1. Chapter 5 Problems
ECET 214
Prof. Park
NJIT

2. Problem 1
The modulation index is: a. top envelope divided by center frequency b. deviation divided by intelligence frequency c. VCO voltage divided by center frequency d. all of the above

3. Problem 2
Noise is usually clipped by: a. amplifiers b. phase detectors c. limiter circuits d. ARC circuits

4. Problem 3
If the S/N of the input signal is 4 and the intelligence signal is 10 kHz, determine the deviation. a. 145 kHz b. 160 kHz c. 200 kHz d. 100 kHz

5. Problem 4
The standard time constant used for pre-emphasis in a non-Dolby system is:
a. 75 μs.
b. 25 μs.
c. 50 μs .
d. 175 μs.

6. Problem 5 Which of the following is indirect FM generation?
a. varactor diode
b. reactance modulator
c. Crosby modulator
d. Armstrong modulator

7. Problem 6 The two types of angle modulation are:
a. amplitude and frequency modulation.
b. phase and frequency modulation.
c. pulse and frequency modulation.
d. phase and amplitude modulation

8. Problem 7 Phase modulation is an indirect form of:
a. amplitude modulation.
b. pulse modulation.
c. frequency modulation.
d. angle modulation.

9. Problem 8 The first working FM system was developed by: a. Marconi.
b. Armstrong.
c. Sarnoff.
d. Hartley.

10. Problem 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.

11. Problem 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.

12. Problem 11
An FM signal has a center frequency of MHz, but is swinging between MHz
and MHz at a rate of 500 times per second. Its input intelligence frequency is:
a. 100 kHz.
b. 50 kHz.
c MHz.
d. 500 Hz.

13. Problem 12
An FM signal has a center frequency of MHz but is swinging between MHz
and MHz at a frequency of 500 times per second. Its input carrier frequency is:
a. 100 kHz.
b. 50 kHz.
c MHz.
d. 500 Hz.

14. Problem 13
An FM signal has a center frequency of MHz but is swinging between
MHz and MHz at a rate of 500 times per second. Its index of modulation is:
a. 50,000.
b. 100.
c. 500
d. 100,000.

15. Problem 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.

16. Problem 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

17. Problem 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.

18. Problem 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.

19. Problem 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

20. Problem 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 MHz, what is the frequency of its highest frequency
component within its bandwidth? (Use the Bessel Chart of Figure 5-1.)
a MHz
b MHz
c MHz
d MHz
e MHz

21. Problem 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 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.

22. Problem 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.

23. Problem 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.

24. Problem 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 watts.
c watts.
d watts.

25. Problem 24
The FM signal given in Figure 5-2 is applied to a 50 ohm load. Its index of modulation is:
a. 4
b. 450 c d

26. Problem 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.

27. Problem 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 kHz.

28. Problem 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.

29. Problem 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

30. Problem 29
Standard FM broadcast stations use a maximum intelligence frequency of:
a. 5 kHz.
b. 15 kHz.
c. 75 kHz.
d. 150 kHz.

31. Problem 30
Standard FM broadcast stations use a maximum frequency deviation of:
a. 5 kHz.
b. 200 kHz.
c. 75 kHz.
d. 150 kHz.

32. Problem 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.

33. Problem 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.

34. Problem 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.

35. Problem 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.

36. Problem 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.

37. Problem 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

38. Problem 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

39. Problem 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

40. Problem 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
d. increasing the relative strength of high-frequency components before being fed into the

41. Problem 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

42. Problem 41 A de-emphasis network has:
a. an upper cutoff frequency of 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.

43. Problem 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.

44. Problem 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.

45. Problem 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.

46. Problem 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

47. Problem 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.