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Block 7 Flashcards

1
Q

What involve many users who send and receive voice and data to and from the distant end?

A

Multichannel communications networks

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2
Q

What are some examples of multichannel communications network devices?

A
  • Satellites and terminals
  • Phones
  • Internet
  • Routers
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3
Q

What are the four time standards?

A
  • Apparent solar time
  • Mean solar time
  • Atomic time
  • Coordinated universal time
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4
Q

Which time scale is based on the location of the sun and is the first known time standard?

A

Apparent solar time

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5
Q

Which is the least accurate time scale?

A

Apparent solar time (high noon is not always at noon)

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6
Q

Which time scale began in 1884 and is referred to as universal time (UT or GMT)?

A

Mean solar scale

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7
Q

Which time scale is more accurate than UT but not used as the world’s time standard?

A

Atomic time

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8
Q

Which time scale replaced GMT as the world’s time standard in 1972?

A

Coordinated universal time (UTC)

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9
Q

Which time scale references atomic time and can keep countries’ clocks within +/-1 msec?

A

Coordinated universal time (UTC)

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10
Q

How many official time zones are there?

A

24

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11
Q

There is a time zone for each hour in a day (T/F)

A

True

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12
Q

The military uses ____ instead of local meridians

A

Time zone Z, zero meridian or Zulu time

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13
Q

The accuracy of a timing source depends on what?

A

How well it maintains a period of a second

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14
Q

How are timing sources categorized?

A
  • Primary source

- Secondary source

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15
Q

____ time sources are calibrated to ____

A
  • Secondary time sources

- A primary time source

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16
Q

What are the two types of oscillators?

A
  • Quartz (crystal) oscillators

- Atomic oscillators

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17
Q

Which is the least accurate oscillator and utilizes the Piezoelectric effect?

A

Quartz (crystal) oscillators

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18
Q

What are the two factors that limit quartz (crystal) oscillators accuracy?

A
  • Temperature

- Aging

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19
Q

Atomic oscillators count the oscillations of ____ to create atomic time

A

Highly stable atoms

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20
Q

What are two common types of atomic oscillators?

A
  • Rubidium

- Cesium

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21
Q

____ oscillators are more accurate than quartz but less accurate than ____

A
  • Rubidium

- Cesium

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22
Q

Rubidium oscillators drift about ____ in 24 hours

A

1 usec

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23
Q

____ oscillators drift about 200 nsec in 24 hours

A

Cesium oscillators

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24
Q

Time is measure by the ____, instead of the time of day

A

Time interval between two events

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25
Q

There are 86,400 seconds or separate events each day (T/F)

A

True

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26
Q

Name three time coordination and distribution agencies

A

– International Bureau of Weights and Measures (BIPM)
– United States Naval Observatory (USNO)
– National Institute of Standards and Technology (NIST)

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27
Q

Which time distribution agency is located in Paris and maintains UTC and is the primary frequency standard of the world?

A

International Bureau of Weights and Measures (BIPM)

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28
Q

Which time distribution agency is the primary frequency source for the DoD and its contractors, and primarily uses GPS?

A

US Naval Observatory (USNO)

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29
Q

Which time distribution agency is the primary frequency standard for the general public and primarily uses radio stations?

A

National Institute of Standards and Technology (NIST)

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30
Q

What is an undesired shift of data or clock?

A

Timing jitter

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31
Q

____ is unwanted change in frequency or phase

A

Analog jitter

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32
Q

____ are pulse variations

A

Digital jitter

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33
Q

What are the two types of timing jitter?

A
  • Short-term jitter

- Long-term jitter

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34
Q

What are the characteristics of short-term jitter?

A
  • Caused by signal fading
  • Jitter fade is very small (short duration)
  • Inaccurate signal strength causes fading
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35
Q

What counteracts short term jitter?

A

Elastic store

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36
Q

In what, is data with jitter clocked into a buffer at its own rate but clocked out at the correct rate (removing the jitter)?

A

Elastic store

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37
Q

When does long-term jitter occur?

A
  • When the source of the jitter is not limited

- When both stations lose synchronization

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38
Q

During long-term jitter ____ improves synchronization despite jitter by synchronizing the line (network) clock with the local (node) clock

A

Phase lock loop

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39
Q

____ ensures that all network stations (nodes) operate at the same clock rate

A

Synchronization

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40
Q

What are the four types of network synchronization?

A
  • Plesiochronus
  • Mutual
  • Master clock
  • Master-Slave
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41
Q

In a ____ network each node produces its own clock. They do not travel the network, they stay at the node.

A

Plesiochronus network

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42
Q

In a ____ network all node clocks are averaged and synchronized back to all nodes

A

Mutual network

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43
Q

In a ____ network nodes are synchronized by a single source

A

Master clock network

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44
Q

In a master clock network if the master node fails, the entire network fails (T/F)

A

True

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45
Q

In a ____ network nodes are synchronized by multiple sources (nodes), if the mast node fails then a secondary node will generate clocks

A

Master-slave network

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46
Q

Which synchronization network is best for the Defense Communications System (DCS) because of its high degree of survivability?

A

Master-slave network

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47
Q

What are the two types of multiplexers?

A
  • Analog

- Digital

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48
Q

____ refers to an infinite number of values (constantly changing amplitudes)

A

Analog

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49
Q

____ refers to a limited number of values (either a logic one or a logic zero)

A

Digital

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50
Q

____ is a binary digit (Logic ones or logic zeros)

A

A bit

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51
Q

Multiplexing combines two or more ____ into a ____

A
  • Users (channels)

- Composite signal (aggregate)

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52
Q

What are the characteristics of multiplexing?

A
  • Simultaneous transmission to the distant end
  • Analog and digital
  • Voice, video and data
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53
Q

____ is looking at portions of the input to determine value

A

Sampling

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54
Q

What are the characteristics of sampling?

A
  • Sampling periods are of the same duration
  • Sequential
  • Analog and digital
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55
Q

Frame consists of a sample from each channel and is constructed sequentially (T/F)

A

True

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56
Q

What are additional bits added to the user’s input data after sampling (not part of the user data)?

A

Non-informational bits

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57
Q

What is used by the demux for timing and synchronization?

A

Non-informational bits

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58
Q

What are the four types of bits?

A
  • Frame bit
  • Start bit
  • Stop bit
  • Stuffing bit
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59
Q

What is the total size or amount of data sent to the distant end?

A

Bandwidth

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60
Q

Bandwidth is measured in ____

A

Bits per second (bps)

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61
Q

____ is a single or a range of frequencies (56 kbps or 300 MHz - 3 GHz)

A

Bandwidth

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62
Q

Asynchronous data enters the ____ at irregular intervals

A

Multiplexer

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63
Q

____ such as keyboard or mouse are considered asynchronous

A

Serial devices (8 bit)

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64
Q

What are the characteristics of asynchronous data?

A
  • Frame bit is for synchronization
  • Start and stop bit is for timing/data processing
  • Stop bits are independent of the next start bit
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65
Q

____ data enters the multiplexer at a fixed rate

A

Synchronous

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66
Q

What are the characteristics of synchronous data?

A
  • Frame bit is for synchronization
  • Timing is derived from the predetermined location of each channel
  • Channel 1 always follows the frame bit
  • Channel 2 always follows channel 1
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67
Q

____ is asynchronous at a synchronous rate

A

Isochronous

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68
Q

What are the characteristics of isochronous data?

A
  • Frame bit is for synchronization
  • Start bit and stop bit for asynchronous timing
  • Stuffing bit is for synchronous timing
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69
Q

What assigns a portion of the total bandwidth to each individual input user?

A

Frequency Division Multiplexing (FDM)

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70
Q

What are the characteristics of time division multiplexing (TDM)?

A

– Assigns each user to a specific time slot
- The number of frames is equal to the sampling rate
- The length of each frame is based on the number of
input channels

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71
Q

A basic ____ interweaves all samples into frames before transmission to the distant end

A

Time division multiplexing (TDM) multiplexer

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72
Q

What are the two modes of time division multiplexing (TDM)?

A
  • Synchronous TDM

- Asynchronous TDM

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73
Q

What are the characteristics of

synchronous TDM?

A

– Assigns time slots to all channels whether active or inactive
– Frame bits only
– Wasted bandwidth

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74
Q

What are the characteristics of

asynchronous TDM?

A

– Assigns time slots only to the active channels
– Statistical multiplexing
- Redefines the frame length when channels are active and inactive
- Multiplexer efficiency

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75
Q

____ data is transmitted as large bulky bytes of words

A

Asynchronous data

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76
Q

When asynchronous data is transmitted at asynchronous rate, ____ are added

A

Stuffing bits

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77
Q

What separates the original user signals into different network lines or paths?

A

Demultiplexing

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78
Q

____ routes each signal to the correct distant end user

A

Demulitplexing

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79
Q

Signal formats are how ____ and ____ are represented

A
  • Logic highs

- Logic lows

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80
Q

What are three signal formats?

A
  • Non-return to zero (NRZ)
  • Return to zero (RZ)
  • Conditioned di-phase (CDI)
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81
Q

____ is the most common format of data as it travels within a multiplexer

A

Non-return to zero (NRZ)

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82
Q

Non-return to zero (NRZ) ____ return to zero volts halfway through the clock cycle

A

Does not

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83
Q

What are the two types of Non-return to zero (NRZ)?

A
  • NRZ neutral

- NRZ polar

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84
Q

In NRZ neutral, a logic one is represented by ____ and a logic zero is represented by ____

A
  • +5v

- 0v

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85
Q

NRZ neutral is NOT self-clocking (T/F)

A

True

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86
Q

In NRZ polar, a logic one is represented by ____ and a logic zero is represented by ____

A
  • +5v

- -5v

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87
Q

NRZ polar is NOT self-clocking (T/F)

88
Q

In ____ data returns to zero volts halfway through the clock cycle

A

Return to zero (RZ)

89
Q

What are the four types of return to zero (RZ)?

A
  • RZ Neutral
  • RZ Polar
  • RZ Bipolar
  • RZ Bipolar with Zero Suppression
90
Q

In RZ neutral, logic ones are represented by a momentary increase to ____ then return to ____ halfway through the clock cycle

91
Q

RZ neutral is NOT self-clocking (T/F)

92
Q

In RZ polar, logic ones are represented by an increase to ____ and logic zeroes are represented by a decrease to ____

93
Q

RZ polar IS self-clocking (T/F)

94
Q

In RZ bipolar, logic ones alternate between ____ and ____, logic zeroes are represented by ____

A
  • +5v
  • -5v
  • 0v
95
Q

RZ biplolar is NOT self-clocking (T/F)

96
Q

What detects a long string of logic zeroes between two logic ones?

A

RZ bipolar with suppression

97
Q

In RZ bipolar with zer suppression, a ____ is inserted

A

Timing bit

98
Q

RZ biplolar with suppression IS self-clocking (T/F)

99
Q

In conditioned di-phase (CDI), logic ones require ____ and logic zeroes are represented by ____

A
  • One transition

- Two transitions

100
Q

CDI IS self-clocking (T/F)

101
Q

What states analog signals must be sampled at least twice the highest frequency before being digitized?

A

Nyquist theroem

102
Q

____ is highest voice frequency (VF)

103
Q

There are ____ samples per second

104
Q

____ is a three step process that converts analog to digital

A

Pulse code modulation (PCM)

105
Q

What are the three steps of pulse code modulation (PCM)?

A
  • Step 1 Sample
  • Step 2 Quantize
  • Step 3 Encode
106
Q

During PCM step 1 (sampling), ____ is received from the user and the voltage levels are read into ____ per second

A
  • Analog signal

- 8,000 samples

107
Q

____ are called pulse amplitude modulated (PAM) pulses

108
Q

During PCM step 2 (quantizing), a decimal value is assigned to each ____

A

PAM pulse (sample)

109
Q

What are the two types of quantizing?

A
  • Uniform

- Non-uniform

110
Q

What are the characteristics of uniform quantizing?

A
  • Steps are equally spaced

- PAM pulse is rounded, in cases of quantization error

111
Q

What are the characteristics of non-uniform quantizing?

A
  • Steps are closer near zero where most of the intel is located
  • Corrects quantization errors
112
Q

During PCM step 3 (encoding), the decimal value is converted to ____

113
Q

What are the characteristics of encoding?

A
  • There are 8 bits for each value from Step 2 (quantizing)
  • First 7 bits are the value of the quantize step (127 max)
  • Eighth bit is either positive or negative
114
Q

____ is the time it takes for one frame to occur

A

Frame period

115
Q

Frame period is based on the ____

A

Sampling rate

116
Q

Frame period = 1/8,000 or ____

117
Q

____ is the time it takes to sample one channel in any given

frame

A

Pulse modulated sample period (PMSP)

118
Q

Pulse modulated sample period (PMSP) is based on the number of ____

A

Input channels

119
Q

How many channels are there in a TDM multiplexer?

120
Q

PMSP = frame period / 24 (125 usec / 24) or ____

121
Q

What are the four types of bandwidth allocations?

A
  • Conventional bandwidth
  • Demand assigned bandwidth
  • Dynamic bandwidth
  • Time of day restrictions
122
Q

What are the characteristics of conventional bandwidth?

A

– The same fixed amount for each user
- 64 Kbps for each user
– Dedicated lines even when user is disconnected
- Bandwidth is wasted

123
Q

What are the characteristics of demand assigned bandwidth?

A

– An exact amount for each user
– No input is dedicated
- Bandwidth available when user disconnects
– Internet

124
Q

What are the characteristics of dynamic bandwidth?

A

– The combined input rates from all users exceeds the available bandwidth - Not everyone is connected simultaneously

  • Not everyone is transmitting when connected
  • Most traffic occurs in bursts with time in between transmissions
125
Q

What are the characteristics of time of day restriction bandwidth?

A

– Exclusive bandwidth set aside for specific dates and times

  • More bandwidth required than normally needed
  • Priority basis
126
Q

A network involves two or more users interchange ____, ____ or _____ traffic

A
  • Voice
  • Data
  • Message
127
Q

_____ was developed for communication between modems and computers

128
Q

EIA-232C transmits ____ kbs up to ____ feet and ____ kbps between ____ and ____ feet without the use of a modem

A
  • 56 kbps
  • 50 feet
  • 9.6 kbps
  • 500 and 5,000 feet
129
Q

What are the characteristics of EIA balanced transmission lines?

A
  • Differential transmission

- Two wires carry the data

130
Q

What are the characteristics of EIA unbalanced transmission lines?

A
  • Singled-ended transmission
  • Only one wire to transmit data in both directions
  • Second wire is grounded
131
Q

____ connectors are installed on each end of the computer-modem interface cable

A

D-shaped (DB) connectors

132
Q

(EIA) For data signals, ____ represents a logic zero and ____ represents a logic one

133
Q

(EIA) For control signals, +V represents a ____ and -V represents a ____

A
  • Logic one

- Logic zero

134
Q

____ was developed in response to slower standards with shorter distances

135
Q

EIA-530 transmits between ____ kbps and ____ Mbps up to ____ miles without the use of a modem

A
  • 20 kbps
  • 2 Mbps
  • 3 miles
136
Q

____ is a device that is the source and destination of data (a computer)

A

Data terminal equipment (DTE)

137
Q

____ is a device that establishes, maintains and ends a data transfer (a modem)

A

Data communications equipment (DCE)

138
Q

What is connected between routers of two separate networks (LAN to WAN) and is on the user side of the network?

A

Digital service unit (DSU)

139
Q

What is connected to the WAN side of two separate networks (LAN to WAN)

A

Channel service unit (CSU)

140
Q

In a network, insufficient bandwidth at one level requires the network to increase to the next highest level (T/F)

141
Q

What multiplexes group port input data and secure and non-secure digital voice orderwire for transfer to the aggregate interface?

A

Vertex nodal satellite multiplexer (NSM)

142
Q

Vertex nodal satellite multiplexer (NSM) ____ incoming aggregate for transfer to the output group ports

A

Demultiplexes

143
Q

Maximum output (aggregate) data rate of the NSM is ____ Mbps

144
Q

What are the two operational modes for the NSM?

A
  • Legacy

- Enhanced

145
Q

What performs tests and loopbacks on a system to adequately analyze signal quality as it travels across a network?

A

Bit error rate test set (BERTS)

146
Q

____ is the number of erroneous bits divided by the total number of bits transmitted, received and processed in a given amount of time

A

Bit error rate (BER)

147
Q

What are the characteristics of the HST-3000?

A
  • Rugged, handheld and battery operated
  • Operates with many communications devices
  • Datacom Module
  • End-to-end testing
  • BER testing
148
Q

What are the three test modes of the HST-300?

A
  • DTE emulation
  • DCE emulation
  • Monitor
149
Q

____ terminates a DataCom interface and emulates DTE to perform test operations

A

DTE emulation

150
Q

____ terminates a DataCom interface and emulates DCE to perform test operations

A

DCE emulation

151
Q

Test mode ____ is non-intrusive performance monitoring of a circuit in both directions

152
Q

____ converts (modulates) digital baseband (BB) to an intermediate frequency (IF) (normally 70 to 700 MHz)

153
Q

____ converts IF to the selected transmit RF (IF + local oscillator (LO frequency)

A

Upconverter

154
Q

What does the final amplification to ensure the RF reaches the distant end?

A

High power amplifier

155
Q

What are the characteristics of low noise amplifier (LNA)?

A
  • High sensitivity for signal recovery
  • Eliminates noise
  • Amplification
156
Q

____ converts RF to IF (receive frequency minus the LO frquency)

A

Downconverter

157
Q

Demodulator converts IF to baseband (BB) (T/F)

158
Q

What provides one-way signal flow to prevent reflected energy from damaging equipment?

159
Q

Isolators provide ____ when transitioning between different mediums

A

Impedance matching

160
Q

____ couple microwave energy to antenna, also provides sample points for performance monitoring

A

Directional coupler

161
Q

What is tuned to pass only desired frequencies and block noise and undesired frequencies?

162
Q

____ allow TX and RX to share the same path without interference

A

Circulators (Diplexers and duplexers)

163
Q

Name the fundamental radio parameters

A
  • Frequency accuracy and stability
  • Bandwidth
  • Frequency response
  • Selectivity
  • Gain
  • Sensitivity
164
Q

What depends on the quality of the oscillator that is used?

A

Frequency accuracy and stability

165
Q

What is used to increase frequency accuracy?

A

Phase lock loop

166
Q

Bandwidth is the difference between the ____ and ____ frequencies at which the radio is designed to operate

A
  • Upper

- Lower

167
Q

____ is the ability to process desired frequencies and reject undesired frequencies

A

Selectivty

168
Q

Gain is the value of ____ that a signal obtains in passage through an amplifying stage or system

A

Amplification

169
Q

What is the receiver’s ability to distinguish between low level signals and noise?

A

Sensitivty

170
Q

What are radio performance measuers?

A
  • Quality
  • Reliability
  • Speed
171
Q

Modems modulate an ____ to encode ____

A
  • Analog carrier

- Digital input data

172
Q

What demodulates the incoming carrier to decode transmitted information?

173
Q

____ is the speed of the bandwidth per second

174
Q

What are the three basic components of modulating an analog carrier signal?

A
  • Frequency
  • Amplitude
  • Phase
175
Q

What type of modulation alternates in frequency only?

A

Frequency shift keying (FSK)

176
Q

What type of modulation alternates in amplitude only?

A

Amplitude shift keying (ASK)

177
Q

____ alternates in phase ONLY if the the logic state changes

A

Binary phase shift keying

178
Q

What is the process of using multiple copies of the same transmitted message to correct for data errors?

A

Forward error correction (FEC)

179
Q

The ____ modem uses forward error correction (FEC)

A

Distant end modem

180
Q

____ mixes data using time division to correct for errors or recover lost bits

A

Interleaving

181
Q

What are the characteristics of fiber optic modems?

A
  • Extremely high data rates
  • Not susceptible to RF or electromagnetic interferences
  • 5 stages
182
Q

What are the five stages of fiber optic modems?

A
  • Stage 1 Modulator
  • Stage 2 Transmitter
  • Stage 3 Receiver
  • Stage 4 Filter
  • Stage 5 Demodulator
183
Q

____ are high performance, secure and portable systems that transfer voice, video and data across satellite networks

A

iDirect modems

184
Q

What uses time division multiple access (TDMA) to multiplex 30 terminals onto just 4 carriers?

A

iDirect modems

185
Q

iDirect modems operate on frequency bands ____, ____, ____ and ____

A
  • C-band
  • X-band
  • Ku-band
  • Ka-band
186
Q

____ is a propagation mode that has no physical obstacles between the transmitting and receiving antennas

A

Line of sight (LOS)

187
Q

Radio horizon extends ____ further than optical horizon and approximately ____ more than true horizon

188
Q

What are the characteristics of LOS propagation?

A
  • Range 20 to 50 miles
  • Frequency 3 to 50 Ghz
    Power 1 to 5 watts
189
Q

What are the four types of repeaters?

A
  • RF repeater
  • IF repeater
  • Baseband repeater
  • Audio repeater
190
Q

Which repeater has the largest amount of distortion?

A

RF repeater

191
Q

____ translates RF and amplifies RF

A

RF repeater

192
Q

____ translates RF and amplifies IF

A

IF repeater

193
Q

____ is used to drop/insert groups of modulated traffic

A

Baseband repeater

194
Q

____ is used to drop/insert user circuits

A

Audio repeater

195
Q

What are the limitations of repeaters?

A
  • Distance
  • Equipment capability
  • Terrain
  • Needs of the communication network
196
Q

What is the noise factor for FDM?

A

8 consecutive links

197
Q

What is the noise factor for TDM?

A

15 consecutive links

198
Q

Tropospheric scatter (TROPO) is a ____ communications method that utilizes the ____

A
  • Beyond LOS

- Troposphere

199
Q

What are the characteristics of tropospheric scatter?

A
  • Range - Up to 595 miles (fixed) or 150 miles (tactical)
  • Frequency 0;350 to 8 GHz
  • Power 300 to 50,000 watts
200
Q

____ is the area of the troposphere common to both antennas

A

Scatter volume (aka common volume)

201
Q

Troposcatter uses a ____ to compensate for blurring

A

Diversity system (Polarization, angle, space and frequency)

202
Q

What is the process of using the same antenna for both TX and RX?

A

Reciprocity

203
Q

Directivity and gain are ____ proportionate

204
Q

Frequency and antenna size are ____ proportionate

205
Q

Type of antenna is dictated by what?

A

Radio path

206
Q

What are the two types of directional antennas?

A
  • Horn antenna

- Parabolic antenna

207
Q

____ is the most common type of parabolic feed

A

Front feed

208
Q

What are the characteristics of the AN/GRC-239 TROPO

SATELLITE SUPPORT RADIO (TSSR)?

A
  • Full-duplex LOS radio terminal
  • Lightweight and field tunable
  • Interconnects ground mobile forces satellite terminals or as a land-based LOS radio
  • Easy to transport
  • Short setup/teardown times
  • Reliable in adverse conditions
209
Q

What are the traffic types for the AN/GRC-239 TROPO

SATELLITE SUPPORT RADIO (TSSR)?

A
  • Conditioned diphase (CDI)
  • Pseudo NRZ
  • Analog or digital voice orderwire (OW)
210
Q

What are the assmbly types for the AN/GRC-239 TROPO

SATELLITE SUPPORT RADIO (TSSR)?

A
  • Baseband (BB) assembly

- RF assembly

211
Q

What are the characteristics of the TSSR baseband (BB) assembly?

A
  • 19 inch rack
  • Tripod
  • Flat surface
212
Q

What are the characteristics of the

TSSR RF assembly?

A
  • 50 foot mast
  • Tripod
  • Pole
213
Q

What are the FIVE line replaceable units (LRUs) of TSSR BASEBAND assembly?

A
  • Orderwire
  • XMTR
  • RCVR
  • Breaker panel
  • Power supply
214
Q

How many LRUs does a TSSR RF assembly have?

215
Q

TSSR RF assembly uses a ____ or ____ antenna

A
  • 1 foot

- 2 foot

216
Q

TSSR connects to the BB assembly via a ____ or ____ cable

A
  • 2 foot

- 150 foot

217
Q

On the TSSR ____ and ____ must be at least ____ apart

RF UR (11 decks)

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