Blake: MCQ in Digital Communications

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(Last Updated On: January 3, 2020)

Blake: MCQ in Digital Communications

This is the Multiple Choice Questions in Chapter 7: Digital Communications from the book Electronic Communication Systems by Roy BlakeBlake: MCQ in Digital Communications. If you are looking for a reviewer in Communications Engineering this will definitely help. I can assure you that this will be a great help in reviewing the book in preparation for your Board Exam. Make sure to familiarize each and every questions to increase the chance of passing the ECE Board Exam.

See also: MCQ in Electronic Communication Systems by George Kennedy

Start Practice Exam Test Questions

Choose the letter of the best answer in each questions.

MULTIPLE CHOICE

1. The first digital code was the:

a. ASCII code

b. Baudot code

c. Morse code

d. none of the above

View Answer:

Answer: Option C

Solution:

2. In digital transmission, signal degradation can be removed using:

a. an amplifier

b. a filter

c. a regenerative repeater

d. all of the above

View Answer:

Answer: Option C

Solution:

3. TDM stands for:

a. Time-Division Multiplexing

b. Time-Domain Multiplexing

c. Ten-Digital Manchester

d. Ten Dual-Manchester

View Answer:

Answer: Option A

Solution:

4. Hartley’s Law is:

a. I = ktB

b. C = 2B log2M

c. C = B log2(1 + S/N)

d. SR = 2fmax

View Answer:

Answer: Option A

Solution:

5. The Shannon-Hartley theorem is:

a. I = ktB

b. C = 2Blog2M

c. C = Blog2(1 + S/N)

d. SR = 2fmax

View Answer:

Answer: Option B

Solution:

6. The Shannon Limit is given by:

a. I = ktB

b. C = 2Blog2M

c. C = Blog2(1 + S/N)

d. SR = 2fmax

View Answer:

Answer: Option C

Solution:

7. The Nyquist Rate can be expressed as:

a. I = ktB

b. C = 2Blog2M

c. C = Blog2(1 + S/N)

d. SR = 2fmax

View Answer:

Answer: Option D

Solution:

8. Natural Sampling does not use:

a. a sample-and-hold circuit

b. true binary numbers

c. a fixed sample rate

d. an analog-to-digital converter

View Answer:

Answer: Option A

Solution:

9. Which is true about aliasing and foldover distortion?

a. They are two types of sampling error.

b. You can have one or the other, but not both.

c. Aliasing is a technique to prevent foldover distortion.

d. They are the same thing.

View Answer:

Answer: Option D

Solution:

10. Foldover distortion is caused by:

a. noise

b. too many samples per second

c. too few samples per second

d. all of the above

View Answer:

Answer: Option C

Solution:

11. The immediate result of sampling is:

a. a sample alias

b. PAM

c. PCM

d. PDM

View Answer:

Answer: Option B

Solution:

12. Which of these is not a pulse-modulation technique:

a. PDM

b. PWM

c. PPM

d. PPS

View Answer:

Answer: Option D

Solution:

13. Quantizing noise (quantization noise):

a. decreases as the sample rate increases

b. decreases as the sample rate decreases

c. decreases as the bits per sample increases

d. decreases as the bits per sample decreases

View Answer:

Answer: Option C

Solution:

14. The dynamic range of a system is the ratio of:

a. the strongest transmittable signal to the weakest discernible signal

b. the maximum rate of conversion to the minimum rate of conversion

c. the maximum bits per sample to the minimum bits per sample

d. none of the above

View Answer:

Answer: Option A

Solution:

15. Companding is used to:

a. compress the range of base-band frequencies

b. reduce dynamic range at higher bit-rates

c. preserve dynamic range while keeping bit-rate low

d. maximize the useable bandwidth in digital transmission

View Answer:

Answer: Option C

Solution:

16. In North America, companding uses:

a. the Logarithmic Law

b. the A Law

c. the α Law (alpha law)

d. the µ Law (mu law)

View Answer:

Answer: Option D

Solution:

17. In Europe, companding uses:

a. the Logarithmic Law

b. the A Law

c. the α Law (alpha law)

d. the µ Law (mu law)

View Answer:

Answer: Option B

Solution:

18. Codec stands for:

a. Coder-Decoder

b. Coded-Carrier

c. Code-Compression

d. none of the above

View Answer:

Answer: Option A

Solution:

19. A typical codec in a telephone system sends and receives:

a. 4-bit numbers

b. 8-bit numbers

c. 12-bit numbers

d. 16-bit numbers

View Answer:

Answer: Option B

Solution:

20. Compared to PCM, delta modulation:

a. transmits fewer bits per sample

b. requires a much higher sampling rate

c. can suffer slope overload

d. all of the above

View Answer:

Answer: Option D

Solution:

21. In delta modulation, “granular noise” is produced when:

a. the signal changes too rapidly

b. the signal does not change

c. the bit rate is too high

d. the sample is too large

View Answer:

Answer: Option B

Solution:

22. Compared to PCM, adaptive delta modulation can transmit voice:

a. with a lower bit rate but reduced quality

b. with a lower bit rate but the same quality

c. only over shorter distances

d. only if the voice is band-limited

View Answer:

Answer: Option B

Solution:

23. Which coding scheme requires DC continuity:

a. AMI

b. Manchester

c. unipolar NRZ

d. bipolar RZ

View Answer:

Answer: Option C

Solution:

24. Manchester coding:

a. is a biphase code

b. has a level transition in the middle of every bit period

c. provides strong timing information

d. all of the above

View Answer:

Answer: Option D

Solution:

25. The number of framing bits in DS-1 is:

a. 1

b. 2

c. 4

d. 8

View Answer:

Answer: Option A

Solution:

26. Framing bits in DS-1 are used to:

a. detect errors

b. carry signaling

c. synchronize the transmitter and receiver

d. all of the above

View Answer:

Answer: Option C

Solution:

27. So-called “stolen” bits in DS-1 are used to:

a. detect errors

b. carry signaling

c. synchronize the transmitter and receiver

d. all of the above

View Answer:

Answer: Option B

Solution:

28. The number of bits per sample in DS-1 is:

a. 1

b. 2

c. 4

d. 8

View Answer:

Answer: Option D

Solution:

29. The number of samples per second in DS-1 is:

a. 8 k

b. 56 k

c. 64 k

d. 1.544 x 106

View Answer:

Answer: Option A

Solution:

30. The bit rate for each channel in DS-1 is:

a. 1.544 Mb/s

b. 64 kb/s

c. 56 kb/s

d. 8 kb/s

View Answer:

Answer: Option B

Solution:

31. In DS-1, bits are transmitted over a T-1 cable at:

a. 1.544 MB/s

b. 64 kb/s

c. 56 kb/s

d. 8 kb/s

View Answer:

Answer: Option A

Solution:

32. A T-1 cable uses:

a. Manchester coding

b. bipolar RZ AMI coding

c. NRZ coding

d. pulse-width coding

View Answer:

Answer: Option B

Solution:

33. The number of frames in a superframe is:

a. 6

b. 12

c. 24

d. 48

View Answer:

Answer: Option B

Solution:

34. A typical T-1 line uses:

a. twisted-pair wire

b. coaxial cable

c. fiber-optic cable

d. microwave

View Answer:

Answer: Option A

Solution:

35. “Signaling” is used to indicate:

a. on-hook/off-hook condition

b. busy signal

c. ringing

d. all of the above

View Answer:

Answer: Option D

Solution:

36. A vocoder implements compression by:

a. constructing a model of the transmission medium

b. constructing a model of the human vocal system

c. finding redundancies in the digitized data

d. using lossless techniques

View Answer:

Answer: Option B

Solution:

37. Compared to standard PCM systems, the quality of the output of a vocoder is:

a. much better

b. somewhat better

c. about the same

d. not as good

View Answer:

Answer: Option D

Solution:

COMPLETION

1. Digitizing a signal often results in ____________________ transmission quality.

View Answer:

Answer: improved / better

Solution:

2. To send it over an analog channel, a digital signal must be ____________________ onto a carrier.

View Answer:

Answer: modulated

Solution:

3. To send it over a digital channel, an analog signal must first be ____________________.

View Answer:

Answer: digitized

Solution:

4. In analog channels, the signal-to-noise ratio of an analog signal gradually ____________________ as the length of the channel increases.

View Answer:

Answer: decreases / get worse

Solution:

5. The ____________________ value of a pulse is the only information it carries on a digital channel.

View Answer:

Answer: binary

Solution:

6. A ____________________ repeater is used to restore the shape of pulses on a digital cable.

View Answer:

Answer: regenerative

Solution:

7. There are techniques to detect and ____________________ some errors in digital transmission.

View Answer:

Answer: correct

Solution:

8. Converting an analog signal to digital form is another source of ____________________ in digital transmission systems.

View Answer:

Answer: error / noise

Solution:

9. ____________________-division multiplexing is easily done in digital transmission.

View Answer:

Answer: Time

Solution:

10. All practical communications channels are band-____________________.

View Answer:

Answer: limited

Solution:

11. ____________________ Law gives the relationship between time, information capacity, and bandwidth.

View Answer:

Answer: Hartley’s

Solution:

12. Ignoring noise, the _________________________ theorem gives the maximum rate of data transmission for a given bandwidth.

View Answer:

Answer: Shannon-Hartley

Solution:

13. The ____________________ limit gives the maximum rate of data transmission for a given bandwidth and a given signal-to-noise ratio.

View Answer:

Answer: Shannon

Solution:

14. ____________________ sampling is done without a sample-and-hold circuit.

View Answer:

Answer: Natural

Solution:

15. The ____________________ Rate is the minimum sampling rate for converting analog signals to digital format.

View Answer:

Answer: Nyquist

Solution:

16. ____________________ distortion occurs when an analog signal is sampled at too slow a rate.

View Answer:

Answer: Foldover

Solution:

17. ____________________ means that higher frequency baseband signals from the transmitter “assume the identity” of low-frequency baseband signals at the receiver when sent digitally.

View Answer:

Answer: Aliasing

Solution:

18. The output of a sample-and-hold circuit is a pulse-____________________ modulated signal.

View Answer:

Answer: amplitude

Solution:

19. ____________________ modulation is the most commonly used digital modulation scheme.

View Answer:

Answer: Pulse-code

Solution:

20. ____________________ noise results from the process of converting an analog signal into digital format.

View Answer:

Answer: Quantizing

Solution:

21. ____________________ is used to preserve dynamic range using a reasonable bandwidth.

View Answer:

Answer: Companding

Solution:

22. In North America, compression is done using the ____________________-law equation.

View Answer:

Answer: µ / mu

Solution:

23. In Europe, compression is done using the ____________________-law equation.

View Answer:

Answer: A

Solution:

24. A ____________________ is an IC that converts a voice signal to PCM and vice versa.

View Answer:

Answer: codec

Solution:

25. In a PCM system, the samples of the analog signal are first converted to ____________________ bits before being compressed to 8 bits.

View Answer:

Answer: 12

Solution:

26. The number of bits per sample transmitted in delta modulation is ____________________.

View Answer:

Answer: 1 / one

Solution:

27. Delta modulation requires a ____________________ sampling rate than PCM for the same quality of reproduction.

View Answer:

Answer: higher

Solution:

28. ____________________ noise is produced by a delta modulator if the analog signal doesn’t change.

View Answer:

Answer: Granular

Solution:

29. In delta modulation, ____________________ overload can occur if the analog signal changes too fast.

View Answer:

Answer: slope

Solution:

30. The ____________________ size varies in adaptive delta modulation.

View Answer:

Answer: step

Solution:

31. Adaptive delta modulation can transmit PCM-quality voice at about ____________________ the bit rate of PCM.

View Answer:

Answer: half

Solution:

32. Unipolar NRZ is not practical because most channels do not have ____________________ continuity.

View Answer:

Answer: DC

Solution:

33. In AMI, binary ones are represented by a voltage that alternates in ____________________.

View Answer:

Answer: polarity

Solution:

34. Long strings of ____________________ should be avoided in AMI.

View Answer:

Answer: zeros

Solution:

35. Manchester code has a level ____________________ in the center of each bit period.

View Answer:

Answer: transition

Solution:

36. Manchester coding provides ____________________ information regardless of the pattern of ones and zeros.

View Answer:

Answer: timing

Solution:

37. There are ____________________ channels in a DS-1 frame.

View Answer:

Answer: 24

Solution:

38. DS-1 uses a ____________________ bit to synchronize the transmitter and receiver.

View Answer:

Answer: framing

Solution:

39. In DS-1, each channel is sampled ____________________ times per second.

View Answer:

Answer: 8000

Solution:

40. Data is carried over a T-1 line at a rate of ____________________ bits per second.

View Answer:

Answer: 1.544 x 106

Solution:

41. A group of 12 DS-1 frames is called a ____________________.

View Answer:

Answer: superframe

Solution:

42. From a group of twelve frames, signaling bits are “stolen” from every ____________________ frame.

View Answer:

Answer: sixth

Solution:

43. ____________________ compression transmits all the data in the original signal but uses fewer bits to do it.

View Answer:

Answer: Lossless

Solution:

SHORT ANSWER

1. Use Hartley’s Law to find how much time it would take to send 100,000 bits over a channel with a bandwidth of 2,000 hertz and a channel constant of k = 10.

View Answer:

Answer: 5 seconds

Solution:

2. Use the Shannon-Hartley theorem to find the bandwidth required to send 12,000 bits per second if the number of levels transmitted is 8.

View Answer:

Answer: 2000 hertz

Solution:

3. What is the Shannon Limit of a channel that has a bandwidth of 4000 hertz and a signal-to-noise ratio of 15?

View Answer:

Answer: 16 kbps

Solution:

4. What is the minimum required number of samples per second to digitize an analog signal with frequency components ranging from 300 hertz to 3300 hertz?

View Answer:

Answer: 6600 samples/second

Solution:

5. What is the approximate dynamic range, in dB, of a linear PCM system that uses 12 bits per sample?

View Answer:

Answer: 74 dB

Solution:

6. What is the approximate data rate for a system using 8 bits per sample and running at 8000 samples per second?

View Answer:

Answer: 64 kbps

Solution:

7. If bits were “stolen” from every DS-1 frame, what would the useable data-rate be for each channel in the frame?

View Answer:

Answer: 56 kbps

Solution:

8. Assuming maximum input and output voltages of 1 volt, what is the output voltage of a µ-law compressor if the input voltage is 0.388 volt?

View Answer:

Answer: 0.833 volt

Solution:

Complete List of MCQ in Electronic Communication Systems by Blake

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