GATE 2018 EC – Question 25
Consider the following amplitude modulated signal:
$$s(t)=\cos(2000\pi t)+4\cos(2400\pi t)+\cos(2800\pi t).$$
The ratio (accurate to three decimal places) of the power of the message signal to the power of the carrier signal is ________.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 0.12 to 0.14
Explanation
The carrier is $4\cos(2400\pi t)$ with power $\frac{16}{2}=8$, and the two side-frequency terms $\cos(2000\pi t)$ and $\cos(2800\pi t)$ carry $\frac12+\frac12=1$ in total. The ratio is $\frac18=0.125$.