I am given a question in which I have to draw the spectrum of the signal $m(t)$ and then draw the spectrum of this modulated signal. The signal is

$$m(t)=\cos(1000\pi t)$$

Now in solution manual what they have done is that they have staright away drawn two pulses. One pulse in positive x-axis at $1000$ and at at negative x-axis at$-1000$. I was looking at the online solution of this question and in that solution following steps were taken:

We know that the Fourier Transform pair is: \begin{align} \cos(2\pi f_ot) &\leftrightarrow \frac{1}{2}[\delta(f-f_o)+\delta(f+f_o)]\\ m(t)&= \cos(1000\pi t)\\ &= \cos(2\pi 500t) \end{align}

Apply Fourier Transform and we get: $$M_1(f)= \frac{1}{2}[\delta(f-500)+\delta(f+500)]$$ Hence two pulses of are drawn at 500 and -500. Which of the above mentioned method is correct. The solution manual is of Modern and Analog Digital Communication 4th edition.

  • 2
    $\begingroup$ you're right, the solution manual isn't. $\endgroup$ – Marcus Müller Apr 19 '19 at 15:15

You're right, the solution manual isn't.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.