Electronic Communications: A Systems Approach

Jeffrey S. Beasley

Chapter 3 ANGLE MODULATION - all with Video Answers

Educators

Chapter Questions

Problem 1

Define angle modulation and list its subcategories.

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02:14

Problem 2

What is the difference between frequency and phase modulation?

Arpit Gupta

Numerade Educator

00:41

Problem 3

What are the merits of an FM communications system compared to an AM system?

Gopal Sharma

Numerade Educator

Problem 4

Why is FM undesirable in the standard AM broadcast band?

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Problem 5

What advantage does FM have over AM and SSB?

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01:20

Problem 6

Explain how a condenser microphone can be used very easily to generate FM.

Ankur S

Numerade Educator

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Problem 7

Define deviation constant.

Emily Himsel

Numerade Educator

01:25

A $50-\mathrm{mV}$ sinusoid, at a frequency of $1 \mathrm{kHz}$, is applied to a capacitor microphone FM generator. If the deviation constant for the capacitor microphone $\mathrm{FM}$ generator is $500 \mathrm{~Hz} / 20 \mathrm{mV}$, determine:
(a) The total frequency deviation. $( \pm 1.25 \mathrm{kHz})$
(b) The rate at which the carrier frequency is being deviated. ( $1 \mathrm{kHz}$ )

Ben Nicholson

Numerade Educator

03:56

Problem 9

Explain how the intelligence signal modulates the carrier.

Nishant Kumar

Numerade Educator

Problem 10

In an FM transmitter, the output is changing between 90.001 and $89.999 \mathrm{MHz} 1000$ times a second. The intelligence signal amplitude is $3 \mathrm{~V}$. Determine the carrier frequency and intelligence signal frequency. If the output deviation changes to between 90.0015 and $89.9985 \mathrm{MHz}$, calculate the intelligence signal amplitude. $(90 \mathrm{MHz}, 1 \mathrm{kHz}, 4.5 \mathrm{~V})$

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Problem 11

What determines the rate of frequency swing for an FM broadcast transmitter?

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Problem 12

Without knowledge of Section 3-3 and using Figure 3-1, write an equation that expresses the output frequency, $f$, of the FM generator. Hint: If there is no input into the microphone, then $f=f_c$, where $f_c$ is the oscillator's output frequency.

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00:45

Problem 13

Define modulation index $\left(m_f\right)$ as applied to an FM system.

Hast Aggarwal

Numerade Educator

Problem 14

What characteristic(s) of an audio tone determines the percentage of modulation of an FM broadcast transmitter?

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11:10

Problem 15

Explain what happens to the carrier in $\mathrm{FM}$ as $m_f$ goes from 0 up to 15.

Mihajlo Grcic

Numerade Educator

Problem 16

Calculate the bandwidth of an FM system (using Table 3-1) when the maximum deviation ( $\delta$ ) is $15 \mathrm{kHz}$ and $f_i=3 \mathrm{kHz}$. Repeat for $f_i=2.5$ and $5 \mathrm{kHz}$. $(48 \mathrm{kHz}, 45 \mathrm{kHz}, 60 \mathrm{kHz})$

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03:08

Problem 17

Explain the purpose of the guard bands for broadcast FM. How wide is an FM broadcast channel?

Keshav Singh

Numerade Educator

Problem 18

What frequency swing is defined as $100 \%$ modulation for an FM broadcast station?

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12:27

Problem 19

What is the meaning of the term center frequency in reference to FM broadcasting?

Sinisa Stura

Numerade Educator

Problem 20

What is the meaning of the term frequency swing in reference to FM broadcast stations?

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Problem 21

What is the frequency swing of an FM broadcast transmitter when modulated $60 \%$ ? $( \pm 45 \mathrm{kHz})$

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00:45

Problem 22

An FM broadcast transmitter is modulated $40 \%$ by a $5-\mathrm{kHz}$ test tone. When the percentage of modulation is doubled, what is the frequency swing of the transmitter?v

Hast Aggarwal

Numerade Educator

Problem 23

An FM broadcast transmitter is modulated $50 \%$ by a $7-\mathrm{kHz}$ test tone. When the frequency of the test tone is changed to $5 \mathrm{kHz}$ and the percentage of modulation is unchanged, what is the transmitter frequency swing?

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Problem 24

If the output current of an FM broadcast transmitter is $8.5 \mathrm{~A}$ without modulation, what is the output current when the modulation is $90 \%$ ?

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Problem 25

An FM transmitter delivers, to a $75-\Omega$ antenna, a signal of $v=1000 \sin \left(10^9 t+4 \sin 10^4 t\right)$. Calculate the carrier and intelligence frequencies, power, modulation index, deviation, and bandwidth. ( $159 \mathrm{MHz}, 1.59 \mathrm{kHz}, 6.67 \mathrm{~kW}, 4,6.37 \mathrm{kHz},-16 \mathrm{kHz}$ )

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Problem 26

Assuming that the $9.892-\mathrm{kW}$ result of Example 3-6 is exactly correct, determine the total power in the $J_2$ sidebands and higher. (171 W)

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Problem 27

Determine the deviation ratio for an FM system that has a maximum possible deviation of $5 \mathrm{kHz}$ and the maximum input frequency is $3 \mathrm{kHz}$. Is this narrow- or wideband $\mathrm{FM}$ ? (1.67. wideband)

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00:57

Problem 28

What types of radio receivers do not respond to static interference?

Keshav Singh

Numerade Educator

Problem 29

What is the purpose of a limiter stage in an FM broadcast receiver?

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Problem 30

Explain why the limiter does not eliminate all noise effects in an FM system.

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Problem 31

Calculate the amount of frequency deviation caused by a limited noise spike that still causes an undesired phase shift of $35^{\circ}$ when $f_i$ is $5 \mathrm{kHz}$. $(3.05 \mathrm{kHz})$

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Problem 32

In a broadcast FM system, the input $S / N=4$. Calculate the worst-case $S / N$ at the output if the receiver's internal noise effect is negligible. (19.8:1)

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Problem 33

Explain why narrowband FM systems have poorer noise performance than wideband systems.

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Problem 34

Explain the capture effect in FM, and include the link between it and FM's inherent noise reduction capability.

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01:36

Problem 35

Why is narrowband FM rather than wideband FM used in radio communications systems?

Arpit Gupta

Numerade Educator

Problem 36

What is the purpose of preemphasis in an FM broadcast transmitter? Of deemphasis in an FM receiver? Draw a circuit diagram of a method of obtaining preemphasis,

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02:07

Problem 37

Discuss the following for frequency modulation systems:
(a) The production of sidebands.
(b) The relationship between the number of sidebands and the modulating frequency.
(c) The relationship between the number of sidebands and the amplitude of the modulating voltage.
(d) The relationship between percentage modulation and the number of sidebands.
(e) The relationship between modulation index or deviation ratio and the number of sidebands.
(f) The relationship between the spacing of the sidebands and the modulating frequency.
(g) The relationship between the number of sidebands and the bandwidth of emissions.
(h) The criteria for determining the bandwidth of emission.
(i) Reasons for preemphasis.

Amit Srivastava

Numerade Educator

03:04

Problem 38

Analyze the effect of an intelligence signal's amplitude and frequency when it frequencymodulates a carrier.

James Kiss

Numerade Educator

02:14

Problem 39

Contrast the modulation indexes for PM versus FM. Given this difference, could you modify a modulating signal so that allowing it to phase-modulate a carrier would result in FM? Explain your answer.

Arpit Gupta

Numerade Educator

Problem 40

Does the maximum deviation directly determine the bandwidth of an FM system? If not, explain how bandwidth and deviation are related.

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Problem 41

An FM transmitter puts out $1 \mathrm{~kW}$ of power. When $m_f=2$, analyze the distribution of power in the carrier and all significant sidebands. Use Bessel functions to verify that the sum of these powers is $1 \mathrm{~kW}$.

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01:23

Problem 42

Why is the FCC concerned if an FM broadcast station overmodulates (deviation exceeds $\pm 75 \mathrm{kHz}$ ?

Hast Aggarwal

Numerade Educator

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