EEEN 462 - ANALOGUE COMMUNICATION

30 Questions on Amplitude Modulation

📝 Test Instructions

This test contains 30 multiple-choice questions on Amplitude Modulation
Each question has four possible answers with only one correct option
Select your answer by clicking the radio button next to your choice
You can submit your answers and check the answer key at the bottom
This test covers key concepts: modulation index, spectrum, power distribution, bandwidth, and applications

1. What does AM stand for in communication systems?

a) Analog Multiplexing b) Amplitude Modulation c) Angular Modulation d) Amplitude Measurement

2. In amplitude modulation, the amplitude of the ______ wave is varied in accordance with the amplitude of the modulating signal.

a) modulating b) carrier c) baseband d) sideband

3. The modulation index of an AM wave is defined as the ratio of:

a) carrier amplitude to modulating signal amplitude b) modulating signal amplitude to carrier amplitude c) carrier frequency to modulating signal frequency d) modulating signal frequency to carrier frequency

4. For a sinusoidal modulating signal, the modulation index (m) is given by:

a) (A_max + A_min) / (A_max - A_min) b) (A_max - A_min) / (A_max + A_min) c) (A_max - A_min) / 2 d) (A_max + A_min) / 2

5. If the modulation index is greater than 1, what happens?

a) The modulation is efficient b) The carrier is overmodulated, leading to distortion c) The bandwidth becomes half d) The sidebands disappear

6. The maximum and minimum amplitudes of an AM wave are 1.5 V and 0.5 V respectively. What is the modulation index?

a) 0.25 b) 0.5 c) 0.75 d) 1.0

7. An AM signal has a carrier frequency of 1 MHz and is modulated by a signal of frequency 5 kHz. What are the frequencies present in the modulated wave?

a) 995 kHz and 1005 kHz b) 1 MHz only c) 995 kHz, 1 MHz, and 1005 kHz d) 5 kHz and 1 MHz

8. The bandwidth required for AM transmission is:

a) Equal to the carrier frequency b) Twice the highest modulating frequency c) Equal to the modulating frequency d) Half the carrier frequency

9. In an AM wave, the majority of the power is contained in the:

a) Upper sideband b) Lower sideband c) Carrier d) Both sidebands equally

10. The total power of an AM wave with carrier power P_c and modulation index m is:

a) P_c (1 + m) b) P_c (1 + m²) c) P_c (1 + m²/2) d) P_c (1 + m/2)

11. An AM transmitter has a carrier power of 1000 W. If the modulation index is 0.8, what is the total power?

a) 1000 W b) 1320 W c) 1640 W d) 1800 W

12. What is the maximum power efficiency of an AM wave for a sinusoidal modulating signal?

a) 25% b) 33.3% c) 50% d) 100%

13. Which of the following is a disadvantage of AM?

a) Simple receiver design b) Susceptibility to noise c) Large bandwidth requirement d) Both b and c

14. Which demodulator is commonly used for AM?

a) Phase detector b) Frequency discriminator c) Envelope detector d) PLL detector

15. For envelope detection to work without distortion, the modulation index must be:

a) Greater than 1 b) Less than or equal to 1 c) Exactly 0.5 d) Zero

16. In AM, the information is contained in the:

a) Carrier wave b) Sidebands c) Modulation index d) Carrier frequency

17. The unit of modulation index is:

a) Hertz b) Volts c) Dimensionless d) Decibels

18. The modulation index can be measured using:

a) Voltmeter b) Oscilloscope c) Spectrum analyzer d) All of the above

19. The expression for an AM wave is given by:

a) A_c sin(ω_ct) + A_m sin(ω_mt) b) A_c [1 + m sin(ω_mt)] sin(ω_ct) c) A_c sin(ω_ct) × A_m sin(ω_mt) d) A_c sin(ω_ct + m sin(ω_mt))

20. What is the purpose of modulation in communication?

a) To reduce antenna size b) To allow multiplexing of signals c) To shift the signal to a higher frequency d) All of the above

21. In an AM wave, if the carrier component is suppressed, what is it called?

a) DSB-SC (Double Sideband Suppressed Carrier) b) SSB (Single Sideband) c) VSB (Vestigial Sideband) d) FM (Frequency Modulation)

22. Double Sideband Suppressed Carrier (DSB-SC) is generated by:

a) Square law modulator b) Switching modulator c) Balanced modulator d) All of the above

23. Compared to DSB-SC, AM has the advantage of:

a) Higher efficiency b) Simpler receiver c) Less bandwidth d) Better noise immunity

24. The peak amplitude of the sidebands for a modulation index m and carrier amplitude A_c is:

a) m A_c b) m A_c/2 c) 2m A_c d) A_c/2

25. What is the condition for overmodulation?

a) m < 1 b) m = 1 c) m > 1 d) m = 0

26. Overmodulation leads to:

a) Increased signal quality b) Distortion in the envelope c) Reduced bandwidth d) Higher efficiency

27. In AM broadcast, which frequency band is used?

a) LF (Low Frequency) b) MF (Medium Frequency) c) HF (High Frequency) d) VHF (Very High Frequency)

28. The modulation index for an AM wave can be determined from the waveform by:

a) (E_max - E_min) / (E_max + E_min) b) (E_max + E_min) / (E_max - E_min) c) E_max / E_min d) E_min / E_max

29. An AM wave has a modulation index of 0.5. The power in the carrier is 400 W. What is the power in one sideband?

a) 25 W b) 50 W c) 100 W d) 200 W

30. The modulation index of an AM wave is changed from 0 to 1. How does the transmitted power change?

a) Remains constant b) Decreases by 50% c) Increases by 50% d) Doubles

🔑 Answer Key

1. b

2. b

3. b

4. b

5. b

6. b

7. c

8. b

9. c

10. c

11. b

12. b

13. d

14. c

15. b

16. b

17. c

18. d

19. b

20. d

21. a

22. c

23. b

24. b

25. c

26. b

27. b

28. a

29. a

30. c