Instruc t or’s
Manu a l
t o a c c om p any
MODERN EL EC TR ONIC
COMMUNICATION
Ni n t h Ed i t i o n
Je f f rey S. Beasley
Ga ry M. M i l ler
______________________________________________________________________________ ____
C o p y r i g h t © 200 8 by Pears o n Ed uc a t i o n, Inc., Uppe r Sa dd le R i ve r, Ne w Je rse y 07 4 5 8. Pearson Prentice Hall. All rights reserved. Printed in the United States of America. This publication is protected by Copyright and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to: Rights and Permissions Department.
Pears o n Pre n t ic e Ha l l ™ is a trademark of Pearson Education, Inc. Pears o n® is a registered trademark of Pearson plc
Pre nt ic e Ha l l® is a registered trademark of Pearson Education, Inc.
Instructors of classes using Beasley/Miller, Modern Electronic Communication, Ninth Edition,may reproduce material
Instructor’s Manual
to Accompany
M
ODERN
E
LECTRONIC
C
OMMUNICATION / 9e
Chapter Overviews
Test Item File
Answers to Chapter Problems
Troubleshooting with Electronics Workbench - Solutions
Laboratory Manual Experiment Results
Electronic Workbench Multisim - Solutions
CONTENTS
Part I: Chapter Overviews
Chapter 1: Introductory Topics 1
Chapter 2: Amplitude Modulation: Transmission 4
Chapter 3: Amplitude Modulation: Reception 7
Chapter 4: Single-Sideband Communication 10
Chapter 5: Frequency Modulation: Transmission 12
Chapter 6: Frequency Modulation: Reception 15 Chapter 7: Communications Techniques 17
Chapter 8: Digital Communication: Coding Techniques 19 Chapter 9: Wired Digital Communication 21
Chapter 10: Wireless Digital Communications 23
Chapter 11: Network Communications 25
Chapter 12: Transmission Lines 28
Chapter 13: Wave Propagation 30
Chapter 14: Antennas 32
Chapter 15: Waveguides and Radar 34
Chapter 16: Microwaves and Lasers 37
Chapter 17: Television 39
Chapter 18: Fiber Optics 42
Part II: Test Item File
Chapter 1 44 Chapter 2 53 Chapter 3 64 Chapter 4 78 Chapter 5 91 Chapter 6 106 Chapter 7 112 Chapter 8 117 Chapter 9 122 Chapter 10 126 Chapter 11 134 Chapter 12 143 Chapter 13 151 Chapter 14 157 Chapter 15 162 Chapter 16 168 Chapter 17 172 Chapter 18 179Part III: Answers to Chapter Problems
Chapter 1 188 Chapter 2 199 Chapter 3 208 Chapter 4 216 Chapter 5 222 Chapter 6 229 Chapter 7 233 Chapter 8 238 Chapter 9 243 Chapter 10 247 Chapter 11 251 Chapter 12 259 Chapter 13 283 Chapter 14 289 Chapter 15 297 Chapter 16 305 Chapter 17 311 Chapter 18 319PART IV: Troubleshooting with EWB Multisim - Solutions
Chapter 1: Understanding the Frequency Spectra 324Chapter 2: AM Measurements 324
Chapter 3: AM Demodulation 325
Chapter 4: Single-Sideband Generation 325
Chapter 5: Generating and Analyzing the FM Signal 326 Chapter 6: FM Receiver Blocks 326
Chapter 7: Mixer and Squelch Circuits 327
Chapter 8: Sampling the Audio Signal 327
Chapter 9: Sequence Detector 328
Chapter 10: BPSK Transmit-Receive Circuit 328
Chapter 11: Audio Signal Measurements 329
Chapter 12: Network Analyzer 329
Chapter 13: Crystals and Crystal Oscillators 330
Chapter 14: Dipole Antenna Simulation and Measurements 330
Chapter 15: Lossy Transmission Lines and Low-Loss Waveguide 331 Chapter 16: Characteristics of High-Frequency Devices 331 Chapter 17: The Television RF Spectrum 332
Chapter 18: Light Budget Simulation 332
Part V: Laboratory Manual Experiment Results
1 Active Filter Networks 333
2 Frequency Spectra of Popular Waveforms 341
3 Tuned Amplifiers and Frequency Multiplication 346 4 Low-Pass Impedance Transformation Networks 350
5 Phase-Shift Oscillator 354
6 LC Feedback Oscillator 358
7 Colpitts RF Oscillator Design 361
8 Hartley RF Oscillator Design 365
9 Swept-Frequency Measurements 368
10 Nonlinear Mixing Principles 374
11 AM Modulation Using an Operational Transconductance Amplifier 378 12 RF Mixers and Superhetereodyne Receivers 386
13 Cascode Amplifiers 394
14 Sideband Modulation and Detection 403
15 Frequency Modulation: Spectral Analysis 412 16 Phase-Locked Loops: Static and Dynamic Behavior 418 17 FM Detection and Frequency Synthesis Using PLLs 424 18 Pulse Amplitude Modulation and Time Division Multiplexing 429 19 Pulse Width Modulation and Detection 436 21 Digital Communication Link Using Delta Modulation Codecs 440 22 Electronics Workbench Multisim - dB Measurements in Communications 446 23 Electronics Workbench Multisim – Smith Chart Measurements 449
Using the EWB Network Analyzer
24 Tone Decoder 452
32 Using a Spectrum Analyzer 454
33 Using Capacitors for Impedance Matching 455 34 Electronics Workbench Multisim – Impedance Matching 457 35 AM Generation Using an Electronic Attenuator 459
36 Generating FM from a VCO 460
Part VI Electronics Workbench Multisim
EWB Complementary Exercises
Experiment 1 – EWB 462
Simulation of an ACTIVE FILTER NETWORKS
Experiment 2 – EWB 464
USING THE SPECTRUM ANALYZER and the SIMULATION and ANALYSIS of COMPLEX WAVEFORMS
Experiment 3 – EWB 467
Simulation of Class C Amplifiers and Frequency Multipliers
Experiment 5 – EWB 469
Simulation of a Phase-Shift Oscillator
Experiment 6 – EWB 471
Simulation of an LC Feedback Oscillator
Experiment 11 – EWB 473
Percentage of Modulation Measurement of an Amplitude Modulated Waveform
OVERVIEW – CHAPTER 1
INTRODUCTORY TOPICS
1-1 INTRODUCTION
Following a brief introduction to the field of electronic communications, the concept of modulation is introduced. At this early stage very basic words such as a carrier “carrying” the information are used. Equation 1-1 shows the three characteristics of a carrier that could be modified to carry the information include the amplitude, frequency, and phase. These concepts form the basis for Chapters 2-6. Table 1-1 describes the sub-divisions within the radio-frequency spectrum and Fig. 1-1 presents a simple communication system in block diagram form. A discussion of it should get your students thinking and whet their appetite for the chapters that follow.
1-2 The dB in COMMUNICATIONS
The dB (decibel) is an extremely important measure in communications. Decibels
are used to specify measured and calculated values in communications system
measurements. The equations for calculating dB using power and voltage ratios are
provided in equations 1-2 and 1-3. Examples 1-1 to 1-3 demonstrate the method for
calculating and converting dB values. Another technique for converting many common
dB values is provided in Table 1-2. Tables and computer programs are often used on the
job for performing most dB calculations or conversions. A list of common decibel terms
is provided in Table 1-3.
1-3 NOISE
A fundamental limitation in communication systems is noise. This, of course, is due to the fact that the signal picked up by the receiver is very small. Separating it from all the various sources of noise is a critical task. The various types of external noise (man-made, atmospheric, and space) and internal noise (thermal, transistor, and flicker) are described. The calculations associated with thermal and noise voltage are facilitated with Examples 1-4 and 1-5.
1-4 NOISE DESIGNATION AND CALCULATION
The important concept of signal-to-noise ratio is introduced as a simple ratio (Eq. 1-12) and in decibel form (Eq. 1-13). This is followed by defining the noise figure as the ratio of S/N at the input over the S/N at the output. Some practice on the related calculations is provided in Example 1-6.
The concepts of reactance noise effects, noise due to amplifiers in cascade, equivalent noise temperature, and equivalent noise resistance close out this section. The importance of related calculations is indicated by the many examples provided to help your students master these topics.
1-5 NOISE MEASUREMENT
The use of a diode noise generator to make some basic noise measurements is introduced. A simple yet effective measurement technique using the diode noise generator is illustrated in Example 1-10. A quick and useful measurement technique using a basic dual-trace oscilloscope
1-6 INFORMATION AND BANDWIDTH
There are two fundamental limitations on the performance of a communication system. Besides the noise effects just introduced, the bandwidth allocated for transmission is the other basic limitation. Hartley’s law states that the amount of information that can be transmitted is proportional to the bandwidth times the time of transmission. To help the student understand the bandwidth that various signals occupy, an introduction to understanding the frequency spectra is provided. This basically non-mathematical approach promotes understanding of a signal’s sinusoidal harmonics and how they combine to form complex signals. The square wave waveform analysis in Fig. 1-9 and 1-10 provides graphic illustration of this process. Visual examples of the frequency components making up complex waveforms are provided in Figures 1-11 and 1-12. These are the FFT representations for a sine wave and a square wave. Table 1-4 gives Fourier expressions for somecommon periodic waveforms. Figure 1-13 demonstrates the effect a bandwidth-limited signal has on a square wave.
1-7 LC CIRCUITS
Sections 1-7 and 1-8 cover some basic characteristics of LC circuits and oscillators. If your students have a good background to this from previous studies, you may wish to omit them. The characteristics of inductors and capacitors are introduced including the concepts of quality (Q) and dissipation (D) factors. This is followed by the concept of resonance and bandpass filters. Examples 1-13 and 1-14 provide practice calculating bandwidth, Q, required component values, and resonant frequencies.
1-8 OSCILLATORS
Oscillators are key elements in communication systems. The concept of creating a sine wave via the “flywheel” effect is introduced with the help of Fig. 1-21. An analysis of some common LC oscillators follows including the Hartley, Colpitts, and Clapp oscillators. The very important crystal oscillator is then detailed. Table 1-5 provides stability and cost information for four different crystal oscillator configurations. A useful crystal test circuit is shown in Fig. 1-29.
1-9 TROUBLESHOOTING
All chapters of this text are concluded with a troubleshooting section. The importance of developing good troubleshooting skills cannot be over-emphasized. Employers and accrediting agencies are in strong agreement on this matter. Each one of these sections provides
troubleshooting skills related to the chapter’s topics. Often some general troubleshooting techniques are also included as is the case with this section.
This section opens with a comprehensive overview of troubleshooting. This is followed by detail on the four types of circuit failures. Detail on the four basic troubleshooting techniques (symptoms, signal tracing and injection, voltage and resistance measurements, and substitution) concludes the general troubleshooting material.
Testing a crystal with the aid of the block diagram in Fig. 1-32 is discussed. This section is concluded with information on testing the inductors and capacitors in a Clapp oscillator. A section on understanding digital sampling oscilloscope waveforms is also included in this section. This section discusses the importance of selecting the sample frequency and the effect an
1-10 TROUBLESHOOTING WITH ELECTRONICS WORKBENCH MULTISIM
Representative computer simulations using Electronics Workbench (EWB) Multisim are provided in each chapter in this text. The computer files are provided in the CD-ROM which comes with the text. The use of virtual instruments is incorporated into each chapter’s presentation on using EWB Multisim. Detailed steps are used in the text to lead the student through each of the virtual experiments.
In Chapter 1, the oscilloscope and the spectrum analyzer virtual instruments are used to examine the properties of a square wave. The performance and operation of these virtual
instruments closely resemble real test equipment and the user has the ability to make connections and adjustments comparable to that made on equipment when working on a bench. Three EWB exercises are included to further develop the student’s understanding of the simulation tool and the virtual instruments. The files provided in the text’s CDROM support both the newer
Multisim 9 (.ms9), Multisim 7 (.ms7) and Multisim 6 (.msm) formats. The files are located in the ms9, ms7 or msm folders in each respective chapter.
OVERVIEW – CHAPTER 2
AMPLITUDE MODULATION: TRANSMISSION
2-1 INTRODUCTION
This is a critical point in your students' study. While modulation has been introduced in Chapter 1, it is now time for the student to really come to an understanding of what it is all about. It may be a good idea to give a quiz after covering Sections 1 through 4 just to make sure that a reasonable level of comprehension has been attained.
2-2 AMPLITUDE MODULATION FUNDAMENTALS
A good way to introduce the basic AM process is to compare the linear combination of two signals in Fig. 2-1 with the nonlinear combination in Fig. 2-2. Emphasize that only the non-linear combination produces an AM signal. You also might want to explain why the transmission of the linear combination would leave just the carrier at the receiver while the AM signal should be received basically as transmitted.
The equation defining the AM waveform is provided in equation 2-1. This is also a good opportunity to review or introduce the importance trigonometric relationship (sin x)(sin y), equation 2-2.
You will find that a thorough discussion of the transmission of a range of modulation frequencies will now be possible. A detailed study of Example 2-1 should be most helpful here. The phasor analysis is also important, as for many students this is when something finally falls together, the light bulb goes on, and now they have seen the light.
2-3 PERCENTAGE MODULATION
The concept of percentage modulation is usually mastered with ease. In fact, your students will probably enjoy making some quantitative calculations such as illustrated in Example 2-2. This is also a good time to introduce the concept of overmodulation and talk about the problems that it causes.
2-4 AM ANALYSIS
Your students may be somewhat resistant to the brief mathematical analysis at the beginning of this section but it is important to their overall understanding. This is their first exposure to a form of modulation and they need to realize that this is not some form of magic—it does withstand analysis with some basic mathematical tools.
The importance of transmitting a high-percentage of modulation is now understandable— just make sure they remember that overmodulation is taboo. It is now time to indicate that the carrier in AM systems effectively wastes a lot of transmitter power. Examples 2-3 through 2-8 illustrate a number of useful calculations regarding percentage modulation, total power, carrier power and sideband power.
2-5 CIRCUITS FOR AM GENERATION
It is now time to introduce some circuits used to create AM. The whole key here is that it takes a nonlinear combination of carrier and intelligence to generate AM. The difference between high-level and low-level modulation is discussed. Be sure to stress that this has nothing to do with high-percentage modulation. Use Fig. 2-12 to help explain the difference between high and low-level modulation.
It is certainly true that IC modulators are used in the majority of new designs.
Introduction of several discrete device designs is still important to overall understanding and in working with older equipment. However, there is certainly nothing wrong with emphasizing the linear integrated circuit designs at this time.
2-6 AM TRANSMITTER SYSTEMS
At this point it is appropriate to talk about a complete transmitter system as opposed to just the AM modulator. The citizens band transmitter described here is simple enough so that the student can comprehend the various system aspects without getting bogged down with too many details. The concept of coupling transmitter power to an antenna is introduced as is some detail on the fabrication and tuning of this compact transmitter.
2-7 TRANSMITTER MEASUREMENTS
At this point your students may be anxious to learn some laboratory measurements useful in AM analysis. The trapezoid pattern technique is very good for measuring percentage
modulation and for pinpointing some specific problems with the modulator. It is also important to realize that some meaningful measurements can be made with a dc ammeter. The spectrum analyzer is also introduced at this point. It is one of the most important instruments available for communication’s equipment and it may be new to some of your students. Its use in making harmonic distortion measurements is provided and Example 2-9 provides a sample computation.
This section is concluded with some precautions to take when making measurements on RF circuits. It is often troublesome for the beginner to understand that the measurement tool can be changing the measurement. It is important to also understand why this is happening.
2-8 TROUBLESHOOTING
The first discussion has to do with the importance of initially inspecting a piece of equipment when repair is necessary. The novice is surprised at how much time is saved by this process. If inspection by itself has not cleared up the problem then a strategy for repair should be developed. This includes verification that a problem exists, isolation of the defective stage, isolation of the defective component, and replacement of the defective component.
Troubleshooting a simple self-biased RF amplifier is then provided. This includes looking at the effects of various components being opened or shorted. It is very important for the student to start thinking about shorts and opens as this is such a prevalent type of failure.
The process of checking an entire transmitter is the next topic. Be sure to emphasize the material on safety provided when working on high voltage systems. Troubleshooting topics covered include improper frequency of operation, measurement of output power, and how to remedy these parameters when they are not in specification.
2.9 TROUBLESHOOTING WITH ELECTRONICS WORKBENCH MULTISIM
The EWB Multisim tools are used to simulate an AM modulator circuit. The
student will gain additional experience measuring the modulation index of an AM
signal. This exercise also enhances the students understanding of the carrier and
modulating signal components of the AM envelope. The oscilloscope virtual
instrument is used extensively in this exercise for making measurements on the
waveform. The EWB exercises provide the opportunity for the student to test their
ability to determine the modulation index and the carrier frequency of an AM signal.
OVERVIEW – CHAPTER 3
AMPLITUDE MODULATION: RECEPTION
3-1 RECEIVER CHARACTERISTICS
You may find it helpful to get your students thinking about a receiver by asking them to think about a desirable design for its block diagram. A likely outcome is the TRF concept introduced in this section. This can then lead to a discussion of receiver sensitivity and selectivity, important concepts to carefully consider at this point.
The basic problem of variable selectivity in a TRF receiver is the main reason that it is not a viable design today. Variable selectivity can easily be shown by working through Example 3-1.
3-2 AM DETECTION
A key to the detection process is to stress that it takes a nonlinear device just as a non-linear device was necessary to create the AM signal. The basic diode detector is described and Fig. 3-3 can be used to explain the waveforms in a typical circuit. The potential problem of diagonal clipping is introduced and the synchronous detector is also provided. An Electronics Workbench Multisim implementation of a synchronous AM detector is provided in Figure 3-5(a).
This is a good place to reinforce the concept of a mixer circuit and the function of the
synchronous detection circuit.
3-3 SUPERHETERODYNE RECEIVERS
The variable selectivity problem with TRF receivers explained in Section 3-1 should be mentioned again at this point because now the solution is at hand. The superheterodyne
(superhet) receiver, first used in the l930’s, has proven to be the dominant receiver format to this day. It should therefore be carefully introduced, as your relatively unsophisticated
communication students will be a bit confused by some of the details of this concept. The frequency conversion process explanation will be enhanced by using the block diagrams of Figs. 3-7 and 3-8.
3-4 SUPERHETERODYNE TUNING
The bulk of today’s receivers use frequency synthesis tuning. This is mentioned here but its detailed discussion is in Chapter 7. It is good to stick to the basics for now as the student’s mastery skills are developing. The variable ganged capacitor tuning is used for the introduction in Section 3-3 and a varicap diode electronic tuning circuit is provided in this section. These tuning methods are still prevalent in low cost receivers. The tracking problems of these tuning systems is explained and the tracking adjustment process described.
3-5 SUPERHETERODYNE ANALYSIS
The problem of image frequency is a bit confusing but by the time the student attains comprehension, the whole superheterodyne concept will usually click into place. If you discuss Figs. 3-13 and 14 an understanding of when images are and are not going to be a problem should be accomplished. The use of double conversion to circumvent the image problem is mentioned but left for a full discussion in Chapter 7.
The remainder of this section introduces various circuits commonly used for RF amplifiers, IF amplifiers and the mixer/local oscillator. You may want to use transparencies of these circuits to enhance your explanation and discussions.
3-6 AUTOMATIC GAIN CONTROL
To initiate AGC discussion, ask your students if all received signals are at the same level. The obvious answer is no, but then ask them why the speaker output is basically constant for all those different signals. This should establish the need for AGC and is a natural lead-in to how it is accomplished. The first step is to obtain the AGC level—some dc level proportional to signal strength. The next step is to control the gain of an amplifier to allow maintaining a relatively constant output level. A discrete AGC circuit illustration is provided in Fig. 3-19 while Fig. 3-20 provides an IC AGC system.
3-7 AM RECEIVER SYSTEMS
We’re now in a position to “put it all together” by looking at a complete AM receiver system. A discussion of the discrete system shown in Fig. 3-21 can be kind of exciting to the student when realization that comprehension of such a complicated schematic is possible. Once again, an overhead transparency display to accompany the discussion (and Fig. 3-22 for an IC receiver) is very helpful. The AM stereo receiver shown in Fig. 3-25 is also appropriate at this time.
This section concludes providing a receiver analysis with respect to the power gain or attenuation of all the various stages. A discussion of Example 3-3 should facilitate an
understanding of the power levels throughout a receiver. It also serves to illustrate the use of dbm and dbW in this type of analysis.
3-8 TROUBLESHOOTING
Some detailed troubleshooting is provided regarding the self-excited mixer shown in Fig. 3-27. Additionally, Table 3-1 provides experience using a troubleshooting chart. The use of these types of troubleshooting aids is common in the industry. A basic series-pass electronically regulated power supply is provided in Fig. 3-28 and detailed techniques for its repair are
3-9 TROUBLESHOOTING WITH ELECTRONICS WORKBENCH MULTISIM
The diode detector circuit is simulated using EWB Multisim in this exercise. A
virtual AM source, provided by the EWB Multisim tool, is used to generate the AM
signal for inputting to the diode detector. The instructor and the student will like the ease
that the AM source can be adjusted. The diode detector circuit also contains a “virtual”
variable capacitor. The student will be able to increase or decrease the value of the
capacitor by pressing c or C to determine if varying the capacitor value effects the
recovered signal.
The chapter 3 EWB Multisim exercise introduces a virtual exercise in
troubleshooting a communications circuit. EWB Multisim provides a feature which
allows for the addition of a component fault in the circuit. The student will be able to test
their troubleshooting knowledge and their understanding of the circuit operation to
determine which component(s) have failed. The student will have many virtual
instruments to use in the troubleshooting process including the oscilloscope and the
multimeter. Component repair is easily accomplished by double-clicking on the
component, and correct the setting under the Fault tab. The EWB exercises include two
virtual circuits which contain faults. These exercises can be used to test the student’s
troubleshooting ability and circuit knowledge. A third exercise requires the student to
adjust virtual capacitors to minimize the RF noise and to record their settings.
OVERVIEW – CHAPTER 4
SINGLE-SIDEBAND COMMUNICATION
4-1 SINGLE-SIDEBAND CHARACTERISTICS
This section begins with a bit of history on the development of SSB. As was mentioned in the AM chapters, the carrier contains no information and yet contains most of the power in the AM transmission. The sidebands contain the information but with (at most) 1/3 the power. A discussion of peak envelope power is also provided.
A number of different types of SSB are used. The remainder of this section introduces them and concludes with a discussion of the advantages of SSB over standard AM.
4-2 SIDEBAND GENERATION: THE BALANCED MODULATOR
The balanced modulator is a widely used circuit in electronic communications. Since this is the first encounter a detailed look at it is given here. The balanced ring modulator and a linear integrated circuit balanced modulator are described. The output of these modulators is a double-sideband signal but the carrier has been suppressed. The next two sections will address changing from this double-sideband signal to a single-sideband signal.
4-3 SSB FILTERS
The elimination of one of the sidebands in a DSB signal can be accomplished with a high-Q filter. Example 4-1 provides clear illustration of this fact. Crystal filters are used in the most demanding of these requirements. Since they were covered in Chapter 1, a relatively brief review is provided at this point.
Ceramic filters are widely used in today’s communication circuits. They offer Q’s that are less than crystal filters but much better than standard LC filters. Surprisingly, mechanical filters are still used in some SSB applications. This section concludes with a discussion of their characteristics.
4-4 SSB TRANSMITTERS
There are two basic systems used to create SSB, the filter method and the phase method. The block diagram in Fig. 4-8 is useful as a transparency to help the student understand the filter method. It is pretty straightforward, but a discussion of the block diagram should make it crystal clear. The phase method is a bit more difficult for the student but the block diagram of Fig. 4-10 along with a mathematical discussion using Eqs. 4-2, 3 and 4 should take care of it.
Also introduced in this section is the concept of amplitude compandoring. This allows the lower level signals to be transmitted with greater power while staying within the PEP ratings of the transmitter. This section concludes with a discussion of linear power amplifiers. You may wish to use Fig. 4-13 as a transparency for a classroom analysis.
4-5 SSB DEMODULATION
Up to this point the many advantages of SSB have been extolled. The demodulation of SSB exposes a fundamental drawback. The carrier must somehow be recombined with a sideband through a non-linear device in order to recover the intelligence. So the carrier that we removed at the transmitter must somehow be recreated at the receiver. Some techniques for doing this are the subject of this section.
4-6 SSB RECEIVERS
The block diagram of a typical SSB receiver is given in Fig. 4-17. It basically looks like a superhet AM receiver except for second mixer (detector) and the block that reinserts the carrier-often referred to as the beat frequency oscillator (BFO). The complete receiver schematic in Fig. 4-18 makes a good discussion circuit when displayed as a transparency.
4-7 TROUBLESHOOTING
The first topic of this section involves a basic balanced modulator circuit. Testing for carrier leakthrough is described using an oscilloscope. Checking carrier suppression using a spectrum analyzer is also introduced. A technique for checking the filter used to suppress one of the sidebands is the next troubleshooting topic. This is followed by an explanation of the two-tone test for testing the linearity of a linear amplifier.
The final topic in this chapter’s troubleshooting section is to discuss a technique for testing an entire receiver by using signal injection. Table 4-1 summarizes the procedure in conjunction with the block diagram shown in Fig. 4-26.
4-8 TROUBLESHOOTING WITH ELECTRONIC WORKBENCH MULTISIM
This exercise demonstrates an important fundamental concept of communications
which is the production of the sum and difference frequencies. A multiplier, provided in
the Multisim tools, is used in this example to produce the sum and difference frequencies
however a balanced modulator and “mixer” circuits produce the same result. The
complex waveform output, generated by the multiplier, is analyzed using the virtual
spectrum analyzer.
The exercise includes a demonstration of removing the lower sideband using a
five-element Chebyshev filter to produce a SSB signal. The spectrum analyzer is used to
verify that the lower sideband has been significant attenuated.
The exercise includes a troubleshooting example in which a fault has been
introduced in the filter. The students are guided through the troubleshooting exercise and
are reminded to perform a visual check of the circuit. The EWB questions include an
exercise where the student must tune a high-pass filter circuit and troubleshoot two
circuits which contain faults
OVERVIEW – CHAPTER 5
FREQUENCY MODULATION: TRANSMISSION
5-1 ANGLE MODULATION
Angle modulation includes phase modulation and frequency modulation. Phase modulation is not widely used but has importance as a means of generating frequency
modulation. The study of FM is crucial to the communication student. A relatively slow start in this study may be beneficial as the initial concepts are a bit more difficult than for amplitude modulation.
5-2 A SIMPLE FM GENERATOR
The capacitor microphone FM generator in Fig. 5-1 provides an excellent starting point for an understanding of FM basics. This circuit is not normally used in practical FM systems but is an excellent learning device. With it, the student can grasp the concept that intelligence amplitude determines the amount of frequency change and intelligence frequency determines the rate of frequency change. Equation 5-1 describes the relationship for the FM signal generate by the capacitor microphone. A discussion of Ex. 5-1 should help to reinforce these concepts as the students work at reorienting themselves from AM systems. We have found it beneficial to remind them as we move on through Chapters 5 and 6 to think back on this simple capacitor mike circuit whenever confusion on the FM basics sets in.
5-3 FM ANALYSIS
This section opens with some basic mathematical analysis of FM and PM. The use of Bessel functions to determine amplitude of the side-frequencies is introduced. Examples 5-3 through 5-5 provide illustration of how to apply this analysis in determination of bandwidth, modulation index and the power in the various side-frequencies. A bandwidth approximation, known as Carson’s rule, is presented in equation 5-7. This important relationship should be included along with the discussion on the Bessel functions.
It is interesting to discuss the fact that at various levels of modulation index the carrier power goes to zero and all the power is in the side-frequencies. The zero carrier amplitude discussion is followed by introduction of broadcast and narrowband FM systems. Example 5-6 does some calculations relative to the broadcast and narrowband systems.
5-4 NOISE SUPPRESSION
One of the main reasons that FM has become so popular is its ability to suppress noise that can be troublesome to AM systems. The concept of a noise spike not passing through a limiter compared to AM systems (where limiter use is not possible since it would destroy the intelligence) is easily demonstrated with the help of Fig. 5-6. Unfortunately, even though the spike is eliminated, not all of its effect is gone since it has also created a phase shift which means an undesired frequency shift. The analysis of how that effect is minimized is explained, and working with Exs. 5-8 and 9 will greatly enhance understanding this process.
Once the noise reduction process is understood it becomes easy to introduce the concept of the capture effect. It also eases one into the need for preemphasis in FM systems and the usefulness of dynamic preemphasis which is what the Dolby system is all about.
5-5 DIRECT FM GENERATION
The two basic categories of FM generation are direct and indirect. In this section some common means of direct generation are introduced. The use of a varactor diode in direct generation is explained with the use of Fig. 5-12. The reactance modulator is also introduced. The easily used linear integrated circuit, voltage-controlled oscillator (LIC-VCO) is then provided and the spec sheet for the 566 VCO is provided in Fig. 5-14.
The Crosby direct FM transmitter is detailed next. A discussion using the block diagram in Fig. 5-15 is very helpful in allowing the student to get the big picture for this type of
transmitter. This section concludes with a discussion of basic frequency doubler operation.
5-6 INDIRECT FM GENERATION
Indirect FM generation is accomplished by first generating phase modulation and then making a conversion to FM. This allows you to apply the modulating signal to a stable crystal oscillator. This type of system is called an Armstrong modulator. The conversion from PM to FM and obtaining enough deviation makes this a fairly complex system. A complete system block diagram with frequencies for a 90.2 MHz carrier is provided in Fig. 5-18.
5-7 PHASE-LOCKED LOOP FM TRANSMITTER
The use of a PLL to generate FM is the topic of this section. The system illustrated in Fig. 5-20 starts with a varactor-controlled crystal oscillator/modulator. Its output is an input of the phase detector in the PLL. A complete PLL FM transmitter schematic is provided in Fig. 5-21. A description of circuit operation is given and detail on alignment and operation on other bands is also discussed. A single-chip FM transmitter is show in Fig. 5-22 using the Maxim 2606 IC. This IC is designed for home audio use and an FM system is very simple for the student to construct.
5-8 STEREO FM
Students are usually quite interested in how stereo FM is implemented. The discussion of how two separate signals can be transmitted in the same bandwidth and still be compatible with a mono broadcast is a good way to introduce the student to a frequency division multiplexing system. You will find it helpful to have the information contained in Figs. 5-23 and 24 on
transparency to help student comprehension. A discussion on why the stereo signal is more prone to noise than the mono broadcast is sometimes helpful to overall student understanding of this system.
5-9 FM TRANSMISSIONS
This section introduces the five major categories of FM transmissions. The ability for FM to use highly efficient Class C power amplifiers as compared to the need for less efficient linear amplifiers for AM and SSB is also discussed.
5-10 TROUBLESHOOTING
The first troubleshooting concept is dealing with FM transmitter systems. Techniques for dealing with no RF output, incorrect frequency and incorrect deviation are provided. A reactance modulator is then analyzed in detail and Table 5-3 provides a summary of problems and probable causes. The next topic deals with troubleshooting the stereo/SCA FM signal generator. This is a good exercise to help the student fully understand its operation as well as troubleshooting
5-11 TROUBLESHOOTING WITH ELECTRONICS WORKBENCH MULTISIM
A simulated voltage controlled oscillator is used to generate an FM signal in this EWB exercise. The student will use the VCO to investigate the effects changes on the input have on the FM signal. The virtual oscilloscope is used to examine the generated FM signal. An exercise is also included which uses the virtual spectrum analyzer to measure the bandwidth of the FM signal. Next, the measured result is compared to the result obtained using Carson’s rule. The exercises reinforce the use the spectrum analyzer to analyze the FM signal.
OVERVIEW – CHAPTER 6
FREQUENCY MODULATION: RECEPTION
6-1 BLOCK DIAGRAM
This section provides an introduction to a basic FM receiver block diagram. The similarities to AM receivers is noted and the differences are also mentioned. These include the fact that we generally use the term discriminator rather than detector for an FM receiver.
Additionally, FM receivers often do not include the AGC function so necessary for AM systems. This is because the limiter can take care of amplitude changes and in FM the intelligence is not contained in the amplitude. The intelligence is carried by the amount of frequency deviation and the rate of that frequency deviation.
6-2 RF AMPLIFIERS
AM receivers often operate without an RF amplifier, but that is seldom the case with FM receivers. For that reason a discussion of these amplifiers is provided here. The advantage of FET vs. BJT designs is provided and relates to the question of intermodulation distortion. The square-law input/output relationship of FETs compared to the exponential relationship for BJTs is the key. The distortion components are much easier to filter out for the FET as a result. A typical design using a MOSFET is illustrated in Fig. 6-2.
The accompanying table provides the component value to change between 100 MHz and 400 MHz operation.
6-3 LIMITERS
The use of a limiter in FM receivers has already been mentioned. A transistor limiter is shown in Fig. 6-3. A key to its operation is the collector resistor, Rc , which is shown in blue. It serves to limit the collector voltage which limits the range of its ac output. The result is the clipped (limited) output shown in Fig. 6-4. As indicated in the figure, passing this clipped signal through an LC tank tuned to its center frequency restores the limited signal to its sinusoidal form. This section concludes with a discussion of the relationship between limiting and the sensitivity of an FM receiver. This important concept is reinforced by thinking through Ex. 6-1.
6-4 DISCRIMINATORS
Extracting the intelligence from the FM signal is sometimes a difficult concept for the student. You will find that reminding them of the capacitor mike generator from Chapter 5 will often help clear the air when they get bogged down in their analysis. An easy way to break into the discriminator discussion is to first introduce the slope detector provided in Fig. 6-6. This is followed by details on the Foster-Seely and ratio detector circuits. Since they are not used often in new designs, you may elect to not cover them. Input from reviewers is mixed on whether they should still be included. A discussion of the quadrature detector concludes this section. A transparency of Fig. 6-10 is helpful in explaining its operation. A block diagram of the Philips TEA 5767 single-chip FM stereo radio is provided in Fig. 6-20.
6-5 PHASE-LOCKED LOOP
The PLL was briefly introduced in Chapter 5 showing its use as an FM generator. We now discuss its use as a demodulator—a much more important application. Because of the importance, a more detailed look at PLL operation is now provided. The three states of operation are discussed—free-running, capture and locked (tracking). A description of how a PLL
demodulates an FM signal is provided followed by a complete specification sheet for the LM565 PLL. Analysis for calculations of its VCO center frequency (free-running frequency), loop gain and hold-in range are provided.
6-6 STEREO DEMODULATION
Figure 6-15 graphically shows the difference between mono and stereo receivers with block diagrams. Students are usually quite interested in the stereo concept so this is a good opportunity for student interaction. The FCC authorized subsidiary communication authorization (SCA) is then introduced and the use of a 565 PLL as an SCA decoder is illustrated in Fig. 6-18. This section is concluded with an analysis of a rather complex LIC, the CA 3090 which is used as a stereo decoder.
6-7 FM RECEIVERS
The single-chip FM stereo radio receiver shown in Fig. 6-20 makes a very good
discussion circuit at this point. The architecture of this IC has dramatically reduced the number of external components. Have the students compare this circuit to the older style FM receiver shown in Fig. 6-21.
6-8 TROUBLESHOOTING
The FM receiver block diagram in Fig. 6-21 is used as the basis for a discussion on locating the defective stage. This step-by-step process involves the signal injection process. Specific detail is given for troubleshooting quadrature detectors and the stereo demodulator. This section is concluded with a detailed description of the process for testing diodes and transistors using a digital multimeter (DMM).
6-9 TROUBLESHOOTING WITH ELECTRONICS WORKBENCH MULTISIM
An implementation of an FM receiver using Multisim is provided in this section.
This example includes a block level implementation so that the student can gain
additional understanding of an FM receiver. The students should be able to follow the
signal from the RF input through to the output amplifier. Each stage is clearly identified
and the block level implementation facilitates easy examination using the oscilloscope.
The exercises include a problem in troubleshooting an FM receiver, a limiter, and an
exercise which reexamines the relationship sin A x sin B.
OVERVIEW – CHAPTER 7
COMMUNICATIONS TECHNIQUES
7-2 FREQUENCY CONVERSION
The problem of image frequencies is often a problem with communication transceivers as was discussed in Chapter 3. A solution is the use of double conversion which is illustrated with the block diagram in Fig. 7-1. A second technique is the use of up-conversion systems. A method of calculating the amount of image frequency rejection is the use of Equation 7-1, and Example 7-6 shows how to apply that equation.
7-3 SPECIAL TECHNIQUES
Since AGC systems somewhat reduce the gain of even weak stations, the use of delayed AGC is utilized in some receivers. Figure 7-5 provides a graphic representation of no AGC, simple AGC and delayed AGC. Auxiliary AGC is also explained and it provides a reduced gain for very strong signals to prevent overloading the receiver. The Analog Devices AD8369 variable gain amplifier is shown in Fig. 7-7(b) and (c).
The next topics covered in this section are variable sensitivity and variable selectivity. This is followed by the use of noise limiters. The schematic of an automatic noise limiter is provided in Fig. 7-9. This section is concluded with introductions to receiver metering and squelch circuitry.
A discussion of squelch techniques has been provided at the end of this section. This discussion examines the different methods used to implement the squelch feature in
communication receivers.
7-4 RECEIVER NOISE, SENSITIVITY, AND DYNAMIC RANGE
RELATIONSHIPS
The effects of noise are a dominating factor in the design of high quality receivers. Equation 7-2 relates the sensitivity with a receivers noise factor and the desired signal to noise ratio. The important concepts of dynamic range and third order intercept are introduced at this point. This is followed by four examples to help tie this all together. The concept of
intermodulation distortion follows this discussion to conclude the section. You will find Figs. 7-12 and 13 helpful in explaining IMD to your students.
7-5 FREQUENCY SYNTHESIS
The use of frequency synthesis to replace the local oscillator is now occurring in even modest cost/performance receivers. The basics of frequency synthesis are provided here with the block diagram of Fig. 7-14 serving as a useful starting point. The concept of programmable division is provided and this is followed by a discussion of two-modulus dividers. It is helpful to discuss the three synthesizer configurations shown in Fig. 7-16 with your students. This will give them a better overall understanding of the frequency synthesis process. A schematic for a CB transceiver synthesizer is shown in Fig. 7-19 and a detailed discussion of its operation is provided. The section is concluded with a discussion of a UHF receiver incorporating a PLL frequency synthesizer circuit. A block diagram of the circuit is provided in Fig. 7-21 and a schematic of the receiver is provided in Fig. 7-22.
7-6 DIRECT DIGITAL SYNTHESIS
The block diagram for a direct digital synthesizer is shown in Fig. 7-23. These
synthesizers have become popular in recent years as the availability and pricing of the complex ICs has become more favorable. The DDS synthesizers offer extremely small frequency increments and have the ability to shift frequencies very quickly. They are limited by operation at the higher frequencies and exhibit more phase noise problems than their analog counterparts.
7-7 HIGH FREQUENCY COMMUNICATION MODULES
This section addresses how the performance of electronic communication circuits
changes extensively with changes in frequency especially when high frequencies are being used. This includes a discussion on assembling high frequency circuits and printed circuit boards. The important issue of how miniaturization of circuitry has changed electronic communication systems is addressed. The section concludes with a discussion on using Mini-Circuits® modules and includes three examples of using modular electronic systems (Mini-Circuits® modules) to implement electronic communication circuitry (AM modulator, FM modulator, and a mixer circuit.)
7-8 TROUBLESHOOTING
The block diagram for a typical FM transmitter is shown in Fig. 7-32. Troubleshooting detail is provided regarding the microphone/audio, modulator, TR switch, power amp, and oscillator. The next topic is a discussion of some basic logic problems you might encounter in a typical communications transceiver. The troubleshooting section concludes with some tips on handling the frequency synthesizer shown in Fig. 7-14.
7-9 TROUBLESHOOTING WITH ELECTRONICS WORKBENCH
MULTISIM
The concept of a mixer circuit is explored in this Multisim exercise. It is very important for the students to understand this relationship. The students will also gain experience examining the spectral output of a mixer circuit using the EWB spectrum analyzer. An exercise working with an implementation of a squelch circuit is provided. The circuit is easy for the student to follow and includes a virtual squelch control. The students enjoy adjusting the control and analyzing the effect its changes have on the circuit. The exercises include troubleshooting the squelch circuitry to determine why the circuit is not functioning. One exercise simulates what might happen if someone dropped a screwdriver into the receiver cabinet with power on. The student is asked to troubleshoot the circuit and correct the problems. Just a note: I never dropped a screwdriver into a receiver chassis …. Well okay, maybe I did once.
OVERVIEW – CHAPTER 8
DIGITAL COMMUNICATION: CODING TECHNIQUES
8-1 INTRODUCTION
The three basic forms of digital communications are shown in Fig. 8-1. They include an analog signal converted to digital for transmission, a digital signal transmitted as a baseband (unmodulated), and a digital signal converted to analog for transmission. The ability of
regeneration for a digital signal is discussed with respect to its ability to deal with noise problems. The use of digital signal processing to perform various operations on a digital communications signal is also described.
8-2 ALPHANUMERIC CODES
The ASCII code is first described here. The concept of parity is introduced. This is followed by introduction of the EBCDIC code and the Baudot code. The Baudot code is
presented so that the student will understanding that there are many ways to present alphanumeric text in a digital format. The various characteristics of these alpha-numeric codes is provided as well as some specific applications. This section concludes with detail on the grey code
commonly used in telemetry systems.
8-3 PULSE-CODE MODULATION
The most common technique for representing an analog signal in digital format is
PCM. This section presents an overview of the sample and hold circuit and the
generation of the pulse amplitude modulated waveform. The sample frequency, as
defined by the Nyquist rate is provided in equation 8-1. Figure 8-11 provides a visual
reference of selecting the sample frequency. Terms such as aliasing, fold-over distortion,
and anti-aliasing filters should be introduced to the student. Be sure and convey their
importance. The concept of quantization and dynamic range are presented for a PCM
system. Equation 8-4 is a useful relationship for the student to know. The section
concludes with a discussion on companding and D/A and A/D convertors. These topics
should be used as needed to supplement the students understanding of the PCM system.
8-4 DIGITAL SIGNAL ENCODING FORMATS
The codes used for PCM systems are covered in this section. First the non-return to zero codes are introduced—NRZ-L, NRZ-M, and NRZ-S. The RZ codes are then presented— RZ(unipolar), RZ(bipolar), and RZ-AMI. The phase-encoded and delay-modulated codes (bi-phase and Miller) codes are provided. They are commonly used in optical systems, satellite telemetry links, and magnetic recording systems. A description of the multilevel binary codes (Dicode NRZ and Dicode RZ) concludes this section.
8-5 CODING PRINCIPLES
This section introduces the concept of increasing the Hamming distance in digital
data. This technique of adding data bits to a digital word facilitates error detection and
8-6 CODE ERROR DETECTION AND CORRECTION
Error detection and correction is very important when dealing with code transmission. Parity is explained as the first issue here. Concepts such as even and odd parity, symbol substitution, and protocols are introduced. The block check character process is explained and followed by detail on cyclic redundancy check. The final topic in this section has to do with forward error-correcting using the Hamming code and Reed-Solomon codes.
8-8 DIGITAL SIGNAL PROCESSING (DSP)
The basics of digital signal processing are presented in this section. The section begins with a basic review of both passive and active analog filters. A block diagram of the DSP process in presented in Fig. 8-38. A discussion of how the sampled signal is processed using a difference equation is presented. This includes the definition of a recursive and non-recursive filters. The section concludes with an example of using a spreadsheet program to demonstrate how a second-order, recursive, low-pass Butterworth filter is processed.
8-9 TROUBLESHOOTING
The digital waveform is initially discussed here. The effect of noise on the pulse is presented along with an analysis of impedance mismatch effects. The effect of low and high-frequency attenuation on a pulse is explained. It is necessary, when troubleshooting digital communication systems, to be able to recognize pulse distortion and what causes it.
8-10 TROUBLESHOOTING WITH ELECTRONICS WORKBENCH
MULTISIM
This exercise demonstrates the use of EWB Multisim to simulate the sampling
process. The students will have the opportunity to experiment with the selection of the
sample frequency and examine the frequency spectra of a sampled signal that contains
aliased frequencies.
OVERVIEW – CHAPTER 9
WIRED DIGITAL COMMUNICATION
9-1 INTRODUCTION
Six possible methods for transmitting analog and digital information are provided in
Fig. 9-1. This figure helps the student to understand the variety of methods possible for
transmitting information.
9-2 BACKGROUND MATERIAL FOR DIGITAL COMMUNICATION
This section introduces some of the basic concepts needed by the student to
understand and appreciate fully the material in chapter 9. This section introduces the
basic concepts of binary coding, code noise immunity, the concept of bit error rate
(BER), the probability of a bit error, and the definitions of the fundamental concepts of
simplex, half duplex, full duplex, synchronous and asynchronous data communications.
9-3 BANDWIDTH CONSIDERATIONS
Begin your discussion on bandwidth with an introduction to the Shannon-Hartley
theorem and the calculation for channel capacity. Example 9-4 demonstrates the
calculation of the capacity of a telephone channel given a S/N of 60 dB. This examples
shows that there is a limitation to the amount of data that can be transmitted down a
telephone line. Equation 9-6 defines how to calculate the minimum bandwidth of a
digital communications link.
9-4 DATA TRANSMISSION
The basic concepts of high serial data transmission are presented in this section.
The objective is to make sure the student understands how data communications is
accomplished over the Telco connection. Concepts presented include data rates and line
coding formats. The student will need to understand the concept of the point of presence
and the requirements of using a CSU/DSU in an interface to a communications carrier.
The concept of packet switching and frame relay are presented and should be briefly
reviewed for the student. The basic operating concept of an ATM system is also
introduced.
9-5 TIME DIVISION MULTIPLE ACCESS (TDMA)
The TDMA concept is extremely important and the student should understand
how many digital communication sources can share a single channel. The data process is
demonstrated in Figs. 9-9 and 9-10. The concepts of slot time, guard times, and
inter-symbol interference are important.
9-6 DELTA AND PULSE MODULATION
The concepts of delta and pulse modulation are introduced. These systems are
relatively simple and easy to implement. Limitations of such a system, such as slope
overload are defined. Pulse modulation techniques including pulse-amplitude
modulation, pulse-width modulation, and pulse-position modulation are presented.
9-7 COMPUTER COMMUNICATION
This section presents a look at computer based serial communications. Topics
include USB and Firewire. Figure 9-26 shows an example of using the MAX3451
transceiver for establishing a USB connection. RS-232 is still extremely important and
plan to devote some time to this topic in class. The signaling concepts are important for
the student to understand. Demonstrate an RS-232 link from one computer to another if
possible. Most computers have the hyper-terminal software available for making the
link. This will make for an exciting demonstration of the concept. A brief coverage of
facsimile machines is good at this point.
9-8 TROUBLESHOOTING
Techniques for troubleshooting telemetry systems are presented. This section
presents a good overview of basic troubleshooting techniques including possible
problems at the transmitter and the encoder/decoder.
9-9 TROUBLESHOOTING WITH ELECTRONICS WORKBENCH MULTISIM
This section examines the use of Electronics Workbench Multisim to simulate a
sequence detector. These type of circuits are often used in communication circuits to
detect the beginning of a serial data stream. The sections guide the student through the
use of the Multisim Word Generator and Logic Analyzer. The students are given the
opportunity to troubleshoot circuit problems using the included Multisim files on the text
CDROM.
OVERVIEW – CHAPTER 10
WIRELESS DIGITAL COMMUNICATIONS
10-1 INTRODUCTION
This section provides an introduction into wireless technologies. An overview of
fixed wireless, mobile wireless, and IR wireless is presented. It is important that the
student understands that although wireless communications is not new, the term
“wireless” is most often used today in conjunction with modern digital communication
systems.
10-2 DIGITAL MODULATION TECHNIQUES
Frequency shift keying is first explained in this section. This is an easy concept
for the students to understand since they have already been introduced to analog FM
transmission and reception. Phase shift keying is next introduced. Fig. 10-3 illustrates a
BPSK constellation. Techniques for generating and receiving a BPSK signal are
presented in Figs. 10-5 and 10-6. The students should understand the concept of a
coherent carrier recovery circuit. The QPSK phase constellation is next presented. A
block diagram of a QPSK demodulating circuit is provided in Fig. 10-9. A QPSK
constellation with noise is presented in Fig. 10-11. This figure illustrates decision
boundaries and data recovery. QAM techniques are also presented and illustrated in Figs.
10-14 and 10-15. The eye pattern is helpful in diagnosing the performance of a digital
modulation system. Figure 10-16 shows what the eye pattern looks like for various
digital communication conditions.
10-3 SPREAD SPECTRUM TECHNIQUES
This section emphasizes the techniques used in modern digital communications
using spread spectrum techniques. Each block of this very important technology is
presented. The first block is the generation of Pseudonoise (PN) codes. The mechanics
and terminology of PN code generation are presented. An EWB Multisim
implementation of a seven-bit PN sequence generator is demonstrated in Fig. 10-18.
Frequency Hopping Spread Spectrum (FHSS) is next presented. A simplified RF
spectrum for FHSS is provided in Fig. 10-22. Direct Sequence Spread Spectrum (DSSS)
is next examined. By this point in the chapter the student should have a good
understanding of PN codes and spread spectrum. This section includes a thorough
discussion of DSSS accompanied by an EWB Multisim implementation of how DSSS
signals are created. Fig.s 10-24 to 10-26 can be used to guide the student through the
process of generating a DSSS signal. The spreading of a BPSK signal is demonstrated in
Figures 10-28 to 10-30. Example 10-3 demonstrates how to calculate the spreading of
the DSSS signal.
10-4 Orthogonal Frequency Division Multiplexing (OFDM)
Many modern wireless digital systems are using this technique for transporting
data. This technique is used in the 802.11a wireless LAN technologies, DSL, and cable
modems. The basic concept of what it means for signals to be orthogonal should be
discussed. An example of an OFDM transmission are presented in Fig. 10-31 and 10-32.
OFDM is not a spread spectrum technology but a version called FLASH OFDM is
considered to be a spread spectrum technology. Another technology that uses OFDM for
transporting the digital data is HD radio. HD radio is a digital radio technology that
operates in the same frequency bands as broadcast AM (530 – 1705 kHZ) and FM (88 –
108 MHz). The RF spectrum for a hybrid (analog and digital) AM and FM transmission
is presented in Figure 10-33 and 10-34. A block diagram of an HD radio is provided in
Figure 10-35.
10-5 TELEMETRY
The block diagram for a telemetry systems is provided in Fig. 10-36. Telemetry
systems can use FDM and TDM techniques as shown in Fig. 10-37.
10-6 TROUBLESHOOTING
This can be a fun section for the students. The topic focuses on the steps used by
technicians to troubleshoot wireless telephone problems. This section explains the
concepts of the wireless phone’s electronic serial number, the mobile identification
number, and the master subsidy lock. The section also explains how water damage is
detected by the technician. Of course, none of us have ever dropped our phone in water
or worse, the toilet……(sigh …).
10-7 TROUBLESHOOTING WITH ELECTRONICS WORKBENCH MULTISIM
An EWB Multisim simulation of a BPSK transmit-receive circuit is demonstrated.
The simulation is based on the BPSK block diagrams presented in Figs. 10-4 to 10-6.
The student should be able to follow the data through the entire path and develop a good
understanding of generating the digital data and data recovery. The student will have the
opportunity to troubleshoot the BPSK circuit in the exercises.
OVERVIEW – CHAPTER 11
NETWORK COMMUNICATIONS
11-1 INTRODUCTION
A network is an interconnection of users that permits communication. The world-wide telephone grid fits into that description and will be introduced in this chapter. Computer networks have rapidly become a major interconnected system and that subject is the topic of the remainder of this chapter. The Internet is the largest of computer networks, and that is a subject of a textbook on its own. It is introduced in Section 11-8.
11-2 BASIC TELEPHONE OPERATION
A short introduction to telephone basics starts this section. The representation of the telephone and the so-called BORSCHT function are illustrated in Fig. 11-1. A complete telephone system block diagram is provided in Fig. 11-3, which makes a good transparency for classroom discussion. Line quality and attenuation distortion are discussed as well as the concept of delay distortion. The problem of dealing with telephone traffic is broadly
introduced by comparing it to vehicular traffic. Telephone traffic is either expressed in erlangs or in hundred-call-seconds. A general discussion of telephone congestion is followed by some detail on traffic observation and measurement.
11-3 TELEPHONE SIGNALING SYSTEMS
This section addresses the role that SS7 plays in the process of establishing
and “tearing down” telephone calls over the PSTN (Public Switched Telephone
Network). A description of each SS7 layer as well as the service it provides is
describe. A section on troubleshooting SS7 networks is also included which
describes how a “Protocol Analyzer” is used to sort through many data messages to
identify a problem with the telephone network.
11-4 MOBILE TELEPHONE SYSTEMS
The Mobile Telephone System has radically changed in the last few years. This section examines the fundamental concepts of a cellular phone system layout (Fig. 11-11) and how the MTSO (mobile telephone switching office) is used to link two mobile users (Fig. 11-13). The section includes material on the latest in mobile communications, GSM and CDMA. This includes discussions on the control signals used in mobile telephone
communications. An example of troubleshooting CDMA systems is discussed and includes a discussion and picture of Walsh codes (Fig. 11-18). The use of a “real-time spectrum
analyzer” is presented which shows how the instrument can be used to isolate interference problems (Figs. 11-19 and 11-20). The section concludes with a look at the path to 3G wireless in the United States.
11-5 LOCAL AREA NETWORKS
This section provides an introduction to computer local area networks. The
students should understand the topologies, particularly the star. Figs. 11-21 to 11-23
minimum, how to construct an ethernet LAN. Make sure the student understands the
concept of a MAC address.
11-6 ASSEMBLING A LAN
This sections describes the techniques for assembling an office and a building
LAN. Wireless LANs, based on the IEEE 802.11b. 802.11a, and 802.11g standards,
are discussed. The section also includes discussions on the broadband wireless
system WiMAX and Bluetooth.
11-7 LAN INTERCONNECTION
The connection of local area networks is described with the help of the open systems interconnection (OSI) reference model. The three basic interconnection methods are
described and they include bridge, router, and gateway methodology. Figures 11-32, 11-33, and 11-34 illustrate these methods.
