. Insufficient modulation is opposite.
题目解析
The correct answer is D: Overmodulation. What is indicated on a waterfall display by one or more vertical lines on either side of a data mode or RTTY signal is overmodulation. Overmodulation causes the signal to extend beyond its intended bandwidth, creating vertical lines (spurious emissions) on the waterfall. For amateur radio operators, this is a visual indicator of overmodulation. Understanding this helps when operating digital modes.
考试技巧
Waterfall vertical lines beside data/RTTY = overmodulation. Think 'V'ertical 'L'ines = 'V'ery 'L'arge modulation (overmodulation). Overmodulation causes signal to extend beyond intended bandwidth, creating vertical lines. Not long path, not backscatter, not insufficient modulation - just overmodulation.
记忆口诀
Waterfall vertical lines beside data/RTTY = overmodulation. Think 'V'ertical 'L'ines = 'V'ery 'L'arge modulation. Overmodulation causes signal to extend beyond intended bandwidth, creating vertical lines. Visual indicator of overmodulation.
实际应用示例
A waterfall display shows a data mode signal. Vertical lines appear on either side of the signal. These lines indicate overmodulation - the signal is extending beyond its intended bandwidth, creating spurious emissions. This is a visual indicator that modulation levels are too high. Overmodulation is the cause.
错误选项分析
Option A (Long path propagation): Incorrect. Long path propagation doesn't create vertical lines - it affects signal strength, not bandwidth. Long path isn't the cause. Option B (Backscatter propagation): Incorrect. Backscatter propagation doesn't create vertical lines - it affects signal characteristics, not bandwidth. Backscatter isn't the cause. Option C (Insufficient modulation): Incorrect. Insufficient modulation would make the signal weaker, not create vertical lines - overmodulation creates the lines. Insufficient modulation is opposite.
知识点
Waterfall display, Vertical lines, Overmodulation, Data mode signals
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.