Microwave MCQ Flashcards
(218 cards)
1
Q
the progressive decrease in signal strength with increasing distance
A
Attenuation
2
Q
if k-factor is greater than 1, the beam is bent …
A
towards the earth
3
Q
The antenna separations (in meters) required for optimum operation of a space diversity system can be calculated from:
A
S = 3λR/L
where R = effective earth radius (m) and L = path length (m)
4
Q
Rainfall is an important factor for fading of radio waves at frequencies above
A
10 GHz
5
Q
Theoretically electromagnetic radiation field strength varies in inverse proportion to the square of the distance, but when atmospheric attenuation effects and the absorption of the terrain are taken into account the attenuation can be as high as the inverse _______ power of the distance.
A
Sixth
6
Q
What do you call an attenuation that occurs over many different wavelengths of the carrier?
A
Slow fading
7
Q
Which of the reception problems below that is not due to multipath?
A
Slow fading
8
Q
Which causes multipath or frequency-selective fading?
A
Large reflector
9
Q
In microwave transmission using digital radio, what causes most intersymbol interference?
A
Delayed spreading
10
Q
A shipboard equipment which measures the distance between the ship’s bottom and the ocean floor.
A
SONAR
11
Q
The cavity resonator
A
Is equivalent to an LC resonant circuit
12
Q
a high-power microwave pulse of the order of megawatts can be generated by
A
magnetron
13
Q
What is the purpose of the electromagnetic field which surrounds a traveling-wave tube?
A
To keep the electrons from spreading out
14
Q
Which of the following is used as an oscillator device in the SHF band?
A
Tunnel diode,
Klystron tube
15
Q
Microwave frequencies are normally regarded as those in the range
A
1 to 100 GHz
16
Q
The highest frequency which a conventional vacuum-tube oscillator can generate is not limited by the
A
Degree of emission from the cathode
17
Q
As the electron beam moves through a klystron’s intercavity drift space
A
Velocity modulation at the input cavity creates density modulation at the output cavity
18
Q
The frequency of the oscillation generated by a magnetron is mainly determined by
A
The dimension of each cavity resonator
19
Q
If the instantaneous RF potentials on the two sides of a magnetron cavity are of opposite polarity, the operation is in
A
π mode
20
Q
The Gunn diode oscillator
A
Depends on the formation of charge domain
21
Q
What ferrite device can be used instead of a duplexer of an isolated microwave transmitter and receiver when both are connected to the same antenna?
A
Circulator
22
Q
To achieve good bearing resolution when using a pulsed-radar set, an important requirement is
A
A narrow antenna-beam width in the horizontal plane
23
Q
When used in conjunction with a radar set, the purpose of an echo box is to provide an artificial target
A
Which may be used to tune the radar receiver
24
Q
In a radar-set receiver, the usual mixer stage is
A
A silicon crystal
25
Klystron oscillators are most often used in the frequency range of
3000 to 30000 MHz
26
Oscillators of a klystron tube are maintained
By bunches of electrons passing the cavity grids
27
What allows microwaves to pass in only one direction?
Ferrite emitter
28
In an SHF pulsed radar set, a reflex klystron can be used as a
Local Oscillator
29
A Class-S Emergency Position-Indicating Radio Beacon (E.P.I.R.B)
1. Must be capable of floating or being secured to survival.
2. Must have its battery replaced after emergency use.
3. May be tested during the first five minutes of any hour
30
A PPI cathode-ray tube as used on a radar set
indicates both the range and azimuth of a target
31
the resonant frequency of a cavity resonator depends upon
Physical Dimensions
32
The maximum usable range of the usual radar set (on any particular range setting) is determined by
The interval between transmitted pulses
33
A reflex klystron is oscillating at the frequency of its resonant cavity. If the reflector voltage is made slightly less negative, the
The frequency will decrease
34
In a pulsed radar set, the STC circuit is used to
Reduce interference from the effects of sea return
35
The coarse frequency adjustment of a reflex klystron is accomplished by
Adjusting the flexible wall of the resonant cavity
36
In a pulsed radar set, the function of the duplexer is to
Allow the transmitter and the receiver to operate from a common antenna
37
A magnetron is operated at a duty cycle of 0.001. It has a peak power output of 100 kilowatts. Its average power is
100 watts
38
The aquadag coating on the inside of PPI tube is used
As a second anode and to prevent the build-up of secondary field
39
If the duration of the radar transmitted pulse, on a particular range of operation, is increased, the required bandwidth of the receiver’s IF amplifiers
May be decreased
40
The main frequency-determining element of a klystron is
Its resonant cavity
41
A thin layer of dirt and grime covers the reflecting surface of the parabolic dish of a radar set. The particular effect on the performance of the radar will be
No noticeable effect
42
Which of the following permits a microwave signal to travel in one direction with virtually no loss, but severely attenuates any signal attempting to travel in the reverse direction?
Isolator
43
It is possible to increase the maximum range of radar equipment by
1. Lowering the pulse frequency
2. Raising the peak power of the transmitter 3. Narrowing the beam width and increasing the pulse duration
44
When it is desired that short-range targets be clearly seen on a pulsed-radar set, it is important that the receiver and display system have
The shortest possible time
45
Which of the following is used as a high-power microwave oscillator?
Magnetron
46
Which of the following operating frequencies is used for the modern loran navigational system?
Loran C: 100 kHz
47
Which ferrite device can be used instead of a duplexer to isolate a microwave transmitter and receiver when both are connected to the same antenna?
Circulator
48
The pulse frequency is equal to
Duty Cycle
49
In a radar set, a blocking oscillator can be used to
Produce a trigger pulse for the transmitter
50
The intensity of the echoes (target definition) on a PPI display is determined by
Pulse frequency and antenna rotation rate
51
A duplexer circuit allows a transmitter and a receiver to operate from the same antenna with virtually no interaction. This circuit may be replaced by a
Circulator
52
The repetition rate of a pulsed radar system indicates the
Frequencies of the duty cycle
53
The radar set, the sensitivity-time control circuit
Can reduce sea-return response
54
Which of the following is the ferrite device that buffers a microwave source from the effects of a varying load, and thereby prevents the formation of standing waves?
Isolator
55
Pulsed radar sets are primarily used to find the
Target’s range and bearing
56
Which of the following factors is mainly concerned in the design of an antenna system for a pulsed radar set?
Radio frequency
57
The main benefit of using microwaves is
More spectrum space for signals
58
Radio communication are regulated in the Philippines by the
NTC
59
Which of the following is not a disadvantage of microwaves?
Higher-cost equipment
60
Which of the following is a microwave frequency?
above 3 GHZ
61
Which of the following is not a common microwave application?
Mobile Radio
62
Coaxial cable is not widely used for long microwave transmission lines because of its
High loss
63
tripline and microstrip transmission lines are usually made with
PCBs
64
The most common cross-section of a waveguide is a
Rectangle
65
A magnetic field is introduced into the waveguide by a
Probe
66
When the electric field in a waveguide is perpendicular to the direction of wave propagation, the mode is said to be
TM
67
Signal propagation in a waveguide is by
Electric and Magnetic Fields
68
Decreasing the volume of a cavity causes its resonant frequency to
Decrease
69
__________ is a popular microwave mixer diode
Hot Carrrier
70
Varactor and step-recovery diodes are widely used in what type of circuit?
Frequency Multiplier
71
Which diode is a popular microwave oscillator?
Gunn diode
72
A reflex klystron is used as
Oscillator
73
For proper operation, a magnetron must be accompanied by a
permanent magnet
74
The operating frequency of klystrons and magnetrons is set by the
cavity resonators
75
A magnetron is used only as a/an
oscillator
76
A common application for magnetron is in
Radar
77
The most widely used microwave antenna
Horn
78
is a measure of reliability expressed as the average number of hours between successive failures
MTBF (Mean Time Between Failures)
79
The free space attenuation between two microwave antennas 40 km apart operating at 8 GHz is
142.55dB
80
An active microwave radio repeater that can provide drops and inserts
Baseband Repeater
81
If the correction factor k equals 4/3 of the earth’s curvature, the microwave beam would have a curvature that is ___________ than that of the earth
More
82
The optimum clearance from an obstacle in a microwave system is accepted as __________ of the first fresnel zone radius.
0.6
83
The microwave beam curves the same as that of the earth when the value of the correction factor k equals
Infinity
84
The ability of a radar to determine the bearing of a target depends upon the
Antenna directivity
85
The Doppler effect allows which characteristics of a target to be measured.
Speed
86
The Doppler effect is a change in what signal characteristics are produced by relative motion between the radar set and a target.
Frequency
87
The most widely used radar transmitter component is a
Magnetron
88
Low-power radar transmitters and receivers use which component?
Gunn diode
89
What component in a duplexer protects the receiver from the higher transmitter output?
Sparkgap
90
Most radar antennas use a
Horn and Parabolic Reflector
91
The most common radar display is the
PPI
92
Which of the following is a typical radar operating frequency?
10 GHZ
93
A microwave system requires the use of repeaters when
The distances involve are greater
94
Are transmission lines which convey electromagnetic waves in highest frequencies
Waveguides
95
A microwave band of 10.9 to 36. GHz is considered as
K-band
96
A microwave communications system space loss calculation formula.
92.4 + 20 log f + 20 log d
97
A waveguide is also a
High Pass Filter
98
A method of diversity reception where the signal is transmitted on two different frequencies over the same path
Frequency Diversity
99
A wire used to reduce the skin effect
Litz wire
100
Space diversity transmission means transmitting and receiving on two or more
Antennas operating in the same frequencies
101
The best system configuration to overcome multipath fading of microwave system over the water
Frequency Diversity
102
When the value of k increases, the effective result is _______ of the equivalent curvature
Flattening
103
What is the cut-off frequency of a waveguide?
The lowest frequency the waveguide operates
104
When the clearance above the obstruction is equal to the radii of even fresnel zones at the point of reflection. The RSL is
Decreased
105
What is the wavelength of a wave in a waveguide?
Greater than in free space
106
Water causes more attenuation particularly on what frequency?
183 GHz
107
At what frequency does oxygen cause excessive attenuation?
60 GHz
108
Which of the following is an atmospheric attenuation?
Attenuation due to water vapor and oxygen
109
_________ is a microwave link between the downtown terminal and another out-of-town terminal.
Terrestrial
110
A method of diversity reception applied to reflective paths to reduce fading.
Space diversity
111
What is the effective earth’s radius used in communications design?
K x 4000 miles
112
IF bandwidth of a radar system is inversely proportional to
Pulse-Width
113
EADI stands for
Electronic Altitude and Director Indicator
114
Which aircraft navigational system determines the time to station (TTS) or time to go (TTG)?
DME (Distance Measuring Equipment)
115
What inflight system allows passengers to make telephone calls, send faxes, computer data shop and play computer games, etc.?
Terrestrial Flight Telephone System
116
ADF stands for
Automatic Distance Finder
117
RADAR stands for
Radio Detection and Ranging
118
What is the effective earth’s radius when Ns = 300?
8500 km
119
A component that combines microwave signals from separate transmission lines into one common transmission line and allows no coupling between the separate lines
Combiner
120
Telemetry is a microwave communications system which operates at
2GHz
121
What is the maximum power that can be obtained from a microwave semiconductor?
10W
122
The cavity magnetron uses strapping to
Prevent mode-jumping
123
As a result of reflections from a plane conducting wall, electromagnetic waves acquire an apparent velocity greater than the velocity of light in space. This is called the
Phase Velocity
124
Which of the following is a method of modulating digital signals onto a microwave carrier?
FSK, BIPHASE, QUADRAPHASED
125
A microwave relay repeater that receives the modulated microwave carrier and obtains the baseband signal from it, and them modulates the baseband signal onto another carries and retransmit the new carrier with the baseband modulated onto it
Baseband Repeater
126
Which is the frequency range of the most common industrial microwave relay band?
6.575 – 6.875 GHz
127
When a particular mode is excited in a waveguide, there appears an extra electric component, in the direction of propagation. The resulting mode is
Transverse-magnetic
128
Waveguide construction
Should not have long horizontal runs
129
A PIN diode is a
microwave switch
130
For some applications, circular waveguides may be used preferred to rectangular ones because
lower attenuation
131
A circulator
Allows one antenna to feed two separate microwave transmitters and receivers at the same time
132
For low attenuation, the best transmission medium is a
Rectangular waveguide
133
IF repeaters are also called
heterodyne receiver
134
It is the difference between the nominal output power of a transmitter and the minimum input power required by a receiver
system gain
135
A phenomenon whereby the frequency of a reflected signal is shifted if there is relative motion between the source and reflecting object
Doppler Effect
136
A ferrite is
a nonconductor with magnetic properties
137
The diameter of a parabolic reflector should be at least how many wavelengths at the operating frequency?
10
138
A type of microwave repeater where the received RF carrier is down-converted to an IF frequency, amplified filtered and further demodulated to baseband.
baseband repeater
139
Refers to more than one transmission path or method of transmission available between transmitter and a receiver.
Diversity
140
A solution to the “blind speed” problem is to
Vary the RF
141
A direct path that exist between the transmit and receive antennas
LOS
142
Type of diversity where it modulates two different RF carrier frequencies with the same IF intelligence, then transmitting both RF signals to a given destination.
Frequency Diversity
143
What happens when a horn antenna is made longer?
Gain increases
144
Type of diversity where the output of the transmitter is fed to two or more antennas that are physically separated by an appreciable wavelengths
space diversity
145
The Doppler effect is used in
moving target plotting in PPI
146
A type of diversity where a single RF carrier is propagated with two different electromagnetic polarization
polarization diversity
147
Type of diversity which consists of a standard frequency diversity path where the two transmitter/receiver pair at one end of the path are separated from each other and connected to different antennas that are vertically separated as in space diversity
Hybrid diversity
148
The combination of the frequency, space, polarization, and receiver diversity into one system
quad diversity
149
An arrangement that avoids a service interruption during periods of deep fades or equipment failures
protection switching arrangement
150
A type of attenuator where attenuation is accomplished by insertion of a thin card of resistive material through a slot in the top of a waveguide
flap attenuator
151
duplexer is used
to allow the one antenna to be used for reception or transmission without mutual interference
152
Type of protection switching arrangement where each working radio channel has a dedicated backup or spare channel
hot standby
153
If a return echo arrives after the allocated pulse interval
the target will appear closer than it is
154
Points in the microwave system baseband signals either originate or terminate
terminal stations
155
A half wavelength, closed section of a waveguide that acts as a parallel resonant circuit is known as
cavity resonator
156
Decreasing the volume of a cavity causes its resonant frequency to
increase
157
Which of the following devices are not being used in microwave power amplifier?
magnetron
158
It is a unidirectional device often made up of ferrite material used in conjunction with a channel-combining network to prevent the output from interfering with the output of another transmitter
isolator
159
The power that leaks out of the back and sides of the transmit antenna interfering with the signal entering with the signal entering the input of a nearby receive antenna
ringaround
160
It is a general term applied to the reduction in signal strength at the input to a receiver
fading
161
If the ratio of the antenna diameter to the wavelength in a radar system is high, this will result in (indicate the false statement)
increased in capture area
162
he most widely used microwave antenna is a
horn
163
Applies to propagation variables in the physical radio path which affect changes in path loss between the transmitter at one station and its normal receiver at the other station
fading
164
Varactor and step-recovery diodes are widely used in what type of circuit?
frequency multiplier
165
It is defined as line loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum with no absorption or reflection of energy from nearby objects
FSL
166
The point where the antenna is mounted with respect to the parabolic reflector is called the
focal point
167
Using a small reflector to beam waves to the larger parabolic reflector is known as
Cassegrain feed
168
When electromagnetic waves are propagated in a waveguide
they are reflected from the walls but do not travel along them
169
Waveguides are used mainly for microwave signals because
they would be too bulky at lower frequencies
170
The wavelength of a wave in a waveguide a
greater than in free space
171
The useful power of the transmitter that is contained in the radiated pulses is termed as ______
peak power
172
The range beyond which targets appear as second return echoes is called
maximum range
173
When electromagnetic waves are reflected at an angle from a wall, their wavelength along the wall is a
greater than in the actual direction of propagation
174
A radar mile is equivalent to
2000 yd
175
As a result of reflections from a plane conducting wall, electromagnetic waves acquire an apparent velocity of light in
phase velocity
176
Indicate the false statement. When the free-space wavelength of a signal equals the cutoff wavelength of the guide
the characteristic impedance of the guide becomes infinite
177
A signal propagated in a waveguide has a full wave electric intensity change between two further walls, and no component of the electric field in the direction of propagation. The mode is
TE 20
178
Which of the following is incorrect? The dominant mode of propagation is preferred with rectangular waveguides because
the resulting impedance can be matched directly to coaxial lines
179
It is a mean of employing radio waves to detect and locate objects such as aircraft, ships and land masses
radars
180
A choke flange may be used to couple two waveguides
to compensate for discontinuities at the join
181
A common omnidirectional microwave antenna is
bicone
182
Which of the following is not a disadvantage of microwave?
line-of-sight transmission
183
Coaxial cable is not widely used for long microwave transmission lines because of its
high loss
184
What are limits of microwaves?
1 – 100,000 GHz
185
The following transmission lines are used for microwave frequencies, except
twin lead
186
How much must a waveguide be?
over a half-wave
187
How high must a waveguide be?
over a quarter wave
188
What is the designation of the lowest-frequency microwave band?
L-band
189
What is the designation of the highest-frequency microwave band
R-band
190
What is reduced by using choke flanges
reflection
191
What is the name of the microwave transmission line that is used in printed circuits?
microstrip
192
What is the advantage of using a circulator with two transmitter and two receivers?
one antenna only
193
Indicate which of the following frequencies cannot be used for reliable beyond-the-horizon terrestrial communications without repeaters:
12 GHz
194
A ship-to-ship communications system is plagued by fading. The best solution seems to be the use of
frequency diversity
195
A range of microwave frequencies more easily passed by the atmosphere than are the others is called
window
196
Frequencies in the UHF range propagate by means of a
space waves
197
Tropospheric scatter is used with frequencies in the following range
UHF
198
When microwave signals follow the curvature of the earth, this is known as a
ducting
199
consists basically of a thin film strip in intimate contact with one side of a flat dielectric substrate, with a similar thin-film ground plane conductor on the other side of the substrate
microstrip
200
The extra strength needed in order to assure that enough signal reaches the receiving antenna and must be made available to compensate for fades; computed as the difference between the received signal strength and the threshold level
Fade Margin
201
The use of redundant system to reduce the effects of multipath fading is
diversity
202
A profile graph of the microwave energy path
Determines the actual clearance, antenna heights and system reliability
203
In locating microwave relay stations, the systems designer must consider
1. Terrain obstructions and reflection points
2. Site security and navigational hazards
3. Availability of power, water source, and accessible roads
204
A microwave path over which radio waves barely touches the obstruction is called
grazing path
205
What is the function of regenerative repeater?
To reshape the pulses after they have become distorted
206
A situation when there is no change in attenuation or “no gain, no loss” occurs when ________ % of the first Fresnel radius clears a path obstruction in microwave systems
60%
207
____________ are concentric circular zones about a direct path of a microwave signal called Huygen’s radiation center, forming an imaginary solid called an ellipsoid __________.
Fresnel Zone
208
Waveguides are used mainly for microwave transmission because
They are bulky at lower frequencies
209
________________ is a graph wherein the terrain in which the microwave beam should traverse
Radio path profile
210
The Fresnel zone is the circular zone about the _______ path
Direct
211
The radius in the circular zone is in the first Fresnel zone when the reflected path is _______ longer than the direct path.
half wavelength
212
t __________ of the first Fresnel zone is a condition where there is no gain and no loss
0.6
213
The weakest signal the receiver could accept to be considered satisfactory.
threshold
214
The frequency band from 8 to 12 GHz is known as the band
X-band
215
The difference between the Received Signal Level and the FM Improvement Threshold
Fade Margin
216
A Fade Margin of 28 dB has a reliability of
99.9%
217
Topographical maps are used for microwave communications systems design because _________ are shown, thereby elevations are known
contour lines
218
