Chapter 5 Problems ECET 214 Prof. Park NJIT. Problem 1 The modulation index is: a. top envelope...

Chapter 5 Problems

ECET 214Prof. Park

NJIT

Problem 1

The modulation index is:

a. top envelope divided by center frequencyb. deviation divided by intelligence frequencyc. VCO voltage divided by center frequencyd. all of the above

Problem 2

Noise is usually clipped by:

a. amplifiersb. phase detectorsc. limiter circuitsd. 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 kHzb. 160 kHzc. 200 kHzd. 100 kHz

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.

Problem 5

• Which of the following is indirect FM generation?

• a. varactor diode• b. reactance modulator• c. Crosby modulator• d. Armstrong modulator

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

Problem 7

• 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


• 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 5-1.)

• 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


• 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:


Problem 30

• Standard FM broadcast stations use a maximum frequency deviation of:


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.

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

• 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



• signal-to-noise ratio is 2:1.• a. 10:1• b. 15:1• c. 30:1• d. 2:1

Problem 38



• 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• modulator of an FM transmitter.

Problem 41

• 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• c. VCO modulator• d. PLL 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.

Chapter 5 Problems ECET 214 Prof. Park NJIT. Problem 1 The modulation index is: a. top envelope...

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