Electronic Communications: A Systems Approach

Jeffrey S. Beasley

Chapter 2 AMPLITUDE MODULATION - all with Video Answers

Educators

Chapter Questions

Problem 1

A $1500-\mathrm{kHz}$ carrier and $2-\mathrm{kHz}$ intelligence signal are combined in a nonlinear device. List all the frequency components produced.

Amit Srivastava

Numerade Educator

02:09

Problem 2

If a $1500-\mathrm{kHz}$ radio wave is modulated by a $2-\mathrm{kHz}$ sine-wave tone, what frequencies are contained in the modulated wave (the actual AM signal)?

Amit Srivastava

Numerade Educator

02:48

Problem 3

If a carrier is amplitude-modulated, what causes the sideband frequencies?

Khoobchandra Agrawal

Numerade Educator

Problem 4

What determines the bandwidth of emission for an AM transmission?

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Problem 5

Explain the difference between a sideband and a side frequency.

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Problem 6

What does the phasor at point 6 in Figure 2-11 imply about the modulation signal?

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03:04

Problem 7

Explain how the phasor representation can describe the formation of an AM signal.

James Kiss

Numerade Educator

Problem 8

Construct phasor diagrams for the AM signal in Figure 2-11 midway between points 1 and 2,3 and 4 , and 5 and 6.

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03:56

Problem 9

Draw a diagram of a carrier wave envelope when modulated $50 \%$ by a sinusoidal wave. Indicate on the diagram the dimensions from which the percentage of modulation is determined.

Nishant Kumar

Numerade Educator

Problem 10

What are some of the possible results of overmodulation?

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01:08

Problem 11

An unmodulated carrier is $300 \mathrm{~V}$ p-p. Calculate $\% m$ when its maximum p-p value reaches 400 , 500 , and 600 V. $(33.3 \%, 66.7 \%, 100 \%)$

Nishant Kumar

Numerade Educator

06:36

Problem 12

If $A=60 \mathrm{~V}$ and $B=200 \mathrm{~V}$ as shown in Figure 2-5, determine \%m. (53.85\%)

Thomas Thompson

Numerade Educator

01:39

Problem 13

Determine $E_c$ and $E_m$ from Problem 12. $\left(E_c=65 \mathrm{Vpk}, E_m=35 \mathrm{Vpk}\right)$

Thomas Thompson

Numerade Educator

03:04

Given that the amplitude of an AM waveform can be expressed as the sum of the carrier peak amplitude and intelligence signal, derive the expression for an AM signal that shows the existence of carrier and side frequencies.

James Kiss

Numerade Educator

01:07

Problem 15

A $100-\mathrm{V}$ carrier is modulated by a $1-\mathrm{kHz}$ sine wave. Determine the side-frequency amplitudes when $m=0.75$. $(37.5 \mathrm{~V})$

Amit Srivastava

Numerade Educator

Problem 16

A $1-\mathrm{MHz}, 40-\mathrm{V}$ peak carrier is modulated by a $5-\mathrm{kHz}$ intelligence signal so that $m=0.7$. This AM signal is fed to a $50-\Omega$ antenna. Calculate the power of each spectral component fed to the antenna. $\left(P_c=16 \mathrm{~W}, P_{\text {wab }}=P_{\text {lsb }}=1.96 \mathrm{~W}\right.$ )

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Problem 17

Calculate the carrier and sideband power if the total transmitted power is $500 \mathrm{~W}$ in Problem 15 . ( $390 \mathrm{~W}, 110 \mathrm{~W}$ )

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Problem 18

The ac rms antenna current of an AM transmitter is $6.2 \mathrm{~A}$ when unmodulated and rises to 6.7 A when modulated. Calculate $\% m .(57.9 \%)$

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00:45

Problem 19

Why is a high percentage of modulation desirable?

Hast Aggarwal

Numerade Educator

Problem 20

During $100 \%$ modulation, what percentage of the average output power is in the sidebands? (33.3\%)

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Problem 21

An AM transmitter has a 1-kW carrier and is modulated by three different sine waves having equal amplitudes. If $m_{\mathrm{eff}}=0.8$, calculate the individual values of $m$ and the total transmitted power. $(0.462,1.32 \mathrm{~kW})$

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Problem 22

A $50-\mathrm{V}$ ms carrier is modulated by a square wave as shown in Table 1-3(c). If only the first four harmonics are considered and $V=20 \mathrm{~V}$, calculate $m_{\text {eff }}(0.77)$

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00:53

Problem 23

An AM transmission of $1000 \mathrm{~W}$ is fully modulated. Calculate the power transmitted if is transmitted as an SSB signal. (167 W)

Hast Aggarwal

Numerade Educator

Problem 24

An SSB transmission drives $121 \mathrm{~V}$ peak into a $50-\Omega$ antenna. Calculate the PEP. (146 W)

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01:24

Problem 25

Explain the difference between rms and PEP designations.

Ajay Singhal

Numerade Educator

Problem 26

Provide detail on the differences between ACSSB, SSB, SSBSC, and ISB transmissions.

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Problem 27

List and explain the advantages of SSB over conventional AM transmissions. Are there any disadvantages?

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Problem 28

A sideband technique called doubled-sideband suppressed carrier (DSBSC) is similar to a regular AM transmission, double-sideband full carrier (DSBFC). Using your knowledge of SSBSC, explain the advantage DSBSC has over regular AM.

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Problem 29

Would the linear combination of a low-frequency intelligence signal and a high-frequency carrier signal be effective as a radio transmission? Why or why not?

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Problem 30

You are analyzing an AM waveform. What significance do the upper and lower envelopes have?

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Problem 31

An AM transmitter at $27 \mathrm{MHz}$ develops $10 \mathrm{~W}$ of carrier power into a $50-\Omega$ load. It is modulated by a $2-\mathrm{kHz}$ sine wave between $20 \%$ and $90 \%$ modulation. Determine:
(a) Component frequencies in the AM signal.
(b) Maximum and minimum waveform voltage of the AM signal at $20 \%$ and $90 \%$ modulation. (25.3 to $37.9 \mathrm{~V}$ peak, 3.14 to $60.1 \mathrm{~V}$ peak)
(c) Sideband signal voltage and power at $20 \%$ and $90 \%$ modulation. $(2.24 \mathrm{~V}, 0.1 \mathrm{~W}, 10.06 \mathrm{~V}$, $2.025 \mathrm{~W}$ )
(d) Load current at $20 \%$ and $90 \%$ modulation. $(0.451 \mathrm{~A}, 0.530 \mathrm{~A})$

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Problem 32

Compare the display of an oscilloscope to that of a spectrum analyzer.

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05:31

Problem 33

If a carrier and one sideband were eliminated from an AM signal, would the transmission still be usable? Why or why not?

Nishant Kumar

Numerade Educator

Problem 34

Explain the principles involved in a single-sideband, suppressed-carrier (SSBSC) emission. How does its bandwidth of emission and required power compare with that of full carrier and sidebands?

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Problem 35

You have been asked to provide SSB using a DSB signal, $\cos \omega_l t, \cos \omega_{\mathrm{C}} t$. Can this be done? Provide mathematical proof of your judgment.

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05:31

Problem 36

If, in an emergency, you had to use an AM receiver to receive an SSB broadcast, what modifications to the receiver would you need to make?

Nishant Kumar

Numerade Educator

Problem 1

Problem 2

Problem 3

Problem 4

Problem 5

Problem 6

Problem 7

Problem 8

Problem 9

Problem 10

Problem 11

Problem 12

Problem 13

Problem 14

Problem 15

Problem 16

Problem 17

Problem 18

Problem 19

Problem 20

Problem 21

Problem 22

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Problem 24

Problem 25

Problem 26

Problem 27

Problem 28

Problem 29

Problem 30

Problem 31

Problem 32

Problem 33

Problem 34

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Problem 36