Question

Select the correct equation that represents an am signal.

a. s(t) = ac[1 + μam cos (2πfmt)] cos (2πfct)
b. s(t) = ac cos [2πfct + βfm *sin(2πfmt)]
c. s(t) = ac cos [2πfct + μp cos (2πfmt)]
d. c(t) = ac cos (2πfct ± φ)

Answer 1

The first choice,

... a. s(t) = ac[1 + μam cos (2πfmt)] cos (2πfct)

has the carrier frequency cos(2πfct) amplitude modulated by the message signal.

The other expressions represent frequency and phase modulation of various kinds.