7. Phase modulation is an indirect form of:
a. amplitude modulation.
b. pulse modulation.
c. frequency modulation.
d. angle modulation.
Answer: c
8. The first working FM system was developed by:
a. Marconi.
b. Armstrong.
c. Sarnoff.
d. Hartley.
Answer: b
9. In an FM modulator, the amplitude of the intelligence signal determines the:
a. rate of the carrier frequency deviation.
b. power level of the FM signal.
c. phase angle of the carrier frequency component.
d. amount of carrier frequency deviation.
Answer: d
10. In an FM modulator, the intelligence frequency determines the:
a. rate of carrier frequency deviation.
b. power level of the FM signal.
c. phase angle of the carrier frequency component.
d. amount of carrier frequency deviation.
Answer: a
11. An FM signal has a center frequency of 154.5 MHz, but is swinging between 154.45 MHz and 154.55 MHz at a rate of 500 times per second. Its input intelligence frequency is:
a. 100 kHz.
b. 50 kHz.
c. 154.5 MHz.
d. 500 Hz.
Answer: d
12. An FM signal has a center frequency of 154.5 MHz but is swinging between 154.45 MHz and 154.55 MHz at a frequency of 500 times per second. Its input carrier frequency is:
a. 100 kHz.
b. 50 kHz.
c. 154.5 MHz.
d. 500 Hz.
Answer: c
TEST ITEM FILE – Chapter 5
13. An FM signal has a center frequency of 154.5 MHz but is swinging between 154.45 MHz and 154.55 MHz at a rate of 500 times per second. Its index of modulation is:
a. 50,000.
b. 100.
c. 500
d. 100,000.
Answer: b
14. The amount of frequency deviation is proportional to the amplitude of the intelligence signal in:
a. an FM signal.
b. a PM signal.
c. both FM and PM signals.
d. neither FM nor PM signals.
Answer: c
15. To solve for the frequency components of an FM signal, what high-level mathematical tool is used?
a. Laplace transforms
b. Calculus
c. Bessel functions d. Fourier transforms Answer: c
16. An FM signal has an intelligence frequency of 5 kHz and a maximum deviation of 30 kHz.
Its index of modulation is:
a. 60.
b. 35.
c. 150.
d. 6.
Answer: d
TEST ITEM FILE – Chapter 5
Figure 5-1
17. An FM signal has an intelligence frequency of 5 kHz and a maximum deviation of 30 kHz.
Its bandwidth, using the Bessel chart of Figure 5-1, is:
a. 6 kHz.
b. 60 kHz.
c. 90 kHz.
d. 45 kHz.
Answer: c
18. An FM signal has an intelligence frequency of 5 kHz and a maximum deviation of 30 kHz. How many frequency components are there in the output spectra? (Use the Bessel Chart of Figure 5-1.)
a. 9
b. 18
c. 19
d. 6
Answer: c
19. An FM signal has an intelligence frequency of 2 kHz and a maximum deviation of 10 kHz.
If its carrier frequency is set at 162.4 MHz, what is the frequency of its highest frequency component within its bandwidth? (Use the Bessel Chart of Figure 5-1.)
a. 162.401 MHz b. 162.400 MHz c. 162.408 MHz d. 162.404 MHz e. 162.416 MHz Answer: c
TEST ITEM FILE – Chapter 5
20. An FM signal has an intelligence frequency of 2 kHz and a maximum deviation of 10 kHz.
If its carrier frequency is set at 162.4 MHz, what is its bandwidth? (Use the Bessel Chart of Figure 5-1.)
a. 32 kHz.
b. 20 kHz.
c. 16 kHz.
d. 10 kHz.
Answer: a 21. Carson's rule is:
a. a quick approximation method to find the bandwidth of an FM signal.
b. a quick approximation method to find the index of modulation of an FM signal.
c. a quick approximation method to find the bandwidth of a PM signal.
d. a quick approximation method to find the index of modulation of a PM signal.
Answer: a
Figure 5-2
22. The FM signal given in Figure 5-2 is applied to a 50 ohm load. Its carrier frequency is:
a. 15 kHz.
b. 300 MHz.
c. 150 kHz.
d. 150 MHz.
Answer: d
23. The FM signal given in Figure 5-2 is applied to a 50 ohm load. Its output power level is approximately:
a. 450 watts.
b. 2025 watts.
c. 2863 watts.
d. 4050 watts.
Answer: b
TEST ITEM FILE – Chapter 5
25. The FM signal given in Figure 5-2 is applied to a 50 ohm load. It has an intelligence frequency of:
a. 30 kHz.
b. 150 MHz.
c. 15 kHz.
d. 10 kHz.
Answer: c
26. The FM signal given in Figure 5-2 is applied to a 50 ohm load. It has a frequency deviation of:
a. 60 kHz.
b. 15 kHz.
c. 30 kHz.
d. 3.75 kHz.
Answer: a
27. The FM signal given in Figure 5-2 is applied to a 50 ohm load. Using Carson's rule, it has a bandwidth of:
a. 120 kHz.
b. 150 kHz.
c. 60 kHz.
d. 75 kHz.
Answer: b
28. Viewing an FM signal on a spectrum analyzer, if the carrier frequency component is zero and there are four or five sidebands on either side of the carrier frequency, the index of modulation is:
a. 0.
b. 2.2.
c. 5.5
d. 8.65.
Answer: b
29. Standard FM broadcast stations use a maximum intelligence frequency of:
a. 5 kHz.
b. 15 kHz.
c. 75 kHz.
d. 150 kHz.
Answer: b
TEST ITEM FILE – Chapter 5
30. Standard FM broadcast stations use a maximum frequency deviation of:
a. 5 kHz.
b. 200 kHz.
c. 75 kHz.
d. 150 kHz.
Answer: c
31. Narrowband FM stations:
a. use a maximum deviation of 10 kHz.
b. use intelligence frequencies ranging from 100 Hz to 3 kHz.
c. are found in police, aircraft, taxicabs, weather service, and industrial applications.
d. all of the above.
Answer: d
32. The modulation index that occurs when the deviation and intelligence frequencies are maximum is called:
a. the maximum bandwidth.
b. the maximum modulation index.
c. the deviation ratio.
d. the maximum side frequency component.
Answer: c
33. The most important advantage of FM over AM is:
a. its limited bandwidth.
b. its conservation of energy.
c. its superior noise characteristics.
d. its frequency stability.
Answer: c
34. The noise characteristics of an FM communication system are mainly due to:
a. its modulator stage.
b. its narrow bandwidth characteristics.
c. its low level of modulation index.
d. its limiter and detector stages.
Answer: d
35. The worst case signal-to-noise ratio at the output of an FM detector occurs when:
a. the desired signal is 90 degrees out of phase with the noise signal.
b. the desired signal is 90 degrees out of phase with the resultant signal of adding the signal to the noise.
c. the noise signal is 90 degrees out of phase with the resultant signal of adding the signal to the noise.
d. the desired signal is 90 degrees out of phase with the intelligence signal.
TEST ITEM FILE – Chapter 5
36. Determine the worst case output signal-to-noise ratio for a broadcast FM receiver with a maximum deviation of 75 kHz and a maximum intelligence frequency of 15 kHz if the input signal-to-noise ratio is 2:1.
a. 5:1
b. 10:1
c. 14.7:1
d. 3:1
Answer: b
37. Determine the worst case output signal-to-noise ratio for a broadcast FM receiver with a maximum deviation of 75 kHz and a maximum intelligence frequency of 10 kHz if the input signal-to-noise ratio is 2:1.
a. 10:1
b. 15:1
c. 30:1
d. 2:1
Answer: b
38. Determine the worst case output signal-to-noise ratio for a broadcast FM receiver with a maximum deviation of 75 kHz and a maximum intelligence frequency of 15 kHz if the input signal-to-noise ratio is 3:1.
a. 5:1
b. 10:1
c. 14.7:1
d. 3:1
Answer: c
39. Pre-emphasis is:
a. increasing the relative strength of low-frequency components before being fed into the modulator of an FM transmitter.
b. decreasing the relative strength of low-frequency components of the output signal of an FM detector in an FM receiver.
c. decreasing the relative strength of high-frequency components at the output signal of an FM detector in an FM receiver.
d. increasing the relative strength of high-frequency components before being fed into the modulator of an FM transmitter.
Answer: d
TEST ITEM FILE – Chapter 5
40. De-emphasis is:
a. increasing the relative strength of low-frequency components before being fed into the modulator of an FM transmitter.
b. decreasing the relative strength of low-frequency components of the output signal of an FM detector of an FM receiver.
c. decreasing the relative strength of high-frequency components of the output signal of an FM detector in an FM receiver.
d. increasing the relative strength of high frequency components before being fed into the modulator of an FM transmitter.
Answer: c
41. A de-emphasis network has:
a. an upper cutoff frequency of 2.120 kHz.
b. a time constant of 75 microseconds.
c. a high-frequency roll-off rate of –20 db per decade.
d. all of the above.
Answer: d
42. The main purpose of pre-emphasis and de-emphasis networks in FM communication systems is to:
a. provide a near constant noise reduction capability between low and high frequency intelligence signals.
b. allow for a reduction in bandwidth of the FM communication channel.
c. allow for stereo broadcasts to be received by a monaural receiver.
d. filter out noise produced by the FM transmitter's modulator stage.
Answer: a
43. Which of the following is not an example of a direct FM modulator?
a. varactor diode modulator.
b reactance modulator.
c. 566 VCO modulator.
d. Armstrong modulator.
Answer: d
44. Which best describes how a varactor diode modulator creates FM?
a. The intelligence signal creates mixing action in the nonlinear varactor diode to create an FM signal.
b. The intelligence signal alters the amount of forward bias of the varactor diode to create an FM signal.
c. The intelligence signal alters the capacitance of the diode to shift the resonant frequency of a tank circuit.
d. The intelligence signal causes the diode to create phase shift which indirectly creates FM.
Answer: c
TEST ITEM FILE – Chapter 5
45. In this modulator, FM is created by having the intelligence signal cause a change in the transconductance of a JFET, which causes a change in the JFET amplifier's input capacitance, which shifts the resonant frequency of a tank circuit.
a. varactor diode modulator b. reactance modulator c. VCO modulator d. PLL modulator
Answer: b
46. The main disadvantage of direct FM modulators is:
a. they have very limited frequency stability.
b. they have insufficient frequency deviation.
c. they can only work at low radio frequencies.
d. they work reliably only with low-level intelligence signals.
Answer: a
47. FM systems utilizing a direct FM modulator with an automatic frequency control (AFC) are known as:
a. Hartley systems.
b. Armstrong systems.
c. Crosby systems.
d. PLL systems.
Answer: c
48. Frequency multipliers:
a. are used to multiply the frequency of the carrier signal of an FM signal.
b. are typical of a Class C amplifier followed by a tank circuit which filters out a single harmonic.
c. are used to multiply the frequency deviation of an FM signal.
d. all of the above.
Answer: d
49. A stage that produces a specific dc output voltage level based on the exact frequency of the input signal is known as:
a. a discriminator.
b. a direct FM modulator.
c. an indirect FM modulator.
d. a frequency multiplier.
Answer: a
TEST ITEM FILE – Chapter 5
50. FM systems that utilize an indirect FM modulator consisting of a phase modulator stage are known as:
a. Hartley systems.
b. Armstrong systems.
c. Crosby systems.
d. PLL systems.
Answer: b
51. The advantage of indirect FM modulation over direct FM modulation is:
a. in their improved frequency stability.
b. in their increased frequency deviation.
c. in their ability to work with small signal amplitudes.
d. in their ability to work at higher intelligence frequencies.
Answer: a
52. The disadvantage of indirect FM modulators is:
a. they have very limited frequency stability.
b. they have insufficient frequency deviation.
c. they can only work at low intelligence frequencies.
d. they only work with large signal amplitudes.
Answer: b
53. A phase modulator can be made to create FM indirectly by:
a. integrating the intelligence signal prior to phase modulation.
b. feeding the intelligence signal through a frequency correcting network.
c. ensuring that the audio signal has an amplitude that varies inversely proportional to its frequency.
d. all of the above.
Answer: d
54. An indirect FM wideband transmitter can have its output signal be at the proper carrier frequency and at the same time have the required deviation by:
a. using a balanced modulator and a 90 degree phase shifter.
b. using combinations of mixers and multiplier stages.
c. using a reactance modulator.
d. using a frequency correcting network.
Answer: b
TEST ITEM FILE – Chapter 5
55. In Figure 5-3, the diode CR3 functions as:
a. the varactor diode used in the FM modulator stage.
b. the varactor diode used in the PM modulator stage.
c. the varactor diode used in the VCO.
d. the varactor diode used in the frequency synthesizer.
Answer: a
56. In Figure 5-3, the diode CR2 functions as:
a. the varactor diode used in the FM modulator stage.
b. the varactor diode used in the PM modulator stage.
c. the varactor diode used in the VCO.
d. the varactor diode used in the frequency synthesizer.
Answer: c
TEST ITEM FILE – Chapter 5
57. In Figure 5-3, the 4044 integrated circuit functions as:
a. the VCO portion of the phase-locked loop used as the frequency synthesizer.
b. a high speed digital divider.
c. the phase detector portion of the phase-locked loop used as a frequency synthesizer.
d. an audio amplifier stage for the intelligence signal.
Answer: c
58. In Figure 5-3, the 82S90 integrated circuit functions as:
a. the VCO portion of the phase-locked loop used as a frequency synthesizer.
b. a high speed digital divider.
c. the phase detector portion of the phase-locked loop used as a frequency synthesizer.
d. an audio amplifier stage for the intelligence signal.
Answer: b
59. In Figure 5-3, the CA3130 integrated circuit functions as:
a. the VCO portion of the phase-locked loop used as a frequency synthesizer.
b. a high speed digital divider.
c. the phase detector portion of the phase-locked loop used as a frequency synthesizer.
d. an audio amplifier stage for the intelligence signal.
Answer: d
60. Multiplex transmission is:
a. using two carriers to transmit two separate channels of information.
b. using two transmitters to transmit two separate channels of information.
c. the technique of separating the L and R signals into L+R and L-R in a stereo FM transmitter.
d. the simultaneous transmission of two or more signals on one carrier.
Answer: d
61. In FM stereo broadcasts, why are the left and right audio signals first converted to L+R and L-R signals before being frequency modulated?
a. This is necessary to be able to be multiplexed properly.
b. This permits higher intelligence frequencies to be used.
c. This permits compatibility between monaural and stereo systems.
d. This produces higher signal-to-noise ratios.
Answer: c
62. In an FM stereo transmitter, the L+R audio signal applied to the FM modulator stage:
a. extends from 0 to 15 kHz.
b. extends only from 23 kHz to 38 kHz..
c. extends only from 38 kHz to 53 kHz.
d. extends from 23 kHz to 53 kHz.
TEST ITEM FILE – Chapter 5
63. In an FM stereo transmitter, the L-R audio signal applied to the FM modulator stage:
a. extends from 0 to 15 kHz.
b. extends from 23 kHz. to 38 kHz.
c. extends from 38 kHz to 53 kHz d. extends from 23 kHz to 53 kHz.
Answer: d
64. An FM stereo broadcast is an example of:
a. time-division multiplexing.
b. frequency-division multiplexing.
c. amplitude-division multiplexing.
d. phase-division multiplexing.
Answer: b
65. In a stereo FM broadcast transmitter, when the 38 kHz pilot carrier is mixed with the L-R signal, what is produced?
a. an FM signal containing L+R and L-R sidebands b. a 38 kHz AM signal
c. an L-R double sideband suppressed carrier signal d. a 19 kHz pilot carrier
Answer: c
66. Why are stereo FM broadcasts more prone to noise than are monophonic FM broadcasts?
a. The L-R signal is weaker than the L+R signal.
b. The L-R signal is at higher modulating frequencies than the L+R signal.
c. Stereo has two separate channels that can become covered by noise rather than the single channel of the monophonic broadcast.
d. All of the above.
Answer: d
67. Why can low-level modulated FM signals be amplified by class C power amplifier stages without distorting unlike AM or SSB signals?
a. These FM signals do not vary in amplitude.
b. These FM signals have only one upper and lower sideband frequency components.
c. The FM signals do not have a carrier frequency component.
d. These FM signals have larger bandwidths than do AM or SSB signals.
Answer: a
68. The deviation return for NTSC broadcast television is a. 1.67
TEST ITEM FILE – Chapter 5
69. The deviation ratio for broadcast FM radio is:
a. 1.67 b. 5 c. .5 d. 2.5 e. 6.71 Answer: b
70. The spectrum analyzer view of an FM signal is shown in figure 5-4. Estimate the 3dB bandwidth.
a. 240 kHz b. 120 MHz c. 24 kHz d. 120 kHz
e. none of the above Answer: d
Figure 5-4