(Last Updated On: February 9, 2020)
This is the Self-test in Chapter 5: Frequency 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. Increasing the reverse bias on a voltage variable capacitor causes its capacitance to
- a. Increase
- b. Decrease
2. Connecting a V VC across a parallel LC circuit causes the resonant frequency to
- a. Increase
- b. Decrease
3. In the circuit of Fig. 5-3, a negative-going modulating signal causes the carrier frequency to
- a. Increase
- b. Decrease
4. A crystal is operating in its series resonant mode. A VVC is connected in series with it. The crystal frequency
- a. Increases
- b. Decreases
5. Which is capable of greater frequency deviation?
- a. LC oscillator
- b. Crystal oscillator
6. Another name for voltage-variable capacitor is _____.
7. Most VVC s have a nominal capacitance in the _____ to _____ pF range.
8. A crystal oscillator has superior _____ over an LC oscillator.
9. The acronym VCO means _____.
10. A voltage-variable crystal oscillator is referred to as a(n) _____.
11. Carrier frequency and frequency deviation may be increased by using a(n) _____ after the carrier oscillator.
12. A reactance modulator is set up to act like an inductive reactance. If the modulating signal increases in amplitude, the effective inductance decreases. This causes. The oscillator frequency to _____.
13. An IC VCO normally uses a combination of _____ and _____ to set the center operating frequency.
14. True or false. Voltage-variable capacitors should not be forward-biased.
15.True or false. For highly stable carrier generators, LC oscillators are preferred over crystal oscillators.
16. True or false. A reactance modulator is used with crystal oscillators.
17. True or false. IC VCO operates primarily at frequencies below 1 MHz.
18. Phase modulation is called _____ FM.
19. True or false. Phase modulation produces frequency variation as well as amplitude variation of the carrier.
20.In a simple RC network, the phase shift is between _____ and _____ degrees.
21. In the circuits of Fig. 5-7, phase is varied by changing the _____ or _____. (page 91-Frenzel)
22. Larger linear phase shifts are obtained with a(n) _____ circuit.
23. The control element in a phase modulator is usually a(n) _____.
24. In Fig. 5-10, the component which adjusts the deviation is _____. (page 93-Frenzel)
25.If a parallel LC circuit is at resonance, increasing C will cause the current to _____ (lead, lag) the applied voltage.
26.In Fig. 5-7(b), if C is decreased, will the phase shift increase or decrease? (page 91-Frenzel)
27. In the phase modulator of Fig. 5-8, the FET current is the phasor sum of the currents produced by _____ and _____.
28. The small phase shifts produced by indirect PM are increased by sending the PM signal to a(n) _____ circuit.
29. In the Foster-Seeley discriminator and ratio detector circuits, an input frequency variation produces a(n) _____ that causes an output voltage variation.
30. In the pulse-averaging discriminator, a low pass filter averages the fixed-width, fixed amplitude pulses from a(n) _____.
31. Should the input frequency increase or decrease for the average voltage output of the low-pass filter in a pulse-averaging discriminator to increase?
32. Quadrature refers to a _____° phase difference.
33. In Fig. 5-13, does input B lag or lead input A? (page 96-Frenzel)
34. The phase detector in a quadrature detector is usually a(n) _____.
35. The quadrature detector input circuit produces a varying _____ as the input frequency changes.
36. The varying-width pulses produced by the quadrature detector are converted into the original modulating signal by a(n) _____.
37. The circuit in a differential peak detector IC that temporarily stores the peak value of an input sine wave is called a(n) _____.
38. In the differential peak detector, the components _____ convert frequency variations into the amplitude variations that ultimately become the output.
39. The three main elements of a PLL are _____.
40. The _____ circuit In a PLL recognizes _____ or _____ changes between the input and VCO signals.
41. The part _____ of a PLL is a simple frequency modulator.
42. It is the _____ signal in the PLL that varies the VCO frequency.
43. The range of frequencies over which a PLL will cause the input and VCO signals to remain synchronized is known as the _____ range.
44. If the PLL input is zero, the VCO will operate at its _____ frequency.
45. The range of frequencies over which a PLL will latch onto or recognize an input signal is called the _____ range.
46. Since a PLL will only respond to signals over a narrow frequency range, it acts like a(n) _____.
47. In a PLL frequency demodulator, the error signal is the _____.
48. In a PLL demodulating an FM signal, the VCO output is an exact reproduction of the _____.
49. True or false. The Foster-Seeley discriminator is sensitive to input amplitude as well as frequency variations.
50. True or false. The ratio detector requires a limiter.
51. True or false. The lock range of a PLL is narrower than the capture range.