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2017 031510

B.Tech 5th Semester Exam., 2017

Time 3 hours
Full Marks 70
Instructions:
  • The marks are indicated in the right-hand margin.
  • There are NINE questions in this paper.
  • Attempt FIVE questions in all.
  • Question No. 1 is compulsory.

Section 1

Q1

Fill in the blanks of the following (any seven) :

a)

The lengths of two discrete time sequences x1(n)x_1(n) and x2(n)x_2(n) are 5 and 7, respectively. The maximum length of a sequence x1(n)x2(n)x_1(n) * x_2(n) is ______.

[2 Marks]
b)

For a signal x(t)x(t), the Fourier transform is X(f)X(f). Then the inverse Fourier transform of X(3f+2)X(3f+2) is ______.

[2 Marks]
c)

Two discrete time systems with impulse responses h1[n]=δ[n1]h_1[n] = \delta[n-1] and h2[n]=δ[n2]h_2[n] = \delta[n-2] are connected in cascade. The overall impulse response of the cascaded system is ______.

[2 Marks]
d)

For a periodic signal v(t)=30sin100t+10cos300t+6sin(500t+π/4)v(t) = 30\sin 100t + 10\cos 300t + 6\sin(500t + \pi/4) the fundamental frequency in rad/s is ______.

[2 Marks]
e)

A discrete time system has impulse response h[n]=2nu(n4)h[n] = 2^n u(n-4). Write 'Yes' if the system is stable or 'No' if the system is not stable. ______

[2 Marks]
f)

The impulse response of a system is h(t)=tu(t)h(t) = t u(t). For an input of u(t2)u(t-2) the output is ______.

[2 Marks]
g)

The average power in the signal s(t)=10cos(20πtπ/2)+6sin(15πt)s(t) = 10\cos(20\pi t - \pi/2) + 6\sin(15\pi t) is ______.

[2 Marks]
h)

$\int_{-\infty}^{\infty} \delta(t) dt = ______.

[2 Marks]
i)

The ROC of Laplace transform does not contain any ______.

[2 Marks]
j)

Z-transform is used for ______ time signal.

[2 Marks]
[14 Marks]

Section 2

Q2

Define the following :

a)

Stability

[2 Marks]
b)

Causality

[2 Marks]
c)

Random signal

[2 Marks]
d)

Time-variant system

[2 Marks]
e)

Linear system

[2 Marks]
f)

Delta function

[2 Marks]
g)

Memoryless system

[2 Marks]
[14 Marks]
Q3a

Consider the system y[n]=2×x[n2]y[n] = 2 \times x[n^2]. Determine whether it is memoryless, causal, linear and time-invariant.

[7 Marks]
Q3b

Determine the average power of the given signal x(t)x(t). [Diagram: Periodic rectangular pulse signal with period T=4T=4 and amplitude A=2A=2 from t=1t=-1 to t=1t=1 in each cycle]

[7 Marks]
Q4

A continuous time signal x(t)x(t) is shown in the figure. Sketch the following signals :

a)

x(3t)x(3-t)

[2 Marks]
b)

x(4t+1)x(4t+1)

[2 Marks]
c)

[x(t)+x(t)]u(t)[x(t) + x(-t)] u(t)

[2 Marks]
d)

[δ(t+1)+δ(t1)]x(t)[\delta(t+1) + \delta(t-1)] x(t)

[2 Marks]
e)

x(t)x(t5)x(t)x(t-5)

[2 Marks]
f)

x(t)δ(t3)x(t)\delta(t-3)

[2 Marks]
g)

x(2t5)x(2t-5)

[2 Marks]
[14 Marks]
Q5a

(i) Find the inverse Fourier transform of X(ω)=12ω2+j3ωX(\omega) = \frac{1}{2-\omega^2 + j3\omega} (ii) Consider a causal LTI system with frequency response H(jω)=1jω+3H(j\omega) = \frac{1}{j\omega + 3}. For a particular input x(t)x(t) this system is observed to produce the output y(t)=e3tu(t)e4tu(t)y(t) = e^{-3t} u(t) - e^{-4t} u(t). Determine x(t)x(t).

[7 Marks]
Q5b

Find the inverse z-transform of X(z)=zz(z1)(z2)2X(z) = \frac{z}{z(z-1)(z-2)^2} for z>2|z| > 2.

[7 Marks]
Q6

Find the Laplace transform and the associated ROC for each of the following signals :

a)

x(t)=δ(tt0)x(t) = \delta(t-t_0)

[2 Marks]
b)

x(t)=u(tt0)x(t) = u(t-t_0)

[2 Marks]
c)

x(t)=e2t[u(t)u(t5)]x(t) = e^{-2t} [u(t) - u(t-5)]

[2 Marks]
d)

x(t)=k=0δ(tkT)x(t) = \sum_{k=0}^\infty \delta(t - kT)

[2 Marks]
e)

x(t)=δ(at+b)x(t) = \delta(at+b), a,ba, b real constants

[2 Marks]
f)

x(t)=1/tx(t) = 1/t

[2 Marks]
g)

x(t)=sintx(t) = \sin t

[2 Marks]
[14 Marks]
Q7

Determine whether or not each of the following signals is periodic. If a signal is periodic, determine its fundamental time period :

a)

x[n]=sin(π2n)x[n] = \sin(\pi^2 n)

[2 Marks]
b)

x(t)=cost+sin3tx(t) = \cos t + \sin 3t

[2 Marks]
c)

x[n]=cosn4x[n] = \cos \frac{n}{4}

[2 Marks]
d)

x[n]=cos2π8nx[n] = \cos^2 \frac{\pi}{8} n

[2 Marks]
e)

x(t)=sint+sin2tx(t) = \sin t + \sin 2t

[2 Marks]
f)

x[n]=sin(5πn)x[n] = \sin(5\pi n)

[2 Marks]
g)

x(t)=ej3π/4x(t) = e^{-j3\pi/4}

[2 Marks]
[14 Marks]
Q8a

Calculate the Fourier series coefficient aka_k for the continuous time periodic signal x(t)x(t) (a sawtooth waveform) shown in the figure.

[7 Marks]
Q8b

The system is described by y(t)+2y(t)=x(t)+x(t)y'(t) + 2y(t) = x(t) + x'(t). Find the impulse response of the LTI system if the system is causal.

[7 Marks]
Q9

Write short notes on any two of the following :

a)

Even and odd symmetric signal

b)

Initial and final value theorem of Laplace transform

c)

Random and deterministic signals

d)

Force voltage analogy

[14 Marks]

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