# Kennedy: MCQs in Frequency Modulation

(Last Updated On: December 8, 2017)

This is the Multiple Choice Questions in Chapter 5: Frequency Modulation from the book Electronic Communication Systems by George Kennedy. 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

Choose the letter of the best answer in each questions.

1. In the stabilize reactance modulator AFC system,

• a. the discriminator must have a fast time constant to prevent demodulation
• b. the higher the discriminator frequency, the better the oscillator frequency stability
• c. the discriminator frequency must not be too low, or the system will fail
• d. phase modulation is converted into FM by the equalizer circuit

2. In the spectrum of a frequency-modulated wave

• a. the carrier frequency disappears when the modulation index is large
• b. the amplitude of any sideband depends on the modulation index
• c. the total number of sidebands depends on the modulation index
• d. the carrier frequency cannot disappear

3. The difference between phase and frequency modulation

• a. is purely theoretical because they are the same in practice
• b. is too great to make the two system compatible
• c. lies in the poorer audio response of phase modulation
• d. lies in the different definitions of the modulation index

4. Indicate the false statement regarding the Armstrong modulation system

• a. The system is basically phase, not frequency modulation,
• b. AFC is not needed, as crystal oscillator is used.
• c. Frequency multiplication must be used
• d. Equalization is unnecessary

5. An FM signal with a modulation index mf is passed through a frequency tripler. The wave in the output of the tripler will have a modulation index of

• a. mf/3
• b. mf
• c. 3mf
• d. 9mf

6. An FM signal with a deviation δ is passed through a mixer, and has its frequency reduced fivefold. The deviation in the output of the mixer is

• a. 5δ
• b. Indeterminate
• c.δ/5
• d. δ

7. A pre-emphasis circuit provides extra noise immunity by

• a. boosting the bass frequencies
• b. amplifying the higher audio frequencies
• c. preamplifying the whole audio band
• d. converting the phase modulation to FM

8. Since noise phase-modulates the FM wave, as the noise sideband frequency approaches the carrier frequency, the noise amplitude

• a. remains constant
• b. is decreased
• c. is increased
• d. is equalized

9. When the modulating frequency is doubled, the modulation index is halved, and the modulating voltage remains constant. The modulation system is

• a. amplitude modulation
• b. phase modulation
• c. frequency modulation
• d. any of the three

10. Indicate which one of the following is not an advantage of FM over AM:

• a. Better noise immunity is provided
• b. Lower bandwidth is required
• c. The transmitted power is more useful
• d. Less modulating power is required

11. One of the following is an indirect way of generating FM. This is the

• a. reactance FET modulator
• b. varactor diode modulator
• c. Armstrong modulator
• d. reactance bipolar transistor modulator

12. In an FM stereo multiplex transmission, the

• a. sum signal modulates 19 kHz subcarrier
• b. difference signal modulates the 19 kHz subcarrier
• c. difference signal modulates the 38 kHz subcarrier
• d. difference signal modulates the 67 kHz subcarrier

### Complete List of MCQs in Electronic Communication Systems by Kennedy

Kennedy: MCQs in Frequency Modulation
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