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Principles of ElectronicCommunication Systems

Third Edition

Louis E. Frenzel, Jr.

Chapter 1

Introduction to Electronic Communication

Topics Covered in Chapter 1

1-1: Significance of Human Communication1-2: Communication Systems1-3: Types of Electronic Communication1-4: Modulation and Multiplexing

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

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.

1-1: Significance ofHuman Communication

Methods of communication:1. Face to face2. Signals3. Written word (letters)4. Electrical innovations:

Telegraph

TelephoneRadioTelevisionInternet (computer)

1-2: Communication Systems

Basic components:

TransmitterChannel or mediumReceiver

Noise degrades or interferes with transmittedinformation.

Figure 1-2: A general model of all 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.

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).

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.

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

AttenuationSignal attenuation, or degradation, exists in all mediaof wireless transmission. It is proportional to the square

of the distance between the transmitter and receiver.

NoiseNoise is random, undesirable electronic energy thatenters the communication system via the

communicating medium and interferes with thetransmitted message.

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.

SimplexThe simplest method of electronic communication isreferred to as simplex .

This type of communication is one-way. Examples are:RadioTV broadcastingBeeper (personal receiver)

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.

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

Analog Signals An analog signal is a smoothly and continuouslyvarying voltage or current. Examples are:

Sine waveVoiceVideo (TV)

Figure 1- 5: Analog signals (a) Sine wave “tone.” (b) Voice. (c) Video (TV) signal.

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)

Figure 1-6: Digital signals (a) Telegraph (Morse code). (b) Continuous-wave (CW)code. (c) Serial binary code.

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.

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.

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.

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.

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.

Figure 1-7: Modulation at the transmitter.

Figure 1-8: Types of modulation. (a) Amplitude modulation. (b) Frequency modulation.

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.

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

Figure 1-11: Multiplexing at the transmitter.

1-5: The Electromagnetic Spectrum

The range of electromagnetic signals encompassingall frequencies is referred to as the electromagneticspectrum.

Figure 1-13: 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).

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).

Figure 1-15: Frequency and wavelength. (a) One cycle. (b) One wavelength.

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)

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.

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

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

Optical SpectrumThe optical spectrum exists directly above themillimeter wave region.

Three types of light waves are:InfraredVisible spectrumUltraviolet

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.

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).

Optical Spectrum: UltravioletUltraviolet is not used for communicationIts primary use is medical.

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.

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.

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.

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.

1 7 A S f

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

1 7 A S f

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)

1 8 J b d C i th

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.

1 8 J b d C i th

Types of JobsEngineers design communication equipment andsystems.

Technicians install, troubleshoot, repair, calibrate, andmaintain equipment.

Engineering Technicians assist in equipment design,testing, and assembly.

1 8 J b d C i th

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.

1 8: Jobs and Careers in the

Major Employers The communication electronics industry is made up ofthe following segments:

Manufacturers

Resellers

Service Organizations

End users

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