Question
What is the frequency deviation for a 12.21 MHz reactance modulated oscillator in a 5 kHz deviation, 146.52 MHz FM phone transmitter?
Answer Options
- A) 101.75 Hz
- B) 416.7 Hz
- C) 5 kHz
- D) 60 kHz
Correct Answer: B
Explanation
In an FM transmitter that uses frequency multiplication, the deviation (\Delta F) is multiplied along with the frequency. To achieve the final desired deviation (\Delta F_{\text{out}}), the initial deviation (\Delta F_{\text{in}}) must be calculated based on the multiplication factor (M). The final frequency is F_{\text{out}} = F_{\text{in}} \times M.
First, find the multiplication factor: M = 146.52 \text{ MHz} / 12.21 \text{ MHz} \approx 12. The required input deviation is \Delta F_{\text{in}} = \Delta F_{\text{out}} / M. Substituting the values: \Delta F_{\text{in}} = \frac{5 \text{ kHz}}{12} = 0.4166 \text{ kHz} \approx 416.7 \text{ Hz.} The required frequency deviation for the 12.21 \text{ MHz} oscillator is 416.7 \text{ Hz}.
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