EET 280

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EET 280
2013-02-27 18:56:11
EET 280

intro to communication systems
Show Answers:

  1. T/F 

    Antenna is part of the transmitter circuit in any communication system.
  2. T/F 

    The input to source encoder can be digital or analog
  3. T/F 

    The encryption process can be done during the decoding process
  4. T/F 

    Super imposing the carrier signal on the message signal is called modulation
  5. T/F 

    the antenna is used to convert electrical signals into EM waves.
  6. T/F 

    A full duplex mode allows for communication in both directions but not at the same time
  7. T/F

    the telephone is an example of analog to digital communication
  8. T/F 

    in space electrical and magnetic waves are displaced by 90 degrees
  9. T/F 

    the number of oscillations per second is called the time period
  10. T/F

    the frequency of a signal is 1Hz when the time period of 1 second
  11. T/F 

    as the frequency increases the velocity of light increases.
  12. T/F 

    the most convenient way to express power loss and gain is in terms of decibels
  13. T/F 

    as the current through a component increases, the noise level it produces increases.
  14. T/F 

    a signal that repeats it self in a predictable manner is called a periodic signal
  15. T/F 

    the size of an antenna can be reduced by using modulation.
  16. T/F 

    modulation and demodulation can be done at the transmitter and receiver respectively
  17. T/F 

    AM, FM, and PM fall under angle modulation techniques
  18. T/F 
    the ratio of the carrier signal amplitude to the message signal amplitude is called as modulation index in AM.
  19. T/F 

    AM in nature is wasteful in nature
  20. T/F 

    an FM signal can be used to generate a PM signal
  21. T/F 

    putting an information signal on to a carrier is called modulation.


  22. T/F 

    a communication system may or may not include channels


  23. T/F

    the carrier frequency is higher than the highest base band


  24. T/F

    for radio signals. longer wave lengths means higher frequency


  25. T/F

    noise is easily removed from an analog signal by using filters


  26. T/F

    audio signals are in the time domain, but radio signals are in the frequency domain


  27. T/F

    digital systems such as computers are not affected by noise


  28. T/F

    every component in an electronic system generates noise


  29. T/F

    the hotter a component gets the more noise it generates


  30. T/F 

    "shot" noise creates a "noise current" in an electronic device such as a transistor


  31. T/F 

    signal - to - noise ration is more important than noise power


  32. Short answer

    a complete communication system must include

    _______, ______, _______.
    • a transmitter 
    • a receiver
    • a channel
  33. Short answer

    in the FM the _______ and in PM the _______ of the modulated carrier signal varies in accordance with the amplitude of the message signal
    Frequency mod

    Phase angular
  34. Short answer

    the modulation index in FM is the ratio of the peak deviation on the __________ frequency.
  35. message
  36. Short answer

    radians per sec is equal to:
  37. Short answer

    when two or more signals are in a common channel, it is called:
  38. Short answer

    the wavelength of a radio signal is:
    • -or-

    the distance a wave travels in one period
  39. Short answer

    noise in a communication system originates in

    _____, _____, ______.
    • the sender
    • the receiver
    • the channel
  40. Short answer

    "man made " noise can come from?

    _____ ___ _____.
    equipment that sparks
  41. Short answer

    thermal noise is generated in :

    ____, _______, ______.
    • transistors and diodes
    • resistors
    • copper wire
  42. Short answer

    shot noise is generated in:

    ______ and ______.
    transistors and diodes
  43. Short answer

    signal to noise ratio is calculated as:
    signal power divided by noise power.


  44. Fill in the blank

    a radio signal's _________________ is the distance it travels in one cycle of the carrier
  45. Fill in the blank

    in free space, radio signals travel at_______ meters per second.
  46. Fill in the blank

    the equipment used to show signals in the frequency domain is the _______
    spectrum analizer
  47. Fill in the blank

    thermal noise is caused by the random motions of _______ in a conductor
  48. Short answer

    name the five elements in a block diagram of a communication system.
    • source
    • transmitter
    • channel
    • receiver
    • final destination
  49. Problem Solving

    the input to an amplifier has a signal to noise ration of 100 dB and an output signal to noise ratio of 80 dB. how do you determine the NF in dB?
    NF = 100 dB - 80 dB

    NF = 20 dB
  50. Problem Solving

    the input to an amplifier has a signal to noise ration of 100 dB and an output signal to noise ratio of 80 dB. how do you determine the NF as a ratio?
    NF = 100 dB - 80 dB, NF = 20 dB

    • 20 = 10 log10 (s/n)
    • 1.58=(s/n)
  51. Problem Solving

    What is the over all gain?

    • overall gain = (-9) + 12
    •                   = 3 dB

    Note: because all the values are in dB they can simply be added.
  52. Problem Solving

    if the output is 200 Watts than what is the input power?

    • x=100.23 watts
  53. Problem Solving

    What is the output if the input is 1 watt

    • x = 1.99
  54. Problem Solving

    what is the formula to find the frequency of a radio signal?
  55. what is PDM
    Pulse-Duration or Width Modulation (PDM or PWM)

    lecture 5
  56. what is PPM
    Pulse positon modulation

    note: PPM has a similar noise performance as FM.
  57. how does PWM work?
    In Pulse Width Modulation (PWM), the width of each pulse is made directly proportional to the amplitude of the information signal.
  58. how does PPM work?
    In Pulse position modulation, constant-width pulses are used, and the position or time of occurrence of each pulse from some reference time is made directly proportional to the amplitude of the information signal.
  59. Name the tree different type of waves.
    1. PAM

    2. PWM

    3. PPM
  60. What is quantization?
    it is the process of converting an analog signal into a digital signal ( bits ).

  61. what type of sampling is this and why?
    ideal sampling

    because the pulse width is zero.

  62. How many leves are there for this signal and what bit type can be produce from it?
    8 Levels

    An 8 bit signal will be produced.
  63. What is quantization error?
    It is an error that occurs due to each point being rounded to the mid point of its correspondent zone. The more zones the smaller the errors.
  64. what is step size in quantization?
    it is the distance between each level.
  65. A sampling has produced the following values:
    -10, 8, -6, -4, 8, 5, 1, 10, 9

    Determine the step size if it has 8 levels.
    Step size (delta)= (the highest - the lowest) / the number of levels

    • =(10 - (-10)) / 8
    • =20/8
    • =2.5
  66. What is theformula to determine the bit rate?
    —The bit rate of a PCM signal can be calculated form the number of bits per sample x the sampling rate

                         Bit rate = nb * fs
  67. Calculate the bit rate.

    levels                    L=8
    bits per sample      n=3
    samples per sec     fs=3M
    • nb=n*fs
    • nb = 9mbpM
  68. is the antenna part of the transmitter?
  69. What i the sampling rate for a frequency of 6MHz?
    12M samples per seec

    Note: the nyquis theorem states that the sampling rate should be twice the highest frequency.
  70. TF

    The rate at which information is transmitted per second is called bit rate
  71. TF

    Sampling transforms a discrete time signal to a continuous time signal

    it transforms a continuous into a discrete time signal.
  72. TF

    Compression is usually done at the receiver

    it is done at the transmitter
  73. TF

    Discretizing the amplitude levels is called quantization
  74. TF

    Sampling and quantization together converts an analog signal into a digital signal
  75. TF

    bandwidth of a digital signal is less than an analog signal
  76. TF

    interpolation is the reverse process of sampling at the receiver side.

    it is "connecting the dots" received from the transmitter in order to reconstruct the signal at the receiver side.
  77. TF

    Line coding are techniques used to convert stream of bits into a signal
  78. TF

    A continuous signal is one that is defined at discrete intervals of time.

    continuous signals have an infinite number of values.
  79. TF

    In ideal sampling, the width of the pulse is zero.

    the ideal sample signal will look like a straight spike with no width
  80. TF

    The sampling rate should equal to the maximum frequency contained in the signal.

    As per the Nyquis theorem, it should at least twice the maximum frequency.
  81. TF

    For a Low pass signal the band width is equal to the max Frequency

    the frequency on a low pass signal begins at 0 and ends at the max frequency.
  82. TF

    As the number of levels in quatization increase the quatization error will decrease.

    more levels mean that the signal will shift less up or down to reach the middle of the level.
  83. TF

    The number of bits required for a 128 level quantizer is 7

    128 equals 2^7. This means that it will require 7 binary units.
  84. TF

    Assigment of non-overlapping frequency ranges to different signals is called FDM.

    FDM stands for frequency division multiplexing
  85. TF

    TDM has high latency when compared with FDM

    • FDM stands for frequency division multiplexing
    • TDM stands for time division multiplexing
  86. TF

    In polar RZ encoding scheme, each symbol has a transition in the middle from high to zero or from low to zero.

    RZ stands for return to zero
  87. T/F

    in TDM the signal uses all the bandwidth but some of the time.
  88. T/F

    A demultiplexer is used at the receiver side

    A demultiplexer separates the different signals that have been converted into one by the multiplexer.
  89. Short answer 

    What is needed to calculate the sampling rate?
    the maximum frequency in the signal
  90. Short answer 

    What two things are needed to calculate the bit rate?
    • The sampling rate
    • The number of bits per sample
  91. Short answer 

    How do you calculate the bit rate?
    Sampling rate times the number of bits per sample.