Question
What is the total bandwidth of an FM phone transmission having 5 kHz deviation and 3 kHz modulating frequency?
Answer Options
- A) 3 kHz
- B) 5 kHz
- C) 8 kHz
- D) 16 kHz
Correct Answer: D
Explanation
The bandwidth (B) of a Frequency Modulation (FM) signal is generally estimated using Carson’s Rule. This rule states that the bandwidth is approximately equal to two times the sum of the maximum frequency deviation (\Delta F) and the maximum modulating frequency (F_{\text{m}}): B = 2(\Delta F + F_{\text{m}}).
Substituting the given values, \Delta F = 5 \text{ kHz} and F_{\text{m}} = 3 \text{ kHz}: B = 2(5 \text{ kHz} + 3 \text{ kHz}) = 2(8 \text{ kHz}) = 16 \text{ kHz.} The total bandwidth of the FM transmission is 16 \text{ kHz}. Note that amateur voice FM typically uses narrow-band FM (NFM) with a total bandwidth of about 10 \text{ kHz}.
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