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BECIL MCQs

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

Question 402
Communication SystemsSampling

If a 4 kHz sinusoid is sampled at 6 kHz, the sampling theorem is?

  • ASatisfied exactly
  • BSatisfied with large margin
  • CNot satisfied
  • DIndependent of sampling rate
Report an error
Correct Answer: C. Not satisfied
Explanation: For fm=4 kHz, the minimum Nyquist rate is 8 kHz. Sampling at 6 kHz can cause aliasing.
Reference: Standard communication systems: sampling
Question 403
Communication SystemsSampling

Aliasing occurs when?

  • ADifferent frequency components become indistinguishable after inadequate sampling
  • BThe carrier amplitude becomes zero
  • CA signal is amplified linearly
  • DQuantization levels become infinite
Report an error
Correct Answer: A. Different frequency components become indistinguishable after inadequate sampling
Explanation: Sampling below the required rate can cause spectral replicas to overlap, making different analog frequencies appear identical in the sampled data.
Reference: Standard communication systems: sampling
Question 404
Communication SystemsSampling

An anti-aliasing filter is normally placed?

  • ABefore the sampler
  • BAfter the final loudspeaker only
  • CInside the DC supply
  • DAcross the antenna mechanically
Report an error
Correct Answer: A. Before the sampler
Explanation: A low-pass anti-aliasing filter limits the input bandwidth before sampling so unwanted high-frequency components do not alias into the desired band.
Reference: Standard communication systems: sampling
Question 409
Communication SystemsPCM

PCM stands for?

  • APulse Code Modulation
  • BPhase Carrier Multiplication
  • CPulse Current Mixing
  • DPeriodic Code Measurement
Report an error
Correct Answer: A. Pulse Code Modulation
Explanation: PCM means Pulse Code Modulation, in which sampled amplitudes are quantized and represented by binary code words.
Reference: Standard communication systems: pcm
Question 411
Communication SystemsPCM

The main operations in a basic PCM transmitter are?

  • ASampling, quantization and encoding
  • BRectification, regulation and inversion
  • CMixing, filtering and mechanical switching only
  • DDemodulation, decoding and amplification only
Report an error
Correct Answer: A. Sampling, quantization and encoding
Explanation: A basic PCM transmitter samples the analog signal, quantizes each sample and encodes the quantized value into a binary word.
Reference: Standard communication systems: pcm
Question 417
Communication SystemsPCM

Companding in PCM telephony is mainly used to?

  • AImprove effective quantization performance for low-level signals
  • BEliminate sampling completely
  • CIncrease antenna height
  • DSuppress every binary zero
Report an error
Correct Answer: A. Improve effective quantization performance for low-level signals
Explanation: Nonuniform quantization implemented through companding gives finer effective resolution to weaker signals and improves their quantization SNR.
Reference: Standard communication systems: pcm
Question 422
Communication SystemsNoise & SNR

Signal-to-noise ratio is defined as the ratio of?

  • ASignal power to noise power
  • BNoise power to signal power
  • CSignal voltage to bandwidth only
  • DCarrier frequency to message frequency
Report an error
Correct Answer: A. Signal power to noise power
Explanation: SNR compares desired signal power with noise power, S/N.
Reference: Standard communication systems: noise & snr
Question 425
Communication SystemsDigital Modulation

In frequency-shift keying (FSK), binary symbols are commonly represented by?

  • ADifferent carrier frequencies
  • BDifferent antenna resistances
  • COnly different DC supply voltages
  • DDifferent sampling periods with no carrier
Report an error
Correct Answer: A. Different carrier frequencies
Explanation: FSK maps different digital symbols to different carrier frequencies.
Reference: Standard communication systems: digital modulation
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Question 427
Communication SystemsDigital Modulation

How many distinct carrier phase states are used in QPSK?

  • A2
  • B4
  • C8
  • D16
Report an error
Correct Answer: B. 4
Explanation: Quadrature phase-shift keying uses four phase states, allowing each symbol to represent two bits.
Reference: Standard communication systems: digital modulation
Question 428
Communication SystemsDigital Modulation

Each QPSK symbol carries how many bits?

  • A1
  • B2
  • C3
  • D4
Report an error
Correct Answer: B. 2
Explanation: Four possible symbols correspond to log2(4)=2 bits per symbol.
Reference: Standard communication systems: digital modulation
Question 431
Communication SystemsNoise Figure

The noise factor of an ideal noiseless receiver is?

  • A0
  • B1
  • C2
  • DInfinite
Report an error
Correct Answer: B. 1
Explanation: Noise factor F=SNRin/SNRout. An ideal noiseless system does not degrade SNR, so F=1, corresponding to 0 dB noise figure.
Reference: Standard communication systems: noise figure
Question 432
Communication SystemsNoise Figure

In a cascade of receiver stages, the overall noise performance is especially sensitive to the noise characteristics of the?

  • AFirst stage
  • BLast stage only
  • CPower supply only
  • DAntenna cable length only regardless of loss
Report an error
Correct Answer: A. First stage
Explanation: Friis' formula shows that noise added by early stages is most important because later-stage noise contributions are divided by preceding gain.
Reference: Standard communication systems: noise figure
Question 433
Communication SystemsReceiver Fundamentals

A low-noise amplifier at the front end of a receiver is mainly used to?

  • AProvide gain while adding as little noise as practical
  • BSuppress the desired signal
  • CConvert all signals to DC
  • DMake channel bandwidth infinite
Report an error
Correct Answer: A. Provide gain while adding as little noise as practical
Explanation: An LNA amplifies weak received signals with minimal added noise, helping preserve receiver SNR.
Reference: Standard communication systems: receiver fundamentals
Question 434
Communication SystemsDigital Receivers

The main purpose of a matched filter in a digital receiver is to?

  • AMaximize output SNR at a specified sampling instant for a known signal in AWGN
  • BEliminate the need for synchronization
  • CMake all symbol waveforms identical
  • DGenerate carrier power
Report an error
Correct Answer: A. Maximize output SNR at a specified sampling instant for a known signal in AWGN
Explanation: For a known signal in additive white Gaussian noise, the matched filter maximizes the signal-to-noise ratio at the decision sampling instant.
Reference: Standard communication systems: digital receivers
Question 435
Communication SystemsDigital Receivers

Intersymbol interference (ISI) occurs when?

  • AOne transmitted symbol interferes with neighboring symbols
  • BNoise power becomes exactly zero
  • COnly one symbol is transmitted
  • DCarrier frequency equals zero
Report an error
Correct Answer: A. One transmitted symbol interferes with neighboring symbols
Explanation: Channel dispersion or bandwidth limitations can spread pulses so that adjacent symbol intervals overlap, causing ISI.
Reference: Standard communication systems: digital receivers
Question 436
Communication SystemsDigital Receivers

The Nyquist zero-ISI criterion is concerned primarily with?

  • APulse shaping to avoid interference at symbol sampling instants
  • BIncreasing thermal noise
  • CGenerating AM sidebands
  • DReducing antenna length
Report an error
Correct Answer: A. Pulse shaping to avoid interference at symbol sampling instants
Explanation: Nyquist pulse-shaping conditions allow neighboring pulses to have zero contribution at the desired sampling instants, ideally eliminating ISI.
Reference: Standard communication systems: digital receivers
Question 438
Communication SystemsError Performance

For binary signaling, bit error rate (BER) is defined as?

  • ANumber of erroneous bits divided by total transmitted or received bits considered
  • BNumber of correct bits divided by bandwidth
  • CCarrier power divided by noise power
  • DSymbols per second divided by bits per symbol
Report an error
Correct Answer: A. Number of erroneous bits divided by total transmitted or received bits considered
Explanation: BER is the fraction of bits detected incorrectly over the observation interval.
Reference: Standard communication systems: error performance
Question 443
Communication SystemsDigital Communication Fundamentals

The term baud refers to the number of?

  • ABits transmitted per second in every case
  • BSymbols transmitted per second
  • CBytes transmitted per second
  • DCarrier cycles per bit only
Report an error
Correct Answer: B. Symbols transmitted per second
Explanation: Baud is the symbol rate. It equals bit rate only when each symbol represents one bit.
Reference: Standard communication systems: digital communication fundamentals
Question 444
Communication SystemsError Performance

Which digital modulation among coherent BPSK and coherent QPSK has the same theoretical BER versus Eb/N0 in ideal AWGN when Gray mapping and coherent detection are used?

  • AQPSK can have the same BER as BPSK
  • BQPSK must always have twice the BER
  • CBPSK always has zero BER
  • DNeither can operate in AWGN
Report an error
Correct Answer: A. QPSK can have the same BER as BPSK
Explanation: Coherent Gray-coded QPSK can be viewed as two orthogonal BPSK channels, giving the same theoretical bit-error performance versus Eb/N0 in ideal AWGN.
Reference: Standard communication systems: error performance
Question 446
Communication SystemsInformation Theory

According to Shannon’s capacity formula for an AWGN channel, channel capacity is?

  • AC=B log2(1+S/N)
  • BC=2B only
  • CC=B(S/N) without logarithm
  • DC=S/N divided by B
Report an error
Correct Answer: A. C=B log2(1+S/N)
Explanation: Shannon's formula gives the theoretical maximum reliable information rate C=B log2(1+S/N) for an ideal band-limited AWGN channel.
Reference: Standard communication systems: information theory
Question 450
Communication SystemsInformation Theory

For a binary symmetric channel with crossover probability p=0, its capacity is?

  • A0 bit per channel use
  • B0.5 bit per channel use
  • C1 bit per channel use
  • D2 bits per channel use
Report an error
Correct Answer: C. 1 bit per channel use
Explanation: With no crossover errors, a binary input can convey one bit of information per channel use.
Reference: Standard communication systems: information theory
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Question 451
Communication SystemsReceivers

The main purpose of automatic gain control (AGC) in a receiver is to?

  • AMaintain a more nearly constant output level despite changes in received signal strength
  • BIncrease carrier frequency continuously
  • CEliminate the local oscillator
  • DCreate intentional aliasing
Report an error
Correct Answer: A. Maintain a more nearly constant output level despite changes in received signal strength
Explanation: AGC automatically varies receiver gain so large variations in received signal strength produce smaller variations in output level.
Reference: Standard communication systems: receivers
Question 453
Communication SystemsFM Receivers

In FM receivers, a limiter stage is used primarily to?

  • ARemove unwanted amplitude variations before frequency detection
  • BIncrease AM modulation index
  • CGenerate PCM codes
  • DReduce IF to zero in every design
Report an error
Correct Answer: A. Remove unwanted amplitude variations before frequency detection
Explanation: Since ideal FM information is carried in frequency, amplitude variations caused by noise can be clipped or limited before demodulation.
Reference: Standard communication systems: fm receivers
Question 454
Communication SystemsFM Receivers

The capture effect is most strongly associated with?

  • AFM reception
  • BIdeal PCM quantization
  • CPure DSB-SC generation
  • DTDM framing only
Report an error
Correct Answer: A. FM reception
Explanation: In FM, when two signals at nearly the same frequency are present, the stronger signal can dominate receiver output; this is called the capture effect.
Reference: Standard communication systems: fm receivers
Question 458
Communication SystemsAngle Modulation

For a sinusoidal message in phase modulation, increasing the message frequency while keeping message amplitude and phase sensitivity fixed causes the peak frequency deviation to?

  • ADecrease
  • BRemain zero
  • CIncrease
  • DRemain independent of frequency
Report an error
Correct Answer: C. Increase
Explanation: In PM, instantaneous frequency deviation is proportional to the time derivative of the message, so for a sinusoid its peak value increases with message frequency.
Reference: Standard communication systems: angle modulation
Question 463
Communication SystemsReceivers

A superheterodyne receiver converts a selected incoming RF signal to a fixed?

  • AAudio frequency only
  • BIntermediate frequency
  • CZero frequency in every receiver
  • DSampling frequency
Report an error
Correct Answer: B. Intermediate frequency
Explanation: A superheterodyne receiver mixes the selected RF signal with a local oscillator to produce a fixed intermediate frequency for convenient filtering and amplification.
Reference: Standard communication systems: receivers
Question 465
Communication SystemsReceivers

In a superheterodyne receiver, the intermediate frequency is produced by a?

  • AMixer
  • BPower amplifier only
  • CEnvelope capacitor only
  • DAntenna reflector
Report an error
Correct Answer: A. Mixer
Explanation: The mixer combines the RF input and local-oscillator signal, producing sum and difference frequency components; one is selected as the IF.
Reference: Standard communication systems: receivers
Question 475
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
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Question 476
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 478
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 479
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 481
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 482
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 484
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 486
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 489
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 490
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 491
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 492
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 493
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
Question 494
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 495
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 496
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 497
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 498
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 499
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
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