# Blake: MCQ in Digital Communications

(Last Updated On: January 3, 2020) This is the Multiple Choice Questions in Chapter 7: Digital Communications from the book Electronic Communication Systems by Roy Blake . 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.

#### 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

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

Solution:

3. TDM stands for:

a. Time-Division Multiplexing

b. Time-Domain Multiplexing

c. Ten-Digital Manchester

d. Ten Dual-Manchester

Solution:

4. Hartley’s Law is:

a. I = ktB

b. C = 2B log2M

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

d. SR = 2fmax

Solution:

5. The Shannon-Hartley theorem is:

a. I = ktB

b. C = 2Blog2M

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

d. SR = 2fmax

Solution:

6. The Shannon Limit is given by:

a. I = ktB

b. C = 2Blog2M

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

d. SR = 2fmax

Solution:

7. The Nyquist Rate can be expressed as:

a. I = ktB

b. C = 2Blog2M

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

d. SR = 2fmax

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

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.

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

Solution:

11. The immediate result of sampling is:

a. a sample alias

b. PAM

c. PCM

d. PDM

Solution:

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

a. PDM

b. PWM

c. PPM

d. PPS

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

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

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

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)

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)

Solution:

18. Codec stands for:

a. Coder-Decoder

b. Coded-Carrier

c. Code-Compression

d. none of the above

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

Solution:

20. Compared to PCM, delta modulation:

a. transmits fewer bits per sample

b. requires a much higher sampling rate

d. all of the above

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

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

Solution:

23. Which coding scheme requires DC continuity:

a. AMI

b. Manchester

c. unipolar NRZ

d. bipolar RZ

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

Solution:

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

a. 1

b. 2

c. 4

d. 8

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

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

Solution:

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

a. 1

b. 2

c. 4

d. 8

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

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

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

Solution:

32. A T-1 cable uses:

a. Manchester coding

b. bipolar RZ AMI coding

c. NRZ coding

d. pulse-width coding

Solution:

33. The number of frames in a superframe is:

a. 6

b. 12

c. 24

d. 48

Solution:

34. A typical T-1 line uses:

a. twisted-pair wire

b. coaxial cable

c. fiber-optic cable

d. microwave

Solution:

35. “Signaling” is used to indicate:

a. on-hook/off-hook condition

b. busy signal

c. ringing

d. all of the above

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

Solution:

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

a. much better

b. somewhat better

d. not as good

Solution:

COMPLETION

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

10. All practical communications channels are band-____________________.

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

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.

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

30. The ____________________ size varies in adaptive delta modulation.

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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.

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.

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?

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?

Solution:

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

Solution:

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

Solution:

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

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?

Solution:

### Complete List of MCQ in Electronic Communication Systems by Blake

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