RF carrier 15 kV at 1 MHz is amplitude modulated and modulation index is 0.8. Find the peak voltage of the signal.

Question

RF carrier 15 kV at 1 MHz is amplitude modulated and modulation index is 0.8. Find the peak voltage of the signal.

1. A. 18 kV
2. B. 12 kV (Correct answer)
3. C. 18.75 kV
4. D. 22 kV

Correct Answer

Option B — 12 kV

Detailed Solution & Explanation

The correct answer is 12 kV.

Key Points

• The modulation index is defined as m = Vm / Vc, where Vm is the peak of the modulating signal and Vc the peak of the carrier.
• Rearranging: Vm = m x Vc.
• Substituting the given values: Vm = 0.8 x 15 = 12 kV.

Additional Information

• The carrier frequency of 1 MHz plays no part in the calculation and is present only as a distractor.
• Do not confuse this with the peak envelope voltage of the modulated wave, which would be Vc (1 + m) = 15 x 1.8 = 27 kV — the question asks specifically for the signal, meaning the modulating signal.