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Frenzel Self-test in Communications Receivers

Frenzel Self-test in Communications Receivers

This is the Self-test in Chapter 7: Communications Receivers from the book COMMUNICATIONS ELECTRONICS by Louis E. Frenzel. 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

Direction: Either Supply the missing word(s) in each statement  or Choose the letter that best answers each question.

1. The ability of a receiver to choose a desired signal frequency while rejecting closely adjacent signal frequencies is known as _____.

2. Decreasing the Q of a resonant circuit causes its bandwidth to _____.

3. Good selectivity usually means _____ (wide, narrow) bandwidth.

4. True or false. A tuned circuit can provide voltage gain.

5. S. Cascading tuned circuits cause the selectivity to _____ (increase, decrease).

6. If the selectivity of a tuned circuit is too sharp, the _____ of the received signal may be attenuated.

7. A tuned circuit has a Q of 100 at its resonant frequency of 500 kHz. Its bandwidth is _____ kHz.

8. A parallel LC tuned circuit has a coil of 3 H and a capacitance of 75 pF. The coil resistance is 10-Ω. The circuit bandwidth is _____ MHz.

9. A tuned circuit has a resonant frequency of 10 MHz and a bandwidth of 100 kHz. The upper and lower cutoff frequencies are f1 (upper) = _____ MHz, f2 (lower) = _____ MHz.

10. To achieve a bandwidth of 3 kHz at 4 MHz, a Q of_____ is required.

11. To narrow the bandwidth of a tuned circuit, the coil resistance must be _____ (increased, decreased).

12. A filter has a 6-dB bandwidth of 500 Hz and a 60-dB bandwidth of 1200 Hz. The shape factor is _____.

13. The greater the gain of the receiver, the better its _____.

14. A receiver that uses only amplifiers and a detector is known as a(n) _____ receiver.

15. A receiver that uses a mixer to convert the received signal to a lower frequency is called a(n) _____.

16. The acronym IF means _____.

17. Tuning a super heterodyne is done by varying the frequency of its _____.

18. Most of the gain and selectivity in a superhet is obtained in the _____.

19. The _____ circuit in a receiver com compensates for a wide range of input signal levels.

20. The mixer output is usually the difference between the _____ frequency and the _____ frequency.

21. The AGC voltage controls the gain of the _____.

22. For best selectivity and stability, the IF should be

  • a. High
  • b. Medium
  • c. Low

23. An interfering signal that is spaced from the desired signal by twice the IF is called a(n) _____.

24. A superhet has an input signal of 15 MHz. The LO is tuned to 18.5 MHz. The IF is _____ MHz.

25. Images are caused by the lack of _____ at the mixer input.

26. A desired signal at 27 MHz is mixed with an LO frequency of 27.5 MHz. The image frequency is _____ MHz.

27. True or false. The LO may be above or below the signal frequency.

28. The main feature of a dual-conversion superhet is that it has two _____ circuits.

29. The image problem can be solved by proper choice of the _____.

30. A dual-conversion superhet has an input frequency of 50 MHz and LO frequencies of 59 MHz and 9.6 MHz. The two IFs are _____ MHz and _____ kHz.

31. List three sources of external noise.

32. List three main types of internal noise.

33. Noise from the sun and stars is called _____ noise.

34. Atmospheric noise comes primarily from _____.

35. List four sources of industrial noise.

36. The main source of internal noise is _____.

37. The SIN ratio is usually expressed in _____.

38. For best reception, the SIN ratio should be _____ (low, high).

39. Increasing the temperature of a component causes its noise power to _____.

40. Thermal noise is sometimes called _____ or _____ noise,

41. Narrowing the bandwidth of a circuit causes the noise level to _____.

42. The noise voltage produced across a 75- input resistance at a temperature of 25°C with a bandwidth of 15 MHz is _____ V.

43. Two types of. noise caused by tubes or transistors are _____ noise and _____ noise.

44. True or false. The noise at the output of a receiver will be less than the noise at the input.

45. True or false. The receiver amplifies noise as well as the signal.

46. The ratio of the SIN power at the input to the SIN power at the output is called the _____.

47. Noise temperature in degrees Kelvin is used to express the noise in a system at _____ (low, microwave) frequencies.

48. The noise figure of an amplifier is 2.6. The noise’ temperature is _____ K.

49. The SINAD method considers the signal, noise, and _____ levels in a receiver.

50. Noise is more or a problem at _____ frequencies.

51. The stages of a receiver that contribute the most noise are the _____ and the _____.

52. True or false. An amplifier with a noise temperature of 170K is better than one with a rating of 235 K.

53. RF amplifiers provide initial _____ and _____ in a receiver but also add _____.

54. A low-noise transistor preferred at microwave frequencies is the _____ made of _____.

55. Most of the gain and selectivity in a superhet is obtained in the _____ amplifier.

56. The selectivity in an IF amplifier is usually produced by using _____ between stages.

57. The bandwidth of a double-tuned transformer depends upon the degree of _____ between primary and secondary windings.

58. In a double-tuned circuit, minimum band width is obtained with _____ coupling, maximum bandwidth with _____ coupling, and peak output with _____ or _____ coupling.

59. An IF amplifier that clips the positive and negative peaks .of a signal is called a(n) _____.

60. Clipping occurs in an amplifier because the transistor is driven by a high-level signal into _____.

61. The gain of a bipolar class A amplifier can be varied by changing the _____.

62. The overall RF-IF gain of a receiver is approximately _____ dB.

63. Using the amplitude of the incoming signal to control the gain of the receiver is known as _____.

64. AGC circuits vary the gain of the_____ amplifier.

65. The dc AGC control voltage is derived from a(n) _____ circuit connected to the _____ or _____ output.

66. Reverse AGC is where a signal amplitude increase causes a(n) _____ in the IF amplifier collector current.

67. Forward AGC uses a signal amplitude increase to _____ the collector current, which decreases the IF amplifier gain.

68. The AGC of a differential amplifier is produced by controlling the current produced by the _____ transistor.

69. In a dual-gate MOSFET IF amplifier, the dc AGC voltage is applied to the _____.

70. Another name for AGC in an AM receiver is _____.

71. In an AM receiver, the AGC voltage is derived from the _____.

72. Large input signals cause the gain of a receiver to be _____ by the AGC.

73. An AFC circuit corrects for frequency drift in the _____ circuit.

74. The AFC de control voltage is derived from the _____ circuit in a receiver.

75. A(n) _____ is used in an AFC circuit to vary the LO frequency.

76. A circuit that blocks the audio until a signal is received is called a(n) circuit.

77. Two types of signals used to operate the squelch circuit are _____.

78. In a CTCS system, a low-frequency _____ is used to trigger the _____ circuit.

79. A BFO is required to receive _____ and _____ signals.

80. What components or circuits in Fig. 7-27 determine the bandwidth of the receiver? (page 166-Frenzel)

81. As R1 is varied so that the voltage on the arm of the pot increases toward +9 V, how does the frequency of the local oscillator vary?

82. If there was no audio output from the speaker but you knew that a signal was present, what two controls would you check first?

83. What component provides most of the gain in this receiver?

84. Is the squelch signal or noise derived?

85. Does this receiver contain a BFO? Could it receive CW or SSB signals?

86. If the dc AGC voltage on pin 5 of U2 was decreased, what would happen to the gain of U2?

87. Where would you inject an audio signal to test the complete audio section of this receiver?

88. What frequency signal would you use to test the IF section of this receiver, and where would you connect it?

89. What component would be inoperable if C31 became shorted?

90. Explain how you would connect a digital counter to this receiver so that it would read the frequency of the signal to which it was tuned.

91. In an FM transceiver, the only shared circuitry is usually the _____.

92. In an SSB transceiver, the shared circuits are the _____ and the _____.

93. The circuit used to generate one or more stable frequencies for the transmitter and receiver is known as a(n) _____.

94. A basic circuit of a frequency synthesizer is a(n) _____.

95. The output frequency of a synthesizer is changed by varying the _____ of the divider between the VCO and phase detector.

96. A frequency synthesizer has a phase detector input reference of 10 kHz. The divide ratio is 286. The output frequency is _____ MHz. The frequency change increment is _____ kHz.

97. The PLL is often combined with _____ circuits to produce multiple frequencies.

98. What three frequencies does the synthesizer in a transceiver usually generate?

Check your work.

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