Deep Dive: E8B05
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.
Why Other Answers 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.
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 Example
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.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E8B
Reference: FCC Part 97.307
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E8B topic.