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 general name given to both PM and PM is _____ modulation.
2. True or false. In FM, the carrier amplitude remains constant with modulation.
3. The amount of frequency shift during modulation is called the _____.
4. The amount of frequency shift in PM is directly proportional to the _____ of the modulating signal.
5. As the modulating signal amplitude goes positive, the carrier frequency _____. As the modulating signal amplitude goes negative, the carrier frequency
6. In PM, the carrier _____ is varied in proportion to the amplitude of the modulating signal.
7. A varying phase shift produces a(n) _____.
8. A phase modulator produces a frequency deviation only when the modulating signal is _____.
9. In PM, the frequency deviation is proportional to both the modulating signal _____ and _____.
10. When the modulating signal amplitude crosses zero, the phase shift and frequency deviation in a phase modulator are
- a. At a maximum
- b. At a minimum
- c. Zero
11. A phase modulator may use a low-pass filter to offset the effect of increasing carrier frequency deviation for increasing modulating
- a. Amplitude
- b. Frequency
- c. Phase shift
12. The FM produced by a phase modulator is known as _____.
13. True or false. An FM signal produces more sidebands than an AM signal.
14. The bandwidth of an FM signal is proportional to the _____.
15. The maximum frequency deviation of an FM signal is 10 kHz. The maximum modulating frequency is 3.33 kHz. The deviation ratio is_____.
16. An FM signal has a modulation index of 2.5. How many significant pairs of sidebands are produced?
(See Fig. 4-6.) (page 75-Frenzel)
17. In an FM signal that modulating frequency is a 1.5-kHz sine wave. The carrier frequency is 1000 kHz.
The frequencies of the third significant sidebands are _____ and _____ kHz.
18. Refer to Fig. 4-6. What is the relative amplitude of the fourth significant pair of sidebands in an FM signal with a deviation ratio of 4? (page 75-Frenzel)
19. The amplitudes of the sidebands in an FM signal are dependent upon a mathematical process known as _____.
20. A PM signal has a deviation ratio of 3. The maximum modulating signal is 5 kHz. The bandwidth of the signal is _____kHz.
21. If the maximum allowed deviation is 5 kHz but the actual deviation is 3.75 kHz, the percentage of modulation is _____ percent.
22. A negative sign on the carrier and sideband amplitudes in Fig. 4-6 means a(n) _____.
23. True or false. The carrier in an FM signal can never drop to zero amplitude.
24. Calculate the bandwidth of an PM signal with a maximum deviation of 10 kHz and a maximum
modulating signal frequency of 4 kHz. Use the two methods given in the text, significant sidebands, and Carson's role, and compare your answers. Explain the difference.
25. The main advantage of FM over AM is its immunity from _____.
26. Noise is primarily a variation in
- a. Amplitude.
- b. Frequency.
- c. Phase.
27. FM receivers reject noise because of built-in circuits.
28. The in an FM receiver causes a stronger signal to dominate a weaker signal on the same frequency.
29. Typically FM transmitters are more efficient than AM transmitters because they use class _____ amplifiers.
30. The biggest disadvantage of FM is its excessive use of _____.
31. True or false. An AM circuit is usually more complex and expensive than an FM circuit.
32. Noise interferes primarily with _____ modulating frequencies.
33. The method used to offset the effect of noise in FM transmissions by boosting high frequencies is known as _____.
34. To boost high frequencies a(n) _____ circuit is used.
35. To correct for the high-frequency boost, a(n) _____ circuit is used at the receiver.
36.The time constant of a pre-emphasis circuit is _____ s.
37. In an FM receiver, frequencies above _____ Hz are attenuated 6 dB per octave.