Chapter 5 Problems
ECET 214
Prof. Park
NJIT
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
Problem 2
Noise is usually clipped by:
a. amplifiers
b. phase detectors
c. limiter circuits
d. ARC circuits
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
Problem 4
• The standard time constant used for preemphasis in a non-Dolby system is:
• a. 75 μs.
• b. 25 μs.
• c. 50 μs .
• d. 175 μs.
Problem 5
• Which of the following is indirect FM
generation?
• a. varactor diode
• b. reactance modulator
• c. Crosby modulator
• d. Armstrong modulator
Problem 6
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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
Problem 7
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Phase modulation is an indirect form of:
a. amplitude modulation.
b. pulse modulation.
c. frequency modulation.
d. angle modulation.
Problem 8
• The first working FM system was developed
by:
• a. Marconi.
• b. Armstrong.
• c. Sarnoff.
• d. Hartley.
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.
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.
Problem 11
• An FM signal has a center frequency of 154.5
MHz, but is swinging between 154.45 MHz
• and 154.55 MHz at a rate of 500 times per
second. Its input intelligence frequency is:
• a. 100 kHz.
• b. 50 kHz.
• c. 154.5 MHz.
• d. 500 Hz.
Problem 12
• An FM signal has a center frequency of 154.5
MHz but is swinging between 154.45 MHz
• and 154.55 MHz at a frequency of 500 times
per second. Its input carrier frequency is:
• a. 100 kHz.
• b. 50 kHz.
• c. 154.5 MHz.
• d. 500 Hz.
Problem 13
• An FM signal has a center frequency of 154.5
MHz but is swinging between 154.45
• MHz and 154.55 MHz at a rate of 500 times
per second. Its index of modulation is:
• a. 50,000.
• b. 100.
• c. 500
• d. 100,000.
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.
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
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.
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.
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 51.)
• a. 9
• b. 18
• c. 19
• d. 6
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 162.4 MHz, what is the
frequency of its highest frequency
• component within its bandwidth? (Use the Bessel
Chart of Figure 5-1.)
• a. 162.401 MHz
• b. 162.400 MHz
• c. 162.408 MHz
• d. 162.404 MHz
• e. 162.416 MHz
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 162.4 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.
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.
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.
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. 2025 watts.
• c. 2863 watts.
• d. 4050 watts.
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. 9.42.
• d. 112.5.
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.
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. 3.75 kHz.
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.
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. 8.65.
Problem 29
• Standard FM broadcast stations use a maximum intelligence
frequency of:
• a. 5 kHz.
• b. 15 kHz.
• c. 75 kHz.
• d. 150 kHz.
Problem 30
• Standard FM broadcast stations use a maximum frequency
deviation of:
• a. 5 kHz.
• b. 200 kHz.
• c. 75 kHz.
• d. 150 kHz.
Problem 31
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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.
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.
Problem 33
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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.
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.
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.
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
Problem 37
• Determine the worst case output signal-tonoise 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
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
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
• FM detector in an FM receiver.
• d. increasing the relative strength of high-frequency
components before being fed into the
• modulator of an FM transmitter.
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
Problem 41
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A de-emphasis network has:
a. an upper cutoff frequency of 2.120 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.
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.
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.
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.
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
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.