NAVEDTRA 14182A Module 10 Chapter 2

Question 1

Which two composite fields (composed of E and H fields) are associated with every
antenna?

Answer 1

Induction field and radiation field

Question 2

What composite field (composed of E and H fields) is found stored in the antenna?

Answer 2

Induction field

Question 3

What composite field (composed of E and H fields) is propagated into free space?

Answer 3

Radiation field

Question 4

What is the term used to describe the basic frequency of a radio wave?

Answer 4

Fundamental frequency

Question 5

What is the term used to describe a whole number multiple of the basic frequency of
a radio wave?

Answer 5

Harmonic frequency or harmonics

Question 6

It is known that WWV operates on a frequency of 10 megahertz. What is the
wavelength of WWV?

Answer 6

30 meters

Question 7

A station is known to operate at 60-meters. What is the frequency of the unknown
station?

Answer 7

5 MHz

Question 8

If a transmitting antenna is placed close to the ground, how should the antenna be
polarized to give the greatest signal strength?

Answer 8

Vertically polarized

Question 9

In the right-hand rule for propagation, the thumb points in the direction of the E field
and the forefinger points in the direction of the H field. In what direction does the middle finger point?

Answer 9

Direction of wave propagation

Question 10

What is one of the major reasons for the fading of radio waves which have been
reflected from a surface?

Answer 10

Shifting in the phase relationships of the wave

Question 11

What are the three layers of the atmosphere?

Answer 11

Troposphere, stratosphere, and ionosphere

Question 12

Which layer of the atmosphere has relatively little effect on radio waves?

Answer 12

Stratosphere

Question 13

What is the determining factor in classifying whether a radio wave is a ground wave or a space wave?

Answer 13

Whether the component of the wave is travelling along the surface or over the surface of the earth

Question 14

What is the best type of surface or terrain to use for radio wave transmission?

Answer 14

Sea water

Question 15

What is the primary difference between the radio horizon and the natural horizon?

Answer 15

Radio horizon is about 1/3 farther

Question 16

What three factors must be considered in the transmission of a surface wave to
reduce attenuation?

Answer 16

(a) electrical properties of the terrain (b) frequency (c) polarization of the
antenna

Question 17

What causes ionization to occur in the ionosphere?

Answer 17

High energy ultraviolet light waves from the sun

Question 18

How are the four distinct layers of the ionosphere designated?

Answer 18

D, E, F1, and F2 layers

Question 19

What is the height of the individual layers of the ionosphere?

Answer 19

D layer is 30-55 miles, E layer 55-90 miles, and F layers are 90-240 miles

Question 20

What factor determines whether a radio wave is reflected or refracted by the
ionosphere?

Answer 20

Thickness of ionized layer

Question 21

There is a maximum frequency at which vertically transmitted radio waves can be
refracted back to Earth. What is this maximum frequency called?

Answer 21

Critical frequency

Question 22

What three main factors determine the amount of refraction in the ionosphere?

Answer 22

(a) density of ionization of the layer (b) frequency (c) angle at which it enters the
layer

Question 23

What is the skip zone of a radio wave?

Answer 23

A zone of silence between the ground wave and sky wave where there is no
reception

Question 24

Where does the greatest amount of ionospheric absorption occur in the ionosphere?

Answer 24

Where ionization density is greatest

Question 25

What is meant by the term "multipath"?

Answer 25

A term used to describe the multiple pattern a radio wave may follow

Question 26

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

Answer 26

Selective fading

Question 27

What are the two main sources of EMI with which radio waves must compete?

Answer 27

Natural and man-made interference

Question 28

Thunderstorms, snowstorms, cosmic sources, the sun, etc., are a few examples of EMI sources. What type of EMI comes from these sources?

Answer 28

Natural

Question 29

Motors, switches, voltage regulators, generators, etc., are a few examples of EMI sources. What type of EMI comes from these sources?

Answer 29

Man-made

Question 30

What are three ways of controlling the amount of transmitter-generated EMI?

Answer 30

(a) filtering and shielding of the transmitter (b) limiting bandwidth (c) cutting the antenna to the correct frequency

Question 31

What are three ways of controlling radiated EMI during transmission?

Answer 31

(a) physical separation of the antenna (b) limiting bandwidth of the antenna (c) use of directional antennas

Question 32

What are the two general types of variations in the ionosphere?

Answer 32

Regular and irregular variations

Question 33

What is the main difference between these two types of variations?

Answer 33

Regular variations can be predicted but irregular variations are unpredictable

Question 34

What are the four main classes of regular variation which affect the extent of ionization in the ionosphere?

Answer 34

Daily, seasonal, 11-year, and 27-days variation

Question 35

What are the three more common types of irregular variations in the ionosphere?

Answer 35

Sporadic E, sudden disturbances, and ionospheric storms

Question 36

What do the letters muf, luf, and fot stand for?

Answer 36

Muf is maximum usable frequency. Luf is lowest usable frequency. Fot is commonly known as optimum working frequency.

Question 37

When is muf at its highest and why?

Answer 37

Muf is highest around noon. Ultraviolet light waves from the sun are most intense

Question 38

What happens to the radio wave if the luf is too low?

Answer 38

When luf is too low it is absorbed and is too weak for reception

Question 39

What are some disadvantages of operating transmitters at or near the luf?

Answer 39

Signal-to-noise ratio is low and the probability of multipath propagation is greater

Question 40

What are some disadvantages of operating a transmitter at or near the muf?

Answer 40

Frequent signal fading and dropouts

Question 41

What is fot?

Answer 41

Fot is the most practical operating frequency that can be relied on to avoid problems of multipath, absorbtion, and noise

Question 42

How do raindrops affect radio waves?

Answer 42

They can cause attenuation by scattering

Question 43

How does fog affect radio waves at frequencies above 2 gigahertz?

Answer 43

It can cause attenuation by absorbtion

Question 44

How is the term "temperature inversion" used when referring to radio waves?

Answer 44

It is a condition where layers of warm air are formed above layers of cool air

Question 45

How does temperature inversion affect radio transmission?

Answer 45

It can cause vhf and uhf transmission to be propagated far beyond normal line-of-sight distances

Question 46

In what layer of the atmosphere does virtually all weather phenomena occur?

Answer 46

Troposphere

Question 47

Which radio frequency bands use the tropospheric scattering principle for propagation of radio waves?

Answer 47

Vhf and above

Question 48

Where is the tropospheric region that contributes most strongly to tropospheric scatter propagation?

Answer 48

Near the mid-point between the transmitting and receiving antennas, just above the radio horizon