This is the Coaching materials in Digital and Data Communications Part 1 as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Digital and Data Communications Coaching Materials Part 1
1. The first digital code was the:
Morse code
2. Advantage of digital over analog transmission.
Noise immunity
3. Hartley’s Law is:
I = ktB
4. The Shannon-Hartley theorem is:
C = 2Blog(2M)
5. The Shannon Limit is given by:
C = B log2 (1 + S/N)
6. In North America, companding uses:
the m Law (mu law)
7. A typical codec in a telephone system sends and receives:
8-bit numbers
8. In delta modulation, “granular noise” is produced when:
the signal does not change
9. Which coding scheme requires DC continuity:
unipolar NRZ
10. Number of independent symbols that can be propagated out through a communications system which is a function of bandwidth.
Information capacity
11. Refers to the rate of change of a signal on a transmission medium after encoding and modulation have occurred.
Baud rate
12. What is the relationship of bit rate and baud in FSK and PSK?
Equal
13. What is the relationship of bit rate and baud in QPSK and 8-PSK?
Bit rate is greater than baud
14. A digital modulation technique also known as “on-off” keying.
Amplitude Shift Keying or ASK
15. From of digital modulation using its modulation signal (a binary pulse stream) that varies between two discrete voltage levels.
FSK
16. In FSK, a figure of merit used to express the degree of modulation.
H-factor
17. Most common modulation technique used for radio telegraphy.
FSK
18. It is a type of FSK where the mark and space frequencies are synchronized with the input binary rate.
Continuous-Phase Frequency-Shift Keying or CPFSK
19. The most common circuit used for demodulating binary FSK signals.
Phase locked loop
20. A form of digital modulation similar to PSK except the digital information is contained in both the amplitude and the phase of the transmitted carrier.
Quadrature Amplitude Modulation
21. If is often used to compare the performance of one digital modulation technique to another
Bandwidth efficiency, Information density of Spectral efficiency
22. It is the ratio of the transmission bit rate to the minimum bandwidth required for a particular modulation scheme.
Bandwidth efficiency, Information density of Spectral efficiency
23. For an 8-PSK system, operating with an information bit rate of 24 kbps, determine the bandwidth efficiency.
3 bits/cycle
24. For a 16-PSK and a transmission system with a 10 kHz bandwidth, determine the maximum bit rate.
40,000 bps
25. A common method of achieving carrier recovery for BPSK.
Squaring loop
26. A modulation technique where data rates I excess of 56 kbps can be achieved over telephone circuits.
Trellis code modulation
27. It is a theoretical expectation of the bit error rate in the system.
Probability of errors
28. It is a function of the carrier-to-noise power ratio and the number of possible encoding conditions used.
Probability of error
29. It is the ratio of the average carrier power to the thermal noise power.
Carrier-to-noise ratio
30. It is the thermal noise power normalized to 1-Hz bandwidth.
Noise power density
31. It is used to compare two or more digital modulation systems that use different transmission rates, modulation scheme or encoding techniques.
Energy per bit-to-noise power density ratio
32. The phase relationship between signaling elements for BPSK is the optimum signaling form and occurs only when two binary signal levels are allowed and when one signal is the exact negative of the other.
Antipodal signaling
33. An “eye pattern” shows a good channel when:
the eye is maximally open
34. What you see in an eye pattern is the effect of:
intersymbol interference
35. High-frequency radioteletype systems commonly use:
FSK
36. In digital modulation, such as FSK, the rate of change of frequency at the input is called
bit rate
37. The fundamental frequency of a binary square wave.
1/2 bit rate
38. In digital communications, employing FSK, baud rate is _____ of bit rate.
Equal
39. Form of angle modulated constant envelope digital modulation.
Phase-shift keying
40. The threshold point of QPSK system is
+ or – 0.785
41. A form of digital modulation similar to PSK, it transmit 2 separate information signal using 2 AM carriers at the same frequency but differ in phase by 90O.
QUAM
42. Table that list all the possible combinations of variables.
Truth table
43. The term used to define jitter above 10 Hz is _____.
Wander
44. He is credited with inventing PCM in 1937.
Alex H. Reeves
45. In PCM, the circuit that periodically samples the analog input and converts it to PAM.
Sample and hold
46. In PCM, it converts the PAM samples to parallel PCM codes.
Analog-to-Digital Converter (ADC)
47. Modern digital systems use a _____ to demodulate a PAM signal.
LPF
48. A signal which varies between 3 levels.
Bipolar code
49. There are how many transistors in CMOS inverter?
2
50. Variation of the PCM that uses a single but PCM code.
Delta modulation
51. In delta modulation method, what causes error in the demodulated signal?
Slope overload
52. In PCM, according to Nyquist sampling theorem to avoid distortions, the minimum sampling rate should be ____ value of the highest audio frequency.
Twice
53. The disadvantage of PC systems is that
it requires a large bandwidth
54. Companding is employed in PCM system
to protect small signals from quantizing distortion
55. An integrated circuit that performs the PCM encoding and decoding functions.
Codec
56. Method of encoding audio signals used in US standard 1.544 Mbps 24-channel PCM system.
Mu-law
57. A digital modulation technique in which the polarity of the transmitted pulse indicates whether the demodulator output should rise or fall at each pulse.
Delta modulation
58. In PCM sampling, the time when the FET is “on” is called
Acquisition
59. The most common method used for sampling voice signals in PCM systems.
Flat-top sampling
60. What is the result if the input of the ADC is changing while performing conversion?
Aperture distortion
61. The result whenever the sampling rate is less than twice the highest audio frequency.
Alias or Foldover distortion
62. It is a process of converting an infinite number of possibilities to a fine number of conditions.
Quantization
63. The magnitude of a quantum in quantization of PCM codes.
Resolution
64. It is a numerical indication of how efficiently a PCM code is utilized.
Coding efficiency
65. BW efficiency is also known as
information capacity
66. Devices used for digitizing speech signals only.
Vocoders
67. Type of PCM that uses single-bit PCM code to achieve digital transmission of analog signals.
Delta modulation
68. A digital modulation technique that does not need to recover the phase coherent carrier.
Differential phase shift keying
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