# ELECTRONICS AND COMMUNICATION ENGINEERING IMPORTANT MCQ-SIGNALS AND SYSTEMS

1)   Which
mathematical notation specifies the condition of periodicity for a continuous
time signal?
a. x(t)
= x(t +T0)
b. x(n) = x(n+ N)
c. x(t) = e-αt
d. None of the above
2)   Which
property of delta function indicates the equality between the area under the
product of function with shifted impulse and the value of function located at
unit impulse instant?
a.
Replication
b. Sampling
c. Scaling
d. Product
3)   Which
among the below specified conditions/cases of discrete time in terms of real
constant ‘a’, represents the double-sided decaying exponential signal?
a. a
> 1
b. 0 < a < 1
c. a < -1
d. -1 < a < 0
 ANSWER: -1 < a < 0
4)   Damped
sinusoids are _____
a.
sinusoid signals multiplied by growing exponentials
b. sinusoid signals divided by growing exponentials
c. sinusoid signals multiplied by decaying exponentials
d. sinusoid signals divided by decaying exponentials
 ANSWER: sinusoid signals multiplied by decaying exponentials
5)   An
amplitude of sinc function that passes through zero at multiple values of an
independent variable ‘x’ ______
a.
Decreases with an increase in the magnitude of an independent variable (x)
b. Increases with an increase in the magnitude of an independent variable (x)
c. Always remains constant irrespective of variation in magnitude of ‘x’
d. Cannot be defined
 ANSWER: Decreases with an increase in the magnitude of an independent variable (x)
6)   A
system is said to be shift invariant only if______
a. a
shift in the input signal also results in the corresponding shift in the
output
b. a shift in the input signal does not exhibit the corresponding shift in
the output
c. a shifting level does not vary in an input as well as output
d. a shifting at input does not affect the output
 ANSWER: a shift in the input signal also results in the corresponding shift in the output
7)   Which
condition determines the causality of the LTI system in terms of its impulse
response?
a. Only
if the value of an impulse response is zero for all negative values of time
b. Only if the value of an impulse response is unity for all negative values
of time
c. Only if the value of an impulse response is infinity for all negative
values of time
d. Only if the value of an impulse response is negative for all negative
values of time
 ANSWER: Only if the value of an impulse response is zero for all negative values of time
8)   Under
which conditions does an initially relaxed system become unstable?
a. only
if bounded input generates unbounded output
b. only if bounded input generates bounded output
c. only if unbounded input generates unbounded output
d. only if unbounded input generates bounded output
 ANSWER: only if bounded input generates unbounded output
9)   Which
among the following are the stable discrete time systems?

1. y(n) = x(4n)
2. y(n) = x(-n)
3. y(n) = ax(n) + 8
4. y(n) = cos x(n)

a. 1
& 3
b. 2 & 4
c. 1, 3 & 4
d. 1, 2, 3 & 4
 ANSWER: 1, 2, 3 & 4
10)   An
equalizer used to compensate the distortion in the communication system by
faithful recovery of an original signal is nothing but an illustration of
_________
a.
Static system
b. Dynamic system
c. Invertible system
d. None of the above
11)   Which
block of the discrete time systems requires memory in order to store the
previous input?
a.
b. Signal Multiplier
c. Unit Delay
12)   Which
type/s of discrete-time system do/does not exhibit the necessity of any
feedback?
a.
Recursive Systems
b. Non-recursive Systems
c. Both a & b
d. None of the above
13)   Which
among the following belongs to the category of non-recursive systems?
a.
Causal FIR Systems
b. Non-causal FIR Systems
c. Causal IIR Systems
d. Non-causal IIR Systems
14)   Recursive
Systems are basically characterized by the dependency of its output on
_______
a.
Present input
b. Past input
c. Previous outputs
d. All of the above
15)   What
does the term y(-1) indicate especially in an equation that represents the
behaviour of the causal system?
a.
initial condition of the system
b. negative initial condition of the system
c. negative feedback condition of the system
d. response of the system to its initial input
 ANSWER: initial condition of the system
16)   Which
type of system response to its input represents the zero value of its initial
condition?
a. Zero
state response
b. Zero input response
c. Total response
d. Natural response
17)   Which
is/are the essential condition/s to get satisfied for a recursive system to
be linear?
a. Zero
state response should be linear
b. Principle of Superposition should be applicable to zero input response
c. Total Response of the system should be addition of zero state & zero
input responses
d. All of the above
18)   Which
among the following operations is/are not involved /associated with the
computation process of linear convolution?
a.
Folding Operation
b. Shifting Operation
c. Multiplication Operation
d. Integration Operation
19)   A LTI
system is said to be initially relaxed system only if ____
a. Zero
input produces zero output
b. Zero input produces non-zero output
c. Zero input produces an output equal to unity
d. None of the above
 ANSWER: Zero input produces zero output
20)   What
are the number of samples present in an impulse response called as?
a.
string
b. array
c. length
d. element
21)   Which
are the only waves that correspond/ support the measurement of phase angle in
the line spectra?
a. Sine
waves
b. Cosine waves
c. Triangular waves
d. Square waves
 ANSWER: Cosine waves Explanation: No explanation is available for this question!
22)   Double-sided
phase & amplitude spectra _____
a.
Possess an odd & even symmetry respectively
b. Possess an even & odd symmetry respectively
c. Both possess an odd symmetry
d. Both possess an even symmetry
 ANSWER: Possess an odd & even symmetry respectively
23)   What
does the first term ‘a0’ in the below stated expression of a line
spectrum indicate?

x(t) = a0 + a1 cos w0 t + a2 cos2
w0t +……+ b1 sin w0 t + b2 sin
w0 t + …..

a. DC
component
b. Fundamental component
c. Second harmonic component
d. All of the above
24)   Which
kind of frequency spectrum/spectra is/are obtained from the line spectrum of
a continuous signal on the basis of Polar Fourier Series Method?
a.
Continuous in nature
b. Discrete in nature
c. Sampled in nature
d. All of the above
25)   Which
type/s of Fourier Series allow/s to represent the negative frequencies by
plotting the double-sided spectrum for the analysis of periodic signals?
a.
Trigonometric Fourier Series
b. Polar Fourier Series
c. Exponential Fourier Series
d. All of the above
26)   What
does the signalling rate in the digital communication system imply?
a.
Number of digital pulses transmitted per second
b. Number of digital pulses transmitted per minute
c. Number of digital pulses received per second
d. Number of digital pulses received per minute
 ANSWER: Number of digital pulses transmitted per second
27)   As
the signalling rate increases, _______
a.
Width of each pulse increases
b. Width of each pulse decreases
c. Width of each pulse remains unaffected
d. None of the above
 ANSWER: Width of each pulse decreases
28)   Which
phenomenon occurs due to an increase in the channel bandwidth during the
transmission of narrow pulses in order to avoid any intervention of signal
distortion?
a.
Compression in time domain
b. Expansion in time domain
c. Compression in frequency domain
d. Expansion in frequency domain
29)   Why
are the negative & positive phase shifts introduced for positive &
negative frequencies respectively in amplitude and phase spectra?
a. To
change the symmetry of the phase spectrum
b. To maintain the symmetry of the phase spectrum
c. Both a & b
d. None of the above
 ANSWER: To maintain the symmetry of the phase spectrum
30)   Duality
Theorem / Property of Fourier Transform states that _________
a.
Shape of signal in time domain & shape of spectrum can be interchangeable
b. Shape of signal in frequency domain & shape of spectrum can be
interchangeable
c. Shape of signal in time domain & shape of spectrum can never be
interchangeable
d. Shape of signal in time domain & shape of spectrum can never be
interchangeable
 ANSWER: Shape of signal in time domain & shape of spectrum can be interchangeable
31)   Which
property of fourier transform gives rise to an additional phase shift of -2π
ftd for the generated time delay in the communication system
without affecting an amplitude spectrum?
a. Time
Scaling
b. Linearity
c. Time Shifting
d. Duality
32)   Which
among the below assertions is precise in accordance to the effect of time
scaling?

A : Inverse relationship exists between the time and frequency domain
representation of signal
B : A signal must be necessarily limited in time as well as frequency domains

a. A is
true & B is false
b. A is false & B is true
c. Both A & B are true
d. Both A & B are false
 ANSWER: A is true & B is false
33)   Which
is/are the mandatory condition/s to get satisfied by the transfer function
for the purpose of distortionless transmission?
a.
Amplitude Response should be constant for all frequencies
b. Phase should be linear with frequency passing through zero
c. Both a & b
d. None of the above
34)   What
is/are the crucial purposes of using the Fourier Transform while analyzing
any elementary signals at different frequencies?
a.
Transformation from time domain to frequency domain
b. Plotting of amplitude & phase spectrum
c. Both a & b
d. None of the above
35)   What
is the possible range of frequency spectrum for discrete time fourier series
(DTFS)?
a. 0 to

b. -π to +π
c. Both a & b
d. None of the above
36)   Which
among the following assertions represents a necessary condition for the
existence of Fourier Transform of discrete time signal (DTFT)?
a.
Discrete Time Signal should be absolutely summable
b. Discrete Time Signal should be absolutely multipliable
c. Discrete Time Signal should be absolutely integrable
d. Discrete Time Signal should be absolutely differentiable
 ANSWER: Discrete Time Signal should be absolutely summable
37)   What
is the nature of Fourier representation of a discrete & aperiodic signal?
a.
Continuous & periodic
b. Discrete & aperiodic
c. Continuous & aperiodic
d. Discrete & periodic
38)   Which
property of periodic signal in DTFS gets completely clarified / identified by
the equation x (n – n0)?
a.
Conjugation
b. Time Shifting
c. Frequency Shifting
d. Time Reversal
39)   A
Laplace Transform exists when ______

A. The function is piece-wise continuous
B. The function is of exponential order
C. The function is piecewise discrete
D. The function is of differential order

a. A
& B
b. C & D
c. A & D
d. B & C
40)   Where
is the ROC defined or specified for the signals containing causal as well as
anti-causal terms?
a.
Greater than the largest pole
b. Less than the smallest pole
c. Between two poles
d. Cannot be defined
41)   What
should be the value of laplace transform for the time-domain signal equation
e-at cos ωt.u(t)?
a. 1 / s + a with ROC σ
> – a
b. ω / (s + a) 2 + ω2 with ROC σ > – a
c. s + a / (s + a)2 + ω2 with ROC σ > – a
d. Aω / s2 + ω2 with ROC σ > 0
 ANSWER: s + a / (s + a)2 + ω2 with ROC σ > – a
42)   According
to the time-shifting property of Laplace Transform, shifting the signal in
time domain corresponds to the ______
a. Multiplication by e-st0
in the time domain
b. Multiplication by e-st0 in the frequency domain
c. Multiplication by est0 in the time domain
d. Multiplication by est0 in the frequency domain
 ANSWER: Multiplication by e-st0 in the frequency domain
43)   Which
result is generated/ obtained by the addition of a step to a ramp function?
a. Step Function shifted
by an amount equal to ramp
b. Ramp Function shifted by an amount equal to step
c. Ramp function of zero slope
d. Step function of zero slope
 ANSWER: Ramp Function shifted by an amount equal to step
44)   Unilateral
Laplace Transform is applicable for the determination of linear constant
coefficient differential equations with ________
a. Zero initial condition
b. Non-zero initial condition
c. Zero final condition
d. Non-zero final condition
45)   What
should be location of poles corresponding to ROC for bilateral Inverse
Laplace Transform especially for determining the nature of time domain
signal?
a. On L.H.S of ROC
b. On R.H.S of ROC
c. On both sides of ROC
d. None of the above
 ANSWER: On both sides of ROC
46)   Generally,
the convolution process associated with the Laplace Transform in time domain
results into________
a. Simple multiplication
in complex frequency domain
b. Simple division in complex frequency domain
c. Simple multiplication in complex time domain
d. Simple division in complex time domain
 ANSWER: Simple multiplication in complex frequency domain
47)   An
impulse response of the system at initially rest condition is basically a
response to its input & hence also regarded as,
a. Black’s function
b. Red’s function
c. Green’s function
d. None of the above
48)   When
is the system said to be causal as well as stable in accordance to pole/zero
of ROC specified by system transfer function?
a. Only if all the poles
of system transfer function lie in left-half of S-plane
b. Only if all the poles of system transfer function lie in right-half of
S-plane
c. Only if all the poles of system transfer function lie at the centre of
S-plane
d. None of the above
 ANSWER: Only if all the poles of system transfer function lie in left-half of S-plane
49)   Correlogram
is a graph of ______
a. Amplitude of one signal
plotted against the amplitude of another signal
b. Frequency of one signal plotted against the frequency of another signal
c. Amplitude of one signal plotted against the frequency of another signal
d. Frequency of one signal plotted against the time period of another signal
 ANSWER: Amplitude of one signal plotted against the amplitude of another signal
50)   Which
theorem states that the total average power of a periodic signal is equal to
the sum of average powers of the individual fourier coefficients?
a. Parseval’s Theorem
b. Rayleigh’s Theorem
c. Both a & b
d. None of the above
51)   According
to Rayleigh’s theorem, it becomes possible to determine the energy of a
signal by________
a. Estimating the area
under the square root of its amplitude spectrum
b. Estimating the area under the square of its amplitude spectrum
c. Estimating the area under the one-fourth power of its amplitude spectrum
d. Estimating the area exactly half as that of its amplitude spectrum
 ANSWER: Estimating the area under the square of its amplitude spectrum
52)   What
would be the value of normalized energy for the causal exponential pulse
shown below?

a. 8α
b. 1 / 8α
c. -1 / 8α
d. -8α
53)   What
does the spectral density function of any signal specify?
a. Distribution of energy
or power
b. Consumption of energy or power
c. Conservation of energy or power
d. Generation of energy or power
 ANSWER: Distribution of energy or power
54)   Which
among the below mentioned transform pairs is/are formed between the
auto-correlation function and the energy spectral density, in accordance to
the property of Energy Spectral Density (ESD)?
a. Laplace Transform
b. Z-Transform
c. Fourier Transform
d. All of the above
55)   The
ESD of a real valued energy signal is always _________
a. An even (symmetric)
function of frequency
b. An odd (non-symmetric) function of frequency
c. A function that is odd and half-wave symmetric
d. None of the above
 ANSWER: An even (symmetric) function of frequency
56)   Which
among the below mentioned assertions is /are correct?

a. Greater the value of correlation function, higher is the similarity level
between two signals
b. Greater the value of correlation function, lower is the similarity level
between two signals
c. Lesser the value of correlation function, higher is the similarity level
between two signals
d. Lesser the value of correlation function, lower is the similarity level
between two signals

a. Only C
b. Only B
c. A & D
d. B & C
57)   Which
function has a provision of determining the similarity between the signal and
its delayed version?
a. Auto-correlation
Function
b. Cross-correlation Function
c. Both a & b
d. None of the above
58)   Which
property is exhibited by the auto-correlation function of a complex valued
signal?
a. Commutative property
b. Distributive property
c. Conjugate property
d. Associative property
59)   Where
does the maximum value of auto-correlation function of a power signal occur?
a. At origin
b. At extremities
c. At unity
d. At infinity
60)   What
does the set comprising all possible outcomes of an experiment known as?
a. Null event
b. Sure event
c. Elementary event
d. None of the above
61)   What
does an each outcome in the sample space regarded as?
a. Sample point
b. Element
c. Both a & b
d. None of the above
62)   Mutually
Exclusive events ________
a. Contain all sample
points
b. Contain all common sample points
c. Does not contain any common sample point
d. Does not contain any sample point
 ANSWER: Does not contain any common sample point
63)   What
would be the probability of an event ‘G’ if G denotes its complement,
according to the axioms of probability?
a. P (G) = 1 / P (G)
b. P (G) = 1 – P (G)
c. P (G) = 1 + P (G)
d. P (G) = 1 * P (G)
 ANSWER: P (G) = 1 – P (G)
64)   What
would happen if the two events are statistically independent?
a. Conditional probability
becomes less than the elementary probability
b. Conditional probability becomes more than the elementary probability
c. Conditional probability becomes equal to the elementary probability
d. Conditional as well as elementary probabilities will exhibit no change
 ANSWER: Conditional probability becomes equal to the elementary probability Explanation: No explanation is available for this question!
65)   What
would be the joint probability of statistically independent events that occur
simultaneously?
a. Zero
b. Not equal to zero
c. Infinite
d. None of the above
66)   Consider
the assertions given below

A : CDF is a monotonously increasing function
B : PDF is a derivative of CDF & is always positive

Which among them is correct according to the properties of PDF?

a. A is true & B is
false
b. A is false & B is true
c. Both A & B are true but B is a reason for A
d. Both A & B are false since B is not a reason for A
 ANSWER: Both A & B are true but B is a reason for A
67)   The
Joint Cumulative Density Function (CDF) _____
a. Is a non-negative
function
b. Is a non-decreasing function of x & y planes
c. Is always a continuous function in xy plane
d. All of the above
68)   What
is the value of an area under the conditional PDF?
a. Greater than ‘0’ but
less than ‘1’
b. Greater than ‘1’
c. Equal to ‘1’
d. Infinite
69)   When
do the conditional density functions get converted into the marginally
density functions?
a. Only if random
variables exhibit statistical dependency
b. Only if random variables exhibit statistical independency
c. Only if random variables exhibit deviation from its mean value
d. None of the above
 ANSWER: Only if random variables exhibit statistical independency
70)   Which
among the below mentioned standard PDFs is/are applicable to discrete random
variables?
a. Gaussian distribution
b. Rayleigh distribution
c. Poisson distribution
d. All of the above
 ANSWER: Poisson distribution Explanation: No explanation is available for this question!
71)   A
random variable belongs to the category of a uniform PDF only when ______
a. It occurs in a finite
range
b. It is likely to possess zero value outside the finite range
c. Both a & b
d. None of the above
72)   What
would happen if the value of term [(m-x) / (σ √2)] increases in the
expression of Guassian CDF?
a. Complementary error
function also goes on increasing
b. Complementary error function goes on decreasing
c. Complementary error function remains constant or unchanged
d. Cannot predict
 ANSWER: Complementary error function goes on decreasing
73)   Which
type of standard PDFs has/ have an ability to describe an integer valued
random variable concerning to the repeated trials carried /conducted in an
experiment?
a. Binomial
b. Uniform
c. Both a & b
d. None of the above