This is the Multiple Choice Questions in Chapter 3: Amplitude Modulation from the book Electronic Communication Systems by Roy Blake
Start Practice Exam Test Questions
Choose the letter of the best answer in each questions.
MULTIPLE CHOICE
1. AM stands for:
- a. Audio Modulation
- b. Amplitude Modulation
- c. Angle Modulation
- d. Antenna Modulation
ANS: B
2. The "envelope" of an AM signal is due to:
- a. the baseband signal
- b. the carrier signal
- c. the amplitude signal
- d. none of the above
ANS: A
3. If the audio Va sin(ωat) modulates the carrier Vc sin(ωct), then the modulation index, m, is:
- a. m = ωa / ωc
- b. m = Va / Vc
- c. m = (Va / Vc)2
- d. m = Va / ωa
ANS: B
4. The equation for full-carrier AM is:
- a. v(t) = (Ec + Em) x sin(ωct)
- b. v(t) = (Ec + Em) x sin(ωmt) + sin(ωct)
- c. v(t) = (Ec x Em) x sin(ωmt) x sin(ωct)
- d. v(t) = (Ec + Em sin(ωmt)) x sin(ωct)
ANS: D
5. Overmodulation causes:
- a. distortion
- b. splatter
- c. both a and b
- d. none of the above
ANS: C
6. The peak voltage of an AM signal goes from Emax to Emin. The modulation index, m, is:
- a. m = Emin / Emax
- b. m = Emax / Emin
- c. m = (Emax – Emin) / (Emax + Emin)
- d. m = (Emax + Emin) / (Emax – Emin)
ANS: C
7. If Va sin(ωat) amplitude modulates the carrier Vc sin(ωct), it will produce the frequencies:
- a. ωc + ωa and ωc – ωa
- b. (ωc + ωa)/2 and (ωc – ωa)/2
- c. ωc + ωa and 2ωc + 2ωa
- d. none of the above
ANS: A
8. At 100% modulation, the total sideband power is:
- a. equal to the carrier power
- b. twice the carrier power
- c. half the carrier power
- d. 1.414 x carrier power
ANS: C
9. If a 5-kHz signal modulates a 1-MHz carrier, the bandwidth of the AM signal will be:
- a. 5 kHz
- b. 10 kHz
- c. 1.005 MHz
- d. none of the above
ANS: B
10. If an AM radio station increases its modulation index, you would expect:
- a. the audio to get louder at the receiver
- b. the received RF signal to increase
- c. the signal-to-noise ratio to increase
- d. all of the above
ANS: D
11. The modulation index can be derived from:
- a. the time-domain signal
- b. the frequency-domain signal
- c. both a and b
- d. none of the above
ANS: C
12. The main problem in using quadrature AM would be:
- a. requires too much bandwidth
- b. requires too much power
- c. incompatibility with ordinary AM radios
- d. all of the above
ANS: C
13. As compared to plain AM, SSB AM:
- a. is more efficient
- b. requires a more complex demodulator circuit
- c. requires less bandwidth
- d. all of the above
ANS: D
14. The SC in SSB SC stands for:
- a. single-carrier
- b. suppressed-carrier
- c. sideband-carrier
- d. none of the above
ANS: B
15. PEP stands for:
- a. Peak Envelope Power
- b. Peak Efficiency Power
- c. Peak Envelope Product
- d. none of the above
ANS: A
16. If an SSB transmitter radiates 1000 watts at peak modulation, what will it radiate with no modulation?
- a. 1000 watts
- b. 500 watts
- c. 250 watts
- d. 0 watts
ANS: D
17. Music on AM radio stations is "low-fidelity" because:
- a. AM is susceptible to noise
- b. commercial AM stations use low power
- c. commercial AM stations have a narrow bandwidth
- d. all of the above
ANS: C
18. The type of information that can be sent using AM is:
- a. audio
- b. video
- c. digital data
- d. all of the above
ANS: D
19. Two tones modulate an AM carrier. One tone causes a modulation index of m1 and the other tone causes a modulation index of m2. The total modulation index is:
- a. m1 + m2
- b. (m1 + m2) / 2
- c. sqrt(m1 x m2 + m2 x m1)
- d. sqrt(m1 x m1 + m2 x m2)
ANS: D
20. To demodulate a USB SSB signal, the receiver must:
- a. be set to USB mode
- b. reinsert the carrier
- c. both a and b
- d. none of the above
ANS: C
COMPLETION
1. An advantage of AM is that the receiver can be very ____________________.
ANS: simple
2. A disadvantage of AM is its ____________________ use of power.
ANS: inefficient
3. The ____________________ of an AM signal resembles the shape of the baseband signal.
ANS: envelope
4. In AM, modulating with a single audio tone produces ____________________ sidebands.
ANS: two
5. Compared to the USB, the information in the LSB is ____________________.
ANS: the same
6. Compared to the USB, the power in the LSB is ____________________.
ANS: the same
7. In AM, total sideband power is always ____________________ than the carrier power.
ANS: less
8. In AM, as the modulation index increases, the carrier power _________________________.
ANS: remains constant
9. The power in an AM signal is maximum when the modulation index is ____________________.
ANS: one
10. In AM, a voice-band signal of 300 Hz to 3000 Hz will require a bandwidth of ____________________.
ANS: 6000 Hz
11. With a 1-MHz carrier, if the LSB extends down to 990 kHz, then the USB will extend up to
____________________.
ANS: 1010 kHz
12. If an AM transmitter puts out 100 watts with no modulation, it will put out ____________________ watts with 100% modulation.
ANS: 150
SHORT ANSWER
1. An AM transmitter generates 100 watts with 0% modulation. How much power will it generate with 20% modulation?
ANS:
102 watts
2. If the carrier power is 1000 watts, what is the power in the USB at 70.7% modulation?
ANS:
125 watts
3. A carrier is modulated by three audio tones. If the modulation indexes for the tones are 0.3, 0.4, and 0.5, then what is the total modulation index?
ANS:
0.707
4. You look at an AM signal with an oscilloscope and see that the maximum Vpp is 100 volts and the minimum Vpp is 25 volts. What is the modulation index?
ANS:
0.6
5. A SSB transmitter is connected to a 50-ohm antenna. If the peak output voltage of the transmitter is 20 volts, what is the PEP?
ANS:
4 watts
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