Block 7 Flashcards
(217 cards)
1
Q
What involve many users who send and receive voice and data to and from the distant end?
A
Multichannel communications networks
2
Q
What are some examples of multichannel communications network devices?
A
- Satellites and terminals
- Phones
- Internet
- Routers
3
Q
What are the four time standards?
A
- Apparent solar time
- Mean solar time
- Atomic time
- Coordinated universal time
4
Q
Which time scale is based on the location of the sun and is the first known time standard?
A
Apparent solar time
5
Q
Which is the least accurate time scale?
A
Apparent solar time (high noon is not always at noon)
6
Q
Which time scale began in 1884 and is referred to as universal time (UT or GMT)?
A
Mean solar scale
7
Q
Which time scale is more accurate than UT but not used as the world’s time standard?
A
Atomic time
8
Q
Which time scale replaced GMT as the world’s time standard in 1972?
A
Coordinated universal time (UTC)
9
Q
Which time scale references atomic time and can keep countries’ clocks within +/-1 msec?
A
Coordinated universal time (UTC)
10
Q
How many official time zones are there?
A
24
11
Q
There is a time zone for each hour in a day (T/F)
A
True
12
Q
The military uses ____ instead of local meridians
A
Time zone Z, zero meridian or Zulu time
13
Q
The accuracy of a timing source depends on what?
A
How well it maintains a period of a second
14
Q
How are timing sources categorized?
A
- Primary source
- Secondary source
15
Q
____ time sources are calibrated to ____
A
- Secondary time sources
- A primary time source
16
Q
What are the two types of oscillators?
A
- Quartz (crystal) oscillators
- Atomic oscillators
17
Q
Which is the least accurate oscillator and utilizes the Piezoelectric effect?
A
Quartz (crystal) oscillators
18
Q
What are the two factors that limit quartz (crystal) oscillators accuracy?
A
- Temperature
- Aging
19
Q
Atomic oscillators count the oscillations of ____ to create atomic time
A
Highly stable atoms
20
Q
What are two common types of atomic oscillators?
A
- Rubidium
- Cesium
21
Q
____ oscillators are more accurate than quartz but less accurate than ____
A
- Rubidium
- Cesium
22
Q
Rubidium oscillators drift about ____ in 24 hours
A
1 usec
23
Q
____ oscillators drift about 200 nsec in 24 hours
A
Cesium oscillators
24
Q
Time is measure by the ____, instead of the time of day
A
Time interval between two events
25
There are 86,400 seconds or separate events each day (T/F)
True
26
Name three time coordination and distribution agencies
– International Bureau of Weights and Measures (BIPM)
– United States Naval Observatory (USNO)
– National Institute of Standards and Technology (NIST)
27
Which time distribution agency is located in Paris and maintains UTC and is the primary frequency standard of the world?
International Bureau of Weights and Measures (BIPM)
28
Which time distribution agency is the primary frequency source for the DoD and its contractors, and primarily uses GPS?
US Naval Observatory (USNO)
29
Which time distribution agency is the primary frequency standard for the general public and primarily uses radio stations?
National Institute of Standards and Technology (NIST)
30
What is an undesired shift of data or clock?
Timing jitter
31
____ is unwanted change in frequency or phase
Analog jitter
32
____ are pulse variations
Digital jitter
33
What are the two types of timing jitter?
- Short-term jitter
| - Long-term jitter
34
What are the characteristics of short-term jitter?
- Caused by signal fading
- Jitter fade is very small (short duration)
- Inaccurate signal strength causes fading
35
What counteracts short term jitter?
Elastic store
36
In what, is data with jitter clocked into a buffer at its own rate but clocked out at the correct rate (removing the jitter)?
Elastic store
37
When does long-term jitter occur?
- When the source of the jitter is not limited
| - When both stations lose synchronization
38
During long-term jitter ____ improves synchronization despite jitter by synchronizing the line (network) clock with the local (node) clock
Phase lock loop
39
____ ensures that all network stations (nodes) operate at the same clock rate
Synchronization
40
What are the four types of network synchronization?
- Plesiochronus
- Mutual
- Master clock
- Master-Slave
41
In a ____ network each node produces its own clock. They do not travel the network, they stay at the node.
Plesiochronus network
42
In a ____ network all node clocks are averaged and synchronized back to all nodes
Mutual network
43
In a ____ network nodes are synchronized by a single source
Master clock network
44
In a master clock network if the master node fails, the entire network fails (T/F)
True
45
In a ____ network nodes are synchronized by multiple sources (nodes), if the mast node fails then a secondary node will generate clocks
Master-slave network
46
Which synchronization network is best for the Defense Communications System (DCS) because of its high degree of survivability?
Master-slave network
47
What are the two types of multiplexers?
- Analog
| - Digital
48
____ refers to an infinite number of values (constantly changing amplitudes)
Analog
49
____ refers to a limited number of values (either a logic one or a logic zero)
Digital
50
____ is a binary digit (Logic ones or logic zeros)
A bit
51
Multiplexing combines two or more ____ into a ____
- Users (channels)
| - Composite signal (aggregate)
52
What are the characteristics of multiplexing?
- Simultaneous transmission to the distant end
- Analog and digital
- Voice, video and data
53
____ is looking at portions of the input to determine value
Sampling
54
What are the characteristics of sampling?
- Sampling periods are of the same duration
- Sequential
- Analog and digital
55
Frame consists of a sample from each channel and is constructed sequentially (T/F)
True
56
What are additional bits added to the user's input data after sampling (not part of the user data)?
Non-informational bits
57
What is used by the demux for timing and synchronization?
Non-informational bits
58
What are the four types of bits?
- Frame bit
- Start bit
- Stop bit
- Stuffing bit
59
What is the total size or amount of data sent to the distant end?
Bandwidth
60
Bandwidth is measured in ____
Bits per second (bps)
61
____ is a single or a range of frequencies (56 kbps or 300 MHz - 3 GHz)
Bandwidth
62
Asynchronous data enters the ____ at irregular intervals
Multiplexer
63
____ such as keyboard or mouse are considered asynchronous
Serial devices (8 bit)
64
What are the characteristics of asynchronous data?
- Frame bit is for synchronization
- Start and stop bit is for timing/data processing
- Stop bits are independent of the next start bit
65
____ data enters the multiplexer at a fixed rate
Synchronous
66
What are the characteristics of synchronous data?
- 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
67
____ is asynchronous at a synchronous rate
Isochronous
68
What are the characteristics of isochronous data?
- Frame bit is for synchronization
- Start bit and stop bit for asynchronous timing
- Stuffing bit is for synchronous timing
69
What assigns a portion of the total bandwidth to each individual input user?
Frequency Division Multiplexing (FDM)
70
What are the characteristics of time division multiplexing (TDM)?
– 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
71
A basic ____ interweaves all samples into frames before transmission to the distant end
Time division multiplexing (TDM) multiplexer
72
What are the two modes of time division multiplexing (TDM)?
- Synchronous TDM
| - Asynchronous TDM
73
What are the characteristics of
| synchronous TDM?
– Assigns time slots to all channels whether active or inactive
– Frame bits only
– Wasted bandwidth
74
What are the characteristics of
| asynchronous TDM?
– Assigns time slots only to the active channels
– Statistical multiplexing
- Redefines the frame length when channels are active and inactive
- Multiplexer efficiency
75
____ data is transmitted as large bulky bytes of words
Asynchronous data
76
When asynchronous data is transmitted at asynchronous rate, ____ are added
Stuffing bits
77
What separates the original user signals into different network lines or paths?
Demultiplexing
78
____ routes each signal to the correct distant end user
Demulitplexing
79
Signal formats are how ____ and ____ are represented
- Logic highs
| - Logic lows
80
What are three signal formats?
- Non-return to zero (NRZ)
- Return to zero (RZ)
- Conditioned di-phase (CDI)
81
____ is the most common format of data as it travels within a multiplexer
Non-return to zero (NRZ)
82
Non-return to zero (NRZ) ____ return to zero volts halfway through the clock cycle
Does not
83
What are the two types of Non-return to zero (NRZ)?
- NRZ neutral
| - NRZ polar
84
In NRZ neutral, a logic one is represented by ____ and a logic zero is represented by ____
- +5v
| - 0v
85
NRZ neutral is NOT self-clocking (T/F)
True
86
In NRZ polar, a logic one is represented by ____ and a logic zero is represented by ____
- +5v
| - -5v
87
NRZ polar is NOT self-clocking (T/F)
True
88
In ____ data returns to zero volts halfway through the clock cycle
Return to zero (RZ)
89
What are the four types of return to zero (RZ)?
- RZ Neutral
- RZ Polar
- RZ Bipolar
- RZ Bipolar with Zero Suppression
90
In RZ neutral, logic ones are represented by a momentary increase to ____ then return to ____ halfway through the clock cycle
- +5v
| - 0v
91
RZ neutral is NOT self-clocking (T/F)
True
92
In RZ polar, logic ones are represented by an increase to ____ and logic zeroes are represented by a decrease to ____
- +5v
| - -5v
93
RZ polar IS self-clocking (T/F)
True
94
In RZ bipolar, logic ones alternate between ____ and ____, logic zeroes are represented by ____
- +5v
- -5v
- 0v
95
RZ biplolar is NOT self-clocking (T/F)
True
96
What detects a long string of logic zeroes between two logic ones?
RZ bipolar with suppression
97
In RZ bipolar with zer suppression, a ____ is inserted
Timing bit
98
RZ biplolar with suppression IS self-clocking (T/F)
True
99
In conditioned di-phase (CDI), logic ones require ____ and logic zeroes are represented by ____
- One transition
| - Two transitions
100
CDI IS self-clocking (T/F)
True
101
What states analog signals must be sampled at least twice the highest frequency before being digitized?
Nyquist theroem
102
____ is highest voice frequency (VF)
3,400 Hz
103
There are ____ samples per second
8,000
104
____ is a three step process that converts analog to digital
Pulse code modulation (PCM)
105
What are the three steps of pulse code modulation (PCM)?
- Step 1 Sample
- Step 2 Quantize
- Step 3 Encode
106
During PCM step 1 (sampling), ____ is received from the user and the voltage levels are read into ____ per second
- Analog signal
| - 8,000 samples
107
____ are called pulse amplitude modulated (PAM) pulses
Samples
108
During PCM step 2 (quantizing), a decimal value is assigned to each ____
PAM pulse (sample)
109
What are the two types of quantizing?
- Uniform
| - Non-uniform
110
What are the characteristics of uniform quantizing?
- Steps are equally spaced
| - PAM pulse is rounded, in cases of quantization error
111
What are the characteristics of non-uniform quantizing?
- Steps are closer near zero where most of the intel is located
- Corrects quantization errors
112
During PCM step 3 (encoding), the decimal value is converted to ____
Binary
113
What are the characteristics of encoding?
- 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
____ is the time it takes for one frame to occur
Frame period
115
Frame period is based on the ____
Sampling rate
116
Frame period = 1/8,000 or ____
125 usec
117
____ is the time it takes to sample one channel in any given
| frame
Pulse modulated sample period (PMSP)
118
Pulse modulated sample period (PMSP) is based on the number of ____
Input channels
119
How many channels are there in a TDM multiplexer?
24
120
PMSP = frame period / 24 (125 usec / 24) or ____
5.28 usec
121
What are the four types of bandwidth allocations?
- Conventional bandwidth
- Demand assigned bandwidth
- Dynamic bandwidth
- Time of day restrictions
122
What are the characteristics of conventional bandwidth?
– The same fixed amount for each user
- 64 Kbps for each user
– Dedicated lines even when user is disconnected
- Bandwidth is wasted
123
What are the characteristics of demand assigned bandwidth?
– An exact amount for each user
– No input is dedicated
- Bandwidth available when user disconnects
– Internet
124
What are the characteristics of dynamic bandwidth?
– 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
What are the characteristics of time of day restriction bandwidth?
– Exclusive bandwidth set aside for specific dates and times
- More bandwidth required than normally needed
- Priority basis
126
A network involves two or more users interchange ____, ____ or _____ traffic
- Voice
- Data
- Message
127
_____ was developed for communication between modems and computers
EIA-232C
128
EIA-232C transmits ____ kbs up to ____ feet and ____ kbps between ____ and ____ feet without the use of a modem
- 56 kbps
- 50 feet
- 9.6 kbps
- 500 and 5,000 feet
129
What are the characteristics of EIA balanced transmission lines?
- Differential transmission
| - Two wires carry the data
130
What are the characteristics of EIA unbalanced transmission lines?
- Singled-ended transmission
- Only one wire to transmit data in both directions
- Second wire is grounded
131
____ connectors are installed on each end of the computer-modem interface cable
D-shaped (DB) connectors
132
(EIA) For data signals, ____ represents a logic zero and ____ represents a logic one
- +V
| - -V
133
(EIA) For control signals, +V represents a ____ and -V represents a ____
- Logic one
| - Logic zero
134
____ was developed in response to slower standards with shorter distances
EIA-530
135
EIA-530 transmits between ____ kbps and ____ Mbps up to ____ miles without the use of a modem
- 20 kbps
- 2 Mbps
- 3 miles
136
____ is a device that is the source and destination of data (a computer)
Data terminal equipment (DTE)
137
____ is a device that establishes, maintains and ends a data transfer (a modem)
Data communications equipment (DCE)
138
What is connected between routers of two separate networks (LAN to WAN) and is on the user side of the network?
Digital service unit (DSU)
139
What is connected to the WAN side of two separate networks (LAN to WAN)
Channel service unit (CSU)
140
In a network, insufficient bandwidth at one level requires the network to increase to the next highest level (T/F)
True
141
What multiplexes group port input data and secure and non-secure digital voice orderwire for transfer to the aggregate interface?
Vertex nodal satellite multiplexer (NSM)
142
Vertex nodal satellite multiplexer (NSM) ____ incoming aggregate for transfer to the output group ports
Demultiplexes
143
Maximum output (aggregate) data rate of the NSM is ____ Mbps
52 Mbps
144
What are the two operational modes for the NSM?
- Legacy
| - Enhanced
145
What performs tests and loopbacks on a system to adequately analyze signal quality as it travels across a network?
Bit error rate test set (BERTS)
146
____ is the number of erroneous bits divided by the total number of bits transmitted, received and processed in a given amount of time
Bit error rate (BER)
147
What are the characteristics of the HST-3000?
- Rugged, handheld and battery operated
- Operates with many communications devices
- Datacom Module
- End-to-end testing
- BER testing
148
What are the three test modes of the HST-300?
- DTE emulation
- DCE emulation
- Monitor
149
____ terminates a DataCom interface and emulates DTE to perform test operations
DTE emulation
150
____ terminates a DataCom interface and emulates DCE to perform test operations
DCE emulation
151
Test mode ____ is non-intrusive performance monitoring of a circuit in both directions
Monitor
152
____ converts (modulates) digital baseband (BB) to an intermediate frequency (IF) (normally 70 to 700 MHz)
Modulator
153
____ converts IF to the selected transmit RF (IF + local oscillator (LO frequency)
Upconverter
154
What does the final amplification to ensure the RF reaches the distant end?
High power amplifier
155
What are the characteristics of low noise amplifier (LNA)?
- High sensitivity for signal recovery
- Eliminates noise
- Amplification
156
____ converts RF to IF (receive frequency minus the LO frquency)
Downconverter
157
Demodulator converts IF to baseband (BB) (T/F)
True
158
What provides one-way signal flow to prevent reflected energy from damaging equipment?
Isolators
159
Isolators provide ____ when transitioning between different mediums
Impedance matching
160
____ couple microwave energy to antenna, also provides sample points for performance monitoring
Directional coupler
161
What is tuned to pass only desired frequencies and block noise and undesired frequencies?
Filters
162
____ allow TX and RX to share the same path without interference
Circulators (Diplexers and duplexers)
163
Name the fundamental radio parameters
- Frequency accuracy and stability
- Bandwidth
- Frequency response
- Selectivity
- Gain
- Sensitivity
164
What depends on the quality of the oscillator that is used?
Frequency accuracy and stability
165
What is used to increase frequency accuracy?
Phase lock loop
166
Bandwidth is the difference between the ____ and ____ frequencies at which the radio is designed to operate
- Upper
| - Lower
167
____ is the ability to process desired frequencies and reject undesired frequencies
Selectivty
168
Gain is the value of ____ that a signal obtains in passage through an amplifying stage or system
Amplification
169
What is the receiver's ability to distinguish between low level signals and noise?
Sensitivty
170
What are radio performance measuers?
- Quality
- Reliability
- Speed
171
Modems modulate an ____ to encode ____
- Analog carrier
| - Digital input data
172
What demodulates the incoming carrier to decode transmitted information?
Modem
173
____ is the speed of the bandwidth per second
Baud
174
What are the three basic components of modulating an analog carrier signal?
- Frequency
- Amplitude
- Phase
175
What type of modulation alternates in frequency only?
Frequency shift keying (FSK)
176
What type of modulation alternates in amplitude only?
Amplitude shift keying (ASK)
177
____ alternates in phase ONLY if the the logic state changes
Binary phase shift keying
178
What is the process of using multiple copies of the same transmitted message to correct for data errors?
Forward error correction (FEC)
179
The ____ modem uses forward error correction (FEC)
Distant end modem
180
____ mixes data using time division to correct for errors or recover lost bits
Interleaving
181
What are the characteristics of fiber optic modems?
- Extremely high data rates
- Not susceptible to RF or electromagnetic interferences
- 5 stages
182
What are the five stages of fiber optic modems?
- Stage 1 Modulator
- Stage 2 Transmitter
- Stage 3 Receiver
- Stage 4 Filter
- Stage 5 Demodulator
183
____ are high performance, secure and portable systems that transfer voice, video and data across satellite networks
iDirect modems
184
What uses time division multiple access (TDMA) to multiplex 30 terminals onto just 4 carriers?
iDirect modems
185
iDirect modems operate on frequency bands ____, ____, ____ and ____
- C-band
- X-band
- Ku-band
- Ka-band
186
____ is a propagation mode that has no physical obstacles between the transmitting and receiving antennas
Line of sight (LOS)
187
Radio horizon extends ____ further than optical horizon and approximately ____ more than true horizon
- 15%
| - 33%
188
What are the characteristics of LOS propagation?
- Range 20 to 50 miles
- Frequency 3 to 50 Ghz
Power 1 to 5 watts
189
What are the four types of repeaters?
- RF repeater
- IF repeater
- Baseband repeater
- Audio repeater
190
Which repeater has the largest amount of distortion?
RF repeater
191
____ translates RF and amplifies RF
RF repeater
192
____ translates RF and amplifies IF
IF repeater
193
____ is used to drop/insert groups of modulated traffic
Baseband repeater
194
____ is used to drop/insert user circuits
Audio repeater
195
What are the limitations of repeaters?
- Distance
- Equipment capability
- Terrain
- Needs of the communication network
196
What is the noise factor for FDM?
8 consecutive links
197
What is the noise factor for TDM?
15 consecutive links
198
Tropospheric scatter (TROPO) is a ____ communications method that utilizes the ____
- Beyond LOS
| - Troposphere
199
What are the characteristics of tropospheric scatter?
- Range - Up to 595 miles (fixed) or 150 miles (tactical)
- Frequency 0;350 to 8 GHz
- Power 300 to 50,000 watts
200
____ is the area of the troposphere common to both antennas
Scatter volume (aka common volume)
201
Troposcatter uses a ____ to compensate for blurring
Diversity system (Polarization, angle, space and frequency)
202
What is the process of using the same antenna for both TX and RX?
Reciprocity
203
Directivity and gain are ____ proportionate
Directly
204
Frequency and antenna size are ____ proportionate
Inversely
205
Type of antenna is dictated by what?
Radio path
206
What are the two types of directional antennas?
- Horn antenna
| - Parabolic antenna
207
____ is the most common type of parabolic feed
Front feed
208
What are the characteristics of the AN/GRC-239 TROPO
| SATELLITE SUPPORT RADIO (TSSR)?
- 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
What are the traffic types for the AN/GRC-239 TROPO
| SATELLITE SUPPORT RADIO (TSSR)?
- Conditioned diphase (CDI)
- Pseudo NRZ
- Analog or digital voice orderwire (OW)
210
What are the assmbly types for the AN/GRC-239 TROPO
| SATELLITE SUPPORT RADIO (TSSR)?
- Baseband (BB) assembly
| - RF assembly
211
What are the characteristics of the TSSR baseband (BB) assembly?
- 19 inch rack
- Tripod
- Flat surface
212
What are the characteristics of the
| TSSR RF assembly?
- 50 foot mast
- Tripod
- Pole
213
What are the FIVE line replaceable units (LRUs) of TSSR BASEBAND assembly?
- Orderwire
- XMTR
- RCVR
- Breaker panel
- Power supply
214
How many LRUs does a TSSR RF assembly have?
Three
215
TSSR RF assembly uses a ____ or ____ antenna
- 1 foot
| - 2 foot
216
TSSR connects to the BB assembly via a ____ or ____ cable
- 2 foot
| - 150 foot
217
On the TSSR ____ and ____ must be at least ____ apart
200 MHz
