Frequency Modulation Test

Undergraduate Engineering Students

1. What does FM stand for in communication systems?

a) Frequency Multiplication
b) Frequency Modulation
c) Frequency Measurement
d) Frequency Magnification

2. In FM, the information is carried by varying:

a) The amplitude of the carrier wave
b) The frequency of the carrier wave
c) The phase of the carrier wave
d) Both amplitude and frequency

3. The amount of frequency deviation in FM is proportional to:

a) The amplitude of the modulating signal
b) The frequency of the modulating signal
c) The phase of the modulating signal
d) Both amplitude and frequency of the modulating signal

4. The modulation index (β) in FM is defined as:

a) Δf/fm
b) fm/Δf
c) Δf × fm
d) Δf + fm

5. Which of the following is NOT an advantage of FM over AM?

a) Better noise immunity
b) More efficient use of transmitter power
c) Smaller bandwidth requirement
d) Less susceptible to signal strength variations

6. The bandwidth of an FM signal is approximately given by:

a) 2(Δf + fm)
b) 2Δf
c) 2fm
d) Δf + fm

7. In FM broadcasting, the maximum frequency deviation is typically:

a) ±5 kHz
b) ±25 kHz
c) ±75 kHz
d) ±200 kHz

8. The capture effect is a characteristic of:

a) AM receivers
b) FM receivers
c) Both AM and FM receivers
d) Digital receivers

9. Which circuit is commonly used to demodulate FM signals?

a) Envelope detector
b) Phase-locked loop
c) Product detector
d) Balanced modulator

10. The pre-emphasis circuit in FM transmitters:

a) Boosts high frequencies before modulation
b) Attenuates high frequencies before modulation
c) Boosts low frequencies before modulation
d) Attenuates low frequencies before modulation

11. The de-emphasis circuit in FM receivers:

a) Boosts high frequencies after demodulation
b) Attenuates high frequencies after demodulation
c) Boosts low frequencies after demodulation
d) Attenuates low frequencies after demodulation

12. Carson's rule is used to estimate:

a) The modulation index of an FM signal
b) The bandwidth of an FM signal
c) The power of an FM signal
d) The frequency deviation of an FM signal

13. The number of significant sidebands in an FM signal depends on:

a) The carrier frequency only
b) The modulation index only
c) Both the modulation index and carrier frequency
d) The amplitude of the modulating signal only

14. Narrowband FM typically has a modulation index:

a) Less than 0.3
b) Between 0.3 and 1.0
c) Greater than 1.0
d) Exactly 1.0

15. Which of the following is a direct method of FM generation?

a) Armstrong modulator
b) Varactor diode modulator
c) Balanced modulator
d) Ring modulator

16. The Armstrong method of FM generation is an example of:

a) Direct FM
b) Indirect FM
c) Both direct and indirect FM
d) Neither direct nor indirect FM

17. In FM, the total power of the modulated signal:

a) Increases with modulation
b) Decreases with modulation
c) Remains constant
d) Depends on the modulation index

18. The frequency spectrum of an FM signal contains:

a) A carrier and one sideband
b) A carrier and two sidebands
c) A carrier and an infinite number of sidebands
d) Only sidebands with no carrier

19. The Bessel functions are used in FM to determine:

a) The power distribution among carrier and sidebands
b) The frequency deviation
c) The modulation index
d) The bandwidth requirements

20. For a given FM signal, if the amplitude of the modulating signal is doubled, the frequency deviation:

a) Remains the same
b) Is halved
c) Is doubled
d) Is quadrupled

21. For a given FM signal, if the frequency of the modulating signal is doubled while keeping its amplitude constant, the modulation index:

a) Remains the same
b) Is halved
c) Is doubled
d) Is quadrupled

22. The noise performance of FM compared to AM is:

a) Worse for all signal levels
b) Better for all signal levels
c) Better for high signal levels but worse for low signal levels
d) The same as AM

23. The threshold effect in FM occurs when:

a) The carrier frequency is too high
b) The signal-to-noise ratio falls below a critical value
c) The modulation index exceeds 1.0
d) The frequency deviation is too large

24. The typical frequency range for FM broadcasting is:

a) 30-300 kHz
b) 300-3000 kHz
c) 30-300 MHz
d) 300-3000 MHz

25. Stereo FM broadcasting uses:

a) Frequency division multiplexing
b) Time division multiplexing
c) Code division multiplexing
d) Space division multiplexing

26. The pilot tone in stereo FM is at:

a) 15 kHz
b) 19 kHz
c) 38 kHz
d) 76 kHz

27. Which of the following is NOT a component of a basic FM receiver?

a) RF amplifier
b) Mixer
c) Envelope detector
d) IF amplifier

28. The limiter circuit in an FM receiver is used to:

a) Remove amplitude variations
b) Remove frequency variations
c) Increase sensitivity
d) Reduce noise

29. The typical IF frequency in FM receivers is:

a) 455 kHz
b) 10.7 MHz
c) 21.4 MHz
d) 45 MHz

30. Frequency modulation is used in which of the following applications?

a) Commercial radio broadcasting
b) Television sound transmission
c) Two-way mobile communications
d) All of the above