现代电子通信（第9版）（影印版）

　　内容包括：幅度调制、单边带通信、频率调制、通信方法、数字通信、网络通信、传输线、波的传播、天线、波导与雷达、微波与激光、电视、光纤等，涉及通信领域很多新技术，如蓝牙、Wi-Max、DTV、DSP、HD-Radio等。本书可作为电子信息工程、通信工程专业本科生教材，也可作为相关领域工程技术人员的参考书。

 

本书内容包括：幅度调制、单边带通信、频率调制、通信技术、编码技术、有线及无线数字通信、网络通信、波的传播、天线、波导与雷达、微波与激光、电视及光纤等，同时涉及通信领域很多新技术，如蓝牙、Wi-Max、DTV、DSP、HD-Radio等。

本书可作为电子信息工程、通信工程专业本科生的双语教材或参考书，也可作为相关领域工程技术人员的参考书。

CHAPTER 1 Introductory Topics
1-1 Introduction
1-2 The dB in Communications
1-3 Noise
1-4 Noise Designation and Calculation
1-5 Noise Measurement
1-6 Information and Bandwidth
1-7 LC Circuits
1-8 Oscillators
1-9 Troubleshooting
1-10 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 2 Amplitude Modulation:Transmission
2-1 Introduction
2-2 Amplitude Modulation Fundamentals
2-3 Percentage Modulation
2-4 AM Analysis
2-5 Circuits for AM Generation
2-6 AM Transmitter Systems
2-7 Transmitter Measurements
2-8 Troubleshooting
2-9 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 3 Amplitude Modulation:Reception
3-1 Receiver Characteristics
3-2 AM Detection
3-3 Superheterodyne Receivers
3-4 Superheterodyne Tuning
3-5 Superheterodyne Analysis
3-6 Automatic Gain Control
3-7 AM Receiver Systems
3-8 Troubleshooting
3-9 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 4 Single-Sideband Communications
4-1 Single-Sideband Characteristics
4-2 Sideband Generation:The Balanced Modulator
4-3 SSB Filters
4-4 SSB Transmitters
4-5 SSB Demodulation
4-6 SSB Receivers
4-7 Troubleshooting
4-8 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 5 Frequency Modulation:Transmission
5-1 Angle Modulation
5-2 A Simple FM Generator
5-3 FM Analysis
5-4 Noise Suppression
5-5 Direct FM Generation
5-6 Indirect FM Generation
5-7 Phase-Locked-Loop FM Transmitter
5-8 Stereo FM
5-9 FM Transmissions
5-10 Troubleshooting
5-11 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 6 Frequency Modulation:Reception
6-1 Block Diagram
6-2 RF Amplifiers
6-3 Limiters
6-4 Discriminators
6-5 Phase-Locked Loop
6-6 Stereo Demodulation
6-7 FM Receivers
6-8 Troubleshooting
6-9 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 7 Communications Techniques
7-1 Introduction
7-2 Frequency Conversion
7-3 Special Techniques
7-4 Receiver Noise,Sensitivity,and Dynamic Range Relationships
7-5 Frequency Synthesis
7-6 Direct Digital Synthesis
7-7 High-Frequency Communication Modules
7-8 Troubleshooting
7-9 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 8 Digital Communications:Coding Techniques
8-1 Introduction
8-2 Alphanumeric Codes
8-3 Pulse-Code Modulation
8-4 Digital Signal Encoding Formats
8-5 Coding Principles
8-6 Code Error Detection and Correction
8-7 DSP
8-8 Troubleshooting
8-9 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 9 Wired Digital Communications
9-1 Introduction
9-2 Background Material for Digital Communications
9-3 Bandwidth Considerations
9-4 Data Transmission
9-5 Time-Division Multiple Access (TDMA)
9-6 Delta and Pulse Modulation
9-7 Computer Communication
9-8 Troubleshooting
9-9 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 10 Wireless Digital Communications
10-1 Introduction
10-2 Digital Modulation Techniques
10-3 Spread-Spectrum Techniques
10-4 Orthogonal Frequency Division Multiplexing (OFDM)
10-5 Telemetry
10-6 Troubleshooting
10-7 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 11 Network Communications
11-1 Introduction
11-2 Basic Telephone Operation
11-3 Telephone Signaling Systems:ISDN and SS7
11-4 Mobile Telephone Systems
11-5 Local Area Networks
11-6 Assembling a LAN
11-7 LAN Interconnection
11-8 Internet
11-9 IP Telephony
11-10 Interfacing the Networks
11-11 Wireless Security
11-12 Troubleshooting
11-13 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 12 Transmission Lines
12-1 Introduction
12-2 Types of Transmission Lines
12-3 Electrical Characteristics of Transmission Lines
12-4 Propagation of DC Voltage Down a Line
12-5 Nonresonant Line
12-6 Resonant Transmission Line
12-7 Standing Wave Ratio
12-8 The Smith Chart
12-9 Transmission Line Applications
12-10 Troubleshooting
12-11 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 13 Wave Propagation
13-1 Electrical to Electromagnetic Conversion
13-2 Electromagnetic Waves
13-3 Waves Not in Free Space
13-4 Ground- and Space-Wave Propagation
13-5 Sky-Wave Propagation
13-6 Satellite Communications
13-7 Figure of Merit and Satellite Link Budget Analysis
13-8 Troubleshooting
13-9 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 14 Antennas
14-1 Basic Antenna Theory
14-2 Half-Wave Dipole Antenna
14-3 Radiation Resistance
14-4 Antenna Feed Lines
14-5 Monopole Antenna
14-6 Antenna Arrays
14-7 Special-Purpose Antennas
14-8 Troubleshooting
14-9 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 15 Waveguides and Radar
15-1 Comparison of Transmission Systems
15-2 Types of Waveguides
15-3 Physical Picture of Waveguide Propagation
15-4 Other Types of Waveguides
15-5 Other Waveguide Considerations
15-6 Termination and Attenuation
15-7 Directional Coupler
15-8 Coupling Waveguide Energy and Cavity Resonators
15-9 Radar
15-10 RFID (Radio Frequency Identification)
15-11 Microintegrated Circuit Waveguiding
15-12 Troubleshooting
15-13 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 16 Microwaves and Lasers
16-1 Microwave Antennas
16-2 Microwave Tubes
16-3 Solid-State Microwave Devices
16-4 Ferrites
16-5 Low-Noise Amplification
16-6 Lasers
16-7 Troubleshooting
16-8 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 17 Television
17-1 Introduction
17-2 Digital Television
17-3 Monitoring the Digital Television Signal
17-4 NTSC Transmitter Principles
17-5 NTSC Transmitter/Receiver Synchronization
17-6 Resolution
17-7 The NTSC Television Signal
17-8 Television Receivers
17-9 The Front End and IF Amplifiers
17-10 The Video Section
17-11 Sync and Deflection
17-12 Principles of NTSC Color Television
17-13 Sound and Picture Improvements
17-14 Troubleshooting
17-15 Troubleshooting with Electronics Workbench^TM Multisim
CHAPTER 18 Fiber Optics
18-1 Introduction
18-2 The Nature of Light
18-3 Optical Fibers
18-4 Fiber Attenuation and Dispersion
18-5 Optical Components
18-6 Fiber Connections and Splices
18-7 System Design and Operational Issues
18-8 Cabling and Construction
18-9 Optical Networking
18-10 Safety
18-11 Troubleshooting
18-12 Troubleshooting with Electronics Workbench^TM Multisim
Acronyms and Abbreviations
Glossary

1 Chapter Outline Objectives

1-1 Introduction

1-2 The dB in Communications

1-3 Noise

1-4 Noise Designation and Calculation

1-5 Noise Measurement

1-6 Information and Bandwidth

1-7 LC Circuits

1-8 Oscillators

1-9 Troubleshooting

1-10 Troubleshooting with Electronics

Workbench? Multisim

? Describe a basic communication system and explain

the concept of modulation

? Develop an understanding of the use of the decibel

(dB) in communications systems

? Define electrical noise and explain its effect at the

first stages of a receiver

? Calculate the thermal noise generated by a resistor

? Calculate the signal-to-noise ratio and noise figure for

an amplifier

? Describe several techniques for making noise

measurements

? Explain the relationship among information,

bandwidth,and time of transmission

? Analyze nonsinusoidal repetitive waveforms via

Fourier analysis

? Analyze the operation of various RLC circuits

? Describe the operation of common LC and crystal

oscillators

INTRODUCTORY TOPICS

Key Terms

INTRODUCTORY TOPICS

modulation

intelligence signal

intelligence

demodulation

transducer

dB

dBm

0 dBm

dBm(600)

dBm(75)

dBm(50)

dBW

dB V

electrical noise

static

external noise

internal noise

wave propagation

atmospheric noise

space noise

solar noise

cosmic noise

Johnson noise

thermal noise

white noise

low-noise resistor

shot noise

excess noise

transit-time noise

signal-to-noise ratio

noise figure

noise ratio

octave

Friiss’s formula

device under test

tangential method

information theory

channel

Hartley’s law

Fourier analysis

FFT

frequency domain record

aliasing

quality

leakage

dissipation

resonance

tank circuit

poles

constant-k filter

m-derived filter

roll-off

stray capacitance

oscillator

flywheel effect

damped

continuous wave

Barkhausen criteria

frequency synthesizer

1-1 INTRODUCTION

This book provides an introduction to all relevant aspects of communications systems.

These systems had their beginning with the discovery of various electrical,

magnetic,and electrostatic phenomena prior to the twentieth century.Starting with

Samuel Morse’s invention of the telegraph in 1837,a truly remarkable rate of

progress has occurred.The telephone,thanks to Alexander Graham Bell,came

along in 1876.The first complete system of wireless communication was provided

by Guglielmo Marconi in 1894.Lee DeForest’s invention of the triode vacuum tube

in 1908 allowed the first form of practical electronic amplification and really

opened the door to wireless communication.In 1948 another major discovery in the

history of electronics occurred with the development of the transistor by Shockley,

Brattain,and Bardeen.The more recent developments,such as integrated circuits,

very large-scale integration,and computers on a single silicon chip,are probably familiar

to you.

The rapid transfer of these developments into practical communications systems

linking the entire globe (and now into outer space) has stimulated a bursting

growth of complex social and economic activities.This growth has subsequently

had a snowballing effect on the growth of the communication industry

with no end in sight for the foreseeable future.Some people refer to this as the

age of communications.

The function of a communication system is to transfer information from one

point to another via some communication link.The very first form of “information”

electrically transferred was the human voice in the form of a code (i.e.,the

Morse code),which was then converted back to words at the receiving site.People

had a natural desire and need to communicate rapidly between distant points on

the earth,and that was the major concern of these developments.As that goal became

a reality,and with the evolution of new technology following the invention

of the triode vacuum tube,new and less basic applications were also realized,such

as entertainment (radio and television),radar,and telemetry.The field of communications

is still a highly dynamic one,with advancing technology constantly making

new equipment possible or allowing improvement of the old systems.

Communications was the basic origin of the electronics field,and no other major

branch of electronics developed until the transistor made modern digital computers

a reality.

Modulation

Basic to the field of communications is the concept of modulation.Modulation is

the process of putting information onto a high-frequency carrier for transmission.In

essence,then,the transmission takes place at the high frequency (the carrier) which

has been modified to “carry” the lower-frequency information.The low-frequency

information is often called the intelligence signal or,simply,the intelligence.It follows

that once this information is received,the intelligence must be removed from

the high-frequency carrier―a process known as demodulation.At this point you

may be thinking,why bother to go through this modulation/demodulation process?

Why not just transmit the information directly? The problem is that the frequency of

the human voice ranges from about 20 to 3000 Hz.If everyone transmitted those frequencies

directly as radio waves,interference would cause them all to be ineffective.

Another limitation of equal importance is the virtual impossibility of transmitting

such low frequencies since the required antennas for efficient propagation would be

miles in length.

The solution is modulation,which allows propagation of the low-frequency

intelligence with a high-frequency carrier.The high-frequency carriers are chosen

such that only one transmitter in an area operates at the same frequency to

minimize interference,and that frequency is high enough so that efficient

antenna sizes are manageable.There are three basic methods of putting lowfrequency

information onto a higher frequency.Equation (1-1) is the mathematical

representation of a sine wave,which we shall assume to be the highfrequency

carrier.

(1-1)

where instantaneous value

peak value

Any one of the last three terms could be varied in accordance with the low-frequency

information signal to produce a modulated signal that contains the intelligence.If

the amplitude term,,is the parameter varied,it is called amplitude modulation

(AM).If the frequency is varied,it is frequency modulation (FM).Varying the phase

angle,,results in phase modulation (PM).In subsequent chapters we shall study

these systems in detail.

Communications Systems

Communications systems are often categorized by the frequency of the carrier.

Table 1-1 provides the names for various frequency ranges in the radio spectrum.

The extra-high-frequency range begins at the starting point of infrared frequencies,

but the infrareds extend considerably beyond 300 GHz ( Hz).After the

infrareds in the electromagnetic spectrum (of which the radio waves are a very

small portion) come light waves,ultraviolet rays,X rays,gamma rays,and cosmic

rays.

300 109

￡

VP

￡ phase angle

v angular velocity 2pf

VP

v

v VP sin 1vt ￡2

Radio-Frequency Spectrum

Frequency Designation Abbreviation

30?300 Hz Extremely low frequency ELF

300?3000 Hz Voice frequency VF

3?30 kHz Very low frequency VLF

30?300 kHz Low frequency LF

300 kHz?3 MHz Medium frequency MF

3?30 MHz High frequency HF

30?300 MHz Very high frequency VHF

300 MHz?3 GHz Ultra high frequency UHF

3?30 GHz Super high frequency SHF

30?300 GHz Extra high frequency EHF

Figure 1-1 represents a simple communication system in block diagram form.

Notice that the modulated stage accepts two inputs,the carrier and the information (intelligence)

signal.It produces the modulated signal,which is subsequently amplified

before transmission.Transmission of the modulated signal can take place by any one

of four means: antennas,waveguides,optical fibers,or transmission lines.These four

modes of propagation will be studied in subsequent chapters.The receiving unit of the

system picks up the transmitted signal but must reamplify it to compensate for attenuation

that occurred during transmission.Once suitably amplified,it is fed to the demodulator

(often referred to as the detector),where the information signal is extracted

from the high-frequency carrier.The demodulated signal (intelligence) is then fed to

the amplifier and raised to a level enabling it to drive a speaker or any other output

transducer.A transducer is a device that converts energy from one form to another.

Many of the performance measurements in communication systems are specified

in dB (decibels).Section 1-2 introduces the use of this very important concept

in communication systems.This is followed by two basic limitations on the performance

of a communications systems: (1) electrical noise and (2) the bandwidth

of frequencies allocated for the transmitted signal.Sections 1-3 to 1-6 are devoted

to these topics because of their extreme importance.

1-2 THE dB IN COMMUNICATIONS

Decibels (dBs) are used to specify measured and calculated values in noise analysis,

audio systems,microwave system gain calculations,satellite system link-budget

analysis,antenna power gain,light-budget calculations,and many other communications

system measurements.In each case,the dB value is calculated with respect to a

standard or specified reference.

The dB value is calculated by taking the log of the ratio of the measured or

calculated power ( ) with respect to a reference power ( ) level.This result is

then multiplied by 10 to obtain the value in dB.The formula for calculating the dB

value of two ratios is shown in Equation (1-2).Equation (1-2) is commonly referred

to as the power ratio form for dB.

(1-2)

By using the power relationship ,the relationship shown in Equation (1-3)

is obtained:

Let:

(1-3)

Note that we have assumed that the resistances ( and ) are equivalent; therefore,

these terms can be ignored in the dB power equation.This is a reasonable assumption

in most communication systems since maximum power transfer (a desirable

characteristic) is obtained when the input and output impedances are matched.

Equation (1-3) can be modified (using a property of logarithms) to provide a relationship

for decibels in terms of the voltage ratios instead of power ratios.This is

called the voltage gain equation and is shown in Equation (1-4).

(1-4)

Applying the dB Value

The dB unit is often used in specifying input- and output-signal-level requirements

for many communication systems.When making dB measurements,a reference

level is specified or implied for that particular application.An example is found in

audio consoles in broadcast systems,where a 0-dBm input level is usually specified

as the required input- and output-audio level for 100% modulation.Notice that a

lowercase m has been attached to the dB unit.This indicates that the specified dB

level is relative to a 1-mW reference.

In standard audio systems 0 dBm is defined as 0.001 W measured with

respect to a load termination of .600 600- balanced audio line is the