Electronics and SignalsChapter 4Chapter 4

Parts of an Atom nucleusnucleus - - the center part of the atom, the center part of the atom,

formed by neutrons and protons formed by neutrons and protons protonsprotons - particles have a positive charge, - particles have a positive charge,

and and along with along with neutrons, neutrons, form the nucleus form the nucleus

neutronsneutrons – particles – particleshave no chargehave no charge(neutral), and along(neutral), and alongwith protons, form with protons, form the nucleus the nucleus

electronselectrons - particles have a negative - particles have a negative charge, and orbit the nucleus charge, and orbit the nucleus

Types of Electrical Materials

insulators—insulators—high resistance to electrical high resistance to electrical currentcurrent plastic, glass, air, wood, paper, rubberplastic, glass, air, wood, paper, rubber

conductors—conducts the flow of electronsconductors—conducts the flow of electrons Copper, silver, goldCopper, silver, gold

semiconductors—control the flow of semiconductors—control the flow of electronselectrons carbon, siliconcarbon, silicon

Measuring Electricity

Voltage (V)—Voltage (V)—electrical force or pressure that electrical force or pressure that occurs when electrons and protons are occurs when electrons and protons are separatedseparated The force that is created pushes toward the The force that is created pushes toward the

oppositeopposite charge and away from the charge and away from the likelike charge. charge.

Voltage can also be created by friction Voltage can also be created by friction (static electricity), by magnetism (electric (static electricity), by magnetism (electric generator), or by light (solar cell). generator), or by light (solar cell).

unit of measurement is VOLTunit of measurement is VOLT

Measuring Electricity

Current (I)—Current (I)—the measurement of electron the measurement of electron flow in an electrical circuitflow in an electrical circuit unit of measurement is unit of measurement is AMPEREAMPERE (amp) (amp)

Resistance (R)—Resistance (R)—amount of opposition to amount of opposition to currentcurrent unit of measurement is the unit of measurement is the OHMOHM ( ())

ELECTRICITY FUNDAMENTALS

Electricity is brought to your home, school, and office by power lines. The power lines carry electricity in the form of alternating current (AC). Another type of current, called direct current (DC) can be found in flashlight batteries, car batteries, and as power for the microchips on the motherboard of a computer. It is important to understand the difference between these two types of current.

Measuring Electricity

Measuring Electricity Alternating Current (AC)Alternating Current (AC)

flows in two directionsflows in two directions Direct Current (DC)Direct Current (DC)

flows in one direction onlyflows in one direction only Impedance--(Z)—unit of measurement (Impedance--(Z)—unit of measurement ())

total opposition to current flowtotal opposition to current flow (due to AC (due to AC and DC voltages)and DC voltages)

resistance--resistance--generally used when referring generally used when referring to DC voltagesto DC voltages

Measuring Electricity current flows through closed loopscurrent flows through closed loops called called

circuitscircuits These These circuitscircuits must be composed of must be composed of

conducting materials and have sources of conducting materials and have sources of voltage.voltage.

The three required parts of an electrical The three required parts of an electrical circuit are circuit are source or battery, complete source or battery, complete path, load or resistancepath, load or resistance..

Voltage causes current to flow while Voltage causes current to flow while resistance and impedance oppose it.resistance and impedance oppose it.

Measuring Electricity

Measuring Electricity For AC and DC electrical systems, the flow For AC and DC electrical systems, the flow

of electrons is always from a of electrons is always from a negativelynegatively charged source to a charged source to a positivelypositively charged charged source.source.

For the controlled flow of electrons to occur, For the controlled flow of electrons to occur, a complete circuit is required.a complete circuit is required.

Electrical current generally follows the path Electrical current generally follows the path of least resistance.of least resistance.

Measuring Electricity Because metals such as copper provide Because metals such as copper provide

little little resistanceresistance, they frequently are used , they frequently are used as as conductorsconductors for electrical current. for electrical current.

Materials such as glass, rubber, and Materials such as glass, rubber, and plastic provide more plastic provide more resistanceresistance; they are ; they are not good not good conductorsconductors and are generally and are generally used as used as insulatorsinsulators..

Measuring Electricity

The purpose of connecting the safety The purpose of connecting the safety ground to exposed metal parts of ground to exposed metal parts of

computing equipment is to prevent such computing equipment is to prevent such metal parts from becoming energized with metal parts from becoming energized with

a hazardous voltage from a wiring fault a hazardous voltage from a wiring fault inside the device.inside the device.

Using a Multimeter to Make Resistance MeasurementsA multimeter can use used to measureA multimeter can use used to measure

voltagevoltage resistanceresistance continuitycontinuity

Using a Multimeter to Make Resistance Measurements If you If you intentionallyintentionally make a path into a low- make a path into a low-

resistance path for use by two connected resistance path for use by two connected electrical devices, then the path has electrical devices, then the path has continuitycontinuity..

If a path is made If a path is made unintentionallyunintentionally into a low- into a low-resistance path, then it is called a resistance path, then it is called a short circuitshort circuit..

The unit of measurement for both is the OHM The unit of measurement for both is the OHM (().).

ContinuityContinuity refers to the level of resistance of a refers to the level of resistance of a pathpath..

Using a Multimeter to Make Resistance Measurements You can perform measurements on the You can perform measurements on the

following:following: CAT 5 cableCAT 5 cable Terminated CAT 5 cableTerminated CAT 5 cable Terminated coaxial cableTerminated coaxial cable Telephone wireTelephone wire CAT 5 jacksCAT 5 jacks SwitchesSwitches Wall outletsWall outlets

Using a Multimeter to Make Voltage Measurements Two types of voltage measurements exist: DC Two types of voltage measurements exist: DC

and AC.and AC. The meter must be set to DC when measuring The meter must be set to DC when measuring

DC voltagesDC voltages. This includes the following:. This includes the following:batteriesbatteriesoutputs of computer power suppliesoutputs of computer power suppliessolar cellssolar cellsDC generatorsDC generators

Using a Multimeter to Make Voltage Measurements Two types of voltage measurements exist: DC Two types of voltage measurements exist: DC

and AC.and AC. The meter must be set to AC when you The meter must be set to AC when you

measure AC voltagesmeasure AC voltages. . If you measure a wall socket, you must If you measure a wall socket, you must

assume that line voltage is present.assume that line voltage is present.Line voltage is 120 V AC in the US and Line voltage is 120 V AC in the US and

220 V AC in most other places around the 220 V AC in most other places around the world.world.

Signals and Noise in Communication Systems The term The term signalsignal refers to a desired refers to a desired electrical electrical

voltagevoltage, , light patternlight pattern, or , or modulated electromagnetic modulated electromagnetic wavewave..

Signals can be created asSignals can be created as electrical pulses that travel over copper wireelectrical pulses that travel over copper wire pulses of light that travel through strands of glass pulses of light that travel through strands of glass

or plasticor plastic radio transmissions that travel over the airwavesradio transmissions that travel over the airwaves as laser or satellite transmissionsas laser or satellite transmissions as infrared pulseas infrared pulse

Signals and Noise in Communication Systems Two main types of signalingTwo main types of signaling

analoganalog change gradually and continuously (change gradually and continuously (will have a will have a

continuously varying voltage-versus-time graphcontinuously varying voltage-versus-time graph)) typical of things in naturetypical of things in nature used widely in telecommunications for more than 100 used widely in telecommunications for more than 100

yearsyears digitaldigital

change one state to another almost instantaneously, change one state to another almost instantaneously, without stopping at an in-between statewithout stopping at an in-between state

discrete or jumpydiscrete or jumpy typical of technology instead of naturetypical of technology instead of nature

Measuring Analog Signals

Analog signals are measured in cycles, with Analog signals are measured in cycles, with one cycle representing the change from one cycle representing the change from highhigh to to lowlow and back again. and back again.

Three characteristics are measured:Three characteristics are measured: amplitudeamplitude frequencyfrequency phasephase

Digital and Analog Signaling

Digital signaling is the most appropriate format Digital signaling is the most appropriate format for transmitting computer data, and most for transmitting computer data, and most networks use digital signaling methods for that networks use digital signaling methods for that reason.reason.

Because it is a simpler technology, digital Because it is a simpler technology, digital signaling has some advantages over analog:signaling has some advantages over analog: generally less expensive to make digital generally less expensive to make digital

equipmentequipment generally less vulnerable to errors caused by generally less vulnerable to errors caused by

interference because the discrete state of interference because the discrete state of onon and and offoff is not as easily affected by a small distortion is not as easily affected by a small distortion as is a continuous waveformas is a continuous waveform

Digital and Analog Signaling

Analog signals also have advantages:Analog signals also have advantages: Signals can be easily mutilplexed; that is signals Signals can be easily mutilplexed; that is signals

can be combined to increase bandwidth.can be combined to increase bandwidth. Signals are less vulnerable to the problem of Signals are less vulnerable to the problem of

attenuationattenuation ( (signal loss due to surroundingssignal loss due to surroundings) ) because of distance so they can travel farther because of distance so they can travel farther without becoming too weak for reliable without becoming too weak for reliable transmission. However, when an analog signal is transmission. However, when an analog signal is amplified, the noise is amplified with the signal.amplified, the noise is amplified with the signal.

Digital connectivity solutions generally offer Digital connectivity solutions generally offer better security, faster performance, and higher better security, faster performance, and higher reliabilityreliability..

Simplex, Half-Duplex, and Full-Duplex Transmission Simplex TransmissionSimplex Transmission

Unidirectional—signal travels in only one Unidirectional—signal travels in only one directiondirection

Television is an example.Television is an example. Half-Duplex TransmissionHalf-Duplex Transmission

Signal can travel in both directions but not at the Signal can travel in both directions but not at the same time.same time.

Full-Duplex TransmissionFull-Duplex Transmission Signal can travel in both directions at the same Signal can travel in both directions at the same

time.time.

Baseband and Broadband The entire capacity of an Ethernet cable is used for The entire capacity of an Ethernet cable is used for

transmitting the data in transmitting the data in oneone channel. channel. This makes Ethernet a BASEBAND technology.This makes Ethernet a BASEBAND technology. A A channelchannel is an allocated portion of the media’s is an allocated portion of the media’s

available available bandwidthbandwidth. . The signal has the benefit of having the entire The signal has the benefit of having the entire

bandwidth to itself.bandwidth to itself. BASEBAND is usually associated with digital BASEBAND is usually associated with digital

signaling (although it can be used with analog).signaling (although it can be used with analog). Most computer communications are baseband.Most computer communications are baseband. BASEBAND signal is BASEBAND signal is bidirectionalbidirectional; the signal can ; the signal can

flow both ways so you can transmit flow both ways so you can transmit andand receive on receive on the same cable.the same cable.

Baseband and Broadband

BROADBAND technologies allow for dividing BROADBAND technologies allow for dividing the capacity of a link into two or more channels, the capacity of a link into two or more channels, each of which can carry a different signal.each of which can carry a different signal.

All channels can send simultaneously.All channels can send simultaneously. ISDN is an example of BROADBAND ISDN is an example of BROADBAND

technology because multiple signals can be technology because multiple signals can be carried over separate channels on a single wire.carried over separate channels on a single wire.

DSL is another example of a BROADBAND DSL is another example of a BROADBAND technology because data technology because data andand voice can travel voice can travel simultaneously over the same line.simultaneously over the same line.

Signaling and Communications Problems PropagationPropagation

ttravel timeravel time; speed depends upon medium; speed depends upon medium As data transmission rates increase, you must As data transmission rates increase, you must

sometimes take into account the amount of sometimes take into account the amount of time it takes the signal to travel.time it takes the signal to travel.

AttenuationAttenuation loss of signal over distance due to loss of signal over distance due to

surroundingssurroundings can affect a network because it limits the can affect a network because it limits the

length of network cabling over which you can length of network cabling over which you can send a messagesend a message

Signaling and Communications Problems ReflectionReflection

caused by discontinuities in the mediumcaused by discontinuities in the medium occurs in electrical signals; can be a result of occurs in electrical signals; can be a result of

kinks in cable or poorly terminated cableskinks in cable or poorly terminated cables networks should have a specific impedance to networks should have a specific impedance to

match the electrical components in the NICsmatch the electrical components in the NICs The result of The result of impedance mismatchimpedance mismatch is reflected is reflected

energyenergy..

Signaling and Communications ProblemsNoiseNoise

unwanted additions to optical/electromagnetic unwanted additions to optical/electromagnetic signalssignals

CrosstalkCrosstalk——electrical noise from other wires in electrical noise from other wires in a cablea cable

EMI (electromagnetic interference) can be EMI (electromagnetic interference) can be caused by electric motorscaused by electric motors..

Cancellation of signals can be avoided Cancellation of signals can be avoided through the twisting of wire pairs to provide through the twisting of wire pairs to provide self-shielding within the network mediaself-shielding within the network media..

Signaling and Communications Problems Timing problemTiming problem

Dispersion—signal broadens in timeDispersion—signal broadens in timecan be fixed by proper cable design, can be fixed by proper cable design,

limiting cable lengths, and finding the limiting cable lengths, and finding the proper impedanceproper impedance

Jitter—source and destination not Jitter—source and destination not synchronizedsynchronizedcan be fixed through hardware and software can be fixed through hardware and software

including protocolsincluding protocols Latency—delay of network signalLatency—delay of network signal

Signaling and Communications Problems CollisionsCollisions

occurs when two bits from different occurs when two bits from different communicating computers are on a shared communicating computers are on a shared medium at the same timemedium at the same time

excessive collisions can slow the networkexcessive collisions can slow the network

Encoding Networking Signals EncodingEncoding means to convert the binary data means to convert the binary data

into a form that can travel on a physical into a form that can travel on a physical communications link such as an electrical communications link such as an electrical pulse on a wire, a light pulse on an optical pulse on a wire, a light pulse on an optical fiber, or an electromagnetic wave in spacefiber, or an electromagnetic wave in space.. two methods for encodingtwo methods for encoding

TTLTTL—high signals or low signals—high signals or low signals ManchesterManchester—more complex and more —more complex and more

immune to noise and better at immune to noise and better at remaining synchronized (remaining synchronized (includes includes NRZs and 4BNRZs and 4B/5B/5B

Encoding Networking Signals

ModulationModulation means using the binary data means using the binary data to manipulate an analog wave.to manipulate an analog wave. taking a wave and changing it so that it taking a wave and changing it so that it

carries informationcarries information AMAM FMFM PMPM