In amplitude modulation, sinusoidal carrier frequency used is denoted by $\omega_{\mathrm{c}}$ and the signal frequency is denoted by $\omega_{\mathrm{m}}$. The bandwidth ( $\Delta \omega_{\mathrm{m}}$ ) of the signal is such that $\Delta \omega_{\mathrm{m}} \ll \omega_{\mathrm{c}}$. Which of the following frequencies is not contained in the modulated wave ?

JEE Main · 2017 · 02 Apr 2017 · Offline · Semiconductors

In amplitude modulation, sinusoidal carrier frequency used is denoted by

ω_{c}

and the signal frequency is denoted by

ω_{m}

. The bandwidth (

Δ ω_{m}

) of the signal is such that

Δ ω_{m} ≪ ω_{c}

. Which of the following frequencies is not contained in the modulated wave ?

Answer: (C)

Amplitude modulation gives

s (t) = A_{c} [1 + m cos ω_{m} t] cos ω_{c} t

, which opens into three cosines: the carrier

ω_{c}

, the upper sideband

ω_{c} + ω_{m}

and the lower sideband

ω_{c} - ω_{m}

. The bare signal frequency

ω_{m}

itself never appears in the modulated wave.

JEE Main · 2017 · 02 Apr 2017 · Offline · Single correct option