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DRDO MCQs

Practice DRDO-oriented Electronics & Telecommunication Engineering MCQs with answers and explanations for technical exam preparation. Questions are arranged in pages of up to 100.

Question 502
Signals & SystemsElementary Signals

The integral of delta(t) from minus infinity to t is?

  • Au(t)
  • Bdelta(t)
  • Ct
  • D0 for every t
Report an error
Correct Answer: A. u(t)
Explanation: Integrating the unit impulse from -infinity up to t produces the unit-step function.
Reference: Standard signals and systems: elementary signals
Question 505
Signals & SystemsPeriodic Signals

The fundamental period of x(t)=cos(20pi t) is?

  • A0.01 s
  • B0.05 s
  • C0.1 s
  • D0.2 s
Report an error
Correct Answer: C. 0.1 s
Explanation: Here omega=20pi rad/s, so f=10 Hz and T=1/f=0.1 s.
Reference: Standard signals and systems: periodic signals
Question 506
Signals & SystemsPeriodic Signals

A continuous-time sinusoidal signal is periodic when its angular frequency is?

  • ANonzero; every single continuous-time sinusoid with fixed nonzero frequency is periodic
  • BAn integer only
  • CLess than 1 rad/s only
  • DExactly pi rad/s only
Report an error
Correct Answer: A. Nonzero; every single continuous-time sinusoid with fixed nonzero frequency is periodic
Explanation: A single continuous-time sinusoid cos(omega0 t+phi) with fixed nonzero omega0 has period 2pi/|omega0|.
Reference: Standard signals and systems: periodic signals
Question 507
Signals & SystemsPeriodic Signals

A discrete-time sinusoid x[n]=cos(omega0 n) is periodic only if?

  • Aomega0/(2pi) is rational
  • Bomega0/(2pi) is irrational
  • Comega0=1 always
  • DIts amplitude is less than one
Report an error
Correct Answer: A. omega0/(2pi) is rational
Explanation: A discrete-time sinusoid is periodic if there exist integers N>0 and k such that omega0 N=2pi k, equivalently omega0/(2pi) is rational.
Reference: Standard signals and systems: periodic signals
Question 509
Signals & SystemsSignal Classification

A signal x(t) is even if it satisfies?

  • Ax(-t)=x(t)
  • Bx(-t)=-x(t)
  • Cx(t+T)=0
  • Dx(t)=delta(t) only
Report an error
Correct Answer: A. x(-t)=x(t)
Explanation: An even signal is symmetric about the vertical axis and obeys x(-t)=x(t).
Reference: Standard signals and systems: signal classification
Question 510
Signals & SystemsSignal Classification

A signal x(t) is odd if it satisfies?

  • Ax(-t)=x(t)
  • Bx(-t)=-x(t)
  • Cx(t)=1 for all t
  • Dx(t)=x(t-1)
Report an error
Correct Answer: B. x(-t)=-x(t)
Explanation: An odd signal has origin symmetry and obeys x(-t)=-x(t).
Reference: Standard signals and systems: signal classification
Question 512
Signals & SystemsSignal Classification

The odd part of a signal x(t) is?

  • A[x(t)+x(-t)]/2
  • B[x(t)-x(-t)]/2
  • Cx(-t) only
  • Dx(t)/2 only
Report an error
Correct Answer: B. [x(t)-x(-t)]/2
Explanation: The odd component is xo(t)=1/2[x(t)-x(-t)].
Reference: Standard signals and systems: signal classification
Question 513
Signals & SystemsSignal Fundamentals

A signal that is defined for every value of continuous time t is called a?

  • AContinuous-time signal
  • BDiscrete-time signal
  • CBinary code only
  • DQuantized sequence only
Report an error
Correct Answer: A. Continuous-time signal
Explanation: A continuous-time signal x(t) is defined over a continuous range of the independent variable t.
Reference: Standard signals and systems: signal fundamentals
Question 515
Signals & SystemsSignal Fundamentals

A discrete-time signal is commonly represented as?

  • Ax(t) only
  • Bx[n]
  • CX(s) only
  • DV/Hz
Report an error
Correct Answer: B. x[n]
Explanation: A discrete-time signal is represented as a sequence x[n], where n is an integer index.
Reference: Standard signals and systems: signal fundamentals
Question 516
Signals & SystemsSignal Transformations

The signal x(2t) is, relative to x(t),?

  • ATime-expanded by 2
  • BTime-compressed by 2
  • CDelayed by 2 s
  • DAmplitude-scaled by 2 only
Report an error
Correct Answer: B. Time-compressed by 2
Explanation: Replacing t by 2t compresses the time axis by a factor of 2.
Reference: Standard signals and systems: signal transformations
Question 518
Signals & SystemsElementary Signals

The continuous-time unit impulse delta(t) has unit?

  • AAmplitude at all times
  • BArea
  • CPeriod
  • DAverage power
Report an error
Correct Answer: B. Area
Explanation: The Dirac impulse is characterized by zero value away from t=0 and unit area over an interval containing the origin.
Reference: Standard signals and systems: elementary signals
Question 519
Signals & SystemsEnergy & Power Signals

A finite-energy signal has energy E that is?

  • AFinite and nonzero, with zero average power
  • BInfinite with finite average power
  • CAlways equal to one
  • DZero for every nonzero signal
Report an error
Correct Answer: A. Finite and nonzero, with zero average power
Explanation: For the usual energy/power classification, an energy signal has 0<E<infinity and average power equal to zero.
Reference: Standard signals and systems: energy & power signals
Question 520
Signals & SystemsEnergy & Power Signals

A nonzero periodic signal with finite average power is generally classified as a?

  • APower signal
  • BEnergy signal with finite nonzero energy
  • CNeither under all conditions
  • DImpulse only
Report an error
Correct Answer: A. Power signal
Explanation: A typical nonzero periodic signal has infinite total energy but finite nonzero average power, so it is a power signal.
Reference: Standard signals and systems: energy & power signals
Question 521
Signals & SystemsEnergy & Power Signals

The total energy of x(t)=e^(-t)u(t) is?

  • A1/4
  • B1/2
  • C1
  • D2
Report an error
Correct Answer: B. 1/2
Explanation: E=∫0^infinity |e^-t|^2 dt=∫0^infinity e^-2t dt=1/2.
Reference: Standard signals and systems: energy & power signals
Question 522
Signals & SystemsSystem Properties

A system is linear if it satisfies the principle of?

  • ASuperposition
  • BAliasing
  • CQuantization
  • DModulation only
Report an error
Correct Answer: A. Superposition
Explanation: Linearity requires additivity and homogeneity, together expressed by the superposition principle.
Reference: Standard signals and systems: system properties
Question 523
Signals & SystemsSystem Properties

A system is time-invariant if?

  • AA time shift of the input produces the same time shift of the output
  • BIts output never changes with time
  • CIt has no memory under all conditions
  • DIts input must be periodic
Report an error
Correct Answer: A. A time shift of the input produces the same time shift of the output
Explanation: For a time-invariant system, delaying the input by t0 delays the corresponding output by the same amount without otherwise changing it.
Reference: Standard signals and systems: system properties
Question 524
Signals & SystemsSignal Transformations

The signal x(t/2) is, relative to x(t),?

  • ATime-compressed by 2
  • BTime-expanded by 2
  • CTime-reversed
  • DDifferentiated
Report an error
Correct Answer: B. Time-expanded by 2
Explanation: Replacing t by t/2 expands the time axis by a factor of 2.
Reference: Standard signals and systems: signal transformations
Question 525
Signals & SystemsSignal Transformations

The transformation x(-t) represents?

  • AAmplitude inversion
  • BTime reversal
  • CTime delay
  • DIntegration
Report an error
Correct Answer: B. Time reversal
Explanation: Changing t to -t reflects the signal about t=0, which is time reversal.
Reference: Standard signals and systems: signal transformations
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Question 528
Signals & SystemsDiscrete-Time LTI

Discrete-time convolution uses?

  • AA summation over an integer index
  • BOnly a continuous integral
  • CMatrix inversion always
  • DDifferentiation only
Report an error
Correct Answer: A. A summation over an integer index
Explanation: y[n]=sum x[k]h[n-k].
Reference: Standard signals and systems: discrete-time lti
Question 529
Signals & SystemsDiscrete-Time LTI

Discrete-time LTI BIBO stability requires?

  • ASum of |h[n]| over all n is finite
  • Bh[n]=n
  • Ch[n] periodic
  • Dh[0]=0
Report an error
Correct Answer: A. Sum of |h[n]| over all n is finite
Explanation: The impulse response must be absolutely summable.
Reference: Standard signals and systems: discrete-time lti
Question 531
Signals & SystemsSystem Properties

A system is causal if its output at any time depends only on?

  • AFuture input values
  • BPresent and past input values
  • CFuture output values only
  • DThe input at t=infinity
Report an error
Correct Answer: B. Present and past input values
Explanation: A causal system cannot depend on future input values; its output may depend on present and past inputs.
Reference: Standard signals and systems: system properties
Question 532
Signals & SystemsFourier Series

Fourier series is primarily used to represent?

  • APeriodic signals
  • BOnly nonperiodic impulses
  • COnly random noise
  • DDC circuits only
Report an error
Correct Answer: A. Periodic signals
Explanation: Fourier series represents periodic signals using harmonically related components.
Reference: Standard signals and systems: fourier series
Question 533
Signals & SystemsSystem Properties

Which system is memoryless?

  • Ay(t)=x(t-2)
  • By(t)=x(t)+x(t-1)
  • Cy(t)=3x(t)
  • Dy(t)=integral from -infinity to t of x(tau)d tau
Report an error
Correct Answer: C. y(t)=3x(t)
Explanation: A memoryless system output at time t depends only on the input at that same time.
Reference: Standard signals and systems: system properties
Question 535
Signals & SystemsSystem Properties

The continuous-time system y(t)=x(t-1) is?

  • ANoncausal
  • BCausal with memory
  • CMemoryless and causal
  • DUnstable for every input
Report an error
Correct Answer: B. Causal with memory
Explanation: It depends on a past input value, so it is causal and has memory.
Reference: Standard signals and systems: system properties
Question 537
Signals & SystemsSystem Properties

A system is BIBO stable if every bounded input produces?

  • AA bounded output
  • BAn unbounded output
  • CZero output only
  • DA periodic output only
Report an error
Correct Answer: A. A bounded output
Explanation: BIBO means bounded-input bounded-output stability.
Reference: Standard signals and systems: system properties
Question 538
Signals & SystemsFourier Series

Fourier-series harmonic frequencies are?

  • AInteger multiples of the fundamental
  • BAlways irrational multiples
  • CAlways lower than fundamental
  • DIndependent of fundamental
Report an error
Correct Answer: A. Integer multiples of the fundamental
Explanation: The kth harmonic is k times the fundamental frequency.
Reference: Standard signals and systems: fourier series
Question 539
Signals & SystemsLTI Systems

For a continuous-time LTI system, BIBO stability requires?

  • AIntegral of |h(t)| over all time is finite
  • Bh(t) must be periodic
  • Ch(t) must be odd
  • DIntegral of h(t) must always be zero
Report an error
Correct Answer: A. Integral of |h(t)| over all time is finite
Explanation: A continuous-time LTI system is BIBO stable if its impulse response is absolutely integrable.
Reference: Standard signals and systems: lti systems
Question 542
Signals & SystemsConvolution

Continuous-time convolution is?

  • AIntegral x(tau)h(t-tau)d tau over all tau
  • BIntegral x(t)h(t)dt only
  • Cx(t)+h(t)
  • Dx(t)/h(t)
Report an error
Correct Answer: A. Integral x(tau)h(t-tau)d tau over all tau
Explanation: Continuous-time convolution integrates x(tau)h(t-tau) over all tau.
Reference: Standard signals and systems: convolution
Question 543
Signals & SystemsConvolution

Which is a property of convolution?

  • Ax*h=h*x
  • Bx*h=x-h
  • CIt is never associative
  • DIt requires x=h
Report an error
Correct Answer: A. x*h=h*x
Explanation: Convolution is commutative.
Reference: Standard signals and systems: convolution
Question 544
Signals & SystemsConvolution

Convolution with the unit impulse gives?

  • A0
  • Bx(t)
  • C1
  • Ddx(t)/dt
Report an error
Correct Answer: B. x(t)
Explanation: The unit impulse is the identity for convolution.
Reference: Standard signals and systems: convolution
Question 545
Signals & SystemsConvolution

x(t)*delta(t-t0) equals?

  • Ax(t+t0)
  • Bx(t-t0)
  • Cdelta(t)
  • Dx(t0) only
Report an error
Correct Answer: B. x(t-t0)
Explanation: A shifted impulse shifts the convolved signal by the same amount.
Reference: Standard signals and systems: convolution
Question 548
Signals & SystemsFourier Series

Parseval’s relation connects average power with?

  • ASquared magnitudes of Fourier-series coefficients
  • BOnly maximum amplitude
  • COnly fundamental period
  • DDerivative at t=0
Report an error
Correct Answer: A. Squared magnitudes of Fourier-series coefficients
Explanation: Parseval expresses signal power through the squared Fourier coefficient magnitudes.
Reference: Standard signals and systems: fourier series
Question 549
Signals & SystemsFourier Series

A standard symmetric 50% duty-cycle square wave contains?

  • AOnly odd harmonics
  • BOnly even harmonics
  • CNo harmonics
  • DOnly second harmonic
Report an error
Correct Answer: A. Only odd harmonics
Explanation: Its even harmonics vanish due to symmetry.
Reference: Standard signals and systems: fourier series
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Question 551
Signals & SystemsFourier Transform

The Fourier transform of delta(t-t0) is?

  • Ae^(-jωt0)
  • Be^(jωt0)
  • Cdelta(ω-t0)
  • D1/(jω)
Report an error
Correct Answer: A. e^(-jωt0)
Explanation: The shifted impulse property gives delta(t-t0) ↔ e^(-jωt0).
Reference: Standard signals and systems: fourier transform
Question 552
Signals & SystemsFourier Transform

If x(t) ↔ X(jω), then x(t-t0) has Fourier transform?

  • AX(jω)e^(-jωt0)
  • BX(jω)e^(jωt0)
  • CX(j(ω-t0))
  • Dt0X(jω)
Report an error
Correct Answer: A. X(jω)e^(-jωt0)
Explanation: A time delay t0 introduces the linear phase factor e^(-jωt0).
Reference: Standard signals and systems: fourier transform
Question 554
Signals & SystemsFourier Transform

Differentiation in time corresponds in the Fourier domain to?

  • ADivision by jω
  • BMultiplication by jω
  • CTime reversal only
  • DMultiplication by t
Report an error
Correct Answer: B. Multiplication by jω
Explanation: If x(t) ↔ X(jω), then dx(t)/dt ↔ jωX(jω), under standard conditions.
Reference: Standard signals and systems: fourier transform
Question 556
Signals & SystemsFourier Transform

Parseval’s relation for the Fourier transform connects signal energy with?

  • AIntegral of |X(jω)|² in frequency
  • BOnly X(0)
  • COnly signal period
  • DMaximum signal amplitude only
Report an error
Correct Answer: A. Integral of |X(jω)|² in frequency
Explanation: Parseval's relation expresses time-domain energy equivalently in terms of the integral of spectral magnitude squared, with the appropriate 1/(2π) factor.
Reference: Standard signals and systems: fourier transform
Question 557
Signals & SystemsLaplace Transform

The bilateral Laplace transform of x(t) is?

  • A∫x(t)e^(-st)dt over all time
  • B∫x(t)e^(st)dt from 0 to 1
  • Cx(t)/s
  • Ddx(t)/dt only
Report an error
Correct Answer: A. ∫x(t)e^(-st)dt over all time
Explanation: The bilateral Laplace transform is X(s)=∫ from -∞ to ∞ x(t)e^(-st)dt.
Reference: Standard signals and systems: laplace transform
Question 562
Signals & SystemsLaplace Transform

For a causal rational LTI system, the ROC of H(s) lies?

  • ATo the right of the rightmost pole
  • BTo the left of the leftmost pole
  • COnly between every pair of poles
  • DExactly on the jω-axis
Report an error
Correct Answer: A. To the right of the rightmost pole
Explanation: A causal rational impulse response is right-sided, so its ROC is to the right of the rightmost pole.
Reference: Standard signals and systems: laplace transform
Question 563
Signals & SystemsLaplace Transform

A causal rational continuous-time LTI system is BIBO stable if all its poles lie?

  • AStrictly in the left half of the s-plane
  • BStrictly in the right half-plane
  • COnly on the jω-axis
  • DAt the origin only
Report an error
Correct Answer: A. Strictly in the left half of the s-plane
Explanation: For a causal rational system, BIBO stability requires the jω-axis to lie in the ROC, which means all poles must be strictly in the left half-plane.
Reference: Standard signals and systems: laplace transform
Question 564
Signals & SystemsZ-Transform

The bilateral Z-transform of x[n] is defined as?

  • AΣ x[n]z^(-n) over all integer n
  • BΣ x[n]z^n for n=0 only
  • Cx[n]/z
  • Ddx[n]/dn
Report an error
Correct Answer: A. Σ x[n]z^(-n) over all integer n
Explanation: The bilateral Z-transform is X(z)=Σ from n=-∞ to ∞ x[n]z^(-n).
Reference: Standard signals and systems: z-transform
Question 565
Signals & SystemsFourier Transform

The continuous-time Fourier transform X(jω) of x(t) is defined as?

  • A∫x(t)e^(-jωt)dt over all time
  • B∫x(t)e^(jωt)dt from 0 to 1
  • Cx(t)e^(-jωt)
  • Ddx(t)/dt
Report an error
Correct Answer: A. ∫x(t)e^(-jωt)dt over all time
Explanation: The CTFT analysis equation is X(jω)=∫ from -∞ to ∞ x(t)e^(-jωt)dt.
Reference: Standard signals and systems: fourier transform
Question 567
Signals & SystemsZ-Transform

For a causal rational discrete-time LTI system, the ROC of H(z) is generally?

  • AOutside the outermost pole
  • BInside the innermost pole
  • COnly on the unit circle
  • DBetween zero and every pole
Report an error
Correct Answer: A. Outside the outermost pole
Explanation: A causal rational impulse response is right-sided, so its ROC extends outward from the outermost pole to infinity.
Reference: Standard signals and systems: z-transform
Question 568
Signals & SystemsZ-Transform

A causal rational discrete-time LTI system is BIBO stable when all its poles are?

  • AStrictly inside the unit circle
  • BStrictly outside the unit circle
  • CExactly on the unit circle
  • DAt z=1 only
Report an error
Correct Answer: A. Strictly inside the unit circle
Explanation: For a causal rational system to be stable, the unit circle must lie in the ROC; therefore all poles must lie strictly inside it.
Reference: Standard signals and systems: z-transform
Question 572
Signals & SystemsSampling

Ideal reconstruction of a properly sampled band-limited signal is theoretically performed using a?

  • AIdeal low-pass reconstruction filter
  • BHigh-pass differentiator only
  • CRectifier
  • DLimiter only
Report an error
Correct Answer: A. Ideal low-pass reconstruction filter
Explanation: After ideal impulse-train sampling above the Nyquist rate, an ideal low-pass filter can select the original baseband spectral replica.
Reference: Standard signals and systems: sampling
Question 574
Signals & SystemsZ-Transform

The Z-transform of a^n u[n] is?

  • A1/(1-az^-1), ROC |z|>|a|
  • B1/(1+az^-1), ROC |z|<|a|
  • Cz-a, all z
  • Da/(z+1), all z
Report an error
Correct Answer: A. 1/(1-az^-1), ROC |z|>|a|
Explanation: For the right-sided sequence a^n u[n], the geometric series gives X(z)=1/(1-az^-1) with ROC |z|>|a|.
Reference: Standard signals and systems: z-transform
Question 575
Signals & SystemsZ-Transform

For a right-sided sequence a^n u[n], the ROC is?

  • A|z|>|a|
  • B|z|<|a|
  • C|z|=|a| only
  • Dz=a only
Report an error
Correct Answer: A. |z|>|a|
Explanation: Convergence of the geometric series requires |az^-1||a|.
Reference: Standard signals and systems: z-transform
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Question 578
Signals & SystemsFrequency Response

If an LTI system has H(jω)=0 at ω=100 rad/s, a sinusoidal component exactly at 100 rad/s is ideally?

  • APassed unchanged
  • BCompletely rejected
  • CFrequency doubled
  • DConverted to DC
Report an error
Correct Answer: B. Completely rejected
Explanation: A zero frequency-response magnitude at that frequency means the corresponding sinusoidal steady-state component is suppressed.
Reference: Standard signals and systems: frequency response
Question 581
Signals & SystemsFilters

A band-pass filter is designed primarily to pass?

  • AA selected range of frequencies
  • BOnly DC
  • CAll frequencies equally
  • DOnly frequencies below zero
Report an error
Correct Answer: A. A selected range of frequencies
Explanation: A band-pass filter passes frequencies within a specified band while attenuating frequencies outside it.
Reference: Standard signals and systems: filters
Question 588
Signals & SystemsSampling

If a band-limited signal is sampled above its Nyquist rate, ideal reconstruction uses sinc interpolation because the ideal reconstruction filter has a?

  • ARectangular frequency response
  • BTriangular time response only
  • CConstant impulse at every sample
  • DHigh-pass response
Report an error
Correct Answer: A. Rectangular frequency response
Explanation: An ideal brick-wall low-pass filter has a rectangular frequency response and a sinc-shaped impulse response, leading to sinc interpolation.
Reference: Standard signals and systems: sampling
Question 591
Signals & SystemsStability

A causal rational continuous-time system has poles at -2 and +1. It is BIBO stable?

  • AYes, because one pole is negative
  • BNo, because a pole lies in the right half-plane
  • CYes, because it is causal
  • DAlways stable if rational
Report an error
Correct Answer: B. No, because a pole lies in the right half-plane
Explanation: For a causal rational CT system, all poles must lie strictly in the left half-plane for BIBO stability.
Reference: Standard signals and systems: stability
Question 592
Signals & SystemsDTFT

The DTFT of delta[n] is?

  • A0
  • B1
  • Ce^(-jω)
  • D2πdelta(ω) only
Report an error
Correct Answer: B. 1
Explanation: By definition, the only nonzero sequence sample is at n=0, so X(e^(jω))=1.
Reference: Standard signals and systems: dtft
Question 595
Signals & SystemsStability

A causal discrete-time system has a pole at z=1.2. Its BIBO stability is?

  • AStable
  • BUnstable
  • CMarginally stable in every sense
  • DIndependent of pole location
Report an error
Correct Answer: B. Unstable
Explanation: For a causal rational DT system, a pole outside the unit circle prevents the unit circle from being in the ROC, so it is not BIBO stable.
Reference: Standard signals and systems: stability
Question 596
Signals & SystemsZ-Transform

If h[n]=(0.5)^n u[n], H(z) is?

  • A1/(1-0.5z^-1)
  • B1/(1+0.5z^-1)
  • Cz^-1/0.5
  • D1-0.5z^-1
Report an error
Correct Answer: A. 1/(1-0.5z^-1)
Explanation: The Z-transform of a^n u[n] is 1/(1-az^-1), with |z|>|a|.
Reference: Standard signals and systems: z-transform
Question 599
Signals & SystemsLTI Frequency Response

For a stable LTI system, a bounded sinusoidal input produces a steady-state sinusoidal output at?

  • AThe same frequency
  • BTwice the input frequency
  • CZero frequency only
  • DA random frequency
Report an error
Correct Answer: A. The same frequency
Explanation: An LTI system does not create new frequencies from a single sinusoidal input in steady state; it changes only amplitude and phase at that frequency.
Reference: Standard signals and systems: lti frequency response
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