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Signals and Systems Question Paper - Dec 18 - Electronics And Telecomm (Semester 3) - Pune University (PU)
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Signals and Systems - Dec 18

Electronics And Telecomm (Semester 3)

Total marks: 80
Total time: 3 Hours
INSTRUCTIONS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Draw neat diagrams wherever necessary.

1.a. Perform the following operations on the given signal $x(t)$ which is defined as : $x(t) = u(t+4)$

  1. Sketch $z(t) = x(-t-1)$
  2. Sketch $y(t) = x(t) +z(t)$.

(4 marks) 00

1.b. Write the expression for energy and power of the signal. Also determine whether the following signals is energy or Power, and find energy or time averaged power of the signal : $x(t) = 5cos(10\pi t)+sin(20\pi t); -\infty \le t \le \infty$.
(4 marks) 00

1.c. Determine whether the following system is Ststic/Dynamic, Casual/Non-casual and Stable/Unstable and justify : $h(t) = e^{-10t}u(t)$.
(5 marks) 00

OR

2.a. Compute the convolution integral by graphical method and sketch the output for the following signals :

  1. $x(t) = u(t)$
  2. $h(t) = e^{-2t}u(t)$.

(5 marks) 00

2.b. Check whether the following signal is even or odd and determine the even and odd part of the signal : $x(t) = u(t)$.

(4 marks) 00

2.c. Compute the convolution integral for the following signal :

$x(t)=u(t), h(t) =\delta (t+1) + \delta (t) + \delta (t-1)$.

(4 marks) 00

3.a. Find the trigonometric Fourier series for the periodic signal $x(t)$ shown in the following figure : enter image description here
(6 marks) 00

3.b. State any six properties of Fourier transform.
(6 marks) 00

OR

4.a. Find the Fourier transform of the following signals :

  1. $x(t)=sng(t)$
  2. $x(t)=cos(\omega_{0} t) u(t)$.

(6 marks) 00

4.b. Write expression for trigonometric Fourier series and exponential Fourier series.
(4 marks) 00

4.c. Define amplitude and phase spectra of the signal.
(2 marks) 00

5.a. Find the inverse laplace transform of $X(s)=\frac{2}{(s+4)(s-1)}$

If the region of convergence is :

  1. $-4 \le Re(s) \lt1$
  2. $Re(s) \gt 1$
  3. $Re(s) \lt -4$.

(6 marks) 00

5.b. A signal $x(t)$ has laplace transform : $X(s) = \frac{s+2}{s^{2}+4s+5}$

Find the laplace transform of the following signals :

  1. $y_{1}(t) = tx(t)$.
  2. $y_{2}(t) = e^{-t}x(t)$.

(6 marks) 00

OR

6.a. Find the laplace transform of the following signal and sketch ROC :

$x(t) = e^{-3t}u(t) + e^{-5t} u(t)$.

(6 marks) 00

6.b. Find the initial and final value of the following signal :$X(s) = \frac {2s+3}{s^{2}+5s-7}$.
(4 marks) 00

6.c. State the relationship between Fourier transform and laplace transform.
(2 marks) 00

7.a. Find the following for the given signal $x(t)$ :

  1. Auto-correlation
  2. Energy from auto-correlation

$x(t)=e^{-10t}u(t)$.

(6 marks) 00

7.b. Define probability and state the properties of PDF. Also state the relationship between CDF and PDF.
(7 marks) 00

OR

8.a. Suppose a certain random variable has CDF :

$F_{x}(x) = 0 , x \le 0$

$F_{x}(x) = k x^{2} , 0 \lt x \le 10$

$F_{x}(x) = 100k , x \gt 10$

Calculate $K$. Find the values of $P(X \le 5)$ and $P(5 < X \le 7)$.

(7 marks) 00

8.b. A coin is tossed three times. Write the sample space which gives all possible outcomes. A random variable X, which represents the number of heads obtained on any tripple toss. Also find the probabilities of X and plot the C.D.F.
(6 marks) 00

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