Question
What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 7.5 kHz if the highest modulation frequency is 3.5 kHz?
Answer Options
- A) 2.14
- B) 0.214
- C) 0.47
- D) 47
Correct Answer: A
Explanation
The deviation ratio is a measure of the extent of frequency modulation applied to a carrier, calculated as the ratio of the maximum frequency deviation (\Delta f) to the maximum audio frequency (f_m). This value is key in determining the necessary spectral allocation of the FM signal.
Given the maximum frequency swing (\Delta f) is 7.5 kHz and the highest modulation frequency (f_m) is 3.5 kHz, the deviation ratio is calculated as 7.5 kHz / 3.5 kHz \approx \mathbf{2.14}. This ratio indicates that the FM signal is slightly wide, meaning its bandwidth will be greater than twice the maximum modulating frequency (2 \times 3.5 kHz = 7 kHz) plus the deviation.
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