Digital Communication Interview Questions & Answers for freshers on “Baseband Transmission”.
1. Application of phase encoded binary signals are
A. Optical communication
B. Magnetic recording
C. Satellite telemetry
D. All of the mentioned
Answer: D
Clarification: Some of the fields where phase encoded waveforms is being used are optical communication, magnetic tape recording, satellite telemetry etc.
2. In which waveform one is represented by half bit wide pulse positioned during the first half and zero is represented by half bit wide pulse positioned in the second half?
A. Bi-p-L
B. Bi-p-M
C. Bi-p-S
D. Delay modulation
Answer: A
Clarification: In bi-phase-level one is represented by half bit wide pulse positioned during the first half and zero is represented by half bit wide pulse positioned in the second half.
3. Which binary waveform uses three levels?
A. Bipolar RZ
B. RZ-AMI
C. Bipolar RZ & RZ-AMI
D. None of the mentioned
Answer: C
Clarification: In PCM waveforms signals generally use two levels. But few signals use three levels such as bipolar RZ, RZ-AMI, dicode, duobinary etc.
4. Which waveform type has the feature of clocking?
A. Manchester coding
B. Bbi-p-M
C. Delay modulation
D. NRZ-L
Answer: A
Clarification: In manchester coding transition occurs in the middle of every bit interval. Thus it has a feature of clocking.
5. Which waveform has the feature of error detection?
A. NRZ-L
B. RZ-AMI
C. Manchester coding
D. Duobinary
Answer: D
Clarification: Duobinary scheme does error detection without introducing any additional error bits into the data sequence.
6. Which waveform scheme introduces bandwidth compression?
A. Duobinary
B. Manchester coding
C. Phase encoded waveform
D. Multilevel codes
Answer: D
Clarification: Multilevel codes increases the bandwidth efficiency by reducing the bandwidth utilization for the given data rate.
7. Which waveform type has better noise immunity?
A. NRZ
B. RZ
C. Phase encoded
D. Multilevel codes
Answer: A
Clarification: NRZ waveforms has better error performance than RZ signal waveforms.
8. In pulse modulation, reciprocal of T(time) is
A. Bandwidth
B. Symbol rate
C. Signal voltage
D. None of the mentioned
Answer: B
Clarification: T is the time period of the signal. In pulse modulation, the symbol rate Rs can be given as reciprocal of T.
9. PCM word size can be described by
A. Time period
B. Symbol rate
C. Number of quantization levels
D. None of the mentioned
Answer: C
Clarification: Each analog sample is transformed into PCM word made up of a group of bits. The PCM word size can be described by number of quantization levels allowed for each sample.
10. Some of the M-ary waveforms are
A. PAM
B. PPM
C. PDM
D. All of the mentioned
Answer: D
Clarification: When we pulse modulate non binary signals we get M-ary waveform. Some of the examples of M-ary waveforms are PAM, PPM, PDM.
11. Which method should be implemented for reducing bandwidth?
A. Multilevel codes
B. Multilevel signalling
C. PAM
D. PDM
Answer: B
Clarification: The transmission bandwidth required for binary digital waveforms is large. To reduce the bandwidth, multilevel signalling method can be used.
12. In M-ary PPM waveform, modulation is effected by
A. Delaying
B. Advancing
C. Delaying & Advancing
D. None of the mentioned
Answer: C
Clarification: In M-ary PPM waveform, modulation is effected by delaying or advancing pulse occurrence by an amount that corresponds to information symbol.
13. For both PPM and PDM _______ is kept constant.
A. Amplitude
B. Time period
C. Frequency
D. Number of levels
Answer: A
Clarification: In PPM waveform delaying or advancing of pulse is done. In PDM the pulse width is varied. Thus in both the cases amplitude is maintained constant.
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