# Frenzel Self-test in Frequency Modulation Circuits

(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

(page 87-Frenzel)

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.

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#### One Response

1. Rohini Sharma