Electronics and Signals Chapter 4

Parts of an Atom nucleus - the center part of the atom, formed by neutrons and protons nucleus - the center part of the atom, formed by neutrons and protons protons - particles have a positive charge, and along with neutrons, form the nucleus protons - particles have a positive charge, and along with neutrons, form the nucleus neutrons – particles have no charge (neutral), and along with protons, form the nucleus neutrons – particles have no charge (neutral), and along with protons, form the nucleus electrons - particles have a negative charge, and orbit the nucleus electrons - particles have a negative charge, and orbit the nucleus

Types of Electrical Materials insulators—high resistance to electrical current insulators—high resistance to electrical current  plastic, glass, air, wood, paper, rubber conductors—conducts the flow of electrons conductors—conducts the flow of electrons  Copper, silver, gold semiconductors—control the flow of electrons semiconductors—control the flow of electrons  carbon, silicon

Measuring Electricity Voltage (V)—electrical force or pressure that occurs when electrons and protons are separated Voltage (V)—electrical force or pressure that occurs when electrons and protons are separated  The force that is created pushes toward the opposite charge and away from the like charge.  Voltage can also be created by friction (static electricity), by magnetism (electric generator), or by light (solar cell).  unit of measurement is VOLT

Measuring Electricity Current (I)—the measurement of electron flow in an electrical circuit Current (I)—the measurement of electron flow in an electrical circuit  unit of measurement is AMPERE (amp) Resistance (R)—amount of opposition to current Resistance (R)—amount of opposition to current  unit of measurement is the OHM (  )

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

Alternating Current (AC) Alternating Current (AC)  flows in two directions Direct Current (DC) Direct Current (DC)  flows in one direction only  Impedance--(Z)—unit of measurement (  )  total opposition to current flow (due to AC and DC voltages)  resistance--generally used when referring to DC voltages

Measuring Electricity current flows through closed loops called circuits current flows through closed loops called circuits  These circuits must be composed of conducting materials and have sources of voltage.  The three required parts of an electrical circuit are source or battery, complete path, load or resistance.  Voltage causes current to flow while resistance and impedance oppose it.

Measuring Electricity

For AC and DC electrical systems, the flow of electrons is always from a negatively charged source to a positively charged source. For AC and DC electrical systems, the flow of electrons is always from a negatively charged source to a positively charged source. For the controlled flow of electrons to occur, a complete circuit is required. For the controlled flow of electrons to occur, a complete circuit is required. Electrical current generally follows the path of least resistance. Electrical current generally follows the path of least resistance.

Measuring Electricity Because metals such as copper provide little resistance, they frequently are used as conductors for electrical current. Because metals such as copper provide little resistance, they frequently are used as conductors for electrical current. Materials such as glass, rubber, and plastic provide more resistance; they are not good conductors and are generally used as insulators. Materials such as glass, rubber, and plastic provide more resistance; they are not good conductors and are generally used as insulators.

Measuring Electricity The purpose of connecting the safety ground to exposed metal parts of computing equipment is to prevent such metal parts from becoming energized with a hazardous voltage from a wiring fault inside the device.

Using a Multimeter to Make Resistance Measurements A multimeter can use used to measure voltage voltage resistance resistance continuity continuity

Using a Multimeter to Make Resistance Measurements If you intentionally make a path into a low- resistance path for use by two connected electrical devices, then the path has continuity. If you intentionally make a path into a low- resistance path for use by two connected electrical devices, then the path has continuity. If a path is made unintentionally into a low- resistance path, then it is called a short circuit. If a path is made unintentionally into a low- resistance path, then it is called a short circuit. The unit of measurement for both is the OHM (  ). The unit of measurement for both is the OHM (  ). Continuity refers to the level of resistance of a path. Continuity refers to the level of resistance of a path.

Using a Multimeter to Make Resistance Measurements You can perform measurements on the following: You can perform measurements on the following: CAT 5 cable CAT 5 cable Terminated CAT 5 cable Terminated CAT 5 cable Terminated coaxial cable Terminated coaxial cable Telephone wire Telephone wire CAT 5 jacks CAT 5 jacks Switches Switches Wall outlets Wall outlets

Using a Multimeter to Make Voltage Measurements Two types of voltage measurements exist: DC and AC. Two types of voltage measurements exist: DC and AC. The meter must be set to DC when measuring DC voltages. This includes the following: The meter must be set to DC when measuring DC voltages. This includes the following: batteries batteries outputs of computer power supplies outputs of computer power supplies solar cells solar cells DC generators DC generators

Using a Multimeter to Make Voltage Measurements Two types of voltage measurements exist: DC and AC. Two types of voltage measurements exist: DC and AC. The meter must be set to AC when you measure AC voltages. The meter must be set to AC when you measure AC voltages. If you measure a wall socket, you must assume that line voltage is present. If you measure a wall socket, you must assume that line voltage is present. Line voltage is 120 V AC in the US and 220 V AC in most other places around the world. Line voltage is 120 V AC in the US and 220 V AC in most other places around the world.

Signals and Noise in Communication Systems The term signal refers to a desired electrical voltage, light pattern, or modulated electromagnetic wave. The term signal refers to a desired electrical voltage, light pattern, or modulated electromagnetic wave. Signals can be created as Signals can be created as electrical pulses that travel over copper wire electrical pulses that travel over copper wire pulses of light that travel through strands of glass or plastic pulses of light that travel through strands of glass or plastic radio transmissions that travel over the airwaves radio transmissions that travel over the airwaves as laser or satellite transmissions as laser or satellite transmissions as infrared pulse as infrared pulse

Signals and Noise in Communication Systems Two main types of signaling Two main types of signaling analog analog change gradually and continuously (will have a continuously varying voltage-versus-time graph) change gradually and continuously (will have a continuously varying voltage-versus-time graph) typical of things in nature typical of things in nature used widely in telecommunications for more than 100 years used widely in telecommunications for more than 100 years digital digital change one state to another almost instantaneously, without stopping at an in-between state change one state to another almost instantaneously, without stopping at an in-between state discrete or jumpy discrete or jumpy typical of technology instead of nature typical of technology instead of nature

Measuring Analog Signals Analog signals are measured in cycles, with one cycle representing the change from high to low and back again. Analog signals are measured in cycles, with one cycle representing the change from high to low and back again. Three characteristics are measured: Three characteristics are measured: amplitude amplitude frequency frequency phase phase

Digital and Analog Signaling Digital signaling is the most appropriate format for transmitting computer data, and most networks use digital signaling methods for that reason. Digital signaling is the most appropriate format for transmitting computer data, and most networks use digital signaling methods for that reason. Because it is a simpler technology, digital signaling has some advantages over analog: Because it is a simpler technology, digital signaling has some advantages over analog: generally less expensive to make digital equipment generally less expensive to make digital equipment generally less vulnerable to errors caused by interference because the discrete state of on and off is not as easily affected by a small distortion as is a continuous waveform generally less vulnerable to errors caused by interference because the discrete state of on and off is not as easily affected by a small distortion as 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 can be combined to increase bandwidth. Signals can be easily mutilplexed; that is signals can be combined to increase bandwidth. Signals are less vulnerable to the problem of attenuation (signal loss due to surroundings) because of distance so they can travel farther without becoming too weak for reliable transmission. However, when an analog signal is amplified, the noise is amplified with the signal. Signals are less vulnerable to the problem of attenuation (signal loss due to surroundings) because of distance so they can travel farther without becoming too weak for reliable transmission. However, when an analog signal is amplified, the noise is amplified with the signal. Digital connectivity solutions generally offer better security, faster performance, and higher reliability. Digital connectivity solutions generally offer better security, faster performance, and higher reliability.

Simplex, Half-Duplex, and Full- Duplex Transmission Simplex Transmission Simplex Transmission Unidirectional—signal travels in only one direction Unidirectional—signal travels in only one direction Television is an example. Television is an example. Half-Duplex Transmission Half-Duplex Transmission Signal can travel in both directions but not at the same time. Signal can travel in both directions but not at the same time. Full-Duplex Transmission Full-Duplex Transmission Signal can travel in both directions at the same time. Signal can travel in both directions at the same time.

Baseband and Broadband The entire capacity of an Ethernet cable is used for transmitting the data in one channel. The entire capacity of an Ethernet cable is used for transmitting the data in one channel. This makes Ethernet a BASEBAND technology. This makes Ethernet a BASEBAND technology. A channel is an allocated portion of the media’s available bandwidth. A channel is an allocated portion of the media’s available bandwidth. The signal has the benefit of having the entire bandwidth to itself. The signal has the benefit of having the entire bandwidth to itself. BASEBAND is usually associated with digital signaling (although it can be used with analog). BASEBAND is usually associated with digital signaling (although it can be used with analog). Most computer communications are baseband. Most computer communications are baseband. BASEBAND signal is bidirectional; the signal can flow both ways so you can transmit and receive on the same cable. BASEBAND signal is bidirectional; the signal can flow both ways so you can transmit and receive on the same cable.

Baseband and Broadband BROADBAND technologies allow for dividing the capacity of a link into two or more channels, each of which can carry a different signal. BROADBAND technologies allow for dividing the capacity of a link into two or more channels, each of which can carry a different signal. All channels can send simultaneously. All channels can send simultaneously. ISDN is an example of BROADBAND technology because multiple signals can be carried over separate channels on a single wire. ISDN is an example of BROADBAND technology because multiple signals can be carried over separate channels on a single wire. DSL is another example of a BROADBAND technology because data and voice can travel simultaneously over the same line. DSL is another example of a BROADBAND technology because data and voice can travel simultaneously over the same line.

Signaling and Communications Problems Propagation Propagation travel time; speed depends upon medium travel time; speed depends upon medium As data transmission rates increase, you must sometimes take into account the amount of time it takes the signal to travel. As data transmission rates increase, you must sometimes take into account the amount of time it takes the signal to travel. Attenuation Attenuation loss of signal over distance due to surroundings loss of signal over distance due to surroundings can affect a network because it limits the length of network cabling over which you can send a message can affect a network because it limits the length of network cabling over which you can send a message

Signaling and Communications Problems Reflection Reflection caused by discontinuities in the medium caused by discontinuities in the medium occurs in electrical signals; can be a result of kinks in cable or poorly terminated cables occurs in electrical signals; can be a result of kinks in cable or poorly terminated cables networks should have a specific impedance to match the electrical components in the NICs networks should have a specific impedance to match the electrical components in the NICs The result of impedance mismatch is reflected energy. The result of impedance mismatch is reflected energy.

Signaling and Communications ProblemsNoise unwanted additions to optical/electromagnetic signals unwanted additions to optical/electromagnetic signals Crosstalk—electrical noise from other wires in a cable Crosstalk—electrical noise from other wires in a cable EMI (electromagnetic interference) can be caused by electric motors. EMI (electromagnetic interference) can be caused by electric motors. Cancellation of signals can be avoided through the twisting of wire pairs to provide self-shielding within the network media. Cancellation of signals can be avoided through the twisting of wire pairs to provide self-shielding within the network media.

Signaling and Communications Problems Timing problem Timing problem Dispersion—signal broadens in time Dispersion—signal broadens in time can be fixed by proper cable design, limiting cable lengths, and finding the proper impedance can be fixed by proper cable design, limiting cable lengths, and finding the proper impedance Jitter—source and destination not synchronized Jitter—source and destination not synchronized can be fixed through hardware and software including protocols can be fixed through hardware and software including protocols Latency—delay of network signal Latency—delay of network signal

Signaling and Communications Problems Collisions Collisions occurs when two bits from different communicating computers are on a shared medium at the same time occurs when two bits from different communicating computers are on a shared medium at the same time excessive collisions can slow the network excessive collisions can slow the network

Encoding Networking Signals Encoding means to convert the binary data into a form that can travel on a physical communications link such as an electrical pulse on a wire, a light pulse on an optical fiber, or an electromagnetic wave in space. Encoding means to convert the binary data into a form that can travel on a physical communications link such as an electrical pulse on a wire, a light pulse on an optical fiber, or an electromagnetic wave in space. two methods for encoding two methods for encoding TTL—high signals or low signals TTL—high signals or low signals Manchester—more complex and more immune to noise and better at remaining synchronized (includes NRZs and 4B /5B Manchester—more complex and more immune to noise and better at remaining synchronized (includes NRZs and 4B /5B

Encoding Networking Signals Modulation means using the binary data to manipulate an analog wave. Modulation means using the binary data to manipulate an analog wave. taking a wave and changing it so that it carries information taking a wave and changing it so that it carries information AM AM FM FM PM PM