Chapter 8: Fundamentals of Communications Key
1. Metallic conductors, such as copper wires, comprise atoms with loosely attached electrons, or negatively
charged particles, around their nuclei.
2. When a voltage/potential difference from an electrical source, such as a battery, is introduced between the
3. You can think of the applied voltage to the two ends of a conductor as an external force pushing the electrons
forward through the conductor with a “strength” measured in Amperes.
4. In conductors, the flow of electrons within the material results in an electric current, with the magnitude of
charge flow (size of electrical current) proportional to the value of the potential difference.
5. The relationship between voltage (V), current (I), and resistance (R) is defined by the following relationship:
V = I/R
6. As the resistance in a circuit increases, the current flowing through the circuit also increases.
7. In 4-ary signaling, four different signal levels are sent over the communication channel, and two bits may be
sent over the channel using a single pulse of electricity.
8. In 8-ary transmission, the transmitter separates the digital information into groups of two bits each and
assigns a unique voltage level to each 2-bit group.
9. The data rate (D) in bits per second for M-ary transmission can be calculated by the following:
D = R log2M
where R is the signaling transmission rate expressed in terms of signals per second.
10. For 4-ary transmission, the data rate is equal to R, where R is the signaling transmission rate.
11. The data rate for a communication system that employs 8-ary signaling and a signal transmission rate of
12. Light is considered to be a form of electromagnetic energy.
13. Gamma Rays are not part of the electromagnetic spectrum.
14. Electromagnetic waves are used as carriers to wirelessly carry both analog and digital information by
altering certain properties of the wave in proportion to the information signal. This process is called
modulation.
15. Wavelength of an electromagnetic wave can be calculated using the following expression:
l=c/f
where c is the speed of EM waves (“the speed of light”) in a vacuum measured in meters per second (m/s), and f
is the frequency of the EM wave in hertz (Hz).
16. One band within the radio spectrum is the VHF band.
17. One band within the radio spectrum is the ULF band.
18. Television stations use the VHF/UHF frequency bands for broadcasting television signals.
19. The Federal Communications Commission (FCC) allocates radio frequencies in the United States.
20. Demodulation techniques superimpose information signals onto a carrier wave, such as a radio wave or a
light wave.
21. ASK, FSK and PSK are all analog modulation techniques.
22. AM is a modulation technique whereby the amplitude of the carrier wave is varied in proportion to the
amplitude of the original analog signal, resulting in the modulated waveform/signal.
23. FM is a modulation technique whereby the amplitude of the carrier wave is varied in proportion to the
amplitude of the original analog signal, resulting in the modulated waveform/signal.
24. Binary amplitude shift keying (ASK) is a technique that varies the amplitude of the carrier wave according
25. Binary frequency shift keying (FSK) is a modulation technique that varies the frequency of the carrier wave
according to the binary amplitude of the information signal.
26. The light spectrum is comprised of the infrared, visible and ultraviolet bands.
27. The light spectrum is comprised of the VHF and UHF bands.
28. When signals travel through any transmission medium, including fiber-optic cable, copper wire, or free
space, they lose energy. The loss of energy, called attenuation, is a significant factor that affects the quality and
distance of communications.
29. Attenuation is measure in terms of volts.
30. Repeaters may be placed within a communications system to overcome the effects of attenuation to some
extent.
31. In digital systems, the data carrying capacity of a channel is governed by two factors: Channel bandwidth
and signal to noise ratio.
32. The lower the signal to noise ratio in a communication channel, the higher the data carrying capacity of the
channel.
33. A single line can simultaneously transmit multiple information-carrying signals using a technique called
multiplexing.
34. TDM combines signals from multiple channels onto a single channel by allocating a specific time slot,
during which each channel transmits.
35. UTP cables have much less EMI acting upon a signal that they carry compared to STP cables.
36. Coaxial cables, or coax, are commonly used for cable television and Internet connectivity via cable
modems.
37. Single parity checking is a type of convolutional encoding technique.
38. The number of “1s” in a transmitted and received bit stream has to be equal to an even number if even parity
checking is used to ensure that no errors have occurred during transmission.
39. Which of the following are conductors of electricity?
40. Which of the following correctly states Ohm’s law?
41. Which of the following is the unit of resistance?
42. How many bits per signal are transmitted in a communications system that uses 16-ary signaling?
43. Calculate the data rate for a communication system that employs 4-ary signaling if the signal transmission
rate is 1000 signals per second.
44. Which of the following are components of the electromagnetic spectrum?
45. Which of the following denotes the relationship between the speed (c) of electromagnetic waves,
wavelength (l) and frequency?
46. Calculate the wavelength of a radio wave with a frequency of 2.5 GHz traveling through a vacuum.
47. Who was the first person to demonstrate long distance radio wave communication?
48. Which of the following are bands within the radio spectrum?
49. Which of the following frequency bands are used for space exploration and astronomy?
50. Which of the following organization regulates and administers frequency band usage within the United
States?
51. Which of the following techniques superimpose information signals onto a carrier wave, such as a radio
wave or a light wave?
52. Which of the followingis the process of extracting information-carrying signals from modulated waves?
53. Which of the following modulation techniques vary the amplitude of the carrier wave in proportion to the
amplitude of the analog information carrying signal?
54. Which of the following modulation techniques vary the frequency of the carrier wave in proportion to the
amplitude of the analog information carrying signal?
55. Which of the following modulation techniques vary the phase of the carrier wave in proportion to the
amplitude of the analog information carrying signal?
56. Which of the following is/are digital modulation techniques?
57. Which of the following types of light have a lower frequency compared to ultraviolet light?
58. Which of the following is the unit of attenuation?
59. Calculate the maximum reliable data carrying capacity of a communication channel with a bandwidth of
200 MHz and a signal to noise ratio of 1023.
60. Which of the following factor/factors affect the maximum data carrying capacity of a communication
channel?
61. Which of the following is a multiplexing technique that combines signals from multiple channels onto a
single channel by allocating a specific time slot, during which each channel transmits?
62. Which of the following is a multiplexing technique that combines signals from multiple channels onto a
single channel by allocating a specific frequency to each channel?
63. Which of the following transmission media comprise of a pair of wires twisted around each other?
64. Which of the following bit streams have been received in error if even parity checking was used prior to
65. Which of the following bit streams have been received in error if odd parity checking was used prior to
66. Which of the following bit streams have been received in error if rectangular coding based on even parity
was used prior to transmission? Keep in mind that the last symbol is the RCC.
67. Because materials such as glass or plastic have tightly attached electrons within their atoms, no electron
flow occurs, even if a voltage difference is applied to them, which classifies these materials as
____________________.
68. Aside from the applied voltage difference, the amount of charge flowing through a conductor also depends
on a fundamental property called the ____________________of the material, which is measured in ohms.
69. Voltage is measured in terms of ____________________.
70. Current is measured in terms of ____________________.
71. Resistance is measured in terms of ____________________.
72. The 4-ary signaling may be generalized to ____________________signaling, whereby M different voltage
levels may be used to transmit log2M groups of bits with one signal.
73. Besides electrical energy transmitted over conductors, ____________________ energy transmitted over air
or a vacuum is also commonly used for analog and digital communications.
74. The EM waves are used as carriers to wirelessly carry both analog and digital information by altering
certain properties of the wave in proportion to the information signal. This process is called
____________________.
75. The various types of EM waves, such as radio waves, light waves, x-rays, and gamma rays, vary within a
range of frequencies called the ____________________, which extends from approximately 3 Hz to more than
1×1020 Hz
76. The ____________________ is simply the physical length between two peaks or two crests of the EM
wave, and is measured in meters.
77. A significant source of natural EM radiation is the ____________________, which exposes us to ultraviolet
rays that can burn our skin, and to infrared radiation that heats the earth’s surface.
78. The frequency range of the EM spectrum between approximately 3 Hz and 300 GHz is called the
____________________, and waves within this spectrum are called radio waves.
79. The ___________________________________ allocates radio frequencies in the United States, and most
countries have a corresponding organization that assigns frequencies.
80. ____________________ techniques superimpose information signals onto a carrier wave, such as a radio
wave or a light wave.
81. In AM, the ____________________ of the carrier wave is varied in proportion to the amplitude of the
original analog signal, resulting in the modulated waveform/signal.
82. In FM,the ____________________ of the carrier wave is varied in proportion to the amplitude of the analog
information signal.
83. In PM, the ____________________ of the carrier wave is varied in proportion to the amplitude of the
analog information carrying signal.
84. AM is more vulnerable to ____________________ compared to FM and PM.
85. ______________________________ is a digital modulation technique whereby the amplitude of the carrier
wave is varied according to the binary amplitude of the digital information signal.
86. _______________________________ is a digital modulation technique whereby the frequency of the
carrier wave is varied according to the binary amplitude of the information signal.
87. _________________________ is a digital modulation technique whereby the phase of the carrier wave is
varied according to the binary amplitude of the information signal.
88. ____________________ is an EM wave that resides in a higher-frequency portion of the EM spectrum than
radio waves, but a lower frequency range than x-rays.
89. In addition to visible light, ____________________ and ____________________ are forms of light with
different frequencies.
90. The loss of signal energy as it travels down a transmission medium is called ____________________, and
is a significant factor that affects the quality and distance of communications.
91. Attenuation is measured in ____________________, and each transmission medium has its own attenuation
figure.
92. A dial-up Internet connection historically has been classified as____________________, while connections
over cable modem, DSL, or fiber-optic cable are conventionally classified as ____________________.
93. In digital systems, the maximum number of bits per second (channel capacity, or C) that can reliably be
carried over a channel depends on the ____________________ (expressed in Hz) of the channel and a unitless
ratio called the _________________________.
94. A source of noise within communication systems is called ____________________ noise which arises from
random agitation of electrons of the conductor material due to heat.
95. A single line can simultaneously transmit multiple information-carrying signals using a technique called
____________________.
96. A device called a ____________________combines multiple signals at the transmitting end of a
communications system, and a device called a ____________________separates the signals at the receiving
97. ______________________________ is a multiplexing technique that combines signals from multiple
channels onto a single channel by allocating a specific time slot, during which each channel transmits.
98. ___________________________________ was the first multiplexing technique used in the telephone
network. Rather than assigning each channel a specific time slot as in TDM, each channel is assigned a specific
carrier frequency for transmission.
99. ____________________ cabling is often used to connect computing devices within local area networks
(LANs) and for telecommunications services, such as home phone service and digital subscriber line (DSL).
100. Twisting the wires around each other in a twisted pair cable helps to reduce the amount of
____________________.
101. A popular plug for connecting UTP cables to devices is the ____________________ connector, which
supports four twisted pairs and is most commonly used to connect a computer to a LAN.
102. _________________________ cabling uses the same fundamental wire configuration as UTP, but adds a
shield surrounding the twisted pairs.
103. The ___________________________________________________________________________ has
defined more than six general categories of twisted pair cables, ranging from CAT1 to CAT6, with data rates
that range from a few Mbps to about 10 Gbps.
104. The structure of a ____________________ cable is fundamentally different from that of twisted pair
cables. It consists of a central, usually solid, cylindrical core conductor made of copper and an insulating
material surrounding the core called a dielectric.
105. Unfortunately, there is no such thing as an ideal transmission medium. Whenever digital information is
sent across any communication channel, be it twisted pair, coax, air, or optical fiber, there is always a
possibility that some bits will arrive at their destination with ____________________.
106. By encoding a bit stream prior to transmission using an assortment of techniques called
____________________, the receiver can detect and sometimes even correct errors that may occur at the
receiver.
107. The complexity of an error detecting/correcting code for communication is generally proportional to the
amount of ____________________added to a bit stream prior to transmission.
108. ____________________ codes are a class of error-control techniques, based on adding redundancy to
fixed lengths or blocks of data.
109. Among the many alternative ECC schemes, probably the easiest to implement is the
_________________________ scheme. This scheme only provides for the detection of errors, not error
correction.
110. __________________ codes are more complex than single parity checking, but they rely on the parity
checking method in an interleaved fashion.
111. ____________________ is another popular technique for detecting errors. It is slightly more complex than
parity checking or rectangular coding and is based on appending a stream of bits to the end of a data block.
112. A novel class of codes has emerged based on the idea of convolutional encoding. These special codes,
called ____________________ codes, encode digital information so it can be retrieved with a very small
amount of errors, even under the highest attenuation and noisy environments.
113. Explain the relationship between current, resistance and voltage in a circuit.
114. List the various types of EM waves found within the EM spectrum.
115. Briefly explain the details of the light spectrum.
116. Briefly explain the Shannon-Hartley capacity theorem and what it implies.
117. List the various types of multiplexing techniques.