NAVEDTRA 14182A, Ch 4

Question 1

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

Answer 1

Hertz and Marconi

Question 2

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

Answer 2

Marconi

Question 3

Hertz antennas are generally used for frequencies above what?

Answer 3

2 megahertz

Question 4

Which three parts does a complete antenna system consist of?

Answer 4

Coupling device, feeder, and antenna

Question 5

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

Answer 5

Antenna

Question 6

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

Answer 6

Reciprocity

Question 7

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

Answer 7

Horizontal poloarization

Question 8

Which frequencies is sky-wave transmission used?

Answer 8

High

Question 9

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?

Answer 9

100

Question 10

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

Answer 10

91

Question 11

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

Answer 11

100 megahertz

Question 12

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

Answer 12

Horizontal

Question 13

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

Answer 13

Radiated energy

Question 14

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?

Answer 14

73

Question 15

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

Answer 15

65

Question 16

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

Answer 16

Radiation pattern

Question 17

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

Answer 17

Isotropic radiation

Question 18

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

Answer 18

Anisotropic

Question 19

What is used to indicate directions of minimum radiation?

Answer 19

Null

Question 20

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

Answer 20

Loading

Question 21

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

Answer 21

Half-wave antenna

Question 22

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

Answer 22

Doublet

Question 23

What is the simplest form of a practical antenna?

Answer 23

Doublet

Question 24

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

Answer 24

1/2 wavelengthth

Question 25

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

Answer 25

Folded dipole

Question 26

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

Answer 26

Director

Question 27

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?

Answer 27

Reflector

Question 28

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

Answer 28

Broadside array

Question 29

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

Answer 29

Collinear

Question 30

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

Answer 30

End-fire

Question 31

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?

Answer 31

Front-to-back Ratio

Question 32

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

Answer 32

Long-wire

Question 33

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

Answer 33

Beverage antenna

Question 34

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

Answer 34

Rhombic

Question 35

What is a half-wave radiator with a reflector?

Answer 35

Corner-Reflector antenna

Question 36

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

Answer 36

Dielectric heating

Question 37

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

Answer 37

Eyes

Question 38

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

Answer 38

Lobe

Question 39

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

Answer 39

Lobe

Question 40

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

Answer 40

.065 wavelength