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RF UR > Block 4 > Flashcards

Block 4 Flashcards

1
Q

What is a conductor that radiates electromagnetic energy?

A

Antenna

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2
Q

What propagates (radiates outward) from a transmitting antenna?

A

Radio signals

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3
Q

How fast do radio waves propagate?

A

Speed of light

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4
Q

What two things do electromagnetic waves consist of ?

A

Electrical fields (E fields) and magnetic fields (H fields)

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5
Q

What are the three characteristics of an electromagnetic wave?

A

Frequency, wavelength and amplitude

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6
Q

The measurement of how many cycles per second in a wave is?

A

Frequency

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7
Q

The distance between two consecutive points in a wave is?

A

Wavelength

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8
Q

The measurement from peak-to-peak in a wave is?

A

Amplitude

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9
Q

When a radio signal radiates outward from a transmitting source, it is called what?

A

Propagation

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10
Q

What are the two basic types of propagtion?

A

Ground waves and sky waves

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11
Q

What are the three components of ground waves?

A
  • Direct waves
  • Ground reflected waves
  • Surface waves
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12
Q

What is another name for direct waves?

A

Line-of-sight (LOS) waves

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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

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14
Q

What kind of wave is electrically coupled to the earth and may travel beyond the horizon?

A

Surface waves

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15
Q

Sky waves reflect off of what?

A

Ionosphere

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16
Q

What is the frequency range of sky waves?

A

2-30 MHz

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17
Q

Higher frequency sky waves are better when?

A

Daytime

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18
Q

Lower frequency sky waves are better when?

A

Nighttime

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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

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20
Q

High frequency (HF) waves (3 MHz to 30 MHz) are what kind of waves?

A

LOS ground waves and BLOS sky waves

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21
Q

Very high frequency (VHF) waves (30 MHz to 300 MHz) are what kind of waves?

A

Primarily ground waves

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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)

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23
Q

Super high frequency (SHF) waves (3 GHz to 30 GHz) are what kind of waves?

A

LOS

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24
Q

Extremely high frequency (EHF) waves (30 GHz to 300 GHz) are what kind of waves?

A

LOS

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25
Q

What are the two types of linear polarization?

A

Vertical and horizontal

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26
Q

What are the two types of non-linear polarization?

A

Circular and elliptical

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27
Q

The orientation of an electromagnetic wave as it travels is called what?

A

Polarization

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28
Q

What is the comparison of power delivered to an antenna versus power radiated out of an antenna?

A

Antenna efficency

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29
Q

Which type of antenna radiates most of the signal?

A

High efficiency antenna

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30
Q

What are the characteristics of a low efficiency antenna?

A
  • Mostly produces reflected energy
  • Reduced radiated signal
  • Impedance mismatch results in dissipated heat
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31
Q

What is defined as the ratio of power radiated in a particular direction versus all directions?

A

Antenna gain

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32
Q

Increase in gain is a result of what?

A

Parameters of the antenna (NOT radio power)

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33
Q

What is defined as the size of an antenna’s peak propagation lobe where power decreases by 50%?

A

Beam width

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34
Q

What is the interference from two or more electrical/electronic systems affecting all systems equally?

A

Mutual interference

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35
Q

What are the causes of mutual interference?

A

Antennas located too close to each other and inadequate filters

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36
Q

What is defined as the relationship between the voltage and current of a signal at the input of an antenna?

A

Impedance matching

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37
Q

What will result from proper impedance matching?

A

Maximum power transferrance

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38
Q

What are the characteristics of a resonant antenna?

A
  • Function best at one frequency
  • Operates at a natural frequency
  • Efficiency
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39
Q

What are the characteristics of a non-resonant antenna?

A
  • Functional at multiple frequencies

- Requires a coupler/tuner to function adequately

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40
Q

What does the law of reciprocity state?

A

That receive and transmit properties of an antenna are identical

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41
Q

What is defined as the difference in length of a wave as it travels through a new medium as compared to free space?

A

Electrical length

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42
Q

Speed of light (c) divided by frequency (f) equals what?

A

Wavelength (λ)

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43
Q

Increasing/decreasing the diameter of the conductor changes what measurement in a wave?

A

Electrical length

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44
Q

____ is how long the signal thinks the antenna is. (measured in wavelengths)

A

Electrical length

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45
Q

____ is the actual length of the antenna, including the cable. (measured in feet/meters)

A

Physical length

46
Q

What are examples of deployable antennas?

A

– AT-197A/GR antenna
– AS-2259 NVIS Antenna
– Barker & Williamson (B & W) Dipole Antenna
– AV2011 SATCOM Antenna

47
Q

What is an example of a deployable mast?

A
  • CTM-15
48
Q

What is the radiation pattern that projects uniformly in all directions on a single plane?

A

Omni-directional radiation pattern

49
Q

What is the radiation pattern that projects in two directions?

A

Bi-directional radiation pattern

50
Q

What is the radiation pattern that projects in one direction?

A

Uni-directional radiation pattern

51
Q

What are the characteristics of a whip antenna?

A
  • Vertically polarized
  • Omni-directional
  • ¼ λ antenna
  • Low angle of radiation
  • Pattern is affected by objects
52
Q

What type of antenna is the most commonly used for mobile and multi-user ground networks?

A

Whip antenna

53
Q

What are the characteristics of a dipole antenna?

A
  • 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
Q

What effects the directivity of horizontal dipole antennas the most?

A

It’s height from the ground

55
Q

What causes a dipole antenna to be more bi-directional?

A

Having the arm higher above the ground (resulting in a lower take-off angle)

56
Q

What causes a dipole antenna to be more omni-directional?

A

Having the arm closer to the ground (resulting in a higher take-off angle)

57
Q

What are the characteristics of an inverted V dipole antenna?

A
  • Arms drop from the center toward the ground

- More omni-directional than a horizontal dipole of a similar center apex

58
Q

What are the characteristics of a long wire antenna?

A
  • At least 1 λ long (usually 2-6 λ)
  • Med/long range sky wave
  • Height and length determine take-off angle
59
Q

What are the characteristics of an array antenna?

A
  • Comprised of two or more antennas
  • Multiple antennas are combined to increase gain
  • Horizontally polarized
60
Q

What are the characteristics of a horn antenna?

A
  • 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
Q

What are the characteristics of a helical antenna?

A
  • Directional antenna resembling a corkscrew
  • Wide bandwidth, unidirectional, circularly
    polarized
  • Sometimes called helix antenna
62
Q

What are the characteristics of a parabolic antenna?

A
  • 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
Q

____ antennas need to be simplistic and portable due to adverse conditions.

A

Deployable

64
Q

What determines antenna characteristics and usage?

A

Terrain

65
Q

What four factors affect antenna site selection and configuration?

A
  • Terrain
  • Distance
  • Polarization and radiation patterns
  • Tactical or fixed situations
66
Q

When erecting any mast for antennas under or near power lines, always add the mast height plus ____ for clearance.

A

50 feet

67
Q

Satellite antennas are primarily LOS (T/F)

A

True

68
Q

Take-off angle is influenced by what?

A
  • Antenna polarization
  • Height above the ground
  • Ground conditions
69
Q

What can determine the radiation pattern of wire antennas?

A

Height from the ground

70
Q

What determines the take-off angle of a horizontal antenna?

A

The relationship between the frequency and the height of the antenna off the ground

71
Q

Which two layers of the atmosphere play a role in radio communications?

A

Troposphere and ionosphere

72
Q

What are the characteristics of the troposphere?

A
  • Lowest layer where weather happens
  • Up to 11 miles high
  • Weather affects all communications
73
Q

What are the characteristics of the ionosphere?

A
  • 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
Q

What determines optimum frequencies when utilizing the ionosphere?

A
  • Time of day
  • Sun’s radiation
  • Location
  • Seasons
75
Q

What are the three regions of the ionosphere?

A

D, E and F (F1 and F2) regions

76
Q

Which is the lowest region of the ionosphere?

A

D region (30 to 65 miles)

77
Q

Which region of the ionosphere utilizes the lowest frequencies?

A

D region (15 MHz and below)

78
Q

What are the characteristics of the F region?

A
  • Divided into F1 and F2 sub-layers

- The sublayers are combined at night

79
Q

Which region of the ionosphere is responsible for long range sky wave propagation during daytime?

A

F2

80
Q

What factor increases the best chance for reflection?

A

Critical angle

81
Q

During reflection what happens if the frequency is too high?

A

It goes into space

82
Q

During reflection what happens if the frequency is too low?

A

It gets absorbed

83
Q

What is refraction?

A

Bending a wave as it enters a medium of different density

84
Q

Wave changes speed when density changes (T/F)

A

True

85
Q

What is the scientific practice involving the bending of a wave as it encounters a constriction of it’s edge?

A

Diffraction

86
Q

Which frequencies diffract more?

A

Lower frequencies (due to longer wavelengths)

87
Q

What is caused by cloud or rain attenuation and tropospheric scintillation?

A

Atmospheric attenuation

88
Q

Attenuation increases as ____ increases.

A

Frequency

89
Q

In tropospheric scintillation what changes the refractive index?

A

Humidity and temperature variations at different altitudes

90
Q

Tropospheric scintillation is more severe at ____ elevation angles.

A

Lower

91
Q

____ is when receiving signals arrive at different times.

A

Multipathing

92
Q

What is another name for multipathing?

A

Fading

93
Q

What causes anomalous propagation?

A

Density variations, obstructions and humidity

94
Q

What is the reduction in total power density of an electromagnetic wave as it propagates?

A

Path loss

95
Q

___ is the difference between power transmitted and power recveived.

A

Path loss

96
Q

What is referred to as a theoretical “perfect” space void of gravitational and electromagnetic fields?

A

Free space

97
Q

The reduction of signal strength as it continues to spread out as it radiates is called what?

A

Free space loss

98
Q

What part of a satellite antenna assists in the antennas elevation and direction?

A

Transit device

99
Q

A transit is a tool used to determine the ____.

A

Azimuth

100
Q

What are some causes of electromagnetic interference (EMI)?

A
  • Enemy (jamming)
  • Neutral (electrical current onto your equipment)
  • Friendly
  • Natural (lightning)
101
Q

What do you refer to when identifying and resolving issues related to interference?

A

AFI 17-221

102
Q

EMI

A

Electromagnetic interference

103
Q

RFI

A

Radio frequency interference

104
Q

ISM

A

Installation spectrum manager

105
Q

UHF SATCOM antennas are sued with ____ radios.

A

TACSAT

106
Q

Deployable satellite antennas typically transmit and receive in a ____ shape.

A

Cone

107
Q

The addition or subtraction of ____ on an antenna will change the focus of the cone.

A

Eleements

108
Q

What are the characteristics of the AV2011 antenna?

A
  • 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
Q

To find the look angle you will use a compass to find what?

A

Azimuth and elevation

110
Q

In look angle what is the side-to-side angle between 0-359*?

A

Azimuth

111
Q

In look angle what is the up-down angle between 0-90*?

A

Elevation

RF UR (11 decks)

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