Volume 1 STQ Flashcards
1
Q
What are the two primary purposes for modulating a signal?
A
Ease of radiation and channel allocation
2
Q
What must we do first to radiate a signal over long distances?
A
Convert the signal to analog format
3
Q
What part of the AM signal does not fluctuate in amplitude by the modulating signal.
A
The carrier
4
Q
What frequencies does the amplitude modulated waveform contain?
A
- Carrier frequency
- Carrier + modulating frequency (USB)
- Carrier minus modulating frequency (LSB)
5
Q
What part of the modulated carrier wave contains the information carrying component?
A
The sidebands
6
Q
In AM, what is the relation between the bandwidth required to transmit the signal and the frequency of the modulating signal?
A
The bandwidth is two times the modulating signal frequency
7
Q
Define percent of modulation.
A
The amount of effect or change which the intelligence has on the carrier
8
Q
Find the %mod if a 4 Vpk-pk RF signal is modulated by a 2.5 Vpk-pk audio signal.
A
%mod = modulating amplitude/carrier amplitude
%mod = 2.5/4 = 62.5%
9
Q
If the signal in figure 1-3C has an Emax of 50 mVrms and an Emin of 5 mVrms, what is its %mod?
A
Emax-Emin/Emax+Emin
45/55 = 81.8%
10
Q
What are two results of overmodulation?
A
- Distortion
- Increased bandwidth
11
Q
What determines the amount of deviation of an FM carrier?
A
The amplitude of the modulating signal
12
Q
How does the rate of deviation relate to the frequency of the modulating signal?
A
Directly proportional
13
Q
To prevent interference with other FM stations, who establishes limits on the maximum amount of deviation in FM?
A
The Federal Communications Commission (FCC)
14
Q
What is a significant sideband?
A
A sideband with at least 1% of the total transmitted power
15
Q
How do you determine the modulation index in FM?
A
By dividing the amount of frequency deviation by the frequency of the modulating signal
16
Q
Whence do FM sidebands get their power?
A
From the unmodulated carrier
17
Q
What is the relationship between modulation index and sideband power?
A
- A higher modulation index means more power in the sidebands
- It is even possible to have all the power in the sidebands and none in the carrier. At this point, any further increase in modulation would take power from the sidebands and place it back into the carrier in a redistribution of power
18
Q
In PM, what effect does the change in carrier frequency have?
A
None: the frequency change in PM is incidental
19
Q
Describe the effect which the positive and negative alterations of a modulating signal have on the phase of the carrier in PM.
A
During the positive alternation of the modulating signal, the phase of the carrier lags behind the unmodulated carrier. During the negative alternation it leads the unmodulated carrier
20
Q
When is the carrier at its rest frequency in PM?
A
During the constant amplitude part of the modulating frequency
21
Q
What part of the modulating signal controls the amount of phase shift in PM?
A
Amplitude
22
Q
What part of the modulating signal controls the rate of phase shift in PM?
A
Frequency
23
Q
What is the advantage for using QPSK over BPSK?
A
QPSK has faster data rates, doubling the data carrying capacity over BPSK
24
Q
How can higher levels of PSK be achieved?
A
By using smaller phase shifts to allow for more phase shifts and increased capacity as each shift represents more bits in combination
25
Define the term digitization.
The process of converting analog signals into digital signals
26
What are the four stages of PCM?
- Band limiting
- Sampling
- Quantizing
- Encoding
27
What is the main purpose of the band-limiting filter?
To ensure the input to the sampler never exceeds a maximum frequency
28
Define sampling.
Conversion of a continuous time signal into a discrete time signal
29
What part of the pulse train is varied using PAM, PWM, and PPM?
- In PAM, amplitude
- In PWM, width or duration
- In PPM, position
30
What is the Nyquist sampling rate?
Sampling at twice the highest frequency in the band limited signal
31
Which step of PCM assigns discrete amplitude values to the sampled amplitude values?
Quantization
32
Which quantization method assigns amplitude values based on an equal amplitude range?
Uniform quantizing
33
What are the two methods of quantization?
- Uniform
| - Non-uniform
34
With ATM (Asynchronous Transfer Mode), what is the length of each transmission unit?
One character
35
What part of an ATM transmission tells the receiving device that a character is coming and the the character has been sent?
The start and stop bits
36
How does the receiving device determine whether it has received a correct character?
By summing the 1 bits. If the character arrives with an even number of 1 bits, the device assumes it has received a correct character
37
What is an advantage of synchronous transmission over asynchronous transmission?
It reduces the overhead costs of data transmission
38
How does synchronous transmission differ from asynchronous transmission?
Synchronous transmission blocks many characters together for transmission, while asynchronous transmission sends single characters
39
What does VRC (vertical redundancy check) check each incoming character for?
Odd or even parity
40
In LRC (longitudinal redundancy check), what transmitted character does the receiver use to determine if a transmission was error-free?
BCC (block check character)
41
When using the checksum method of error detection, what binary number is used to divide the sum of all the characters in order to derive the checksum?
255
42
How does the CRC (cyclic redundancy check) method of error detection determine the dividend when computing the BCC (block check character)
It treats the binary ones and zeros in the frame address, control, and information field as one long binary number
43
How effective is CRC at detecting errors in most applications?
99 percent
44
How does ARQ (automatic retransmit on request) work?
The receiver automatically sends a retransmittal request to the sender if it finds an error in a received frame
45
Using forward error control, at which end of the transmission link are errors corrected?
Receiving end
46
In forward error control, what is the transmitter's function in error correction?
To transmit multiple copies of the same message to the distant end
47
In forward error control, what is the receiver's function in error correction?
To compare all copies of a transmitted message and reconstruct it using the good portions of the message copies received
48
What are the three basic components that make up a fiber optics link?
- Optical transmitter
- Transmission medium
- Detector or optical receiver
49
What are the three components that make up an optical transmitter?
- Driver
- Optical source
- FO pigtail
50
What are the three main types of light sources for optic waveguides?
- LED
- Semiconductor laser diode
- Non-semiconductor laser diode
51
What are the three main requirements of a light source?
- Operating speed or rise time must be fast enough to meet the application's bandwidth requirements
- Sufficient optical power to operate the detector must be provided
- The wavelength produced must take advantage of the fiber's low-loss propagation characteristics
52
What are the advantages of LEDs over lasers?
- Small size
- Ruggedness
- Capability of single and direct modulation
- Reduced expense
- Spectral match with both fiber waveguides and silicon photodetectors
53
What are two basic designs of LED?
- Edge emitter
| - Surface emitter
54
How are lasers different from LEDs?
LED output is incoherent, whereas laser output is coherent
55
How is a laser's output power measured?
In milliwatts
56
What are lasers sensitive to?
Temperature
57
What factors limit a detector's performance?
Dispersion and attenuation
58
What two factors control the light signal that's received by the detector?
- Noise floor (noise equivalent power)
| - Signal-to-noise ratio (SNR)
59
What terms refer to the relationship between the signal and noise?
- Signal-to-noise ration (SNR)
| - Bit error rate (BER)
60
Upon what does a detector's responsivity depend?
Wavelength of light
61
What are the two main types of photodetectors?
- Positive intrinsic negative (PIN) diode
| - Avalanche photodiode (APD)
62
For what type of application are APDs ideally suited?
High speed, long distance applications
63
What are the purposes of repeaters in fiber optics communications links?
To extend transmission distance and preserve signal integrity
64
How do regenerators work?
They receive incoming low-level, dispersed (distorted) digital pulses. After conversion to the electrical domain, the pulses are regenerated (i.e. the leading and falling edges are sharpened and the pulses are amplified). These regenerated pulses are transmitted optically.
65
Which repeater device does not require converting to and from the electical domain for amplification?
Optical repeater
66
Describe the differences between fiber optic patch cords, pigtails, and breakout cables.
Fiber optic patch cord - A short section of single fiber cable with a connector on each end
Pigtail - Similar to a patch cord but with a connector on one end as opposed to both
Breakout cable - Similar to a pigtail but spliced into multiple fiber cables
67
Which type of fiber optic connector has a conical shape?
Biconic Connector
68
Which type of fiber optic connector uses a push-pull arrangement for mating?
SC (subscriber connector) connector
69
Which type of fiber optic connector is used in high-vibration environments?
FC (field connector) connector
70
Which type of fiber optic connector is the most widely used fiber optic connector for local area networks and premise wiring?
ST (straight-tip) connector
71
Which type of fiber optic connector uses a threaded coupling nut without a keying device?
SMA (sub-miniature, type a) connector
72
Which type of fiber optic connector uses quick release keyed bayonet couplings?
ST (straight-tip) connector
73
Which type of fiber optic connector was the first connector used on single-mode fiber optic cable?
Biconic connector
74
What are tunable fiber optic connectors?
Connectors which have keying slots which can be rotated to find the optimal alignment
75
Why are SC fiber optic connectors better for use in high-density applications than other types of connectors?
Other types of connectors require room to twist them for alignment. SC connectors use a push-pull arrangement and do not need this extra room
76
What activity must occur to produce an EMP?
A nuclear explosion
77
Which two elements of a nuclear explosion produce the EMP effects?
- Gamma rays
| - Secondary neutron radiation
78
What are the electromagnetic pulse forms produced by a nuclear explosion derived environment?
- HEMP (high-altitude electromagnetic pulse)
- SGEMP (system generated electromagnetic pulse)
- SREMP (source region electromagnetic pulse)
79
Why is high-altitude electromagnetic pulse environment protection important for critical, time urgent mission systems?
Because high-altitude electromagnetic pulse can effect many systems simultaneously
80
Why is system generated electromagnetic pulse a problem for satellites and reentry vehicles?
Because satellites and reentry vehicles are directly exposed to nuclear radiation from a high altitude burst
81
What are the two distinct regions of importance for SREMP (source region electromagnetic pulse)?
- Source
| - Radiated
82
What effects on communications are there after a nuclear detonation?
Scintillation and blackout
83
What capability can be employed by MILSTAR to mitigate communications loss within a contaminated area?
Crosslink
84
Describe the difference between long-line and local effects of EMP on facilities.
Long-line effects are currents and voltages conducted to the facility from long distances away, whereas local effects are currents and voltages induced directly onto the facility shield, building structure, wiring, equipment cables, etc.
85
How can a facility be made survivable against EMP?
- Shielding
- All openings filtered and protected
- Isolation from any external electromagnetic signal propagation from the earth
86
What happens in an EMP induced event?
A magnetic or electric field is induced in an electrical circuit which causes errors in the response of the circuit
87
Why is bonding important in EMP protection?
To ensure a mechanically strong, low-impedance connection between metal objects
88
Where should all metallic penetrations entering the protected area be located?
At a common location
89
To reduce coupling into susceptible circuits, what element is installed on both signal and power lines?
Filters
90
What is electromagnetic interference?
Any electromagnetic disturbance which interrupts, obstructs, or otherwise degrades or limits the effective performance of electronic equipment
91
How does one differentiate between unintentional interference and intentional interference (jamming)?
- By searching the surrounding area for a cause
- By moving the receiver short distances. If the movement causes the interference to vary, it is likely to be unintentional. If the interference does not vary with such movement of the receiver, the interference is likely to be jamming.
92
What type of EMI occurs when an unwanted carrier frequency follows the normal signal path through the affected receiver?
Co-channel
93
How can one eliminate broadband transmitter noise?
By using a band pass filter
94
When do spurious responses occur?
When the receiver responds to off frequency signals
95
What type of equipment often generates spurious transmissions?
Rapid tuning transmitters
96
What intermodulation frequency components can cause EMI in the receiver/transmitter?
The sum and difference
97
What type of intermodulation can have a very large bandwidth and cause more severe interference problems than intermodulation products created in either transmitters or receivers?
Rusty bolt
98
What type of EMI occurs when high level radiated signals penetrate and induce a radio frequency voltage into the internal circuits of a system or equipment?
Brute force
99
What amplitude modulation (AM) receivers are particularly susceptible to power line noise?
High frequency and very-high frequency
100
Relays may cause interference inside receivers because of broadband radiated noise originating from what?
The opening and closing of the contacts
101
How would one normally eliminate electromagnetic interference caused by sodium and mercury vapor lights?
By installing a new bulb
102
What is the purpose of the AFSIR (Air Force Spectrum Intererence Resolution) program?
To document and resolve spectrum interference problems
103
Under the AFSIR program, what organizational level must begin an investigation to identify the source of EMI?
The lowest unit level
104
Why must one ensure personnel responsible for the affected equipment check it before submitting an EMI report?
To ensure the equipment is not causing the problem
105
How does one confirm an EMI problem?
Check with users of the same frequency and determine whether they receive interference also
106
If EMI sounds like noise, what are its possible sources?
Power lines, welding equipment, etc.
107
Who is responsible for recording specific information concerning EMI?
The operator
108
What types of EMI are exempt from AFSIR reporting?
- EMI experienced by units under control of a combatant command
- Transient EMI from natural sources
- EMI suspected or confirmed to be caused by space weather
- EMI experienced aboard flying ISR aircraft over localized areas
- EMI experienced on frequencies assigned on a noninterference basis for training purposes
109
How should an AFSIR report be submitted?
Through the affected unit's chain of command and MAJCOM to the AFSMO (Air Force Spectrum Management Office)
110
What document contains guidelines for classifying EMI reports?
CJCSI 3320.02B, Joint Spectrum Interference Resolution (JSIR)
111
What service provided by the 85th EIS analyzes and recommends corrective actions for reported EMI problems?
Quick fix interference resolution capability (QFIRC)
112
What is the objective of the JSIR program?
To report and assist with resolution of EW and recurring EMI
113
Who maintains a central database of EMI cases, resolutions, and lessons learned for all EMI experienced by the DoD?
The joint spectrum center
114
Which control do you use to select the Fluke 8025A Multimeter's different measurement functions?
Rotary switch
115
What are the four types of information presented in the Fluke 8025A multimeter's display section?
- Digital display
- Visual annunciators
- Analog bar graph
- Range indicator
116
Which information in the display section shows the absolute value of the input?
Analog bar graph
117
Describe the function of the range push button.
It allows one to manually select the measurement range
118
What is the purpose of the touch-hold push button?
It locks the measurement into display for viewing and automatically updates the display when another measurement is taken
119
What are the Fluke 8025A multimeter's four input jacks?
1. amperes
2. milliamps/microamps
3. volts/ohms/diode
4. common
120
When does the 8025A perform a power-up self test?
When one moves the rotary switch to any position from the OFF position
121
What two ranges of DC voltages can one measure using the 8025A multimeter?
- -1000 to +1000 VDC
| - -320 to +320 mVDC
122
What is the maximum amount of continuous AC current which can be measured with the 8025A multimeter?
10 amps
123
When using the Fluke 8025A, how can one determine if the multimeter is in the resistance measurement function?
The Ω annunciator is showing in the display
124
How does one determine if one is testing a properly functioning diode with the 8025A?
Placing the leads across the diode produces OL in the display, while reversing the leads produces a continuous audible tone
125
What type of display does the oscilloscope present?
Amplitude vs time
126
On which axis of an oscilloscope is voltage, time, and depth information presented?
Voltage - vertical axis
Time - horizontal axis
Depth - intensity
127
What is the purpose of the delay line at the input of the vertical amplifier?
To allow the sweep generator circuitry time to start a sweep before the signal reaches the cathode ray tube's vertical deflection plates. This enables one to view the leading edge of the signal waveform
128
What position of the input coupling switch is used to view digital-type or square wave signals?
DC coupling
129
What is the basic purpose of the oscilloscope probe?
To provide isolation for scope inputs and prevent circuit loading
130
What are four types of probes?
1. high resistance
2. passive divider and x1 probe
3. active (field effect transistor)
4. current
131
What is the typical input impedance of most oscilloscopes?
1 MΩ shunted by 20 pF of capacitance
132
When making an amplitude measurement and the source impedance is unknown, greatest accuracy is achieved when the probe's Z in is what?
Highest (maximum)
133
What is the biggest difference between digital storage oscilloscopes and analog scopes?
Digital oscilloscopes digitize the input signal for storage or display
134
What is the function of charged coupled devices in the digital storage oscilloscope's signal sampling process?
They accept fast-changing data and send it to the analog-digital converter at a slower rate for more accurate data collection
135
What are waveform points?
Sampled data points stored in a digital storage oscilloscopes memory
136
What is a waveform record?
Stored waveform points that make up the waveform
137
What is record length?
The number of waveform points that make up the waveform record
138
What advantage does retrieving data from memory have on the cathode ray tube?
It allows the cathode ray tube to receive data at a slower rate, as opposed to keeping up with a high frequency signal fired directly onto it
139
What are two digital storage oscilloscope sampling techniques?
- Real-time
| - Repetitive
140
What is interpolation?
A process that estimates what the signal will look like between samples and fills in the blank space between data points
141
What are the two types of interpolation?
- Linear
| - Sine
142
What is the difference between sequential and random sampling?
Sequential sampling takes samples at predetermined intervals after the trigger until there are enough data points to construct several periods of the signal, whereas random sampling takes samples at undetermined intervals and stores them
143
What is a common cause of aliasing?
Undersampling due to having the time base turned down too low, thus using a sample rate on a frequency that is too high for the given setting
144
Describe the three types of acquisition modes on the digital storage oscilloscope.
1. sample mode - the digital oscilloscope creates a record point by saving the first sample in a collection of sample points
2. peak detect mode - the digital storage oscilloscope saves the highest and lowest points in a collection of samples
3. averaging mode - the digital storage oscilloscope shows a record that is a collection of several acquisitions of a repeated signal averaged over time
145
What is the function of the acquisition controls on the digital storage oscilloscope?
To set the digital storage oscilloscope's sampling rate, determine what type of processing will occur, and determine how many record points can be shown
146
What is the range of record points that the Tektronix 2230 digital storage oscilloscope can acquire?
1000 to 4000
147
Which control on the digital storage oscilloscope sets up acquisition to occur either before a trigger or at the beginning of a waveform?
The PRETRIG/POSTTRIG switch
148
On the digital storage oscilloscope, what happens to the NORM and P-P AUTO trigger modes while in ROLL mode?
These triggers are disabled, allowing the digital storage oscilloscope to continuously acquire and display incoming signals
149
In the NORM trigger mode on the digital storage oscilloscope, how are the pre trigger waveform and post trigger scan updated?
The pre trigger waveform is updated by the trigger and the post trigger scan is updated from the trigger position to the right
150
In the SAVE mode on the digital storage oscilloscope, what happens to the acquisition and display update in progress
It stops
151
On the digital storage oscilloscope, what types of measurements in the STORE mode are made with CURSORS controls?
- delta volts
- delta time
- 1/delta time
- delay time
152
Which switch on the digital storage oscilloscope establishes the function of the CURSORS position control?
The POSITION/CURS/SELECT WAVEFORM switch
153
Explain how a 4K record length is shown on the display.
In 4 1K samples
- A 4-bar graph on the screen shows which portion of the record is being viewed
154
In the SELECT WAVEFORM mode on the digital storage oscilloscope, using the SELECT C1/C2 (cursor-select) switch, what happens when the C1/C2 switch is pressed?
The cursor set is moved between different waveforms
155
What is the purpose of the MEMORY and MENU controls on the digital storage oscilloscope?
They control the MENU operation while the MENU is displayed, and they control the storage and display of the SAVE reference waveforms when the MENU is not displayed
156
What is the purpose of the bit error rate test set?
To provide a bit error detection system that can determine the received data quality
157
What type of tests can the bit error rate test set perform?
- Bit error analysis
- Timing analysis
- Delay measurements
- It can serve as a source of PCM data used to test a communications data link or a bit synchronizer output
- It can generate command test patterns, telemetry PCM formats, and bit coding patterns at telemetry data rates
158
What is the purpose of the internal clock generator in a bit error rate test set?
To provide an internal clock reference
159
What is the purpose of the voltage controlled oscillator in a bit error rate test set, and how is it calibrated?
- As the basic clock generator, it provides all clock phases
| - It is periodically frequency calibrated by a crystal controlled oscillator in the AUTO-CAL section
160
What is the purpose of the countdown section of the internal clock generator in a bit error rate test set?
To divide the voltage controlled oscillator clock and provide a frequency equal to the bit rate selected
161
What is the purpose of the digital-to-analog converter and the decode range splitter in a bit error rate test set?
To use the binary coded decimal information to control the voltage controlled oscillator center frequency, and control the range the countdown circuits will decode.
162
What is the purpose of the pattern simulator on a bit error rate test set?
To accept either the external or internal clock and generate either a pseudo-random noise pattern or a 48-bit pattern the operator programs from the front panel
163
Which pattern simulator section on a bit error rate test set controls the clock selector, selecting either the external clock or the internal clock for processing?
The Data/clock select encoder
164
What is the purpose of the pseudo random noise generator in a bit error rate test set?
To receive the internal clock from the clock selector and generate a 2047 bit long pseudo random pattern
165
What is the purpose of the pseudo random noise blanking generator in a bit error rate test set and what are the blanking periods?
To provide a blanking period at the start of the 2047 bit pseudo random noise frame (under the control of the blanking selector switch). The blanking period can be 0, 32, 64, 96, or 128 bits long
166
What is the purpose of the 48-bit register and 8-bit word display on a bit error rate test set?
To accept six 8-bit words, one word at a time, from the data entry switches and store them in a 48-bit register
167
What controls the data/clock select encoder in a bit error rate test set and what does it generate?
The pattern select and clock select switched control the data/clock select encoder. It generates a data select code and a clock select code
168
Which pattern simulator section in a bit error rate test set selects either pseudo random noise data, external data, or 48-bit data, depending on which code is received?
The Data/sync selector
169
What is the purpose of the code converter in the bit error rate test set?
To convert the non-return-zero-level (NRZ-L) data into the desired coding, such as NRZ-mark (NRZ-M)
170
What is the purpose of the clock drivers and the data drivers in a bit error rate test set, and where are their outputs sent?
The clock drivers convert the selected clock signal to a system compatible level and a buffered transistor-transistor logic (TTL) level.
The data drivers convert the encoded data signal to a system compatible level and a buffered TTL level.
The outputs are input to the pattern synchronizer and error counter data/clock receivers block.
171
What is the output from the output amplfier in a bit error rate test set?
After mixing the three input signals linearly, it provides a front panel adjustable offset and output level for a low impedance load
172
What is the purpose of the pattern synchronizer and error counter in a bit error rate test set?
To receive the selected pattern, automatically synchronize on the pattern, and determine the bit error rate induced after transmission through the system
173
What are the inputs to the data/clock receivers in a bit error rate test set?
Either system compatible data or buffered TTL data from the clock drivers and the data
174
In a bit error rate test set, which pattern synchronizer and error counter sections combine (OR) the system compatible and TTL signals together so only one signal will be present at one time?
The data/clock receivers
