document electronics
TRANSCRIPT
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Principles of ElectronicCommunication Systems
Third Edition
Louis E. Frenzel, Jr.
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Chapter 1
Introduction to Electronic Communication
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Topics Covered in Chapter 1
1-1: Significance of Human Communication1-2: Communication Systems1-3: Types of Electronic Communication1-4: Modulation and Multiplexing
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Topics Covered in Chapter 1(continued)
1-5: The Electromagnetic Spectrum1-6: Bandwidth1-7: A Survey of Communication Applications1-8: Jobs and Careers in the Communication Industry
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1-1: Significance ofHuman Communication
Communication is the process of exchanginginformation.
Main barriers are language and distance.
Contemporary society’s emphasis is now theaccumulation, packaging, and exchange ofinformation.
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1-1: Significance ofHuman Communication
Methods of communication:1. Face to face2. Signals3. Written word (letters)4. Electrical innovations:
Telegraph
TelephoneRadioTelevisionInternet (computer)
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1-2: Communication Systems
Basic components:
TransmitterChannel or mediumReceiver
Noise degrades or interferes with transmittedinformation.
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1-2: Communication Systems
Figure 1-2: A general model of all communication systems.
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1-2: Communication Systems
TransmitterThe transmitter is a collection of electroniccomponents and circuits that converts the electrical
signal into a signal suitable for transmission over agiven medium.
Transmitters are made up of oscillators, amplifiers,
tuned circuits and filters, modulators, frequency mixers,frequency synthesizers, and other circuits.
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1-2: Communication Systems
Communication ChannelThe communication channel is the medium by whichthe electronic signal is sent from one place to another.
Types of media includeElectrical conductorsOptical mediaFree space
System-specific media (e.g., water is the medium for sonar).
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1-2: Communication Systems
Receivers A receiver is a collection of electronic components andcircuits that accepts the transmitted message from the
channel and converts it back into a form understandableby humans.Receivers contain amplifiers, oscillators, mixers, tunedcircuits and filters, and a demodulator or detector that
recovers the original intelligence signal from themodulated carrier.
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1-2: Communication Systems
Transceivers A transceiver is an electronic unit that incorporatescircuits that both send and receive signals.Examples are:• Telephones• Fax machines• Handheld CB radios
• Cell phones• Computer modems
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1-2: Communication Systems
AttenuationSignal attenuation, or degradation, exists in all mediaof wireless transmission. It is proportional to the square
of the distance between the transmitter and receiver.
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1-2: Communication Systems
NoiseNoise is random, undesirable electronic energy thatenters the communication system via the
communicating medium and interferes with thetransmitted message.
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1-3: Types of ElectronicCommunication
Electronic communications are classified accordingto whether they are1. One-way (simplex) or two-way (full duplex or half
duplex) transmissions2. Analog or digital signals.
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1-3: Types of ElectronicCommunication
SimplexThe simplest method of electronic communication isreferred to as simplex .
This type of communication is one-way. Examples are:RadioTV broadcastingBeeper (personal receiver)
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1-3: Types of ElectronicCommunication
Full Duplex Most electronic communication is two-way and isreferred to as duplex .
When people can talk and listen simultaneously, it iscalled full duplex . The telephone is an example of thistype of communication.
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1-3: Types of ElectronicCommunication
Half Duplex The form of two-way communication in which only oneparty transmits at a time is known as half duplex .
Examples are:Police, military, etc. radio transmissionsCitizen band (CB)Family radio
Amateur radio
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1-3: Types of ElectronicCommunication
Analog Signals An analog signal is a smoothly and continuouslyvarying voltage or current. Examples are:
Sine waveVoiceVideo (TV)
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1-3: Types of ElectronicCommunication
Figure 1- 5: Analog signals (a) Sine wave “tone.” (b) Voice. (c) Video (TV) signal.
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1-3: Types of ElectronicCommunication
Digital Signals Digital signals change in steps or in discreteincrements.
Most digital signals use binary or two-state codes.Examples are:
Telegraph (Morse code)Continuous wave (CW) code
Serial binary code (used in computers)
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1-3: Types of ElectronicCommunication
Figure 1-6: Digital signals (a) Telegraph (Morse code). (b) Continuous-wave (CW)code. (c) Serial binary code.
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1-3: Types of ElectronicCommunication
Digital SignalsMany transmissions are of signals that originate indigital form but must be converted to analog form to
match the transmission medium.Digital data over the telephone network.
Analog signals.They are first digitized with an analog-to-digital (A/D)
converter.The data can then be transmitted and processed bycomputers and other digital circuits.
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1-4: Modulation and Multiplexing
Modulation and multiplexing are electronictechniques for transmitting information efficiently fromone place to another.
Modulation makes the information signal morecompatible with the medium.Multiplexing allows more than one signal to betransmitted concurrently over a single medium.
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1-4: Modulation and Multiplexing
Baseband Transmission Baseband information can be sent directly andunmodified over the medium or can be used tomodulate a carrier for transmission over the medium.
In telephone or intercom systems, the voice is placed onthe wires and transmitted.In some computer networks, the digital signals are applieddirectly to coaxial or twisted-pair cables for transmission.
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1-4: Modulation and Multiplexing
Broadband Transmission A carrier is a high frequency signal that is modulated byaudio, video, or data.
A radio-frequency (RF) wave is an electromagneticsignal that is able to travel long distances throughspace.
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1-4: Modulation and Multiplexing
Broadband Transmission A broadband transmission takes place when a carriersignal is modulated, amplified, and sent to the antenna
for transmission.The two most common methods of modulation are:
Amplitude Modulation (AM)Frequency Modulation (FM)
Another method is called phase modulation (PM), inwhich the phase angle of the sine wave is varied.
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1-4: Modulation and Multiplexing
Figure 1-7: Modulation at the transmitter.
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1-4: Modulation and Multiplexing
Figure 1-8: Types of modulation. (a) Amplitude modulation. (b) Frequency modulation.
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1-4: Modulation and Multiplexing
Broadband TransmissionFrequency-shift keying (FSK) takes place when datais converted to frequency-varying tones.
Devices called modems (mo dulator- dem odulator)translate the data from digital to analog and back again.
Demodulation or detection takes place in the receiverwhen the original baseband (e.g. audio) signal isextracted.
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1-4: Modulation and Multiplexing
MultiplexingMultiplexing is the process of allowing two or moresignals to share the same medium or channel.
The three basic types of multiplexing are:Frequency divisionTime divisionCode division
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1-4: Modulation and Multiplexing
Figure 1-11: Multiplexing at the transmitter.
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1-5: The Electromagnetic Spectrum
The range of electromagnetic signals encompassingall frequencies is referred to as the electromagneticspectrum.
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1-5: The Electromagnetic Spectrum
Figure 1-13: The electromagnetic spectrum.
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1-5: The Electromagnetic Spectrum
Frequency and Wavelength: Frequency A signal is located on the frequency spectrum accordingto its frequency and wavelength.Frequency is the number of cycles of a repetitive wavethat occur in a given period of time.
A cycle consists of two voltage polarity reversals,current reversals, or electromagnetic field oscillations.Frequency is measured in cycles per second (cps).The unit of frequency is the hertz (Hz).
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1-5: The Electromagnetic Spectrum
Frequency and Wavelength: Wavelength Wavelength is the distance occupied by one cycle of awave and is usually expressed in meters.Wavelength is also the distance traveled by anelectromagnetic wave during the time of one cycle.The wavelength of a signal is represented by the Greekletter lambda ( λ).
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1-5: The Electromagnetic Spectrum
Figure 1-15: Frequency and wavelength. (a) One cycle. (b) One wavelength.
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1-5: The Electromagnetic Spectrum
Example:What is the wavelength if the frequency is 4MHz?
Frequency and Wavelength: Wavelength
Wavelength ( λ) = speed of light ÷ frequencySpeed of light = 3 × 10 8 meters/second
Therefore:λ = 3 × 10 8 / f
λ = 3 × 10 8 / 4 MHz= 75 meters (m)
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1-5: The Electromagnetic Spectrum
Frequency Ranges from 30 Hz to 300 GHzThe electromagnetic spectrum is divided into segments:
Extremely Low Frequencies (ELF) 30 – 300 Hz.
Voice Frequencies (VF) 300 – 3000 Hz.
Very Low Frequencies (VLF) include the higher end of thehuman hearing range up toabout 20 kHz.
Low Frequencies (LF) 30 – 300 kHz.
Medium Frequencies (MF) 300 – 3000 kHz AM radio 535 – 1605 kHz.
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1-5: The Electromagnetic Spectrum
Frequency Ranges from 30 Hz to 300 GHz
High Frequencies (HF)(short waves; VOA, BBC
broadcasts; government andmilitary two-way communication;amateur radio, CB.
3 – 30 MHz
Very High Frequencies (VHF)FM radio broadcasting (88 – 108MHz), television channels 2 – 13.
30 – 300 MHz
Ultra High Frequencies (UHF)TV channels 14 – 67, cellularphones, military communication.
300 – 3000 MHz
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1-5: The Electromagnetic Spectrum
Frequency Ranges from 30 Hz to 300 GHz
Microwaves and Super HighFrequencies (SHF)
Satellite communication, radar,wireless LANs, microwave ovens
1 – 30 GHz
Extremely High Frequencies (EHF)Satellite communication, computer
data, radar
30 – 300 GHz
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1-5: The Electromagnetic Spectrum
Optical SpectrumThe optical spectrum exists directly above themillimeter wave region.
Three types of light waves are:InfraredVisible spectrumUltraviolet
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1-5: The Electromagnetic Spectrum
Optical Spectrum: InfraredInfrared radiation is produced by any physicalequipment that generates heat, including our bodies.Infrared is used:
In astronomy, to detect stars and other physical bodies in theuniverse,For guidance in weapons systems, where the heat radiatedfrom airplanes or missiles can be detected and used to guidemissiles to targets.In most new TV remote-control units, where special codedsignals are transmitted by an infrared LED to the TV receiver tochange channels, set the volume, and perform other functions.In some of the newer wireless LANs and all fiber-opticcommunication.
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1-5: The Electromagnetic Spectrum
Optical Spectrum: The Visible SpectrumJust above the infrared region is the visible spectrum we refer to as light.
Red is low-frequency or long-wavelength lightViolet is high-frequency or short-wavelength light.Light waves’ very high frequency enables them tohandle a tremendous amount of information (the
bandwidth of the baseband signals can be very wide).
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1-5: The Electromagnetic Spectrum
Optical Spectrum: UltravioletUltraviolet is not used for communicationIts primary use is medical.
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1-6: Bandwidth
Bandwidth (BW) is that portion of the electromagneticspectrum occupied by a signal.
Channel bandwidth refers to the range offrequencies required to transmit the desiredinformation.
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1-6: Bandwidth
More Room at the TopToday, virtually the entire frequency spectrum betweenapproximately 30 kHz and 300 MHz has been spokenfor.There is tremendous competition for these frequencies,between companies, individuals, and governmentservices in individual carriers and between the differentnations of the world.The electromagnetic spectrum is one of our mostprecious natural resources.
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1-6: Bandwidth
More Room at the TopCommunication engineering is devoted to making thebest use of that finite spectrum.
Great effort goes into developing communicationtechniques that minimize the bandwidth required totransmit given information and thus conserve spectrumspace.
This provides more room for additional communicationchannels and gives other services or users anopportunity to take advantage of it.
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1-6: Bandwidth
Spectrum Management and StandardsSpectrum management is provided by agencies set upby the United States and other countries to controlspectrum use.
The Federal Communications Commission (FCC)and the National Telecommunications andInformation Administration (NTIA) are two agenciesthat deal in spectrum management.
Standards are specifications and guidelines necessaryto ensure compatibility between transmitting andreceiving equipment.
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1-7: A Survey ofCommunications Applications
Simplex AM and FMbroadcasting
Digital radioTV broadcastingDigital television (DTV)Cable televisionFacsimileWireless remote control
Paging servicesNavigation and
direction-findingservicesTelemetryRadio astronomySurveillanceMusic servicesInternet radio andvideo
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1-7: A Survey ofCommunications Applications
DuplexTelephonesTwo-way radioRadarSonar
Amateur radioCitizens radio
Family Radio serviceThe InternetWide-area networks(WANs)Metropolitan-areanetworks (MANs)
Local area networks(LANs)
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© 2008 The McGraw-Hill Com anies
1-8: Jobs and Careers in theCommunication Industry
The electronics industry is roughly divided intofour major specializations:1. Communications (largest in terms of people
employed and the dollar value of equipment
purchased)2. Computers (second largest).3. Industrial controls.4. Instrumentation.
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© 2008 The McGraw-Hill Com anies
1-8: Jobs and Careers in theCommunication Industry
Types of JobsEngineers design communication equipment andsystems.
Technicians install, troubleshoot, repair, calibrate, andmaintain equipment.
Engineering Technicians assist in equipment design,testing, and assembly.
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© 2008 The McGraw-Hill Com anies
1-8: Jobs and Careers in theCommunication Industry
Types of JobsTechnical sales representatives determine customerneeds and related specifications, write proposals andsell equipment.
Technical writers generate technical documentation forequipment and systems.
Trainers develop programs, generate training andpresentation materials, and conduct classroom training.
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1-8: Jobs and Careers in theCommunication Industry
Major Employers The communication electronics industry is made up ofthe following segments:
Manufacturers
Resellers
Service Organizations
End users
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