MCQ in Digital Communications Part 1 | ECE Board Exam

This is the Multiple Choice Questions in Digital Communications Part 1 of the Series as one of the Electronics Systems and Technologies Examination topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electronics Systems and Technologies scope, Electronics Communications Books, Journals and other Electronics Communications References.

MCQ Topic Outline included in ECE Board Exam Syllabi

3. Digital Communications

• MCQ in Introduction to Digital Communications Systems
• MCQ in Digital Transmission
• MCQ in PAM, PWM, PPM, Pulse Code Modulation
• MCQ in Digital Communications
• MCQ in ASK, FSK, PSK, QAM
• MCQ in Basics of Information Theory
• MCQ in Error Detection
• MCQ in FDM, TDM, WDM, FDMA, CDMA, TDMA

Start Practice Exam Test Questions Part 1 of the Series

Choose the letter of the best answer in each questions.

1. _______ is continuous in time and assumes only a limited number of values in a given range (maintains a constant level and then changes to another constant level).

A. analog signal

B. analog data

C. digital signal

D. digital data

2. The factors affecting the successful interpreting of signals are:

A. signal level, bit rate, data rate

B. SNR, data rate, bandwidth

C. baud rate, data rate, bandwidth

D. SNR, data rate, baud rate

3. ______ is used when the entire medium (or bandwidth) is dedicated to two devices or when devices alternate in transmission.

A. baseband channel

B. low-pass channel

C. band-pass channel

D. wideband channel

4. Which of the following is the idea of modulating the carrier wave with data?

A. AM

B. PSK

C. PCM

D. AMI

5. A unit of signaling speed equal to the number of signal events per second?

A. bit rate

B. pulse rate

C. baud rate

D. Nyquist rate

6. The maximum rate at which digital data can be transmitted over a channel of a bandwidth [B] Hz refers to:

A. bandwidth efficiency

B. Nyquist Theorem

C. Bit error rate (BER)

D. Throughput

7. The maximum data rate of a channel depends on the following except:

A. number of levels in digital signal

B. level of noise

C. number of digital signal

D. bandwidth available

8. Television channels are 6 MHz wide. How many bits/sec can be sent if four-level digital signals are used? Assume a noiseless channel.

A. 6 Mbps

B. 12 Mbps

C. 24 Mbps

D. 48 Mbps

9. We have a 3 kHz channel whose signal to noise ratio is 20 dB. A binary signal is sent by this channel. What is the maximum achievable data rate?

A. 20 kbps

B. 10 kbps

C. 6 kbps

D. 3 kbps

10. Determine the required information capacity in order to transmit voice to a standard voice grade channel (Public Telephone System).

A. 9,453 bps

B. 15,586 bps

C. 22,390 bps

D. 46,341 bps

11. Converting from an analog to a digital signal for digital transmission is achieved by:

A. sampling the analog signal using Pulse Amplitude Modulation, and formatting the samples using Pulse Code Modulation

B. measuring the analog time differential and coding the difference using TDM.

C. A to D conversion using frequency division multiplexing.

D. A to D conversion using pulse position multiplexing.

12. The basic operations of PCM in the receiver section are:

A. Sampling, Quantizing and Encoding

B. Regeneration of impaired signals, Decoding, and Reconstruction

C. Reconstruction, Decoding, and Regeneration of impaired signals

D. Encoding, Quantizing and Sampling

13. What stage of PCM system ensures accurate reproduction of an analog signal for the receiver?

A. Quantization

B. Reconstruction

C. Encoding

D. Sampling

14. Determine the Nyquist rate of the frequency spectrum of a signal that has a bandwidth of 500Hz with the highest frequency at 600 Hz?

A. 500 samples/sec

B. 600 samples/sec

C. 1000 samples/sec

D. none of the above

15. Quantization in level refers to:

A. sampling rate

B. sampling depth

C. quantization interval

D. signal quantizer

16. Assume uniform quantizing in PCM system, what is the S/N if there are 256 levels of quantization?

A. 27.5 dB

B. 43.8 dB

C. 49.8 dB

D. 53.7 dB

17. In the quantization stage, SNR will increase by ____ for every additional bit used?

A. 3 dB

B. 6 dB

C. 9 dB

D. 12 dB

18. What is the dynamic range in dB of an 8-bit linear sign magnitude PCM spectrum whose maximum decoded voltage at the receiver is 2.75 Vp?

A. 22 dB

B. 35 dB

C. 42 dB

D. 49 dB

19. For a dynamic range of 200, how many bits are required in the PCM code?

A. 6

B. 7

C. 8

D. 9

20. Is numerical indication of how efficiently a PCM code is utilized:

A. Throughput

B. transmission rate of information bits

C. coding efficiency

D. gain

21. The process of compressing and then expanding a signal refers to:

A. compression

B. bit encoding

C. companding

D. multiplexing

22. Determine the compressed output voltage for a maximum input voltage of 4 V and an input voltage of 0.25 V.

A. 1.6 V

B. 2.04 V

C. 2.8 V

D. 1.91 V

23. In adaptive delta modulation, for better performance, the value of delta is:

A. fixed

B. not fixed

C. infinity

D. zero

24. 12 voice channels are sampled at 8,000 sampling rate and encoded into 8-bit quantization. Determine the rate of the data stream.

A. 64 kbps

B. 128 kbps

C. 384 kbps

D. 768 kbps

25. _______ is employed since the medium is bandpass and/or multiple users need to share the medium.

A. Analog-to-Digital conversion

B. Digital-to-Analog conversion

C. Digital-to-Digital conversion

D. Line Encoding

26. The simplest and most common form of ASK that operates as a switch, using the presence of a carrier wave for binary one and its absence for binary zero?

A. OFDM

B. DPCM

C. OOK

D. QAM

27. For a binary FSK modulator with space, rest and mark frequencies of 40, 50 and 60 MHz, respectively and an input bit rate of 20 Mbps, determine the minimum required BW.

A. 20 MHz

B. 40 MHz

C. 60 MHz

D. 80 MHz

28. Which of the following uses two-dimensional signaling?

A. FSK

B. QAM

C. PSK

D. ASK

29. If a QPSK modulation has a carrier frequency of 70 MHz, and an input rate of 40 Mbps, determine the minimum Nyquist bandwidth.

A. 5 MHz

B. 10 MHz

C. 20 MHz

D. 70 MHz

30. Used to represent possible symbols that may be selected by a given modulation scheme as points in 2D plane.

A. truth table

B. phasor diagram

C. constellation diagram

D. Argand diagram

31. What is often used to measure how quickly data can be transmitted in an assigned bandwidth? It’s also used to compare the performance of one digital modulation technique to another.

A. BW efficiency

B. information density

C. spectral efficiency

D. all of the above

32. For an 8-PSK with an information bit rate of 24kbps, determine the BW efficiency.

A. 1 b/cycle

B. 2 b/cycle

C. 3 b/cycle

D. 4 b/cycle

33. In the presence of noise, bit error rate of PSK and QPSK are about ____ superior to ASK and FSK.

A. 3 dB

B. 6 dB

C. -6 dB

D. -3 dB

34. What provides superior performance when the transmission channel (including transmitter and receiver) has significant nonlinear components? The effect of nonlinearities is a spreading of the signal bandwidth, which may result in adjacent channel interference. It is easier to control this spreading if the phase changes are smaller.

A. QPSK

B. MPSK

C. QAM

D. OQPSK

35. Which of the following signaling elements is considered “less than one bit”?

A. Manchester coding

B. NRZ-L

C. FSK

D. QPSK

36. In baseband digital transmission, which line coding format binary 0 represents by NO pulse and binary 1 is represented by a positive pulse?

A. NRZ Bipolar format

B. NRZ Polar format

C. Manchester format

D. NRZ Unipolar format

37. This is applied in complex transmission layouts, since it is easy to lose sense of polarity, where data represented by changes rather than levels. A more reliable detection of transition rather than level.

A. Differential Encoding

B. return to zero (RZ)

C. Manchester encoding

D. Non-return to zero Inverted (NRZ-I)

38. Which of the following signal remain in the assigned binary level for the entire period of the bit?

A. Manchester Encoding

B. Bi-phase Encoding

C. NRZ

D. RZ

39. This technique consists in translating each intelligence to a different position in the frequency spectrum? It refers to channel plans based on carrier multiple frequencies.

A. TDM

B. WDM

C. AM

D. FDM

40. A technology that enables many optical signals to be transmitted simultaneously by a single fiber cable.

A. FDM

B. TDM

C. WDM

D. CDMA

41. The technique of combining signals coming from low-speed channels to share time on a high-speed path. It divides RF into time slot that are allocated to multiple users.

A. FDM

B. TDM

C. WDM

D. CDMA

42. The ____ at the central office translates between analog customer signals and digital internal signal.

A. CSU

B. Modem

C. Codec

D. Translator

43. A hierarchy of digital lines designed to carry speech and other signals in digital forms.

A. T lines

B. E lines

C. M lines

D. more than one of the choices

44. A pure digital technique also known as spread spectrum because it takes the digitized version of an analog signal and spreads it out over a wider bandwidth at a lower power level. It spreads the signal by assigning each user a unique code sequence.

A. Direct sequence spread spectrum (DSSS)

B. Frequency hopping spread spectrum (FHSS)

C. Time hopping spread spectrum (THSS)

D. Code Division Multiple Access (CDMA)

45. What modulating technique involves simultaneously high-speed bit stream with multiple “channels?”

A. FDM

B. OFDM

C. PSK

D. FSK

46. The process of taking a group of bits from each input line for multiplexing is:

A. bit synchronization

B. interleaving

C. asynchronous transmission

D. synchronous transmission

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