What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 5 kHz if the highest modulation frequency is 3 kHz?
The correct answer is D: 1.67. The deviation ratio of an FM phone signal with maximum frequency swing of ±5 kHz and highest modulation frequency of 3 kHz is 1.67. Deviation ratio = maximum frequency deviation / highest modulating frequency.
Calculation: Deviation ratio = 5 kHz / 3 kHz = 1.67. The deviation ratio is similar to modulation index but is specifically defined as the ratio of maximum deviation to highest modulating frequency. A deviation ratio of 1.67 means the maximum frequency deviation is 1.67 times the highest modulating frequency. This ratio helps determine the bandwidth requirements and signal characteristics of the FM transmission.
Exam Tip
Deviation ratio = Deviation / Highest modulating frequency. Remember: Deviation ratio = maximum frequency deviation divided by highest modulating frequency. With ±5 kHz deviation and 3 kHz modulating frequency, ratio = 5 / 3 = 1.67.
Memory Aid
"**D**eviation **R**atio = **5** kHz / **3** kHz = **1**.**67** (think 'DR = 5/3 = 1.67')"
Real-World Application
You're transmitting FM with ±5 kHz peak deviation and the highest audio frequency is 3 kHz. The deviation ratio is 5 kHz / 3 kHz = 1.67. This ratio helps determine the bandwidth and signal characteristics of your FM transmission.
FCC Part 97.307Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. 6 would be approximately 2 × 3 or some other calculation error. The correct value is 5 / 3 = 1.67.
Option B: Incorrect. 0.167 would be 3 / 5, which is the inverse of the correct calculation. Deviation ratio = deviation / modulating frequency.
Option C: Incorrect. 0.6 would be 3 / 5, which is still the inverse. The correct calculation is 5 / 3 = 1.67.
题目解析
The correct answer is D: 1.67. The deviation ratio of an FM phone signal with maximum frequency swing of ±5 kHz and highest modulation frequency of 3 kHz is 1.67. Deviation ratio = maximum frequency deviation / highest modulating frequency. Calculation: Deviation ratio = 5 kHz / 3 kHz = 1.67. The deviation ratio is similar to modulation index but is specifically defined as the ratio of maximum deviation to highest modulating frequency. A deviation ratio of 1.67 means the maximum frequency deviation is 1.67 times the highest modulating frequency. This ratio helps determine the bandwidth requirements and signal characteristics of the FM transmission.
考试技巧
Deviation ratio = Deviation / Highest modulating frequency. Remember: Deviation ratio = maximum frequency deviation divided by highest modulating frequency. With ±5 kHz deviation and 3 kHz modulating frequency, ratio = 5 / 3 = 1.67.
记忆口诀
**D**eviation **R**atio = **5** kHz / **3** kHz = **1**.**67** (think 'DR = 5/3 = 1.67')
实际应用示例
You're transmitting FM with ±5 kHz peak deviation and the highest audio frequency is 3 kHz. The deviation ratio is 5 kHz / 3 kHz = 1.67. This ratio helps determine the bandwidth and signal characteristics of your FM transmission.
错误选项分析
Option A: Incorrect. 6 would be approximately 2 × 3 or some other calculation error. The correct value is 5 / 3 = 1.67. Option B: Incorrect. 0.167 would be 3 / 5, which is the inverse of the correct calculation. Deviation ratio = deviation / modulating frequency. Option C: Incorrect. 0.6 would be 3 / 5, which is still the inverse. The correct calculation is 5 / 3 = 1.67.
知识点
Deviation ratio, FM calculation, Frequency deviation, Modulating frequency
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.