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This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

1.

Cumulative distributive function is(a) Non negative(b) Non decreasing(c) Non negative & decreasing(d) None of the mentionedI had been asked this question in quiz.My question is based upon Signals topic in section Signals and Spectra of Digital Communications

Answer»

Correct answer is (c) NON NEGATIVE & decreasing

Explanation: CUMULATIVE distribution FUNCTION is non negative and non decreasing function.

2.

Which are non negative functions?(a) PDF(b) PMF(c) PDF & PMF(d) None of the mentionedI got this question in an interview for internship.Query is from Signals topic in division Signals and Spectra of Digital Communications

Answer» CORRECT choice is (C) PDF & PMF

Explanation: PDF, PMF and CDF are non negative FUNCTIONS.
3.

Which are orthonormal signal representation?(a) Sine and cosine at same frequency(b) Wavelets(c) Complex sinusoids at a different frequency(d) All of the mentionedI got this question in quiz.My question is from Signals in chapter Signals and Spectra of Digital Communications

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Right choice is (d) All of the mentioned

To explain I would SAY: Some of the common ORTHONORMAL signal representations are sine and cosine at the same frequency, Fourier serier, SINC functions CENTERED at sampling times, wavelets ETC.

4.

Constellation diagram is plotted in(a) Constellation space(b) Signal space(c) Orthogonal space(d) Boundary spaceThe question was asked during an internship interview.Enquiry is from Signals topic in chapter Signals and Spectra of Digital Communications

Answer» RIGHT OPTION is (B) SIGNAL space

The explanation: The constellation diagram is PLOTTED in a space called as signal space.
5.

A band-pass signal has(a) DC component(b) No DC component(c) No side lobes(d) Cannot be determinedThis question was posed to me during an interview.This interesting question is from Signals in section Signals and Spectra of Digital Communications

Answer» RIGHT choice is (b) No DC component

To elaborate: A band-pass SIGNAL has no DC components and has Fourier transform equal to ZERO. OUTSIDE the band it will not be exactly zero. Thus this results in presence of side lobes.
6.

A band-pass signal has a Fourier transform equal to(a) One(b) Zero(c) Infinity(d) Cannot be determinedThe question was posed to me in quiz.I'm obligated to ask this question of Signals in portion Signals and Spectra of Digital Communications

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Right answer is (b) ZERO

To EXPLAIN: A band-pass signal has a Fourier transform EQUAL to zero for all VALUE in both frequency and time domain.

7.

Which can be used for periodic and non periodic?(a) Fourier series(b) Fourier transforms(c) Fourier series & transforms(d) None of the mentionedI had been asked this question in an internship interview.My question is from Signals topic in portion Signals and Spectra of Digital Communications

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Correct option is (B) Fourier transforms

For explanation I would SAY: Fourier series is limited to only PERIODIC signals where as Fourier transforms and LAPLACE transforms can be used for both periodic and non periodic signals.

8.

Random things in a communication system are(a) Timing offset(b) Device frequency(c) Attenuation(d) All of the mentionedThe question was posed to me in an international level competition.Question is taken from Signals topic in portion Signals and Spectra of Digital Communications

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Right answer is (d) All of the mentioned

For explanation I would say: Some of the random things in the communication SYSTEM are noise in the channel, attenuation, FADING, channel filtering, DEVICE frequency, PHASE and timing offset.

9.

Fourier transform of a signal gives the(a) Frequency content(b) Bandwidth(c) Frequency content & Bandwidth(d) None of the mentionedThis question was posed to me in unit test.The above asked question is from Signals in portion Signals and Spectra of Digital Communications

Answer» RIGHT choice is (c) Frequency content & Bandwidth

To ELABORATE: Fourier transform of a signal GIVE the frequency content and also DETERMINES the bandwidth of the signal.
10.

ADSL has _____ information channels.(a) One(b) Three(c) Four(d) None of the mentionedI got this question during an internship interview.Asked question is from Signals in chapter Signals and Spectra of Digital Communications

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The correct choice is (b) Three

To elaborate: Asymmetric digital subscriber line has three information channels – a high speed DOWNSTREAM channel, ISDN channel and medium speed DUPLEX channel.

11.

In down-conversion multiplication with cosine wave is followed by(a) Low pass filter(b) High pass filter(c) Bandpass filter(d) Bandstop filterThis question was posed to me during an interview.The doubt is from Signals in portion Signals and Spectra of Digital Communications

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Correct choice is (a) LOW pass filter

For EXPLANATION: Downconversion of bandpass signal INCLUDES multiplication with sine wave followed by low pass FILTERING.

12.

A band-pass signal can be down-converted using(a) Sine wave(b) Cosine wave(c) Time delayed wave(d) None of the mentionedI had been asked this question in an interview for internship.This is a very interesting question from Signals topic in division Signals and Spectra of Digital Communications

Answer» CORRECT choice is (b) Cosine wave

Easy EXPLANATION: For down-conversion of a band-pass signal also cosine signal is USED and multiplied with it.
13.

A base-band signal can be up-converted using(a) Sine wave(b) Cosine wave(c) Filtering(d) None of the mentionedThe question was asked in a national level competition.My question is from Signals topic in section Signals and Spectra of Digital Communications

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The correct ANSWER is (b) COSINE wave

For EXPLANATION: A base-band signal can be up-converted to band-pass FILTER by applying cosine wave.

14.

Properties of Fourier transform are(a) Duality property(b) Time shifting property(c) Modulation property(d) All of the mentionedThe question was asked in semester exam.The origin of the question is Signals in section Signals and Spectra of Digital Communications

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Right choice is (d) All of the mentioned

The BEST I can explain: Some of the properties of FOURIER transform are duality PROPERTY, time scaling property, time shifting property, modulation property and MANY more.

15.

Properties of impulse function are(a) Symmetry(b) Time scaling(c) Shifting(d) All of the mentionedThis question was posed to me in an online interview.The query is from Signals topic in division Signals and Spectra of Digital Communications

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The CORRECT answer is (d) All of the mentioned

For EXPLANATION I WOULD say: Some of the properties of impulse function are symmetry, time scaling and SHIFTING.

16.

In the digital communication system, signals in different frequency bands are(a) Orthogonal(b) Non orthogonal(c) Orthogonal & Non orthogonal(d) None of the mentionedThis question was posed to me by my college professor while I was bunking the class.I would like to ask this question from Signals in division Signals and Spectra of Digital Communications

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The correct CHOICE is (a) Orthogonal

To explain I would SAY: In digital communication system, SIGNALS from DIFFERENT frequency BANDS are orthogonal thus interference won’t occur.

17.

Voltage generated by lightning is an example for(a) Energy signal(b) Power signal(c) Energy & Power signal(d) None of the mentionedThe question was posed to me in class test.Enquiry is from Types of Processes in portion Signals and Spectra of Digital Communications

Answer» RIGHT option is (a) Energy signal

The best explanation: VOLTAGE generated by LIGHTNING is an example for energy signal and it has very HIGH POWER.
18.

Which has minimum power loss during transmission?(a) Twisted Copper cable at 1KHz(b) Optical fiber(c) Twisted copper cable at 100KHz(d) Wave guideThis question was posed to me during an internship interview.I need to ask this question from Types of Processes in section Signals and Spectra of Digital Communications

Answer»

The correct option is (a) TWISTED Copper CABLE at 1KHz

For EXPLANATION I would say: Twisted copper wire at 1KHz have low power LOSS.

19.

Possible timing error detection methods are(a) Early late(b) Zero crossing(c) Early late & Zero crossing(d) None of the mentionedThis question was posed to me during an online exam.This question is from Types of Processes topic in portion Signals and Spectra of Digital Communications

Answer»

The CORRECT option is (c) Early late & Zero crossing

Explanation: Methods for timing error DETECTIONS are early late timing error DETECTION and zero crossing timing error detection METHOD.

20.

Two clock with rates T1 and T2 are incommensurate if its ratio is(a) Rational(b) Irrational(c) Equal(d) None of the mentionedI got this question in an online interview.Query is from Types of Processes topic in portion Signals and Spectra of Digital Communications

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Correct ANSWER is (b) IRRATIONAL

Explanation: Two clock with rates T1 and T2 are incommensurate if its RATIO is irrational.

21.

Non uniform tree _____ bit rate.(a) Increases(b) Decreases(c) Does not affect(d) None of the mentionedI got this question by my college professor while I was bunking the class.I need to ask this question from Types of Processes topic in portion Signals and Spectra of Digital Communications

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Right choice is (a) Increases

The BEST EXPLANATION: Non uniform tree for BINARY SEARCH increases the BIT rate.

22.

The weighing matrix is(a) Positive quantity(b) Inverse of covariance matrix of the input vector(c) Positive quantity & Inverse of a covariance matrix of the input vector(d) None of the mentionedThis question was addressed to me in exam.Question is from Types of Processes topic in section Signals and Spectra of Digital Communications

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Right choice is (C) Positive quantity & INVERSE of a COVARIANCE matrix of the input VECTOR

Explanation: W is a positive definite weighing matrix and it is inverse of covariance matrix of the input vector.

23.

Ionospheric communication can take place in(a) High frequency band(b) Very high frequency band(c) Ultra high frequency band(d) Super high frequency bandI got this question during a job interview.Query is from Types of Processes topic in chapter Signals and Spectra of Digital Communications

Answer»

Correct ANSWER is (a) High frequency band

To ELABORATE: IONOSPHERIC COMMUNICATION takes place in high frequency band.

24.

Satellite communication takes place in(a) Ultra high frequency band(b) Super high frequency band(c) Ultra & Super high frequency band(d) None of the mentionedI got this question in an internship interview.Question is from Types of Processes topic in portion Signals and Spectra of Digital Communications

Answer»

The correct option is (c) Ultra & Super HIGH frequency band

The best I can EXPLAIN: Satellite communication takes PLACE in ultra high and super high frequency BANDS.

25.

The auto-correlation of white noise is(a) A delta function(b) A constant(c) Gaussian(d) None of the mentionedThis question was posed to me by my college professor while I was bunking the class.Enquiry is from Types of Processes topic in section Signals and Spectra of Digital Communications

Answer»

The CORRECT answer is (a) A delta function

For EXPLANATION: The auto-correlation of WHITE noise is a delta function.

26.

The line code has a zero dc component for pulse transmission of random binary data is(a) NRZ(b) RZ(c) Alternate mark inversion(d) None of the mentionedThe question was posed to me in homework.This intriguing question originated from Types of Processes topic in division Signals and Spectra of Digital Communications

Answer» RIGHT ANSWER is (C) ALTERNATE mark inversion

To explain I would say: The line code has a zero dc component for pulse transmission of random binary DATA is alternate mark inversion.
27.

For a periodic function, the spectral density and auto correlation functions form(a) Fourier transform pair(b) Laplace transform pair(c) Hilbert transform pair(d) Z transform pairI have been asked this question during an internship interview.This interesting question is from Types of Processes topic in chapter Signals and Spectra of Digital Communications

Answer»

Correct ANSWER is (a) Fourier transform pair

Easiest EXPLANATION: For a PERIODIC function, the spectral DENSITY and auto CORRELATION function forms fourier transform pair.

28.

A rectangular pulse of duration T is applied to a matched filter. The output of the filter is a(a) Rectangular pulse of duration T(b) Rectangular pulse of duration 2T(c) Triangular pulse(d) Sine functionI had been asked this question in a national level competition.My doubt is from Types of Processes topic in division Signals and Spectra of Digital Communications

Answer»

The correct answer is (c) Triangular pulse

To ELABORATE: The output of the matched FILTER when a RECTANGULAR pulse of duration T is APPLIED is a triangular pulse.

29.

In a communication system, a process in which statistical averages and time averages are equal is called as(a) Stationary(b) Ergodic(c) Gaussian(d) PoissonThe question was asked in a job interview.My enquiry is from Types of Processes topic in division Signals and Spectra of Digital Communications

Answer»

Right option is (B) Ergodic

The best EXPLANATION: In ergodic process STATISTICAL AVERAGES and time averages are equal.

30.

The capacity of a channel is given by(a) Number of digits used in coding(b) Volume of information it can take(c) Maximum rate of information transmitted(d) Bandwidth requires informationThis question was addressed to me during an online interview.Question is from Types of Processes topic in section Signals and Spectra of Digital Communications

Answer»

The correct CHOICE is (c) Maximum rate of INFORMATION transmitted

For explanation: The CAPACITY of the CHANNEL is given by a maximum rate of information transmitted.

31.

The power spectral density function of the stochastic process is(a) Real(b) Odd(c) Real & odd(d) None of the mentionedThis question was addressed to me in quiz.This interesting question is from Types of Processes topic in portion Signals and Spectra of Digital Communications

Answer»

The correct choice is (a) REAL

Easiest EXPLANATION: The power SPECTRAL density function of a stochastic function is real and EVEN.

32.

A stationary stochastic process has(a) Finite energy signal(b) Infinite zero signal(c) Zero energy signal(d) None of the mentionedThis question was addressed to me during an interview.My enquiry is from Types of Processes in section Signals and Spectra of Digital Communications

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Right ANSWER is (b) Infinite zero signal

To explain: A stationary stochastic PROCESS is an infinite energy signal and hence its fourier transform does not EXIST.

33.

Loop filter is a ______ used to reduce noise.(a) Low pass filter(b) High pass filter(c) Band pass filter(d) Band reject filterI had been asked this question by my school teacher while I was bunking the class.This intriguing question comes from Digital Communication System in division Signals and Spectra of Digital Communications

Answer»

The correct choice is (a) Low PASS FILTER

To elaborate: Loop filter is a low pass filter used to REDUCE noise.

34.

In flat top sampling scheme, ______ is kept constant after sampling.(a) Amplitude(b) Phase(c) Frequency(d) Time periodThis question was addressed to me in class test.The doubt is from Digital Communication System topic in division Signals and Spectra of Digital Communications

Answer»

Correct answer is (a) Amplitude

The best explanation: In flat TOP SAMPLING SCHEME, the amplitude is KEPT constant after sampling.

35.

Which is practically realizable?(a) A train of pulses(b) Impulse train(c) All of the mentioned(d) None of the mentionedThis question was posed to me in unit test.Query is from Digital Communication System topic in section Signals and Spectra of Digital Communications

Answer»

Right choice is (a) A train of pulses

The EXPLANATION is: A train of pulses with narrow bandwidth is REALIZABLE than the IMPULSE train.

36.

A signal can be recovered from its sample by using(a) Low pass filter(b) High pass filter(c) Band pass filter(d) Band stop filterThis question was posed to me in exam.My query is from Digital Communication System topic in division Signals and Spectra of Digital Communications

Answer»
37.

Sampling theorem is used for converting(a) Continuous time signal to discrete(b) Discrete to continuous time signal(c) Continuous time signal to discrete & vice versa(d) None of the mentionedThe question was asked during a job interview.My doubt stems from Digital Communication System topic in section Signals and Spectra of Digital Communications

Answer»
38.

Ground wave communication occurs in(a) Low frequency band(b) Medium frequency band(c) Low & Medium frequency band(d) None of the mentionedThis question was posed to me in my homework.The above asked question is from Digital Communication System topic in portion Signals and Spectra of Digital Communications

Answer»

The CORRECT option is (c) Low & Medium FREQUENCY band

For explanation I WOULD say: Ground WAVE communication can take place in both low frequency and medium frequency bands.

39.

Modulation channel consists of(a) Amplifier(b) Signal processing units(c) Amplifier & Signal processing units(d) None of the mentionedI got this question during an interview for a job.My question is based upon Digital Communication System in chapter Signals and Spectra of Digital Communications

Answer»
40.

If operating frequency bands are higher ______ is available.(a) Smaller bandwidth(b) Larger bandwidth(c) Smaller & Larger bandwidth(d) Cannot be determinedThe question was posed to me in an internship interview.Origin of the question is Digital Communication System in section Signals and Spectra of Digital Communications

Answer»

Correct CHOICE is (B) LARGER bandwidth

Explanation: Larger bandwidth is AVAILABLE when operating frequency BANDS are higher.

41.

Modulation channel does not accept an analog input signal.(a) True(b) FalseThe question was asked in quiz.My query is from Digital Communication System topic in chapter Signals and Spectra of Digital Communications

Answer» RIGHT CHOICE is (b) False

To EXPLAIN: Modulation channel accepts ANALOG signal as input and delivers another version of modulated signal as analog WAVEFORM.
42.

The basic transmission-reception system is a ______ system.(a) Two block system(b) Three block system(c) Four block system(d) None of the mentionedI had been asked this question during an online exam.My query is from Digital Communication System in division Signals and Spectra of Digital Communications

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The correct option is (b) Three block system

To explain: The basic transmission-reception consists of three BLOCKS – transmitter, transmission MEDIUM, receiver.

43.

Which are the common transmission media used in digital communication system?(a) Coaxial cable(b) Twisted copper cable(c) Radio frequency bands(d) All of the mentionedI have been asked this question in an international level competition.My question is taken from Digital Communication System in chapter Signals and Spectra of Digital Communications

Answer»

Correct OPTION is (d) All of the mentioned

Explanation: Some of the commonly used physical transmission media are twisted COPPER cable, good QUALITY coaxial cable and RADIO frequency bands.

44.

The information source of a digital communication system can be(a) Packetized(b) Continuous(c) Packetized & Continuous(d) Noneof the mentionedI have been asked this question in semester exam.My doubt is from Digital Communication System in chapter Signals and Spectra of Digital Communications

Answer» CORRECT choice is (c) Packetized & Continuous

For explanation: INFORMATION source comes from a HIGHER NETWORKING LAYER. It can be continuous or packetized.
45.

Digital communication system can handle(a) Analog signals(b) 1D signals(c) 2D signals(d) All of the mentionedThis question was addressed to me in an interview.This key question is from Digital Communication System in portion Signals and Spectra of Digital Communications

Answer»

The correct OPTION is (d) All of the mentioned

For EXPLANATION I would say: Digital COMMUNICATION system can handle signals that are analog or those that are already digital. It can ALSO handle 1D and 2D signals.

46.

Matched filter can also be used as least squares estimator.(a) True(b) FalseThe question was posed to me in homework.Question is from Digital Communication System topic in chapter Signals and Spectra of Digital Communications

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The correct option is (a) True

For explanation I would SAY: A matched FILTER can ALSO be used as a least SQUARES ESTIMATOR.

47.

Matched filter technique is used to(a) Increase SNR(b) Decrease SNR(c) SNR is not affected(d) None of the mentionedI have been asked this question by my college professor while I was bunking the class.Question is taken from Digital Communication System in section Signals and Spectra of Digital Communications

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The CORRECT choice is (a) Increase SNR

The best I can explain: Matched filter technique is a DEMODULATION process USED to increase SNR.

48.

Transmission media used for medium frequency band are(a) Coaxial cable(b) Copper cable(c) Optical fiber(d) All of the mentionedI have been asked this question in an international level competition.My question is from Digital Communication System in portion Signals and Spectra of Digital Communications

Answer»

The CORRECT option is (b) Copper CABLE

To elaborate: For medium frequency band communication air and copper cable can only be USED as a TRANSMISSION medium.

49.

Transmission media used in low frequency band are(a) Air(b) Water(c) Copper cable(d) All of the mentionedI have been asked this question in unit test.This question is from Digital Communication System in chapter Signals and Spectra of Digital Communications

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The correct option is (d) All of the mentioned

The best I can EXPLAIN: Air, WATER and copper cable can be used as transmission MEDIA in LOW frequency band COMMUNICATION.

50.

What are the main features of a transmitter?(a) Higher clock speed(b) Linear power amplifier(c) Directional antennas(d) All of the mentionedThe question was asked in semester exam.My doubt stems from Digital Communication System in portion Signals and Spectra of Digital Communications

Answer» RIGHT OPTION is (d) All of the mentioned

For explanation: Some of the main FEATURES which make the transmitter complex are higher clock speed, higher transmit power, directional antennas and need for a LINEAR AMPLIFIER.