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Substitute Exam 2024 > NAVEDTRA 14182A Chapter 4 > Flashcards

NAVEDTRA 14182A Chapter 4 Flashcards

1
Q

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

A

Hertz and Marconi

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2
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

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3
Q

Hertz antennas are generally used for what frequencies above what?

A

2 megahertz

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4
Q

Which three parts does a complete antenna system consist of?

A

Coupling device, feeder, and antenna

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5
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

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6
Q

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

A

Reciprocity

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7
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 and polarization

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8
Q

Which frequencies is sky-wave transmission used?

A

High

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9
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

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10
Q

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

A

91

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11
Q

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

A

100 megahertz

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12
Q

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

A

Horizontal

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13
Q

What is the useful part of the transmitters signal?

A

Radiated energy

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14
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

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15
Q

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

A

65

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16
Q

What is a plot of the radiated energy from an antenna?

A

Radiation pattern

17
Q

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

A

Isotropic radiation

18
Q

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

A

Anisotropic

19
Q

What is used to indicate directions of minimum radiation?

20
Q

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

21
Q

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

A

Half-wave antenna

22
Q

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

23
Q

What is the simplest form of a practical antenna?

24
Q

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

A

1/2 wavelength

25
Q

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

A

Folded dipole

26
Q

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

27
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?

28
Q

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

A

Broadside array

29
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?

30
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?

31
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

32
Q

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

33
Q

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

A

Beverage antenna aka wave antenna

34
Q

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

35
Q

What is half-wave radiator with a reflector?

A

Corner-reflector antenna

36
Q

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

A

Dielectric heating

37
Q

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

38
Q

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

39
Q

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

A

.065 wavelength

Substitute Exam 2024 (12 decks)

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