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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.

Which of the following requires a synchronizing signal?(a) Single channel PPM system(b) PAM(c) DM(d) All of the mentionedThe question was posed to me during an online interview.Enquiry is from PAM,PWM and TDM in section Modulation and Coding Trade-off of Digital Communications

Answer»

The CORRECT option is (b) PAM

To EXPLAIN: PAM requires a SYNCHRONIZING signal.

2.

The use of non uniform quantization leads to(a) Reduction in transmission bandwidth(b) Increase in maximum SNR(c) Increase in SNR for low level signals(d) Simplification of quantization processThe question was asked in final exam.This intriguing question originated from PAM,PWM and TDM in section Modulation and Coding Trade-off of Digital Communications

Answer»

Right option is (c) Increase in SNR for LOW LEVEL SIGNALS

Explanation: The use of non UNIFORM quantization leads to increase in SNR for low level signals.

3.

QAM uses ______ as the dimensions.(a) In phase(b) Quadrature(c) In phase & Quadrature(d) None of the mentionedI have been asked this question during an online exam.The question is from Modulation Techniques topic in division Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT option is (C) In PHASE & QUADRATURE

Explanation: QAM uses in phase and quadrature which is cosine and sine respectively as the dimensions.
4.

Which system uses QAM?(a) Digital microwave relay(b) Dial up modem(c) Digital microwave relay & Dial up modem(d) None of the mentionedI got this question in an online quiz.Origin of the question is Modulation Techniques topic in portion Modulation and Coding Trade-off of Digital Communications

Answer»

Correct answer is (c) DIGITAL microwave RELAY & DIAL up modem

To explain: Digital microwave relay, dial up modem and etc uses QAM modulation TECHNIQUE.

5.

Which is called as on-off keying?(a) Amplitude shift keying(b) Uni-polar PAM(c) Amplitude shift keying & Uni-polar PAM(d) None of the mentionedThe question was posed to me in examination.This intriguing question comes from Modulation Techniques in portion Modulation and Coding Trade-off of Digital Communications

Answer»

The correct option is (c) AMPLITUDE SHIFT keying & Uni-polar PAM

Easy explanation: Amplitude shift keying and uni-polar PAM both SCHEMES are called as on off keying.

6.

Simulation is used to determine(a) Bit error rate(b) Symbol error rate(c) Bit error(d) Symbol errorThe question was asked in class test.Question is taken from Modulation Techniques topic in portion Modulation and Coding Trade-off of Digital Communications

Answer»

Right answer is (a) BIT error rate

Explanation: A SIMULATION of digital communication SYSTEM is USED to estimate bit error rate.

7.

If we correlate the received signal with both orthogonal function the inner product will be(a) In phase(b) Quadrature(c) In phase and quadrature(d) UnityThe question was asked in an internship interview.I need to ask this question from Modulation Techniques in chapter Modulation and Coding Trade-off of Digital Communications

Answer»

The CORRECT answer is (c) In phase and quadrature

To explain: If we CORRELATE the received signal with both the orthogonal function, the TWO INNER products obtained will be in phase and quadrature.

8.

Matched filter is a _____ technique.(a) Modulation(b) Demodulation(c) Modulation & Demodulation(d) None of the mentionedI have been asked this question during an online exam.This question is from Modulation Techniques topic in portion Modulation and Coding Trade-off of Digital Communications

Answer»

The CORRECT ANSWER is (B) Demodulation

Explanation: Matched FILTER is a demodulation technique with LTI.

9.

Every frequency has ____ orthogonal functions.(a) One(b) Two(c) Four(d) SixI have been asked this question during an online interview.My question comes from Modulation Techniques topic in chapter Modulation and Coding Trade-off of Digital Communications

Answer»

The correct CHOICE is (b) Two

Best EXPLANATION: EVERY frequency has two orthogonal functions – sine and cosine.

10.

If we correlate the received signal with any one of the two orthogonal function, the obtained inner product will be(a) In phase(b) Quadrature(c) Zero(d) Cannot be determinedThis question was posed to me in an interview for job.This question is from Modulation Techniques in division Modulation and Coding Trade-off of Digital Communications

Answer»

Right answer is (c) Zero

The explanation is: If we correlate the received SIGNAL with only one of the orthogonal function for example SINE, the inner PRODUCT OBTAINED will be zero.

11.

In non coherent reception _____ is measured.(a) Phase(b) Energy(c) Power(d) None of the mentionedThe question was asked during an interview.I need to ask this question from Modulation Techniques topic in division Modulation and Coding Trade-off of Digital Communications

Answer»
12.

FSK reception uses(a) Correlation receiver(b) PLL(c) Correlation receiver & PLL(d) None of the mentionedThis question was posed to me in unit test.My query is from Modulation Techniques topic in chapter Modulation and Coding Trade-off of Digital Communications

Answer»

Right answer is (c) Correlation RECEIVER & PLL

To explain I would say: Frequency SHIFT KEYING uses correlation receiver and phase locked LOOP.

13.

FSK reception is(a) Phase Coherent(b) Phase non coherent(c) Phase Coherent & non coherent(d) None of the mentionedThe question was posed to me in examination.This question is from Modulation Techniques topic in chapter Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT option is (C) Phase Coherent & NON coherent

Easiest explanation: RECEPTION of FSK can be either phase coherent or phase non coherent.
14.

Which FSK has no phase discontinuity?(a) Continuous FSK(b) Discrete FSK(c) Uniform FSK(d) None of the mentionedThe question was asked in an interview for job.Origin of the question is Modulation Techniques in portion Modulation and Coding Trade-off of Digital Communications

Answer» RIGHT option is (a) Continuous FSK

To EXPLAIN I would SAY: Continuous frequency shift KEYING has no phase DISCONTINUITY between symbols.
15.

Average energy per bit is given by(a) average energy symbol/log2 M(b) average energy symbol * log2 M(c) log2 M/ Average energy symbol(d) none of the mentionedI got this question during an interview.Query is from Modulation Techniques topic in division Modulation and Coding Trade-off of Digital Communications

Answer»

Right option is (a) average energy symbol/LOG2 M

Explanation: Average energy PER BIT is given by average energy symbol DIVIDED by log2 M.

16.

Entropy of N random variables is the _____ of the entropy of individual random variable.(a) Sum(b) Product(c) Sum of squares(d) AverageThe question was posed to me in an interview for job.The origin of the question is Modulation and Entropy in portion Modulation and Coding Trade-off of Digital Communications

Answer»

Right ANSWER is (a) Sum

Explanation: ENTROPY of N random variables is the sum of the entropy of INDIVIDUAL random variable.

17.

Entropy calculation returns(a) Random variable(b) Deterministic number(c) Random number(d) None of the mentionedI had been asked this question in homework.Question is from Modulation and Entropy topic in section Modulation and Coding Trade-off of Digital Communications

Answer»

Correct answer is (b) DETERMINISTIC number

Explanation: ENTROPY CALCULATION returns a deterministic number and not a random variable.

18.

In TDM, at the receiver end, ____ filter is used.(a) Low pass(b) High pass(c) Band pass(d) Band stopThis question was addressed to me in final exam.My query is from Modulation and Entropy in portion Modulation and Coding Trade-off of Digital Communications

Answer» RIGHT choice is (a) Low PASS

For explanation: In TDM, at the receiver END low pass FILTERING is done to obtain individual signals.
19.

Which provides more secure communication?(a) CDMA(b) FDMA(c) TDMA(d) None of the mentionedThe question was asked by my college director while I was bunking the class.Asked question is from Modulation and Entropy in division Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT choice is (a) CDMA

For EXPLANATION I would SAY: CDMA PROVIDES more secure COMMUNICATION than TDMA and FDMA.
20.

Time division multiplexing uses(a) High pass filter(b) Commutator(c) High pass filter & Commutator(d) None of the mentionedI had been asked this question in an international level competition.This interesting question is from Modulation and Entropy in chapter Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT answer is (B) Commutator

Best EXPLANATION: Time division multiplexing uses low pass filter and commutator.
21.

Which has higher error probability performance?(a) Uni-polar base-band signalling(b) Bipolar base-band signalling(c) ASK(d) FSKI got this question by my school teacher while I was bunking the class.Enquiry is from Modulation and Entropy in chapter Modulation and Coding Trade-off of Digital Communications

Answer»

The correct choice is (b) Bipolar base-band SIGNALLING

Easy EXPLANATION: Bipolar base-band signalling has high error PROBABILITY performance than the OTHERS. The probability of error value is A2T.

22.

Which has same probability of error?(a) ASK and FSK(b) ASK and PSK(c) PSK and FSK(d) None of the mentionedI had been asked this question in an interview for job.This intriguing question originated from Modulation and Entropy in section Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT answer is (C) PSK and FSK

Best explanation: Uni-polar base-band signalling, PSK and FSK has same probability of error.
23.

Modulation process corresponds to ______ the amplitude, frequency or phase.(a) Switching(b) Keying(c) Switching or keying(d) None of the mentionedThis question was addressed to me during an internship interview.I want to ask this question from Modulation and Entropy topic in chapter Modulation and Coding Trade-off of Digital Communications

Answer»

Right OPTION is (C) Switching or keying

The best explanation: Modulation PROCESS CORRESPONDS to switching or keying the amplitude, frequency or phase of CW carrier.

24.

Matched filter(a) Is a non linear filter(b) Produces maximum output SNR(c) All of the mentioned(d) None of the mentionedThe question was posed to me in unit test.I would like to ask this question from Modulation and Entropy topic in portion Modulation and Coding Trade-off of Digital Communications

Answer»

Right choice is (b) PRODUCES MAXIMUM output SNR

The best I can explain: MATCHED filter is a linear filter which produces maximum output SNR for a given transmitted signal.

25.

For which quantization process is used?(a) Amplitude discretization(b) Time discretization(c) Amplitude & Time discretization(d) None of the mentionedThe question was posed to me in quiz.The question is from Modulation and Entropy topic in portion Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT OPTION is (a) Amplitude discretization

The BEST explanation: Sampling process is USED for time discretization and QUANTIZATION process is used for amplitude discretization.
26.

PCM includes the process of(a) Amplitude discretization(b) Time discretization(c) Amplitude & Time discretization(d) None of the mentionedThis question was addressed to me in a national level competition.This key question is from Modulation and Entropy in division Modulation and Coding Trade-off of Digital Communications

Answer»

Right option is (C) Amplitude & TIME DISCRETIZATION

Best EXPLANATION: Time discretization and amplitude discretization are the two PROCESSES done in PCM system.

27.

Operations performed by switching system(a) Path establishment(b) Information exchange(c) Tariff computation(d) All of the mentionedThis question was posed to me in an international level competition.I'm obligated to ask this question of Modulation and Multiplexing in portion Modulation and Coding Trade-off of Digital Communications

Answer»

Right ANSWER is (d) All of the mentioned

Easy EXPLANATION: Operations performed by switching network are path ESTABLISHMENT, information EXCHANGE, tariff computation, maintenance, billing ETC.

28.

Analogue switches provides(a) Good bandwidth(b) Low distortion(c) Low cost(d) All of the mentionedThis question was posed to me during a job interview.I need to ask this question from Modulation and Multiplexing topic in section Modulation and Coding Trade-off of Digital Communications

Answer»
29.

In time division, connection is established using(a) Data exchange(b) Galvanic connection(c) Data exchange & Galvanic connection(d) None of the mentionedThe question was asked during an interview.Origin of the question is Modulation and Multiplexing topic in division Modulation and Coding Trade-off of Digital Communications

Answer»

The correct choice is (a) DATA EXCHANGE

Easy EXPLANATION: In time DIVISION, connection is established using data exchange and in space division it is established using galvanic connections.

30.

In time division system, the actual switch is called as(a) Speech memory(b) Cross point(c) Connecting point(d) None of the mentionedI had been asked this question in a job interview.My question is taken from Modulation and Multiplexing in section Modulation and Coding Trade-off of Digital Communications

Answer»
31.

Space division has dedicated(a) Paths(b) Time slots(c) Paths & Time slots(d) None of the mentionedI got this question in an interview for internship.Question is taken from Modulation and Multiplexing topic in chapter Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT option is (a) Paths

Explanation: Space DIVISION has DEDICATED paths and time division has dedicated time slots.
32.

Switching exists in(a) Point to point communication(b) Broadcast communication(c) Point to point & Broadcast communication(d) None of the mentionedI got this question in class test.The question is from Modulation and Multiplexing topic in section Modulation and Coding Trade-off of Digital Communications

Answer»

The CORRECT choice is (a) Point to point communication

Best EXPLANATION: Circuit CONNECTION in point to point communication is called as switching. Switching does not EXIST in broadcast communication or network.

33.

In channel encoding procedure(a) Redundancy bits are added(b) Errors are corrected(c) Redundancy bits are added & Errors are corrected(d) None of the mentionedThis question was addressed to me in an interview.Enquiry is from Modulation and Multiplexing in section Modulation and Coding Trade-off of Digital Communications

Answer» RIGHT answer is (C) Redundancy BITS are added & Errors are corrected

The explanation is: In channel encoding includes addition of redundancy to the SIGNAL such that any BIT errors can be corrected.
34.

When probability of receiving a symbol is 1 then how much information will be obtained?(a) Little information(b) Much information(c) No information(d) None of the mentionedThis question was addressed to me in exam.My enquiry is from Modulation and Multiplexing topic in portion Modulation and Coding Trade-off of Digital Communications

Answer»

The CORRECT ANSWER is (C) No information

To explain I would say: When the probability of receiving a symbol is 1 then the information obtained is ZERO.

35.

Modulation process includes(a) Analog to digital conversion(b) Digital to analog conversion(c) All of the mentioned(d) None of the mentionedThe question was posed to me in my homework.The question is from Modulation and Multiplexing in section Modulation and Coding Trade-off of Digital Communications

Answer»

Correct answer is (b) Digital to analog conversion

To EXPLAIN I WOULD say: Modulation procedure includes digital to analog conversion which PRODUCES a continuous time signal that can be SENT through the CHANNEL.

36.

Source of noise in delta modulation is(a) Granularity(b) Slope overload(c) Granularity & Slope overload(d) None of the mentionedThe question was posed to me in an internship interview.This intriguing question originated from Modulation and Multiplexing in section Modulation and Coding Trade-off of Digital Communications

Answer» RIGHT answer is (c) GRANULARITY & Slope overload

The explanation is: Sources of NOISE in delta MODULATION are granularity and slope overload.
37.

The demodulator in delta modulation technique is(a) Differentiator(b) Integrator(c) Quantizer(d) None of the mentionedThis question was posed to me in final exam.I'm obligated to ask this question of Modulation and Multiplexing topic in section Modulation and Coding Trade-off of Digital Communications

Answer»

The CORRECT option is (b) Integrator

Easiest explanation: The demodulator USED in DELTA modulation is a SIMPLE form of integrator.

38.

Delta modulation is ______ conversion.(a) Analog to digital(b) Digital to analog(c) Analog to digital and digital to analog(d) None of the mentionedThis question was posed to me in semester exam.My doubt stems from Modulation and Multiplexing in division Modulation and Coding Trade-off of Digital Communications

Answer»

The correct answer is (C) Analog to DIGITAL and digital to analog

The explanation: Delta modulation is the PROCESS of analog to digital and digital to analog CONVERSION technique USED for transmission of voice signals.

39.

In bipolar codes, pulses can be(a) Positive(b) Negative(c) Absent(d) All of the mentionedI got this question in a job interview.The above asked question is from Modulation and Multiplexing in section Modulation and Coding Trade-off of Digital Communications

Answer»

Correct answer is (d) All of the mentioned

The EXPLANATION: In bipolar CODES, the pulses can be POSITIVE, NEGATIVE or absent.

40.

To achieve high signal to noise ratio, delta modulation must use(a) Under sampling(b) Over sampling(c) Aliasing(d) None of the mentionedI got this question in final exam.This interesting question is from Modulation and Multiplexing topic in portion Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT option is (B) Over sampling

Easiest explanation: To achieve high signal to noise ratio, delta modulation MUST USE over sampling techniques.
41.

Properties used to determine stream’s fidelity(a) Sampling rate(b) Bit depth(c) Sampling rate & Bit depth(d) None of the mentionedThe question was asked by my college director while I was bunking the class.Question is from Modulation and Multiplexing topic in division Modulation and Coding Trade-off of Digital Communications

Answer»
42.

Which has the maximum power efficiency?(a) Class A(b) Class B(c) Class C(d) Class ABThe question was asked during an online interview.Origin of the question is M-ary Modulation and Amplifiers in portion Modulation and Coding Trade-off of Digital Communications

Answer»

Right option is (C) Class C

To elaborate: Class C has the maximum power EFFICIENCY when compared to the other LINEAR AMPLIFIERS.

43.

Class B linear amplifiers have maximum power efficiency of(a) 50%(b) 75%(c) 78.5%(d) None of the mentionedThe question was posed to me during a job interview.This interesting question is from M-ary Modulation and Amplifiers in division Modulation and Coding Trade-off of Digital Communications

Answer»

The correct choice is (c) 78.5%

To elaborate: Class B linear amplifiers have MAXIMUM POWER efficiency of 78.5%.

44.

An amplifier uses ______ to take input signal.(a) DC power(b) AC power(c) DC & AC power(d) None of the mentionedThis question was addressed to me in semester exam.This interesting question is from M-ary Modulation and Amplifiers topic in portion Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT choice is (a) DC POWER

To explain I would say: An amplifier USES DC power to take an input signal and increase its AMPLITUDE at the OUTPUT.
45.

Which generates high distortion?(a) Class A(b) Class B(c) Class C(d) Class ABI have been asked this question during an interview.Enquiry is from M-ary Modulation and Amplifiers in chapter Modulation and Coding Trade-off of Digital Communications

Answer»

Correct option is (c) Class C

Explanation: Class C AMPLIFIERS GENERATE high distortion and it is closer to SWITCH than an amplifier.

46.

Which has 50% maximum power efficiency?(a) Class A(b) Class B(c) Class AB(d) None of the mentionedI had been asked this question in an online quiz.My question comes from M-ary Modulation and Amplifiers topic in division Modulation and Coding Trade-off of Digital Communications

Answer» RIGHT CHOICE is (a) Class A

Explanation: Class A AMPLIFIERS have 50% maximum POWER efficiency.
47.

TDM requires(a) Constant data transmission(b) Transmission of data samples(c) Transmission of data at random(d) Transmission of data of only one measuredThis question was posed to me in an interview for job.My question comes from PAM,PWM and TDM in chapter Modulation and Coding Trade-off of Digital Communications

Answer»

Correct OPTION is (B) TRANSMISSION of data samples

Explanation: TDM requires transmission of data samples.

48.

Which modulation technique have the same bit and symbol error probability?(a) BPSK(b) DPSK(c) OOK(d) All of the mentionedThis question was addressed to me during an online exam.This key question is from M-ary Modulation and Amplifiers topic in division Modulation and Coding Trade-off of Digital Communications

Answer»
49.

For non coherent reception of PSK _____ is used.(a) Differential encoding(b) Decoding(c) Differential encoding & Decoding(d) None of the mentionedThe question was posed to me in semester exam.This interesting question is from M-ary Modulation and Amplifiers topic in section Modulation and Coding Trade-off of Digital Communications

Answer» CORRECT answer is (c) Differential encoding & DECODING

Easiest explanation: For non coherent RECEPTION of PSK, differential encoding is USED at the transmitter and decoding is used at the receiver.
50.

In M-ary FSK as M tends to infinity, probability of error tends to(a) Infinity(b) Unity(c) Zero(d) None of the mentionedI had been asked this question in a job interview.The origin of the question is M-ary Modulation and Amplifiers topic in portion Modulation and Coding Trade-off of Digital Communications

Answer»

The correct ANSWER is (C) Zero

Easy explanation: In M-ary FSK as M TENDS to infinity, PROBABILITY of error becomes zero.