Deep Dive: E8B06
The correct answer is A: 2.14. The deviation ratio of an FM phone signal with maximum frequency swing of ±7.5 kHz and highest modulation frequency of 3.5 kHz is 2.14. Deviation ratio = maximum frequency deviation / highest modulating frequency. Calculation: Deviation ratio = 7.5 kHz / 3.5 kHz = 2.14. The deviation ratio tells you how many times the maximum deviation exceeds the highest modulating frequency. A deviation ratio of 2.14 means the carrier frequency can deviate up to 2.14 times the highest audio frequency, which affects the bandwidth and sideband structure of the FM signal.
Why Other Answers Are Wrong
Option B: Incorrect. 0.214 would be 3.5 / 7.5, which is the inverse of the correct calculation. Deviation ratio = deviation / modulating frequency. Option C: Incorrect. 0.47 would be approximately 3.5 / 7.5, still the inverse. The correct value is 7.5 / 3.5 = 2.14. Option D: Incorrect. 47 is way too large and doesn't match any reasonable calculation.
Exam Tip
Deviation ratio = Deviation / Highest modulating frequency. Remember: Deviation ratio = maximum frequency deviation divided by highest modulating frequency. With ±7.5 kHz deviation and 3.5 kHz modulating frequency, ratio = 7.5 / 3.5 = 2.14.
Memory Aid
**D**eviation **R**atio = **7**.**5** / **3**.**5** = **2**.**14** (think 'DR = 7.5/3.5 = 2.14')
Real-World Example
You're transmitting FM with ±7.5 kHz peak deviation and the highest audio frequency is 3.5 kHz. The deviation ratio is 7.5 kHz / 3.5 kHz = 2.14. This means the maximum frequency deviation is 2.14 times the highest modulating frequency.
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.