Pulse Modulation Techniques Questions and Answers

Answer: A

Amplitude modulation comes first, because coding begins by taking amplitude samples and then quantising them; the width and position schemes encode into other parameters and lead nowhere digital. Delta modulation is an alternative digital scheme rather than a precursor. Tracing which analogue scheme a digital one grew out of explains why sample-and-hold circuits sit at the front of every coder.

Answer: B

Position modulation encodes into timing while holding amplitude constant, so a receiver can threshold the pulses and discard amplitude noise entirely. All three amplitude variants carry the message in the very quantity noise adds to, and whether the sampling is natural or flat-top makes no difference to that. Noise immunity always comes from encoding into a parameter the noise does not share.

Answer: C

Coding replaces one amplitude sample with a group of bits, multiplying the pulse rate by the word length, and bandwidth follows the pulse rate. The sampling rate is the same for both, and amplitude is irrelevant to bandwidth. Guard bands belong to frequency division multiplexing. Coding buys noise immunity and regeneration by spending bandwidth, which is the same trade wideband FM makes by other means.

Answer: D

Both are true and the second is the reason for the first: once folded down, the alias is at a frequency the wanted signal also occupies and no filter can tell them apart. That is why the anti-alias filter must precede the sampler rather than follow it. The structure of the argument is identical to the receiver's image response, and recognising the shared shape saves learning the two facts separately.

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.

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.

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.

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.

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.

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.