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Match the Column I with Column II and select the correct answer using the codes given below :

Column IColumn II
(P) \(Km(t) A \sin(\omega_{c}t)\)(W) PM
(Q) \(A \sin[\omega_{c}t + Km(t)]\)(X) FM
(R) \([1 + Km(t)] A \sin(\omega_{c}t)\)(Y) AM
(S) \(A \sin\left[\omega_{c}t + K\int_{-\infty}^{t} m(t)\, d\tau\right]\)(Z) DSBSC

  • A.P-Z, Q-W, R-Y, S-X
  • B.P-W, Q-Z, R-Y, S-X
  • C.P-X, Q-W, R-Z, S-Y
  • D.P-Y, Q-Z, R-W, S-X

Answer: A

The correct matching is P-Z, Q-W, R-Y, S-X.

  • \(Km(t)A\sin(\omega_{c}t)\) is the message times the carrier with no carrier term left: DSBSC (Z).
  • \(A\sin[\omega_{c}t + Km(t)]\) has the phase proportional to the message: PM (W).
  • \([1 + Km(t)]A\sin(\omega_{c}t)\) adds the carrier back, so the envelope follows the message: AM (Y).
  • Phase proportional to the integral of the message means instantaneous frequency proportional to the message: FM (X).

The main trap is FM against PM: the integral inside the phase is the signature of FM, because differentiating the phase gives a frequency deviation proportional to m(t).

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