Pulse Modulation Techniques Questions and Answers

Q: Assertion (A): Assertion: Regeneration removes quantisation noise from a coded signal. Reason (R): Reason: A regenerator reconstructs each pulse cleanly regardless of the noise on it. Select the correct answer from the options below.

The reason is true but the assertion is false: quantisation noise is built into the coded values themselves, so a perfect regenerator reproduces it faithfully. What regeneration removes is noise the channel added. The distinction is the whole reason coder resolution is specified separately from link quality: one impairment can be cleaned up along the route and the other cannot.

Q: Assertion (A): Assertion: Pulse width modulation has better noise immunity than pulse amplitude modulation. Reason (R): Reason: Its pulse amplitude is constant, so the receiver may limit the pulses. Select the correct answer from the options below.

Both hold and the second explains the first: because amplitude carries nothing, clipping the pulses to a standard height discards amplitude noise without losing information. It is exactly the argument that gives frequency modulation its advantage over amplitude modulation, applied to a pulse train instead of a carrier. The same asymmetry between signal and noise is being exploited in both cases.

Q: Consider the following statements about the sampling theorem. 1. The sampling rate must be at least twice the highest signal frequency 2. An anti-alias filter is needed before the sampler 3. Aliasing can be corrected by a filter after the sampler Which of the statements given above is or are correct?

The first two are correct and the third is not: aliasing is irreversible, because the folded component lands on a frequency the signal itself occupies. That single fact is what makes the anti-alias filter mandatory rather than optional, and it is why the sampling rate and the filter's cut-off are chosen as one decision rather than two.

Q: Consider the following statements about delta modulation. 1. It transmits one bit per sample 2. It needs a much higher sampling rate than pulse code modulation 3. Its step size must satisfy two opposing requirements Which of the statements given above is or are correct?

All three are correct. One bit per sample is the definition, the high rate is the price of that simplicity, and the step size is caught between slope overload if it is too small and granular noise if it is too large. A parameter bracketed by two opposing failures always has an optimum rather than a direction of improvement, and adaptive step sizing is the engineering answer to it.

Q: Statement I: Time division multiplexing requires good linearity in the transmission path. Statement II: Frequency division multiplexing requires good linearity in the transmission path. In the light of the above statements, choose the correct answer.

The second is true and the first is not: time division keeps only one channel present at any instant, so non-linearity has nothing to mix, whereas frequency division has every channel coexisting and intermodulation puts them into one another. Time division's own demand is on timing accuracy instead. Whether channels coexist or take turns is what decides which kind of imperfection a system can tolerate.

Q: Match each pulse scheme with the parameter that carries the message. List I A. Pulse amplitude modulation B. Pulse width modulation C. Pulse position modulation List II P. Pulse height Q. Pulse duration R. Pulse displacement in time Select the correct match.

The pairing is A-P, B-Q, C-R, and it settles the noise behaviour of all three at once: only the first puts information into amplitude, so only the first is vulnerable to amplitude noise. Naming the parameter that carries the message is the single most useful thing to establish about any modulation scheme, pulse or continuous.

Q: Match each impairment with where it arises. List I A. Aliasing B. Quantisation noise C. Crosstalk List II P. At the sampler, from too low a rate Q. In the coder, from finite levels R. In the channel, from limited bandwidth Select the correct match.

The correct pairing is A-P, B-Q, C-R. Locating each impairment matters because it decides the remedy: a higher sampling rate or a better filter for the first, more bits for the second, and more bandwidth or longer guard time for the third. An impairment attributed to the wrong stage leads to an expensive change that fixes nothing.

Q: Arrange the stages of a pulse code modulation transmitter in order. 1. Anti-alias filtering 2. Sampling 3. Quantising 4. Encoding into bits Select the correct sequence.

The order is 1, 2, 3, 4, and each position is forced: filtering must precede sampling because aliasing is irreversible, quantising needs a sample to act on, and encoding needs a level to represent. A signal chain whose order can be reconstructed from the reasons for it never has to be memorised as a list.

Q: Three schemes are compared for the same message bandwidth. SchemeParameter variedNoise immunity PAMAmplitudePoorPWMDurationGoodPPMPositionGood Which conclusion follows from the table?

Reading down the table, the two schemes holding amplitude constant are the two with good immunity, which identifies the mechanism rather than merely ranking the schemes. Duration is a varied parameter rather than a lever on immunity, the bandwidth is held equal across the comparison, and narrowing the pulses would not remove amplitude modulation's dependence on amplitude. A table read for the property the winners share is more informative than one read as a ranking.

51.

Assertion (A): Assertion: Regeneration removes quantisation noise from a coded signal.

Reason (R): Reason: A regenerator reconstructs each pulse cleanly regardless of the noise on it.

Select the correct answer from the options below.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: A

The reason is true but the assertion is false: quantisation noise is built into the coded values themselves, so a perfect regenerator reproduces it faithfully. What regeneration removes is noise the channel added. The distinction is the whole reason coder resolution is specified separately from link quality: one impairment can be cleaned up along the route and the other cannot.

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52.

Assertion (A): Assertion: Pulse width modulation has better noise immunity than pulse amplitude modulation.

Reason (R): Reason: Its pulse amplitude is constant, so the receiver may limit the pulses.

Select the correct answer from the options below.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

Both hold and the second explains the first: because amplitude carries nothing, clipping the pulses to a standard height discards amplitude noise without losing information. It is exactly the argument that gives frequency modulation its advantage over amplitude modulation, applied to a pulse train instead of a carrier. The same asymmetry between signal and noise is being exploited in both cases.

Discuss in Forum

53.

Consider the following statements about the sampling theorem.

1. The sampling rate must be at least twice the highest signal frequency

2. An anti-alias filter is needed before the sampler

3. Aliasing can be corrected by a filter after the sampler

Which of the statements given above is or are correct?

A.2 and 3 only
B.1, 2 and 3
C.1 and 2 only
D.1 and 3 only

Answer: C

The first two are correct and the third is not: aliasing is irreversible, because the folded component lands on a frequency the signal itself occupies. That single fact is what makes the anti-alias filter mandatory rather than optional, and it is why the sampling rate and the filter's cut-off are chosen as one decision rather than two.

Discuss in Forum

54.

Consider the following statements about delta modulation.

1. It transmits one bit per sample

2. It needs a much higher sampling rate than pulse code modulation

3. Its step size must satisfy two opposing requirements

Which of the statements given above is or are correct?

A.1 and 2 only
B.2 and 3 only
C.1 and 3 only
D.1, 2 and 3

Answer: D

All three are correct. One bit per sample is the definition, the high rate is the price of that simplicity, and the step size is caught between slope overload if it is too small and granular noise if it is too large. A parameter bracketed by two opposing failures always has an optimum rather than a direction of improvement, and adaptive step sizing is the engineering answer to it.

Discuss in Forum

55.

Statement I: Time division multiplexing requires good linearity in the transmission path.

Statement II: Frequency division multiplexing requires good linearity in the transmission path.

In the light of the above statements, choose the correct answer.

A.Statement I is incorrect but Statement II is correct
B.Both Statement I and Statement II are correct
C.Both Statement I and Statement II are incorrect
D.Statement I is correct but Statement II is incorrect

Answer: A

The second is true and the first is not: time division keeps only one channel present at any instant, so non-linearity has nothing to mix, whereas frequency division has every channel coexisting and intermodulation puts them into one another. Time division's own demand is on timing accuracy instead. Whether channels coexist or take turns is what decides which kind of imperfection a system can tolerate.

Discuss in Forum

56.

Match each pulse scheme with the parameter that carries the message.

List I

A. Pulse amplitude modulation

B. Pulse width modulation

C. Pulse position modulation

List II

P. Pulse height

Q. Pulse duration

R. Pulse displacement in time

Select the correct match.

A.A-P, B-R, C-Q
B.A-P, B-Q, C-R
C.A-Q, B-P, C-R
D.A-R, B-Q, C-P

Answer: B

The pairing is A-P, B-Q, C-R, and it settles the noise behaviour of all three at once: only the first puts information into amplitude, so only the first is vulnerable to amplitude noise. Naming the parameter that carries the message is the single most useful thing to establish about any modulation scheme, pulse or continuous.

Discuss in Forum

57.

Match each impairment with where it arises.

List I

A. Aliasing

B. Quantisation noise

C. Crosstalk

List II

P. At the sampler, from too low a rate

Q. In the coder, from finite levels

R. In the channel, from limited bandwidth

Select the correct match.

A.A-R, B-Q, C-P
B.A-P, B-R, C-Q
C.A-P, B-Q, C-R
D.A-Q, B-P, C-R

Answer: C

The correct pairing is A-P, B-Q, C-R. Locating each impairment matters because it decides the remedy: a higher sampling rate or a better filter for the first, more bits for the second, and more bandwidth or longer guard time for the third. An impairment attributed to the wrong stage leads to an expensive change that fixes nothing.

Discuss in Forum

58.

Arrange the stages of a pulse code modulation transmitter in order.

1. Anti-alias filtering

2. Sampling

3. Quantising

4. Encoding into bits

Select the correct sequence.

A.2, 1, 3, 4
B.1, 3, 2, 4
C.1, 2, 4, 3
D.1, 2, 3, 4

Answer: D

The order is 1, 2, 3, 4, and each position is forced: filtering must precede sampling because aliasing is irreversible, quantising needs a sample to act on, and encoding needs a level to represent. A signal chain whose order can be reconstructed from the reasons for it never has to be memorised as a list.

Discuss in Forum

59.

Consider the following pairs of scheme and its principal weakness.

Pulse amplitude modulation - Sensitivity to amplitude noise

Pulse position modulation - Dependence on accurate synchronisation

Pulse code modulation - Large bandwidth requirement

Delta modulation - Inability to be multiplexed

How many of the pairs given above are correctly matched?

A.Only three
B.Only one
C.Only two
D.All four

Answer: A

The first three are correctly paired and the fourth is not, so three match. Delta modulation multiplexes as readily as any other digital scheme; its real weaknesses are slope overload and granular noise, the two opposing consequences of a fixed step size. A proposed weakness that would rule a scheme out of practical use, when the scheme is in practical use, is worth doubting on that ground alone.

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60.

Three schemes are compared for the same message bandwidth.

Scheme	Parameter varied	Noise immunity
PAM	Amplitude	Poor
PWM	Duration	Good
PPM	Position	Good

Which conclusion follows from the table?

A.Amplitude modulation would improve if its pulses were made narrower
B.Constant amplitude is what confers the immunity
C.A longer pulse duration always improves the noise immunity obtained
D.Immunity depends on the message bandwidth rather than on the scheme

Answer: B

Reading down the table, the two schemes holding amplitude constant are the two with good immunity, which identifies the mechanism rather than merely ranking the schemes. Duration is a varied parameter rather than a lever on immunity, the bandwidth is held equal across the comparison, and narrowing the pulses would not remove amplitude modulation's dependence on amplitude. A table read for the property the winners share is more informative than one read as a ranking.

Discuss in Forum

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