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Question 20302
JEE Physics · Hard

Principles of Communication: Amplitude Modulation MCQ

Solve this quality-checked JEE multiple-choice question, then review the correct answer and explanation.

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Amplitude ModulationHardQuestion 20302

Question

In Double Sideband Suppressed Carrier (DSB-SC), the transmitted signal is v(t) = A_m cos ω_m t × A_c cos ω_c t. Expanding this gives frequency components at:
  1. A
    ω_c only
  2. B
    ω_m only
  3. C
    ω_c + ω_m and ω_c − ω_m only (no carrier)
    Correct
  4. D
    ω_m, ω_c, ω_c + ω_m, ω_c − ω_m

Correct answer

ω_c + ω_m and ω_c − ω_m only (no carrier)

Explanation

Using product-to-sum: cos A cos B = ½[cos(A−B) + cos(A+B)]. So DSB-SC: v(t) = (A_mA_c/2)[cos(ω_c−ω_m)t + cos(ω_c+ω_m)t]. No carrier term at ω_c. Advantage: 100% of power in sidebands. Disadvantage: requires coherent (synchronous) demodulation — complex receiver.

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