(Last Updated On: February 9, 2020)
This is the Self-test in Chapter 3: Amplitude Modulation Circuits 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. In the modulator, circuit of Fig. 3-2, the carrier and modulating signals are (page 39-Frenzel)
- a. Added
- b. Subtracted
- c. Multiplied
- d. Divided
2. In Fig. 3-2,D1 acts as a(n) (page 39-Frenzel)
- a. Capacitor
- b. Rectifier
- c. Variable resistor
- d. Adder
3. In Fig. 3-4, D1 acts as a(n) (page 41-Frenzel)
- a. Capacitor
- b. Rectifier
- c. Variable resistor
- d. Adder
4. AM can be produced by passing the carrier through a circuit whose _____ or _____ can be varied in accordance with the modulating signal.
5. The name of the nonlinear response of a device that produces AM with only second-order products is _____.
6. A component that has an exponential response ideal for producing AM is the _____.
7. In Fig. 3-2, the negative peaks of the AM signal are supplied by the _____. (page 39-Frenzel)
8. In Fig. 3-5, the FET acts like a(n) _____. (page 41-Frenzel)
9. In Fig. 3-5, AM is produced by varying the _____of the op-amp circuit. (page 41-Frenzel)
10. In Fig. 3-5, a positive-going modulating signal causes the current in the FET to _____, its resistance to _____, and the gain of the circuit to _____.(page 41-Frenzel)
11. When forward-biased, a PIN diode acts like a(n) _____.
12. PIN diode modulators are used only at frequencies above about _____.
13. A PIN diode modulator is a variable
14. High current in a PIN diode means that its resistance is_____.
15. The AM signals generated by low-level modulating circuits must have their power level increased by a(n) _____ before being transmitted.
16. In a high-level AM transmitter, the output stage is usually a class _____ amplifier.
17. A high-level modulator like that in Fig. 3-8 is referred to as a _____ modulator. (page 43-Frenzel)
18. The output of a high-level modulator causes the _____ applied to the final RF amplifier to vary with the amplitude of the modulating signal.
19. The final amplifier of a high-level modulation CB transmitter has an input power of 5 W. The modulator must be able to supply a power of _____ W for 100 percent modulation.
20. The final RF power amplifier has a supply voltage of 12V. For 100 percent AM using a high-level modulator, the peak ac output of the modulation transformer must be _____ V.
21. To achieve 100 percent high-level modulation of an RF power amplifier, its _____ must also be modulated.
22. The purpose of a _____ is to recover the original modulating signal from an AM wave.
23. The most widely used amplitude demodulator is called a _____.
24. The most critical component in the circuit of Fig. 3-11 is _____.(page 46-Frenzel)
25. The charging and discharging of C1 in Fig. 3-11 produces _____ which causes _____ of the modulating signal. (page 46-Frenzel)
26. Another name for the demodulator in Fig. 3-11 is _____ detector.
27. List the two main benefits of the full-wave amplitude demodulator over the half wave circuit.
28. True or false. An amplitude demodulator is a complete radio receiver.
29. A balanced modulator eliminates which of the following from its output?
- a. Upper sideband
- b. Lower sideband
- c. Carrier
- d. Both sidebands
30. The output signal of a balanced modulator is.
- a. AM
- b. SSB
- c. FM
- d. DSB
31. Which has better carrier suppression?
- a. Lattice modulator
- b. IC balanced modulator
32. A balanced modulator using a diode bridge is called a(n) _____. (page 48-Frenzel)
33. In the balanced modulator of Fig. 3-14, the diodes are used as _____.
34. A balanced modulator has a carrier frequency of 1.9 MHz and a modulating sine wave of 2.6 kHz. The output signals are _____ and _____kHz.
35. In Fig. 3-18, transistors _____ supply a constant current. (page 51-Frenzel)
36.In Fig. 3-18, transistors Q1 to Q4 operate as_____. (page 51-Frenzel)
37. True or false. An IC analog multiplier may be used for DSB signal generation.
38. The most common way of generating an SSB signal is the _____ method.
39. A filter capable of passing the desired sideband while rejecting the other sideband must have good_____.
40. A balanced modulator has a 3-MHz carrier input and a modulating signal input of 1.5 kHz to pass the lower sideband, a filter must have a center frequency of _____ MHz.
41. The most popular filter used to select the desired sideband in an SSB generator uses _____ for selectivity.
42. Name the two ways of generating either the upper or lower sideband in a filter type SSB generator.
43. A quartz crystal acts like a highly selective _____ circuit.
44. In a filter-type SSB generator, a crystal lattice filter is used. The two crystal frequencies are 3.0 and 3.0012 MHz. The filter bandwidth is approximately _____ kHz.
45. Mechanical filters provide selectivity because they _____ at a specific frequency.
46. A ceramic filter is similar in operation to a(n) _____ filter.
47. The operating frequency range of a mechanical filter is _____ to _____ kHz.
48. In the phasing method of SSB generation, _____ is used to cancel the undesired sideband.
49. A _____ circuit is commonly used to demodulate or recover an SSB signal.
50. The circuit used to demodulate an SSB signal is typically called a(n) _____.
51. The mixing process is
- a. Linear.
- b. Nonlinear.
52. In up conversion, which signal is selected?
- a. f1 – f2
- b. f1 + f2
53. Which transistor mixer is preferred?
- a. Bipolar
- b. FET
54. Another name for the mixing process is _____.
55. The purpose of a mixer is to perform _____.
56.The output signals produced by a mixer with inputs f1 and f2 are _____, _____, _____, and _____.
57. The type of mixer most used at microwave frequencies is a(n) _____.
58. The two mixers preferred at VHF and UHF are _____.
59. Transistor mixers provide _____, while diode mixers do not.
60. A mixer producing down conversion has an input of 1390 kHz and an LO frequency of 1845 kHz. The output is _____ kHz.
61. A single-transistor circuit that combines the mixer and LO functions is known as a(n) _____.
62. The mixer circuit in the popular NE602 IC is _____.
63. In addition to a mixer and a voltage regulator, the NE602 mixer IC contains a(n) _____.
64. The output of a NE602 mixer IC is 5.5 MHz. The local oscillator is set to 26.8 MHz. The input frequency is _____.
65. True or false. Mixing is the same as AM.
66. True or false. Any balanced modulator may be used as a mixer.