Electronics and Signals by pmv64896

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									Electronics and Signals
Chapter 4
Parts of an Atom
   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
   neutrons – particles
    have no charge
    (neutral), and along
    with protons, form
    the nucleus
   electrons - particles have a negative charge,
    and orbit the nucleus
Types of Electrical Materials
 insulators—high resistance to electrical
  current
    plastic, glass, air, wood, paper, rubber

 conductors—conducts the flow of electrons
    Copper, silver, gold

 semiconductors—control the flow of
  electrons
    carbon, silicon
Measuring Electricity
   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
    unit of measurement is AMPERE (amp)

 Resistance (R)—amount of opposition to
  current
    unit of measurement is the OHM ()
ELECTRICITY FUNDAMENTALS
Measuring Electricity
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)
    flows in two directions

 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
      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
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 the controlled flow of electrons to occur,
  a complete circuit is required.
 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.
 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
   resistance
   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 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
    ().
   Continuity refers to the level of resistance of a
    path.
Using a Multimeter to Make
Resistance Measurements
   You can perform measurements on the
    following:
      CAT 5 cable
      Terminated CAT 5 cable
      Terminated coaxial cable
      Telephone wire
      CAT 5 jacks
      Switches
      Wall outlets
Using a Multimeter to Make
Voltage Measurements
   Two types of voltage measurements exist: DC
    and AC.
      The meter must be set to DC when measuring
       DC voltages. This includes the following:
         batteries
         outputs of computer power supplies
         solar cells
         DC generators
Using a Multimeter to Make
Voltage Measurements
   Two types of voltage measurements exist: DC
    and AC.
      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.
         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.
   Signals can be created as
      electrical pulses that travel over copper wire
      pulses of light that travel through strands of glass
       or plastic
      radio transmissions that travel over the airwaves
      as laser or satellite transmissions
      as infrared pulse
Signals and Noise in
Communication Systems
   Two main types of signaling
       analog
          change  gradually and continuously (will have a
           continuously varying voltage-versus-time graph)
          typical of things in nature
          used widely in telecommunications for more than 100
           years
       digital
          change  one state to another almost instantaneously,
           without stopping at an in-between state
          discrete or jumpy
          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.
 Three characteristics are measured:
     amplitude
     frequency
     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.
   Because it is a simpler technology, digital
    signaling has some advantages over analog:
     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
Digital and Analog Signaling
   Analog signals also have advantages:
     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.
   Digital connectivity solutions generally offer
    better security, faster performance, and higher
    reliability.
Simplex, Half-Duplex, and Full-
Duplex Transmission
   Simplex Transmission
     Unidirectional—signal travels in only one
      direction
     Television is an example.
   Half-Duplex Transmission
       Signal can travel in both directions but not at the
        same time.
   Full-Duplex Transmission
       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.
   This makes Ethernet a BASEBAND technology.
   A channel is an allocated portion of the media’s
    available bandwidth.
   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).
   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 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.
   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.
   DSL is another example of a BROADBAND
    technology because data and voice can travel
    simultaneously over the same line.
Signaling and Communications
Problems
   Propagation
     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.
   Attenuation
     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
Signaling and Communications
Problems
   Reflection
     caused  by discontinuities in the medium
     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
     The result of impedance mismatch is reflected
      energy.
Signaling and Communications
Problems
Noise
   unwanted   additions to optical/electromagnetic
    signals
   Crosstalk—electrical noise from other wires
    in a cable
   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.
Signaling and Communications
Problems
   Timing problem
     Dispersion—signal    broadens in time
        can be fixed by proper cable design,
         limiting cable lengths, and finding the
         proper impedance
     Jitter—source and destination not
      synchronized
        can be fixed through hardware and software
         including protocols
     Latency—delay of network signal
Signaling and Communications
Problems
   Collisions
     occurs when two bits from different
      communicating computers are on a shared
      medium at the same time
     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.
     two methods for encoding
        TTL—high signals or low signals
        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.
      taking a wave and changing it so that it
        carries information
      AM
      FM
      PM

								
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