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ET1 SEP EXAM 2018 > NAVEDTRA 14182A, NAVY ELECTRICITY AND ELECTRONICS TRAINING SERIES, MODULE 10-WAVE PROPAGATION, TRANSMISSION LINES, AND ANTENNAS > Flashcards

NAVEDTRA 14182A, NAVY ELECTRICITY AND ELECTRONICS TRAINING SERIES, MODULE 10-WAVE PROPAGATION, TRANSMISSION LINES, AND ANTENNAS Flashcards

1
Q

Which two basic fields are associated with every antenna?

A

Induction and Radiation

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2
Q

Which field is associated with the energy stored in the antenna?

A

Induction

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3
Q

Which type of antenna has an electrical length equal to half the wavelength of the signal being transmitted?

A

Half-wave

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4
Q

What is an energy wave called that is generated by a transmitter?

A

Radio wave

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5
Q

What is the basic shape of the wave generated by a transmitter?

A

Sine wave

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6
Q

What is the number of cycles of a sine wave that are completed in 1 second known as?

A

Frequency

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7
Q

The frequencies falling between 3 kHz and what are called radio frequencies (abbreviated rf) since they are commonly used in radio communications?

A

300 GHz

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8
Q

The usable radio-frequency range is roughly 10 kilohertz to what?

A

100 gigahertz

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9
Q

What is the VLF frequency range?

A

3 to 30 KHz

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10
Q

What is the LF frequency range?

A

30 to 300 KHz

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11
Q

What is the MF frequency range?

A

300 to 3000 KHz

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12
Q

What is the HF frequency range?

A

3 to 30 MHz

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13
Q

What is the VHF frequency range?

A

30 to 300 MHz

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14
Q

What is the UHF frequency range?

A

300 to 3000 MHz

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15
Q

What is the SHF frequency range?

A

3 to 30 GHz

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16
Q

What is the EHF frequency range?

A

30 to 300 GHz

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17
Q

Any frequency that is a whole number multiple of a smaller basic frequency is known as what property of that basic frequency?

A

Harmonic

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18
Q

What is the property of a radio wave which is simply the amount of time required for the completion of one full cycle?

A

Period

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19
Q

What is the space called occupied by one full cycle of a radio wave at any given instant?

A

Wavelength

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20
Q

The velocity (or speed) of a radio wave radiated into free space by transmitting antenna is equal to the speed of light– which is how many miles per second?

A

186,000

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21
Q

Where must the receiving antenna be located for maximum absorption of energy from the electromagnetic fields?

A

Plane of polarization

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22
Q

Troposphere, Stratosphere, along with what else are the three separate regions, or layers that the Earth’s atmosphere is divided into?

A

Ionosphere

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23
Q

The troposphere is the portion of the Earth’s atmosphere that extends from the surface of the Earth to a height of about 3.7 miles (6 km) at the North Pole or the South Pole and how many miles at the equator?

A

11.2

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24
Q

Which atmosphere layer has relatively little effect on radio waves because it is a relatively calm region with little or no temperature changes?

A

Stratosphere

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25
Q

The Ionosphere extends upward from about 31.1 miles to a height of about how many miles?

A

250

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26
Q

What is the most important region of the atmosphere for long distance point-to-point communication?

A

Ionosphere

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27
Q

What are the two principal ways in which electromagnetic (radio) energy travels from a transmitting antenna to a receiving antenna?

A

Ground and sky waves

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28
Q

The surface wave is impractical for long distance transmissions at frequencies above what frequency?

A

2 megahertz

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29
Q

Which frequency band is used for sky wave propagation?

A

High Frequency (HF)

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30
Q

What is the process known as of upsetting electrical neutrality?

A

Ionization

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31
Q

What occurs when the free electrons and positive ions collide with each other?

A

Recombination

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32
Q

How many layers is the Ionosphere composed of?

A

Three

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33
Q

Each ionospheric layer has a maximum frequency at which radio waves can be transmitted vertically and refracted back to the Earth which is known as what?

A

Critical frequency

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34
Q

What is the distance from the transmitter to the point where the sky wave is first returned to Earth?

A

Skip distance

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35
Q

What is a zone of silence between the point where the ground wave becomes too weak for reception and the point where the sky wave is first returned to Earth?

A

Skip zone

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36
Q

What results in the loss of energy of a radio wave and has a pronounced effect on both the strength of received signals and the ability to communicated over long distances?

A

Absorption

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37
Q

Fading on ionospheric circuits is mainly a result of what?

A

Multipath propagation

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38
Q

In what practice are two transmitters and two receivers used, each pair turned to a different frequency, with the same information being transmitted simultaneously over both frequencies?

A

Frequency diversity

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39
Q

When a wide band of frequencies is transmitted simultaneously, each frequency will vary in the amount of fading. What is this variation called?

A

Selective fading

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40
Q

The combined effects of absorption, ground reflection loss, and what else account for most of the energy losses of radio transmissions propagated by the ionosphere?

A

Free space loss

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41
Q

There is little natural interference above which frequency?

A

30 megahertz

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42
Q

How many main classes can the regular variations that affect the extent of ionization in the ionosphere be divided into?

A

Four

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43
Q

What are responsible for variations in the ionization level of the ionosphere?

A

Sunspots

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44
Q

Long distance propagation of hf radio waves is almost totally “blanked out” when what occurs?

A

Sudden Ionospheric Disturbance (SID)

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45
Q

An ionospheric storm that is associated with sunspot activity may begin anytime from 2 days before an active sunspot crosses the central meridian of the sun until how many days after it passes the central meridian?

A

Four

46
Q

For a given angle of incidence and time of day, there is a maximum frequency that can be used for communications between two given locations. What is this frequency known as?

A

Maximum Usable Frequency (MUF)

47
Q

Raindrops cause greater attenuation by scattering than by absorption at frequencies above what?

A

100 megahertz

48
Q

Fog can cause serious attenuation by absorption at frequencies above what?

A

2 gigahertz

49
Q

What is the condition when layers of warm air are formed above layers of cool air known as?

A

Temperature inversion

50
Q

As the lowest region of the Earth’s atmosphere, the troposphere extends from the Earth’s surface to a height of slightly over how many miles?

A

7

51
Q

What region does virtually all weather phenomena occur in?

A

Troposphere

52
Q

Radio waves of frequencies below what normally have wavelengths longer than the size of what weather turbulences?

A

30 megahertz

53
Q

The usable frequency range for tropospheric scattering is from about 100 megahertz to what?

A

10 gigahertz

54
Q

A correctly designed tropospheric scatter circuit will provide highly reliable service for distances ranging from 50 miles to how many miles?

A

500

55
Q

Which device is designed to guide electrical energy from one point to another?

A

Transmission line

56
Q

Which type of line is most often used for power lines, rural telephone lines, and telegraph lines?

A

Two-wire open line

57
Q

Which type of line consists of two insulated wires twisted together to form a flexible line without the use of spacers?

A

Twisted pair

58
Q

Leakage caused by the condensation of moisture is prevented in some rigid line applications by the use of what?

A

Inert gas

59
Q

What was developed to replace rubber and eliminate high-frequency losses associated with rubber insulators?

A

Polyethylene plastic

60
Q

The radius of bends in the waveguide must measure greater than how many wavelengths at the operating frequency of the equipment to avoid excessive attenuation?

A

Two

61
Q

Line losses may be any of three types –Radiation/Induction, Dielectric, and what else?

A

Copper

62
Q

Copper losses can be minimized and conductivity increased in an RF line by plating the line with what?

A

Silver

63
Q

Which type of losses occur because some magnetic lines of force about a conductor do not return to the conductor when the cycle alternates?

A

Radiation

64
Q

What determines the amount of current that can flow when a given voltage is applied to an infinitely long time?

A

Characteristic impedance

65
Q

The characteristic impedance of lines in actual use normally lies between 50 and how many ohms?

A

600

66
Q

When a transmission line is “short” compared to the length of the radio-frequency waves it carries, the opposition presented to the input terminals is determined primarily by what?

A

Load impedance

67
Q

If a line is not terminated in characteristic impedance, what is it said to be?

A

Finite

68
Q

What are voltages called that are moving toward the receiving end of a line?

A

Incident voltages

69
Q

Which type of line has no standing waves of current and voltage?

A

Nonresonant

70
Q

Which type of line has a finite length and is not terminated in its characteristic impedance?

A

Resonant

71
Q

What is the ratio of maximum voltage to minimum voltage on a line called?

A

VSWR

72
Q

What are hollow metal tubes used to transfer energy from one point to another?

A

Waveguides

73
Q

What are theoretical properties (inductance, resistance, and capacitance) of a transmission line that are lumped into a single component?

A

Lumped constants

74
Q

Which two basic classifications are most practical transmitting antennas divided into?

A

Hertz and Marconi

75
Q

Which type of antennas operate with one end grounded and are mounted perpendicular to the Earth or to a surface acting as a ground?

A

Marconi

76
Q

Hertz antennas are generally used for frequencies above what?

A

2 megahertz

77
Q

Which three parts does a complete antenna system consist of?

A

Coupling device, feeder, and antenna

78
Q

What is defined as a conductor or group of conductors used either for radiating electromagnetic energy into space or for collecting it from space?

A

Antenna

79
Q

What is the interchangeability of the same antenna for transmitting and receiving known as?

A

Reciprocity

80
Q

What cannot be used at medium and low frequencies because the electric lines of force are parallel to and touch the earth?

A

Horizontal polarization

81
Q

Which frequencies is sky-wave transmission used?

A

High

82
Q

From approximately 50 to how many megahertz, vertical polarization results in a slightly stronger signal than does horizontal polarization with antennas at the same height?

A

100

83
Q

At 30 megahertz, vertical polarization is better for antenna heights below about how many meters?

A

91

84
Q

At ordinary antenna mast heights of 12 meters (40 feet), vertical polarization is advantageous for frequencies less than about what?

A

100 megahertz

85
Q

Which type of polarization is used by VHF and UHF transmissions?

A

Horizontal

86
Q

What is the useful part of the transmitter’s signal?

A

Radiated energy

87
Q

For the antenna in free space, that is, entirely removed from any objects that might affect its operation, the radiation resistance is how many ohms?

A

73

88
Q

For most half-wave wire antennas, the radiation resistance is about how many ohms?

A

65

89
Q

What is a plot of radiated energy from an antenna?

A

Radiation pattern

90
Q

What is it known as when antenna sources radiate energy equally in all directions?

A

Isotropic radiation

91
Q

Which type of radiators emit (radiate) stronger radiation in one direction than in another?

A

Anisotropic

92
Q

What is used to indicate directions of minimum radiation?

A

Null

93
Q

The electrical length of any antenna wire can be increased or decreased by what way?

A

Loading

94
Q

What is the basic unit from which many complex antennas are constructed?

A

Half-wave antenna

95
Q

What term is used to indicate an antenna that is very short compared with the wavelength of the operating frequency?

A

Doublet

96
Q

What is the simplest form of a practical antenna?

A

Doublet

97
Q

What type of antenna is the shortest antenna that can be used in free space?

A

1/2 wavelength

98
Q

What is an ordinary half-wave antenna that has one or more additional conductors connected across its ends?

A

Folded dipole

99
Q

What is a parasitic element referred to as when it operates to reinforce energy coming from the driver toward itself?

A

Director

100
Q

What is a parasitic element referred to as if it is placed so it causes maximum energy radiation in a direction away from itself and toward the driven element?

A

Reflector

101
Q

What designates an array in which the direction of maximum radiation is perpendicular to the plane containing these elements?

A

Broadside array

102
Q

What type of array is it when all the elements lie in a straight line with no radiation at the ends of the array?

A

Collinear

103
Q

What type of array is it when the principal direction of radiation is along the plane of the array and perpendicular to the elements?

A

End-fire

104
Q

What property of an array is the proportion of energy radiated in the principal direction of radiation to the energy radiated in the opposite direction?

A

Front-to-back ratio

105
Q

What is an antenna that is a wavelength or longer at the operating frequency?

A

Long-wire

106
Q

What is a horizontal, long-wire antenna designated especially for the reception and transmission of low-frequency, vertically polarized ground waves?

A

Beverage antenna

107
Q

What is one of the most popular fixed-station antennas because it is very useful in point-to-point communications?

A

Rhombic

108
Q

What is a half-wave radiator with a reflector?

A

Corner-reflector antenna

109
Q

What is the heating of an insulating material by placing it in a high-frequency electric field?

A

Dielectric heating

110
Q

What parts of the human body are highly susceptible to dielectric heating?

A

Eyes

111
Q

What is the area of a radiation pattern that is covered by radiation?

A

Lobe

112
Q

The optimum gain of a broadside array is obtained when the elements are spaced what distance apart?

A

0.65 wavelength

ET1 SEP EXAM 2018 (28 decks)

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