Block 4 Flashcards
(111 cards)
1
Q
What is a conductor that radiates electromagnetic energy?
A
Antenna
2
Q
What propagates (radiates outward) from a transmitting antenna?
A
Radio signals
3
Q
How fast do radio waves propagate?
A
Speed of light
4
Q
What two things do electromagnetic waves consist of ?
A
Electrical fields (E fields) and magnetic fields (H fields)
5
Q
What are the three characteristics of an electromagnetic wave?
A
Frequency, wavelength and amplitude
6
Q
The measurement of how many cycles per second in a wave is?
A
Frequency
7
Q
The distance between two consecutive points in a wave is?
A
Wavelength
8
Q
The measurement from peak-to-peak in a wave is?
A
Amplitude
9
Q
When a radio signal radiates outward from a transmitting source, it is called what?
A
Propagation
10
Q
What are the two basic types of propagtion?
A
Ground waves and sky waves
11
Q
What are the three components of ground waves?
A
- Direct waves
- Ground reflected waves
- Surface waves
12
Q
What is another name for direct waves?
A
Line-of-sight (LOS) waves
13
Q
Which wave type has multi-pathing issues where the signal arrives at the same place twice, causing echos and fading?
A
Ground reflected waves
14
Q
What kind of wave is electrically coupled to the earth and may travel beyond the horizon?
A
Surface waves
15
Q
Sky waves reflect off of what?
A
Ionosphere
16
Q
What is the frequency range of sky waves?
A
2-30 MHz
17
Q
Higher frequency sky waves are better when?
A
Daytime
18
Q
Lower frequency sky waves are better when?
A
Nighttime
19
Q
Medium frequency (MF) waves (300 KHz to 3 MHz) are what kind of waves?
A
Primarily ground waves but sky waves under particular conditions
20
Q
High frequency (HF) waves (3 MHz to 30 MHz) are what kind of waves?
A
LOS ground waves and BLOS sky waves
21
Q
Very high frequency (VHF) waves (30 MHz to 300 MHz) are what kind of waves?
A
Primarily ground waves
22
Q
Ultra high frequency (UHF) waves (300 MHz to 3 GHz) are what kind of waves?
A
LOS and troposphere scatter over-the-horizon (OTH)
23
Q
Super high frequency (SHF) waves (3 GHz to 30 GHz) are what kind of waves?
A
LOS
24
Q
Extremely high frequency (EHF) waves (30 GHz to 300 GHz) are what kind of waves?
A
LOS
25
What are the two types of linear polarization?
Vertical and horizontal
26
What are the two types of non-linear polarization?
Circular and elliptical
27
The orientation of an electromagnetic wave as it travels is called what?
Polarization
28
What is the comparison of power delivered to an antenna versus power radiated out of an antenna?
Antenna efficency
29
Which type of antenna radiates most of the signal?
High efficiency antenna
30
What are the characteristics of a low efficiency antenna?
- Mostly produces reflected energy
- Reduced radiated signal
- Impedance mismatch results in dissipated heat
31
What is defined as the ratio of power radiated in a particular direction versus all directions?
Antenna gain
32
Increase in gain is a result of what?
Parameters of the antenna (NOT radio power)
33
What is defined as the size of an antenna's peak propagation lobe where power decreases by 50%?
Beam width
34
What is the interference from two or more electrical/electronic systems affecting all systems equally?
Mutual interference
35
What are the causes of mutual interference?
Antennas located too close to each other and inadequate filters
36
What is defined as the relationship between the voltage and current of a signal at the input of an antenna?
Impedance matching
37
What will result from proper impedance matching?
Maximum power transferrance
38
What are the characteristics of a resonant antenna?
- Function best at one frequency
- Operates at a natural frequency
- Efficiency
39
What are the characteristics of a non-resonant antenna?
- Functional at multiple frequencies
| - Requires a coupler/tuner to function adequately
40
What does the law of reciprocity state?
That receive and transmit properties of an antenna are identical
41
What is defined as the difference in length of a wave as it travels through a new medium as compared to free space?
Electrical length
42
Speed of light (c) divided by frequency (f) equals what?
Wavelength (λ)
43
Increasing/decreasing the diameter of the conductor changes what measurement in a wave?
Electrical length
44
____ is how long the signal thinks the antenna is. (measured in wavelengths)
Electrical length
45
____ is the actual length of the antenna, including the cable. (measured in feet/meters)
Physical length
46
What are examples of deployable antennas?
– AT-197A/GR antenna
– AS-2259 NVIS Antenna
– Barker & Williamson (B & W) Dipole Antenna
– AV2011 SATCOM Antenna
47
What is an example of a deployable mast?
- CTM-15
48
What is the radiation pattern that projects uniformly in all directions on a single plane?
Omni-directional radiation pattern
49
What is the radiation pattern that projects in two directions?
Bi-directional radiation pattern
50
What is the radiation pattern that projects in one direction?
Uni-directional radiation pattern
51
What are the characteristics of a whip antenna?
- Vertically polarized
- Omni-directional
- ¼ λ antenna
- Low angle of radiation
- Pattern is affected by objects
52
What type of antenna is the most commonly used for mobile and multi-user ground networks?
Whip antenna
53
What are the characteristics of a dipole antenna?
- Horizontally polarized
- ½ λ antenna
- Conductive wire total length ½ λ of the lowest operating frequency
- Two ¼ λ antenna elements
- Can be center fed, end fed or offset
54
What effects the directivity of horizontal dipole antennas the most?
It's height from the ground
55
What causes a dipole antenna to be more bi-directional?
Having the arm higher above the ground (resulting in a lower take-off angle)
56
What causes a dipole antenna to be more omni-directional?
Having the arm closer to the ground (resulting in a higher take-off angle)
57
What are the characteristics of an inverted V dipole antenna?
- Arms drop from the center toward the ground
| - More omni-directional than a horizontal dipole of a similar center apex
58
What are the characteristics of a long wire antenna?
- At least 1 λ long (usually 2-6 λ)
- Med/long range sky wave
- Height and length determine take-off angle
59
What are the characteristics of an array antenna?
- Comprised of two or more antennas
- Multiple antennas are combined to increase gain
- Horizontally polarized
60
What are the characteristics of a horn antenna?
- Flared apertures to increase directivity and decrease loss
- Wide bandwidth, high gain, low loss
- Used from 300 MHz to over 140 GHz
- Uni-directional, vertical or horizontally
polarized
- Fed by a waveguide
61
What are the characteristics of a helical antenna?
- Directional antenna resembling a corkscrew
- Wide bandwidth, unidirectional, circularly
polarized
- Sometimes called helix antenna
62
What are the characteristics of a parabolic antenna?
- Consists of a small feed horn, pointed at parabolic reflector, which has one focal point
- Have high gain (+30 to 50 dBi), limited bandwidth
- Uni-directional, vertical or horizontal polarized
- Large dish operate at VHF while small dishes operate at 1 GHz and above
- Used for microwave LOS links, satellite dishes
63
____ antennas need to be simplistic and portable due to adverse conditions.
Deployable
64
What determines antenna characteristics and usage?
Terrain
65
What four factors affect antenna site selection and configuration?
- Terrain
- Distance
- Polarization and radiation patterns
- Tactical or fixed situations
66
When erecting any mast for antennas under or near power lines, always add the mast height plus ____ for clearance.
50 feet
67
Satellite antennas are primarily LOS (T/F)
True
68
Take-off angle is influenced by what?
- Antenna polarization
- Height above the ground
- Ground conditions
69
What can determine the radiation pattern of wire antennas?
Height from the ground
70
What determines the take-off angle of a horizontal antenna?
The relationship between the frequency and the height of the antenna off the ground
71
Which two layers of the atmosphere play a role in radio communications?
Troposphere and ionosphere
72
What are the characteristics of the troposphere?
- Lowest layer where weather happens
- Up to 11 miles high
- Weather affects all communications
73
What are the characteristics of the ionosphere?
- Ranges from ~30 miles to 600 miles above earth
- Radiation causes the ionosphere to be ionized
- Three regions are used for sky waves
- Reflects/refracts HF waves back to earth
74
What determines optimum frequencies when utilizing the ionosphere?
- Time of day
- Sun's radiation
- Location
- Seasons
75
What are the three regions of the ionosphere?
D, E and F (F1 and F2) regions
76
Which is the lowest region of the ionosphere?
D region (30 to 65 miles)
77
Which region of the ionosphere utilizes the lowest frequencies?
D region (15 MHz and below)
78
What are the characteristics of the F region?
- Divided into F1 and F2 sub-layers
| - The sublayers are combined at night
79
Which region of the ionosphere is responsible for long range sky wave propagation during daytime?
F2
80
What factor increases the best chance for reflection?
Critical angle
81
During reflection what happens if the frequency is too high?
It goes into space
82
During reflection what happens if the frequency is too low?
It gets absorbed
83
What is refraction?
Bending a wave as it enters a medium of different density
84
Wave changes speed when density changes (T/F)
True
85
What is the scientific practice involving the bending of a wave as it encounters a constriction of it's edge?
Diffraction
86
Which frequencies diffract more?
Lower frequencies (due to longer wavelengths)
87
What is caused by cloud or rain attenuation and tropospheric scintillation?
Atmospheric attenuation
88
Attenuation increases as ____ increases.
Frequency
89
In tropospheric scintillation what changes the refractive index?
Humidity and temperature variations at different altitudes
90
Tropospheric scintillation is more severe at ____ elevation angles.
Lower
91
____ is when receiving signals arrive at different times.
Multipathing
92
What is another name for multipathing?
Fading
93
What causes anomalous propagation?
Density variations, obstructions and humidity
94
What is the reduction in total power density of an electromagnetic wave as it propagates?
Path loss
95
___ is the difference between power transmitted and power recveived.
Path loss
96
What is referred to as a theoretical "perfect" space void of gravitational and electromagnetic fields?
Free space
97
The reduction of signal strength as it continues to spread out as it radiates is called what?
Free space loss
98
What part of a satellite antenna assists in the antennas elevation and direction?
Transit device
99
A transit is a tool used to determine the ____.
Azimuth
100
What are some causes of electromagnetic interference (EMI)?
- Enemy (jamming)
- Neutral (electrical current onto your equipment)
- Friendly
- Natural (lightning)
101
What do you refer to when identifying and resolving issues related to interference?
AFI 17-221
102
EMI
Electromagnetic interference
103
RFI
Radio frequency interference
104
ISM
Installation spectrum manager
105
UHF SATCOM antennas are sued with ____ radios.
TACSAT
106
Deployable satellite antennas typically transmit and receive in a ____ shape.
Cone
107
The addition or subtraction of ____ on an antenna will change the focus of the cone.
Eleements
108
What are the characteristics of the AV2011 antenna?
- Foldable, high-gain, UHF SATCOM antenna
- Frequency Range 240 to 318 MHz
- Right hand circularized polarization
- Uni-directional
- Designed to withstand 80 mph wind
109
To find the look angle you will use a compass to find what?
Azimuth and elevation
110
In look angle what is the side-to-side angle between 0-359*?
Azimuth
111
In look angle what is the up-down angle between 0-90*?
Elevation
