Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1)
Attenuation in a coaxial cable will increase if ________.
1)
A)
cabling length decreases
B)
skin effect increases
C)
temperature increases
D)
cable resistance decreases
2)
A type of time division multiplexing that improves channel efficiency is ________.
2)
A)
bit–interleaved
B)
byte–interleaved
C)
synchronous
D)
statistical
3)
Synchronous time division multiplexing is inefficient because ________.
3)
A)
the sender and receive clocks must be frequently resynchronized
B)
data must be buffered before transmission
C)
time slots assigned to an inactive data source will not be used
D)
it requires the use of synchronous memory
4)
All of the following are methods for modulating analog signals with digital data except ________.
4)
A)
QAM
B)
ASK
C)
FSK
D)
SNR
5)
Coaxial cable supports data rates up to about ________.
5)
A)
5 GHz
B)
1 GHz
C)
500 MHz
D)
25 MHz
6)
The most common type of coaxial connector is the ________.
6)
A)
alligator clip
B)
BNC connector
C)
banana jack
D)
stereo phono jack
7)
An intersective method of pulse width modulation ________.
7)
A)
compares the value of a reference sine wave intersecting the modulating signal to determine
the pulse width
B)
compares the value of a sawtooth waveform intersecting the modulating signal to determine
the pulse width
C)
compares the value of a pulse waveform intersecting the modulating signal to determine the
pulse width
D)
compares the value of a reference dc voltage intersecting the modulating signal to determine
the pulse width
B
8)
All of the following are typical connector types for fiber–optic systems except ________.
8)
A)
BNC
B)
ST
C)
FDDI
D)
LC
A
9)
Synchronous data is sent in ________.
9)
A)
frames
B)
packets
C)
continuous bit streams
D)
bunches
A
10)
Communication in the infrared region can be ________.
10)
A)
single–mode
B)
dispersed
C)
diffused
D)
multimode
C
B
11)
In 64–QAM the “64” means ________.
11)
A)
the method was introduced as a standard in 1964
B)
the method uses 64–bit frames
C)
there are 64 different modulation states
D)
the method can represent 64–bit binary groups
12)
The simplest connection between a sending device and receiving device is ________.
12)
A)
a shielded twisted pair
B)
a coaxial cable
C)
a wire
D)
a fiber optic cable
13)
Inductance, capacitance, and resistance in a wire cable can cause ________.
13)
A)
waveform distortion
B)
ringing
C)
phase distortion
D)
all of the above
14)
Shielded twisted pair cable provides more protection from ________ than unshielded twisted pair
cable.
14)
A)
PSK
B)
SNR
C)
EMI
D)
STP
15)
EMI stands for ________.
15)
A)
electromagnetic interference
B)
external magnetic inductance
C)
electromotive induction
D)
excessive measured interference
Explanation:
16)
A data transmission system does not require ________.
16)
A)
a transmission medium
B)
a receiving device
C)
a monitoring station
D)
a sending device
17)
The ways in which radio frequency and microwave signals propagate through the atmosphere
include all of the following except ________.
17)
A)
stratospheric
B)
ionospheric
C)
ground wave
D)
line–of–sight
18)
Fiber optic cable functions due to a phenomenon called ________.
18)
A)
absorption
B)
total internal reflection
C)
total internal refraction
D)
dispersion
19)
Pulse code modulation ________.
19)
A)
is used to convert digital values into analog signals
B)
is used for digital audio, Blu–Ray, CD, and DVD formats
C)
has less accuracy the faster data is sampled
D)
has few practical applications
20)
Sample–and–hold circuitry is associated with ________.
20)
A)
quadrature amplitude modulation
B)
pulse–coded modulation
C)
pulse amplitude modulation
D)
pulse width modulation
21)
The error check in the frame check field of a data frame consists of ________.
21)
A)
a CRC value
B)
a parity bit
C)
a checksum
D)
any of the above
22)
Transmission of data through space without the use of connections between sending and receiving
systems is called ________.
22)
A)
sonar
B)
wireless communications
C)
full–duplex communications
D)
line–of–sight communications
B
23)
The purpose of twisted pair cables is to minimize ________.
23)
A)
cabling distances
B)
data transmission rates
C)
power dissipation
D)
cross–talk
D
24)
An asynchronous data packet typically includes all of the following bit types except ________.
24)
A)
stop
B)
retry
C)
start
D)
data
B
25)
For a return to zero data format ________.
25)
A)
a single pulse during a bit time represents a 0 and absence of a pulse represents a 1
B)
a single pulse during a bit time represents a 1 and absence of a pulse represents a 0
C)
the format is meaningless because there is no return to zero data format
D)
a change during a bit time represents a 1 and no change represents a 0
B
D
Explanation:
26)
The construction of a coaxial cable does not include ________.
26)
A)
an insulating jacket
B)
a dielectric surrounded by a copper shield
C)
a center conductor
D)
a highly reflective outer layer
27)
Parallel data transmission ________.
27)
A)
does not required reduced data rates to prevent errors
B)
is typically faster than serial transmission
C)
does not have problems with data skew
D)
all of the above
28)
Transmission modes include all of the following except ________.
28)
A)
free–form
B)
half–duplex
C)
full–duplex
D)
simplex
29)
For long distance communications system typically will transmit data in ________.
29)
A)
parallel format
B)
serial format
C)
ASCII
D)
both A and B
30)
The difference between broadband and baseband transmissions is ________.
30)
A)
broadband transmissions modulate the data
B)
baseband means that the system is receiving the transmission
C)
baseband transmissions modulate the data
D)
baseband means that the system is sending the transmission
31)
All of the following factors affect the transmitted signal quality of fiber optic communications
except ________.
31)
A)
bending
B)
cross–talk
C)
absorption
D)
attenuation
32)
BPSK stands for ________.
32)
A)
binary phase shift keying
B)
bit pulse standardized keying
C)
byte protocol signal keying
D)
bidirectional parallel synchronous keying
A
33)
The bit rate is defined as ________.
33)
A)
bits per second
B)
packets per second
C)
symbols per second
D)
half the baud rate
A
34)
In pulse position modulation ________.
34)
A)
the amplitude of a pulse varies based upon its position relative to the zero–crossing of the
modulating signal
B)
the position of a pulse relative to a reference signal varies based upon the value of the
modulating signal
C)
the position of a pulse relative to a reference signal varies based upon its amplitude relative to
the amplitude of the modulating signal
D)
the frequency of a pulse waveform varies based upon the position of the zero–crossing of the
modulating signal relative to a reference signal
B
B
35)
To correct for drift between the sending and receiving oscillators, asynchronous communication
systems ________.
35)
A)
use a third system oscillator to establish a reference frequency
B)
coordinate transmissions with a recognized NIST time signal
C)
require periodic calibration by authorized service personnel
D)
use the start bit of each data packet to resynchronize the oscillators
36)
Digital data transmission channels can be all of the following except ________.
36)
A)
wireless
B)
thermal transmission
C)
optical fiber
D)
wire cable
37)
The fiber optic core for single–mode propagation is ________.
37)
A)
much smaller in diameter than in multimode propagation
B)
much larger in diameter than in multimode propagation
C)
about the same diameter as in multimode propagation
D)
somewhat larger in diameter than in multimode propagation
38)
A constellation map graphically displays ________.
38)
A)
the phase and amplitude of a modulated signal
B)
the data rate and frame size of a modulated signal
C)
the number of frames and detected errors for a modulated signal
D)
the baud rate and data efficiency for a modulated signal
39)
Advantages of fiber optic cable over copper cables include all of the following except ________.
39)
A)
faster data rates
B)
transmission over longer distances
C)
immunity from EMI
D)
lower cost
40)
Time division multiplexing include all of the following except ________.
40)
A)
bit–interleaved
B)
statistical
C)
asynchronous
D)
byte–interleaved
41)
Frequency division multiplexing ________.
41)
A)
transmits data from each source on a different frequency
B)
varies how frequently data from each source is transmitted
C)
allows only one source to transmit at a time
D)
all of the above
42)
A simple way to convert parallel to serial data is to use ________.
42)
A)
a binary to hexadecimal converter
B)
a full–adder
C)
a FIFO memory
D)
a parallel in serial out shift register
43)
Synchronous data formats include all of the following except ________.
43)
A)
non–return to zero
B)
Manchester encoding
C)
return to zero
D)
duplex cycling
44)
One–way communications, such as that between a computer and a simple printer, would probably
use ________.
44)
A)
full–duplex communications
B)
free–form communications
C)
simplex communications
D)
half–duplex communications
45)
Penetration losses of radio frequency signals occur because of ________.
45)
A)
wave diffraction and absorption
B)
cross–talk and electromagnetic interference
C)
propagation losses and multipath effects
D)
resistance and skin effect
46)
The baud rate is defined as ________.
46)
A)
twice the bit rate
B)
symbols per second
C)
bits per second
D)
packets per second
B
47)
The preamble of a frame ________.
47)
A)
is used to synchronize the receiver’s clock with that of the sender
B)
alerts the receiver that a new frame has arrived
C)
is located at the start of a frame
D)
all of the above
D
48)
Noise ________.
48)
A)
is the primary cause of error in fiber optic communications
B)
is produced by man–made sources only
C)
can result from natural sources
D)
is greater when the SNR value is larger
C
49)
Common fiber optic data rates are ________.
49)
A)
50 MHz to 100 MHz
B)
10 GHz to 40 GHz
C)
500 MHz to 1 GHz
D)
1 MHz to 5 MHz
B
A
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
50)
Coaxial connections typically use BNC connectors.
50)
51)
Quadrature amplitude modulation uses a combination of frequency shift keying and amplitude
modulation.
51)
52)
ASK stands for asynchronous serial keying.
52)
53)
In a synchronous communications system, the receiving system provides the clock signal.
53)
54)
The relative strength of a signal compared to the noise present is called the signal–to–noise ratio.
54)
55)
In multimode propagation light propagates through the fiber core as a single ray.
55)
56)
When data is transmitted without modulation, it is called broadband transmission.
56)
57)
Bit–interleaved time division multiplexing uses a start and stop bit to synchronize the multiplexing
and demultiplexing of transmitted data.
57)
58)
In asynchronous communication systems, the sender and receiver oscillators operate at the same
frequency.
58)
59)
Statistical time division multiplexing improves channel efficiency by ensuring that every time slot
contains data.
59)
60)
Manchester encoding is a type of synchronous communications that requires only a single line.
60)
61)
“Return to zero” and “return to one” are types of synchronous communications that use separate
clock and data lines.
61)
62)
Frequency shift keying is a type of encoding in which a digital signal modulates the frequency of a
higher frequency sine wave is frequency shift keying.
62)
63)
In general, parallel data transmission is faster than serial data transmission.
63)
64)
Most signal loss in coaxial cable or twisted pair media is because of resistance.
64)
65)
In simplex communications, data always travels in the same direction.
65)
66)
Wireless communication in the infrared frequency band are limited to line–of–sight
communications.
66)
67)
An advantage of parallel communications is that multiple transmission lines avoid skew in the
transmitted data.
67)
68)
Wireless media does not suffer from signal losses as do physical media like copper wire or fiber
optic cable.
68)
69)
Wireless transmission systems do not have a physical connection between the sending and
receiving systems.
69)
70)
The loss of energy as a signal propagates through the transmission medium is called cross–talk.
70)
71)
Statistical time division multiplexing functions by using variable time slot assignments.
71)
72)
The three components of a data transmission system are a sending device, receiving device, and
transmission medium.
72)
73)
The simplest connection between sending and receiving devices is a coaxial cable.
73)
74)
Time division multiplexing switches multiple data sources onto and off of a single transmission
line in a specific sequence.
74)
75)
The unwanted change in the shape of a waveform is referred to as modulation.
75)
76)
Serial–to–parallel and parallel–to–serial converters allow computers to communicate with external
devices.
76)
77)
A commonly used type of pulse modulation is pulse width modulation.
77)
78)
Bluetooth is an example of phase shift keying.
78)
79)
Synchronous time division multiplexing is inefficient because a time slot must be reserved even if
there is no data to transmit in that time slot.
79)
80)
Noise is an unwanted electrical disturbances caused by natural and man–made sources.
80)
81)
Single–mode propagation has greater bandwidth than multimode propagation.
81)
82)
Baud rate is another term for bit rate.
82)
83)
Optical fiber cables get their name from originally carrying video communications.
83)
84)
Conversion of optical power to heat is one result of absorption in fiber optic cables.
84)
85)
Optical fiber cables can support faster data rates than copper conductors.
85)
86)
Inductance, capacitance, and resistance in a signal wire can result in oscillations called ringing.
86)
87)
FDM stands for fixed delay modulation.
87)
88)
The two types of digital data transmission are baseband and highband.
88)
89)
Resistance is a major factor in causing waveform distortion in cables.
89)
90)
Optical fiber is used when a data transmission system requires a cheap transmission medium.
90)
91)
An advantage of twisted pair cable is that cross–talk is minimized.
91)
92)
A modulation method used to convert the amplitude of an analog signal to digital values is pulse
amplitude modulation.
92)
93)
A vector representation that graphically shows the symbol values and corresponding phases being
transmitted by a system is called a star chart.
93)
94)
Synchronous communication systems send data in groups called packets.
94)
95)
The data efficiency of a system is the percentage of the total communications time spent
transmitting data bits.
95)
96)
Another name for pulse position modulation is pulse phase modulation.
96)
97)
Diffusion is one cause of signal attenuation in fiber optic cable.
97)
98)
Each modulation state in a 16–QAM system represents a specific 4–bit group.
98)
99)
A disadvantage of bit–interleaved time division multiplexing is that the sending system must
buffer data before transmitting it.
99)
Answer Key
Testname: C13
Answer Key
Testname: C13