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DDC Flashcards

1
Q

Shannon’s Limit for Information
Capacity

A. Any of these choices
B. It states that information capacity is
proportional to the bandwidth of the
system and the number of possible states
per symbol.
C. It states that information capacity is
directly proportional to bandwidth and
transmission time of the system.
D. It states that information capacity is a
function of bandwidth and signal-to-
noise ratio of the system.

A

D. It states that information capacity is a
function of bandwidth and signal-to-
noise ratio of the system.

Hartley’s Law (Ralph Hartley) - it states
that information capacity is directly
proportional to bandwidth and
transmission time of the system.
Shannon’s Limit for Information
Capacity (Claude E. Shannon) - it states
that information capacity is a function
of bandwidth and signal-to-noise ratio
of the system.
Shannon-Hartley Theorem - it states
that information capacity is proportional to the bandwidth of the system and the number of possible states per symbol.

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2
Q

The rate of change at the output of the
modulator:

A. Bit Rate
B. Baud Rate
C. Information Capacity
D. Nyquist Bandwidth

A

B. Baud Rate

Bit Rate (fb)- the rate of change at the input of the modulator and has a unit of bits per second (bps). Determines the
line speed.
Baud Rate (Baud) - the rate of change
at the output of the modulator.
Determines the line speed.

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3
Q

If a symbol is composed of 3 bits, there
are _____ data levels.

A. 16
B. 2
C. 4
D. 8

A

D. 8

M=2=2=8

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4
Q

A constant amplitude modulation
similar to conventional phase
modulation except that the input signal
is a binary digital signal:

A. PSK
B. FSK
C. QAM
D. ASK

A

A. PSK

Phase Shift Keying (PSK)- a constant
amplitude modulation similar to
conventional phase modulation (PM)
except that with PSK the input signal is
a binary digital signal.

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5
Q

If the bit rate for an ASK signal is 1200
bps, the baud rate is_

A. 600
B. 300
C. 1200
D. 400

A

C. 1200

Baud = fb = 1200 baud

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6
Q

It is the regeneration of clocks at the
receiver that are synchronous with
those at the transmitter for the precise
timing or clock synchronization
between transmit and receive circuitry.

A. Clock Recovery
B. Carrier Recovery
C. Any of these choices
D. Baseband Recovery

A

A. Clock Recovery

Carrier Recovery - the process of
extracting a phase-coherent reference
carrier from a receiver signal.
Sometimes called Phase Referencing.
Clock Recovery - it is the regeneration of clocks at the receiver that are
synchronous with those at the
transmitter for the precise timing or
clock synchronization between transmit
and receive circuitry.

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7
Q

It is a form of constant-amplitude angle modulation and similar to conventional frequency modulation except that the
modulating signal is a binary signal that
varies between two discrete voltage
levels:

A. PSK
B. FSK
C. ASK
D. QAM

A

B. FSK

Frequency Shift Keying (FSK)- also
known as Binary Frequency Shift Keying
(BFSK). Binary FSK is a form of
constant-amplitude angle modulation and similar to conventional frequency modulation (FM) except that the
modulating signal is a binary signal that
varies between two discrete voltage
levels.

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8
Q

It is determined after transmission is
done:

A. BER
B. SNR
C. P(e)
D. NF

A

A. BER

Bit Error Rate - an empirical record of a system’s actual error performance. It is determined after the transmission is done. Based on the previous (historical/ empirical).
Probability of Error, P(e) - it is a
theoretical expectation of the bit error
rate of the given system. It is
determined before transmission. Based on the future (expectation/theoretical/mathematical).

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9
Q

In 8PSK, if the C input is low, it indicates:

A. Positive Polarity
B. Negative Polarity
C. 0.541 V Magnitude
D. 1.307 V Magnitude

A

C. 0.541 V Magnitude

8 Phase Shift Keying:
The Q/1 bits both indicates the polarity
of the signal:
LOGIC 1 - Positive Polarity
LOGIC 0 - Negative Polarity
The C bit indicates the magnitude of the
signal:
LOGIC 1 -1.307V
LOGIC 0-0.541V

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10
Q

In ASK, if the binary input bit is high, the
output is:

A. there is no output
B. the space frequency
C. the carrier signal
D. the mark frequency

A

C. the carrier signal

Amplitude Shift Keying:
LOGIC 1 - the output is the carrier
signal.
LOGIC O - there is no output signal.

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11
Q

In 16QAM, if the Q’/l’ input is high, it
indicates:

A. Negative Polarity
B. Positive Polarity
C. 0.22 V Magnitude
D. 0.821 V Magnitude

A

D. 0.821 V Magnitude

16 Quadrature Amplitude Modulation:The Q/l bits both indicates the polarity of the signal:
LOGIC 1 - Positive Polarity
LOGIC 0 - Negative Polarity
The Q’/l’ bit indicates the magnitude of
the signal:
LOGIC 1-0.821V
LOGIC 0-0.22V

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12
Q

In FSK, which frequency is always lesser
in value?

A. Either Mark or Space Frequency
B. Mark and Space Frequency are equal
C. Space Frequency
D. Mark Frequency

A

A. Either Mark or Space Frequency

Mark frequency is logic 1. Space
frequency is logic 0. The mark and
space frequencies is separated from the carrier by the peak frequency deviation.Either of the mark or space can be
greater or lesser.

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13
Q

It is the ratio of the transmission rate to
the minimum bandwidth:

A. Spectral Efficiency
B. Modulation Efficiency
C. Any of these choices
D. Information Density

A

C. Any of these choices

Bandwidth Efficiency - also known as
the Information Density, Modulation
Efficiency and Spectral Efficiency. Used
to compare the performance of one
digital modulation technique to another.It is the ratio of the transmission rate in bps to the minimum bandwidth and has a unit of bps per Hertz (bps/Hz) or bits per cycle (bits/cycle).

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14
Q

16PSK has:

A. Tribit
B. Single Bit
C. Dibit
D. Quadbit

A

D. Quadbit

16 Phase Shift Keying (16PSK) - it is an
M-ary encoding technique where M =
16. There are sixteen different possible states. The incoming data in groups of four bits called Quadbits.

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15
Q

As the bit rate of an FSK signa
increases, the bandwidth _____

A. Remains the same
B. Decreases
C. Doubles
D. Increases

A

D. Increases

The bandwidth of FSK is computed
using Carson’s Rule:
B=2(△f+fh)

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16
Q

8PSK has:

A. Tribit
B. Dibit
C. Single Bit
D. Quadbit

A

A. Tribit

8 Phase Shift Keying (8PSK) - it is an M-ary encoding technique where M = 8 The incoming bits are considered in
groups of three bits called Tribit. The
input data is in the form of QIC, where Q means Quadrature Bit, I means In-Phase Bit and C means Control Bit.

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17
Q

In 8PSK, the outputs are separated by.

A. 22.5 degrees
B. 45 degrees
C. 90 degrees
D. 180 degrees

A

B. 45 degrees

8 Phase Shift Keying (8PSK) - it is an M-ary encoding technique where M = 8.The incoming bits are considered in
groups of three bits called Tribit. The
input data is in the form of QIC, where Q means Quadrature Bit, I means In-Phase Bit and C means Control Bit.

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18
Q

What is the unit for Bandwidth
Efficiency?

A. bits/cycle
B. unitless
C. Hz/bits
D. bits/second

A

A. bits/cycle

Bandwidth Efficiency - also known as
the Information Density, Modulation
Efficiency and Spectral Efficiency. Used
to compare the performance of one
digital modulation technique to another.It is the ratio of the transmission rate in bps to the minimum bandwidth and has a unit of bps per Hertz (bps/Hz) or bits per cycle (bits/cycle).

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19
Q

It is a form of digital modulation where the digital information is contained in both amplitude and phase of the transmitted carrier.

A. ASK
B. PSK
C. QAM
D. FSK

A

C. QAM

ASK - amplitude FSK- frequency PSK- phase
QAM - phase and amplitude

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20
Q

In ASK, if the binary input bit is low, the
output is:

A. the carrier signal
B. the mark frequency
C. the space frequency
D. there is no output

A

D. there is no output

Amplitude Shift Keying:
LOGIC 1 - the output is the carrier
signal.
LOGIC O - there is no output signal.

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21
Q

In 16PSK, the outputs are separated by:

A. 45 degrees
B. 90 degrees
C. 180 degrees
D. 22.5 degrees

A

D. 22.5 degrees

16 Phase Shift Keying (16PSK) - it is an
M-ary encoding technique where M =
16. There are sixteen different possible states. The incoming data in groups of four bits called Quadbits.

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22
Q

It uses XNOR as its primary circuit:

A. QAM
B. BPSK
C. QPSK
D. DPSK

A

D. DPSK

Differential Phase Shift Keying (DPSK)-
primary advantage is simplicity with
which it can be implemented. No carrier
recovery is needed. Uses XNOR as its
primary circuit. Two input bits
determines the phase shift of the signal.

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23
Q

In QPSK, if the Q/l input is low, it
indicates:

A. Positive Polarity
B. 1.307 V Magnitude
C. Negative Polarity
D. 0.541 V Magnitude

A

C. Negative Polarity

Quaternary Phase Shift Keying:
The Q/l bits both indicates the polarity
of the signal:
LOGIC 1 - Positive Polarity
LOGIC 0 - Negative Polarity

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24
Q

Two output phases are possible for a
single carrier frequency.

A. Biphase Modulation
B. Any of these choices
C. Binary Phase Shift Keying
D. Phase Reversal Keying

A

B. Any of these choices

Binary Phase Shift Keying (BPSK) - also known as Phase Reversal Keying (PRK)and Biphase Modulation. Two output
phases are possible for a single carrier frequency. One output represents logic 1. Another output represents logic 0.

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25
Q

Which modulation technique involves tribits, eight different phase shifts, and one amplitude?

A. FSK
B. ASK
C. 4-PSK
D. 8-PSK

A

D. 8-PSK

8 Phase Shift Keying (8PSK) - it is an M-ary encoding technique where M= 8.The incoming bits are considered in
groups of three bits called Tribit. The
input data is in the form of QlC, where Q means Quadrature Bit, I means In-Phase Bit and C means Control Bit.

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26
Q

In 8PSK, if the C input is high, it
indicates:

A. Positive Polarity
B. 0.541 V Magnitude
C. 1.307 V Magnitude
D. Negative Polarity

A

C. 1.307 V Magnitude

8 Phase Shift Keying:
The Q/l bits both indicates the polarity
of the signal:
LOGIC 1- Positive Polarity
LOGIC 0 - Negative Polarity
The C bit indicates the magnitude of the
signal:
LOGIC 1-1.307V
LOGIC 0-0.541V

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27
Q

In FSK, if the binary input bit is low, the
output is:

A. the carrier signal
B. there is no output
C. the space frequency
D. the mark frequency

A

C. the space frequency

LOGIC 1 - the output frequency is the
mark frequency.
LOGIC O - the output frequency is the
space frequency

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28
Q

The bit rate always equal the baud rate
in which type of signal?

A. FSK
B. QAM
C. 4-PSK
D. All of these choices

A

A. FSK

Frequency Shift Keying (FSK)- also
known as Binary Frequency Shift Keying
(BFSK). Binary FSK is a form of
constant-amplitude angle modulation and similar to conventional frequency modulation (FM) except that the
modulating signal is a binary signal that
varies between two discrete voltage
levels.

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29
Q

In PSK, as the level (M) increases, the
transmission time:

A. increases by 50%
B. decreases
C. decreases by 50%
D. increases

A

D. increases

As the level (M) of the PSK increases,
the transmission time is faster.
However, the signal’s spacing is
decreased and can cause interferences
and errors.

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30
Q

The companding occurs before
converting the signal to digital form:

A. Level Companding
B. Word Companding
C. Digital Companding
D. Analog Companding

A

D. Analog Companding

Analog Companding - companding
occurs before converting the signal to
digital form.
Digital Companding - companding occurs after converting the signal to digital for. Easier than analog
companding.

31
Q

For every one cycle there must be at
least _____ samples.

A. four
B. three
C. one
D. two

A

D. two

Sampling Rate - the minimum sampling
rate is equal to twice the highest audio
input frequency. Aliasing or Foldover
Distortion will occur if the condition is
not met. For every one cycle, there must be at least two samples. Also known as Nyquist Criterion.

32
Q

The companding occurs after
converting the signal to digital form:

A. Analog Companding
B. Digital Companding
C. Level Companding
D. Word Companding

A

B. Digital Companding

Analog Companding - companding
occurs before converting the signal to
digital form.
Digital Companding - companding occurs after converting the signal to digital form. Easier than analog companding.

33
Q

The companding standard used by
United States of America and Japan:

A. u-Law Companding
B. C-Law Companding
C. D-Law Companding
D. A-Law Companding

A

A. u-Law Companding

u-Law Companding - companding standard used by United States of America and Japan.
A-Law Companding - companding
standard used by European countries.

34
Q

The process of converting an infinite
number of possibilities to a finite
number of conditions:

A. Coding
B. Quantizing
C. Companding
D. Sampling

A

B. Quantizing

Sampling - to sample periodically the continually changing analog signal and convert the samples to a series of
constant amplitude PAM levels. The
process of obtaining samples.
Quantizing - the process of converting an infinite number of possibilities to a finite number of conditions. Rounding
off the amplitudes of flat-top samples to
a manageable number of levels.
Assigning PCM codes to absolute
magnitude.
Coding - the quantized intervals are
assigned to the individual PAM samples
into binary signals.

35
Q

The companding standard used by
European countries:

A. D-Law Companding
B. u-Law Companding
C. C-Law Companding
D. A-Law Companding

A

D. A-Law Companding

u-Law Companding - companding standard used by United States of America and Japan.
A-Law Companding - companding
standard used by European countries.

36
Q

A pulse modulation technique in which
the pulse width is proportional to the
amplitude of the analog signal:

A. PCM
B. PAM
C. PWM
D. PPM

A

C. PWM

Pulse Width Modulation (PWM)- a
method sometimes called Pulse
Duration Modulation (PDM) or Pulse
Length Modulation (PLM). The pulse
width is proportional to the amplitude of
the analog signal.

37
Q

It occurs when Nyquist Criterion is not
met:

A. Foldover Distortion
B. Overload Distortion
C. Aperture Distortion
D. Quantization

A

A. Foldover Distortion

Aperture Error (Aperture Distortion)-
when the amplitude of the sampled
signal changes during the sample pulse
time.
Aliasing (Foldover Distortion) - will
occur if Nyquist Criterion is not met.
Quantization Error (Quantization Noise)
- the error produced by rounding off
values.
Peak Limiting (Overload Distortion) - if the magnitude of the sample exceeds the highest quantization interval.

38
Q

Which quantization level results in a
more faithful reproduction of the signal?

A. 2
B. 16
C. 32
D. 8

A

C. 32

To reduce the quantization error,
increase the number of levels thus increasing the quality however it will also increase the memory size of the data.

39
Q

It is a numerical indication of how
efficiently a PCM code is utilized.

A. Bandwidth Efficiency
B. Spectral Efficiency
C. Nyquist Criterion
D. Coding Efficiency

A

D. Coding Efficiency

Coding Efficiency - it is a numerical
indication of how efficiently a PCM code is utilized. It is the ratio of the minimum number of bits required to achieve a
certain dynamic range to the actual
PCM bits used.

40
Q

The smallest possible magnitude that
can be decoded by the DAC:

A. Both Resolution & Minimum Voltage
B. Quantum
C. Minimum Voltage
D. Resolution

A

D. Resolution

Resolution - the smallest possible
magnitude that can be decoded by the DAC. The magnitude of the quantum. It is equal to the minimum step-size which is equal to the voltage of the LSB of the PCM code.

41
Q

The input analog waveform is sampled
by a sampling pulse with an output
sampled waveform that is flattened at
the top:

A. Natural Sampling
B. Ideal Sampling
C. Sample & Hold
D. Any of these choices

A

C. Sample & Hold

Natural Sampling - the input analog
waveform is sampled by a sampling
pulse with an output sampled waveform obtaining the shape of the input analog waveform.
Flat Top Sampling - also known as
Sample & Hold. The input analog
waveform is sampled by a sampling
pulse with an output sampled waveform
that is flattened at the top (staircase
waveform). Most commonly used.

42
Q

It is used to protect the lower amplitude
signals from noise:

A. Encryption
B. Companding
C. De-emphasis
D. Pre-emphasis

A

B. Companding

Companding - it is the process of
compressing then expanding. The
higher-amplitude analog signals are
compressed prior to transmission then
expanded at the receiver. It is used to
protect the lower amplitude signals from noise. Means of improving the dynamic range of a communications systems.

43
Q

A pulse modulation technique in which the position of the constant-width pulse within a prescribed time slot is varied
according to the amplitude of the
analog signal:

A. PPM
B. PAM
C. PCM
D. PWM

A

A. PPM

Pulse Position Modulation (PPM) - the
position of the constant-width pulse
within a prescribed time slot is varied
according to the amplitude of the
analog signal.

44
Q

In order to reduce quantization error, the
number of quantization level must be _____

A. increased
B. increased by 50%
C. decreased
D. decreased by 50%

A

A. increased

To reduce the quantization error,
increase the number of levels thus
increasing the quality however it will also increase the memory size of the data.

45
Q

It is designed specifically to take
advantage of bits:

A. Adaptive Delta Modulation PCM
B. Automatic Delta Modulation PCM
C. Delta Modulation PCM
D. Differential PCM

A

D. Differential PCM

Differential PCM - the difference in
amplitude of two successive samples is
transmitted rather than the actual
sample. Designed specifically to take
advantage of bits.

46
Q

A type of PCM code in which the first bit is the sign bit and the rest of the bits are magnitude bits.

A. Magnitude PCM
B. Linear PCM
C. Sign-Magnitude PCM
D. Linear Sign PCM

A

C. Sign-Magnitude PCM

Linear PCM - all the bits are magnitude bits. Sign-Magnitude PCM - one bit is a sign bit and the rest of the bits are
magnitude bits.

47
Q

If the first bit of the sign-magnitude
PCM code is low, then it is:

A. Neither Positive nor Negative
B. Positive
C. Negative
D. Either Positive or Negative

A

C. Negative

Sign-Magnitude PCM (Sign Bit):
LOGIC 1 - Positive
LOGIC 0 - Negative

48
Q

The Nyquist theorem specifies the
minimum sampling rate to be _____

A. Twice the highest frequency of a signal
B. Twice the bandwidth of a signal
C. Equal to the highest frequency of a signal
D. Equal to the lowest frequency of a signal

A

A. Twice the highest frequency of a signal

Sampling Rate - the minimum sampling
rate is equal to twice the highest audio
input frequency. Aliasing or Foldover
Distortion will occur if the condition is
not met. For every one cycle, there must be at least two samples. Also known as Nyquist Criterion.

49
Q

The error produced by rounding off
values:

A. Quantization Noise
B. Aperture Distortion
C. Overload Distortion
D. Foldover Distortion

A

A. Quantization Noise

Aperture Error (Aperture Distortion) - when the amplitude of the sampled signal changes during the sample pulse time.
Aliasing (Foldover Distortion) - will
occur if Nyquist Criterion is not met.
Quantization Error (Quantization Noise)— the error produced by rounding off values.
Peak Limiting (Overload Distortion) - if the magnitude of the sample exceeds the highest quantization interval.

50
Q

In Delta Modulation PCM, it occurs
when the input changes very fast:

A. Aperture Error
B. Granular Noise
C. Slope Overload
D. Aliasing

A

C. Slope Overload

Slope Overload - it happens when the input changes very fast. Solution to this problem is to increase the step-size.
Granular Noise - it happens when the input does not change. Solution to this problem is to decrease the step-size.

51
Q

The maximum quantization noise equal
to _____ the resolution.

A. half
B. twice
C. one-thirds
D. thrice

A

A. half

Quantization Error (Quantization Noise)
- the error produced by rounding off
values.

52
Q

In Delta Modulation PCM, it occurs
when the input does not change:

A. Slope Overload
B. Granular Noise
C. Aliasing
D. Aperture Error

A

B. Granular Noise

Slope Overload - it happens when the input changes very fast. Solution to this problem is to increase the step-size.
Granular Noise - it happens when the input does not change. Solution to this problem is to decrease the step-size.

53
Q

A pulse modulation technique in which
the analog signal is sampled and
converted to a fixed-length, serial binary
number for transmission:

A. PPM
B. PAM
C. PWM
D. PCM

A

D. PCM

Pulse Code Modulation (PCM) - the
analog signal is sampled and converted
to a fixed-length, serial binary number
for transmission. The binary number
varies according to the amplitude of the analog signal. It was invented by Alex H.Reeves.

54
Q

To sample periodically the continually
changing analog signal and convert the
samples to a series of constant
amplitude PAM levels:

A. Coding
B. Sampling
C. Quantizing
D. Companding

A

B. Sampling

Sampling - to sample periodically the continually changing analog signal and convert the samples to a series of
constant amplitude PAM levels. The
process of obtaining samples.
Quantizing - the process of converting an infinite number of possibilities to a finite number of conditions. Rounding
off the amplitudes of flat-top samples to
a manageable number of levels.
Assigning PCM codes to absolute
magnitude.
Coding - the quantized intervals are
assigned to the individual PAM samples
into binary signals.

55
Q

What is the solution for slope overload
in Delta Modulation PCM?

A. Increase the step-size
B. Increase the input signal
C. Decrease the step size
D. Decrease the input signal

A

A. Increase the step-size

Slope Overload - it happens when the
input changes very fast. Solution to this
problem is to increase the step-size.
Granular Noise - it happens when the input does not change. Solution to this problem is to decrease the step-size.

56
Q

It is the ratio of the largest possible
magnitude to the smallest possible
magnitude that can be decoded by the
DAC.

A. Nyquist Criterion
B. Quantum Interval
C. Dynamic Range
D. Resolution

A

C. Dynamic Range

Dynamic Range - abbreviated DR, DNR or DYR is the ratio between the largest and smallest values that a certain quantity can assume.

57
Q

To form a mastergroup, it needs to have
how many supergroups?

A. 17
B. 10
C. 13
D. 15

A

B. 10

AT&T FDM Hierarchy:
(Group)- 12 voice-band channels
(Supergroup) - 5 groups (60 VC)
(Mastergroup) - 10 supergroups (600 VC)
(Jumbogroup) - 6 mastergroups (3600 VC)
(Superjumbogroup) - 3 jumbogroups (10800 VC)

58
Q

The process of simultaneously
transmitting two or more individual
signals over a single communications
channel:

A. Emphasizing
B. Demultiplexing
C. Companding
D. Multiplexing

A

D. Multiplexing

Multiplexing - the process of
simultaneously transmitting two or more individual signals over a single communications channel. MUX and DEMUX are kept on step by a sync pulse.

59
Q

The data rate of T1 carriers is:

A. 1.544 Mbps
B. 1.536 Mbps
C. 3.152 Mbps
D. 6.312 Mbps

A

A. 1.544 Mbps

North American Digital Hierarchy:
T1 (DS-1) - 24 voice channels, 1.544 Mbps
T1C(DS-1C)- 48 voice channels, 3.152 Mbps
T2(DS-2) - 96 voice channels, 6.312 Mbps
T3(DS-3)-672 voice channels, 44.736 Mbps
T4(DS-4)- 4032 voice channels, 274.176 Mbps
T5(DS-5) - 8064 voice channels, 560.16 Mbps

60
Q

To form a jumbogroup, it needs to have
how many mastergroups?

A. 10
B. 6
C. 12
D. 5

A

B. 6

AT&T FDM Hierarchy:
(Group)- 12 voice-band channels
(Supergroup) -5 groups (60 VC)
(Mastergroup) - 10 supergroups (600 VC)
(Jumbogroup) - 6 mastergroups (3600 VC)
(Superjumbogroup) - 3 jumbogroups (10800 VC)

61
Q

A multiplexing technique in which
multiple sources that originally
occupied the same frequency spectrum
are each converted to a different
frequency band and transmitted
simultaneously over a single
transmission medium:

A. PDM
B. WDM
C. TDM
D. FDM

A

D. FDM

Frequency Division Multiplexing (FDM)
- multiple sources that originally
occupied the same frequency spectrum
are each converted to a different
frequency band and transmitted
simultaneously over a single
transmission medium.

62
Q

How many voice-band channels are
there in a supergroup?

A. 3600
B. 60
C. 600
D. 10800

A

B. 60

AT&T FDM Hierarchy:
(Group)- 12 voice-band channels
(Supergroup) -5 groups (60 VC)
(Mastergroup) - 10 supergroups (600 VC)
(Jumbogroup) - 6 mastergroups (3600 VC)
(Superjumbogroup) - 3 jumbogroups (10800 VC)

63
Q

The data rate of T3 carriers is:

A. 274.176 Mbps
B. 560.16 Mbps
C. 6.312 Mbps
D. 44.736 Mbps

A

D. 44.736 Mbps

North American Digital Hierarchy:
T1 (DS-1) - 24 voice channels, 1.544 Mbps
T1C(DS-1C)- 48 voice channels, 3.152 Mbps
T2(DS-2) - 96 voice channels, 6.312 Mbps
T3(DS-3)-672 voice channels, 44.736 Mbps
T4(DS-4)- 4032 voice channels, 274.176 Mbps
T5(DS-5) - 8064 voice channels, 560.16 Mbps

64
Q

An FDM hierarchy which is formed by
frequency - division multiplexing five
groups containing 12 channels each for
a combined bandwidth of 240 kHz.

A. Group
B. Jumbogroup
C. Mastergroup
D. Supergroup

A

D. Supergroup

AT&T FDM Hierarchy:
(Group)- 12 voice-band channels
(Supergroup) -5 groups (60 VC)
(Mastergroup) - 10 supergroups (600 VC)
(Jumbogroup) - 6 mastergroups (3600 VC)
(Superjumbogroup) - 3 jumbogroups (10800 VC)

65
Q

How many voice-band channels are
there in a jumbogroup?

A. 10800
B. 3600
C. 600
D. 60

A

B. 3600

AT&T FDM Hierarchy:
(Group)- 12 voice-band channels
(Supergroup) -5 groups (60 VC)
(Mastergroup) - 10 supergroups (600 VC)
(Jumbogroup) - 6 mastergroups (3600 VC)
(Superjumbogroup) - 3 jumbogroups (10800 VC)

66
Q

A multiplexing technique which
constitutes propagating signals from different sources on different cables that are contained within the same
trench:

A. PDM
B. TDM
C. SDM
D. WDM

A

C. SDM

Space Division Multiplexing (SDM)-constitutes propagating signals from different sources on different cables that are contained within the same trench (transmission medium).

67
Q

The Nyquist theorem specifies the
minimum sampling rate to be _____

A. Twice the highest frequency of a signal
B. Equal to the lowest frequency of a signal
C. Equal to the highest frequency of a signal
D. Twice the bandwidth of a signal

A

A. Twice the highest frequency of a signal

Sampling Rate - the minimum sampling rate is equal to twice the highest audio input frequency. Aliasing or Foldover
Distortion will occur if the condition is
not met. For every one cycle, there must be at least two samples. Also known as Nyquist Criterion.

68
Q

Generation of PCM in order:
A. encoding, sampling, quantizing
B. sampling, quantizing, decoding
C. decoding, sampling, quantizing
D. sampling, quantizing, encoding

A

D. sampling, quantizing, encoding

Sampling - to sample periodically the continually changing analog signal and convert the samples to a series of
constant amplitude PAM levels. The
process of obtaining samples.
Quantizing - the process of converting an infinite number of possibilities to a finite number of conditions. Rounding
off the amplitudes of flat-top samples to
a manageable number of levels.
Assigning PCM codes to absolute
magnitude.
Coding - the quantized intervals are
assigned to the individual PAM samples
into binary signals.

69
Q

The biggest disadvantage of PCM is

A. the large bandwidths that are required
for it
B. its inability to handle analog signals
C. the high error rate which is quantizing
noise introduces
D. its incompatibility with TDM

A

A. the large bandwidths that are required
for it

Pulse Code Modulation (PCM) - the
analog signal is sampled and converted
to a fixed-length, serial binary number
for transmission. The binary number
varies according to the amplitude of the analog signal. It was invented by Alex H.Reeves.

70
Q

ASK, PSK, FSK and QAM are examples
of ______ modulation.

A. Analog-to-digital
B. Digital-to-analog
C. Analog-to-analog

A

B. Digital-to-analog

Digital Radio (Digital Modulation)- it is
the transmittal of digitally modulated
analog carriers between two or more
points in a communication system. An analog carrier is modulated by a digital signal. Digital information, analog
carrier. The medium can be wired or
wireless.

71
Q

It is the distance between symbols on
the constellation diagram:

A. Skip Distance
B. Euclidean Distance
C. Laplacian Distance
D. Any of these choices

A

B. Euclidean Distance

Constellation Diagram - sometimes called Signal State-Space Diagram. A pattern showing all the possible combinations of amplitude and phase
for a signal.

72
Q

In FSK, the mark and space frequency
are separated by.

A. Carrier Swing
B. Bandwidth
C. Any of these choices
D. Peak Frequency Deviation

A

D. Peak Frequency Deviation

Mark frequency is logic 1. Space
frequency is logic 0. The mark and
space frequencies is separated from the carrier by the peak frequency deviation.Either of the mark or space can be greater or lesser.

73
Q

In QPSK, the outputs are separated by.

A. 180 degrees
B. 22.5 degrees
C. 90 degrees
D. 45 degrees

A

C. 90 degrees

Quaternary Phase Shift keying (QPSK)-
also known as Quadrature Phase Shift
Keying. It is a M-ary coding technique where M = 4. It has binary input data combined into group called Dibit. The input data is in the form of Ql, where Q means Quadrature Bit and I means InPhase Bit.

74
Q

In PSK, if the signal’s spacing is
decreased further, it can cause:

A. Attenuation
B. Absorption
C. Noise
D. Interference

A

D. Interference

As the level (M) of the PSK increases,
the transmission time is faster.
However, the signal’s spacing is
decreased and can cause interferences
and errors.

EST (10 decks)

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