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LOOKS FAM > NEETS 10 Wave Propagation > Flashcards

NEETS 10 Wave Propagation Flashcards

1
Q

What is propagation?

A

Propagation means spreading out.

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2
Q

How is a wave defined as it applies to wave

propagation?

A

A wave is a disturbance which moves through a medium

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3
Q

What is wave motion?

A

A means of transferring energy from one place to

another.

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4
Q

What are some examples of wave motion?

A

Sound waves, light waves, radio waves, heat waves, water waves

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5
Q

What type of wave motion is represented by the motion

of water?

A

Transverse waves

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6
Q

What are some examples of transverse waves?

A

Radio waves, light waves, and heat waves

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7
Q

What example of a longitudinal wave was given in the text?

A

A sound wave.

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8
Q

What are the three requirements for a wave to be propagated?

A

A source, medium, and detector (receiver).

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9
Q

What is a cycle?

A

A sequence of events, such as the positive and negative

alternation of electrical current

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10
Q

What is wavelength (λ)?

A

The space occupied by one cycle of a radio wave at any

given instant.

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11
Q

What is the law of reflection

A

The law of reflection states: The angle of incidence is

equal to the angle of reflection.

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12
Q

When a wave is reflected from a surface, energy is

transferred. When is the transfer of energy greatest?

A

When the incident wave is nearly parallel with the

surface

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13
Q

When is the transfer of energy minimum?

A

When the incident wave is perpendicular to the surface.

Also a dull (or black) surface reflects very little regardless of the angle

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14
Q

A refracted wave occurs when a wave passes from one medium into another medium. What determines the angle of refraction?

A

The density of the two mediums, and the velocity of the waves

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15
Q

The apparent change in frequency or pitch because

of motion is explained by what effect?

A

The Doppler Effect

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16
Q

What term describes sounds capable of being heard

by the human ear?

A

Sonics

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17
Q

Are all sounds audible to the human ear? Why?

A

Sonics.

Actual Answer:
No, the ave human ear cannot hear all sounds in the infrasonic and ultrasonic regions

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18
Q

Sound waves transmitted from a source are sometimes weak when they reach the detector. What instrument is needed to boost the weak signal?

A

An Amplifier

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19
Q

What are the three basic requirements for sound?

A

A source, medium, and detector (receiver).

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20
Q

What are the two general groups of sound?

A

Noise and tones

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21
Q

What are the three basic characteristics of sound

A

Pitch, intensity, and quality

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22
Q

What is the normal audible range of the human ear

A

20 Hz to 20 kHz.

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23
Q

What is intensity as it pertains to sound?

A

The amount of energy transmitted from a source.

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24
Q

What characteristic of sound enables a person to
distinguish one musical instrument from another, if
they are all playing the same note?

A

Quality.

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25
Q

How does density and temperature affect the velocity of sound?

A

Velocity increases as density decreases and temperature increases.

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26
Q

What term is used in describing the science of sound?

A

Acoustics.

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27
Q

A sound wave that is reflected back toward the source is known as what type of sound?

A

Echo

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28
Q

What is the term for multiple reflections of sound waves?

A

Reverberation.

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29
Q

A cavity that vibrates at its natural frequency
produces a louder sound than at other frequencies.
What term is used to describe this phenomenon?

A

Resonance

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30
Q

What do we call a disturbance that distracts or

distorts the quality of sound?

A

Noise

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31
Q

What are three means of producing light?

A

Mechanical, electrical, and chemical.

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32
Q

What is the smallest unit of radiant energy?

A

A photon.

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33
Q

What unit is used to measure the different wavelengths of light?

A

Angstrom

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34
Q

What are the three primary colors of light?

A

Red, green and blue.

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35
Q

Which two composite fields (composed of E and H

fields) are associated with every antenna?

A

Induction field and radiation field.

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36
Q

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

A

Induction field.

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37
Q

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

A

Radiation field.

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38
Q

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

A

Fundamental frequency.

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39
Q

What is the term used to describe a whole number

multiple of the basic frequency of a radio wave?

A

Harmonic frequency or harmonics

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40
Q

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

A

30 Meters

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41
Q

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

A

5 megahertz

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42
Q

If a transmitting antenna is placed close to the

ground, how should the antenna be polarized to give the greatest signal strength?

A

Vertically polarized

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43
Q

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?

A

Direction of wave propagation.

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44
Q

What is one of the major reasons for the fading of

radio waves which have been reflected from a surface?

A

Shifting in the phase relationships of the wave.

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45
Q

What are the three layers of the atmosphere?

A

Troposphere, stratosphere, and ionosphere.

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46
Q

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

A

Stratosphere.

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47
Q

What is the determining factor in classifying

whether a radio wave is a ground wave or a space wave?

A

Whether the component of the wave is travelling along

the surface or over the surface of the earth.

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48
Q

What is the best type of surface or terrain to use

for radio wave transmission?

A

Radio horizon is about 1/3 farther.

Actual Answer:
Sea Water

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49
Q

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

A

Sea Water

Actual Answer:
Radio horizon is about 1/3 farther

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50
Q

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

A

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

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51
Q

What causes ionization to occur in the ionosphere?

A

High energy ultraviolet light waves from the sun.

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52
Q

How are the four distinct layers of the ionosphere

designated?

A

D, E, F1, and F2 layers.

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53
Q

What is the height of the individual layers of the

ionosphere?

A

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

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54
Q

What factor determines whether a radio wave is

reflected or refracted by the ionosphere?

A

Thickness of ionized layer.

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55
Q

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

A

Critical frequency.

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56
Q

What three main factors determine the amount of

refraction in the ionosphere?

A

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

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57
Q

What is the skip zone of a radio wave?

A

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

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58
Q

Where does the greatest amount of ionospheric

absorption occur in the ionosphere?

A

Where ionization density is greatest.

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59
Q

What is meant by the term “multipath”?

A

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

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60
Q

When a wide band of frequencies is transmitted

simultaneously, each frequency will vary in the amount of fading. What is this variable fading called?

A

Selective fading.

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61
Q

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

A

Natural and man-made interference.

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62
Q

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

A

Natural

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63
Q

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

A

Man-made.

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64
Q

What are three ways of controlling the amount of

transmitter-generated emi?

A

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

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65
Q

What are three ways of controlling radiated emi

during transmission?

A

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

66
Q

What are the two general types of variations in the

ionosphere?

A

Regular and irregular variations.

67
Q

What is the main difference between these two types

of variations?

A

Regular variations can be predicted but irregular

variations are unpredictable

68
Q

What are the four main classes of regular variation

which affect the extent of ionization in the ionosphere?

A

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

69
Q

What are the three more common types of irregular

variations in the ionosphere?

A

Sporadic E, sudden disturbances, and ionospheric

storms.

70
Q

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

A

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

71
Q

When is muf at its highest and why?

A

Muf is highest around noon. Ultraviolet light waves from

the sun are most intense

72
Q

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

A

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

73
Q

What are some disadvantages of operating

transmitters at or near the luf?

A

Signal-to-noise ratio is low and the probability of

multipath propagation is greater.

74
Q

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

A

Frequent signal fading and dropouts

75
Q

What is fot?

A

Fot is the most practical operating frequency that can

be relied on to avoid problems of multipath, absorbtion, and noise.

76
Q

How do raindrops affect radio waves?

A

They can cause attenuation by scattering

77
Q

How does fog affect radio waves at frequencies above

2 gigahertz?

A

It can cause attenuation by absorbtion

78
Q

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

A

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

79
Q

How does temperature inversion affect radio

transmission?

A

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

80
Q

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

A

Troposphere.

81
Q

Which radio frequency bands use the tropospheric

scattering principle for propagation of radio waves?

A

Vhf and above.

82
Q

Where is the tropospheric region that contributes

most strongly to tropospheric scatter propagation?

A

Near the mid-point between the transmitting and

receiving antennas, just above the radio horizon.

83
Q

What connecting link is used to transfer energy from
a radio transmitter to its antenna located on the mast
of a ship?

A

Transmission line.

84
Q

What term is used for the end of the transmission line

that is connected to a transmitter?

A

Input end, generator end, transmitter end, sending end,

and source.

85
Q

What term is used for the end of the transmission line

that is connected to an antenna?

A

Output end, receiving end, load end and sink.

86
Q

List the five types of transmission lines in use

today.

A

Parallel two-wire, twisted pair, shielded pair, coaxial

line and waveguide.

87
Q

Name two of the three described uses of a two-wire

open line.

A

Power lines, rural telephone lines, and telegraph lines.

88
Q

What are the two primary disadvantages of a two-wire

open line?

A

High radiation losses and noise pickup.

89
Q

What type of transmission line is often used to

connect a television set to its antenna?

A

Twin lead.

90
Q

What is the primary advantage of the shielded pair?

A

The conductors are balanced to ground.

91
Q

What are the two types of coaxial lines in use today?

A

Air coaxial (rigid) and solid coaxial (flexible).

92
Q

What is the chief advantage of the air coaxial line?

A

The ability to minimize radiation losses.

93
Q

List the three disadvantages of the air coaxial line.

A

Expensive to construct, must be kept dry, and high
frequency losses limit the practical length of
the line.

94
Q

List the two common types of waveguides in use today.

A

Cylindrical and rectangular.

95
Q

What are the three types of line losses associated

with transmission lines?

A

Copper, dielectric, and radiation.

96
Q

Losses caused by skin effect and the I 2 R (power)

loss are classified as what type of loss?

A

Copper losses.

97
Q

What types of losses cause the dielectric material

between the conductors to be heated?

A

Dielectric losses.

98
Q

What must the physical length of a transmission line

be if it will be operated at 15,000,000 Hz?

A

20 meters

99
Q

What are two of the three physical factors that

determine the values of capacitance and inductance of a transmission line?

A

(1) Type of line used,
(2) dielectric in the line, and
(3) length of line.

100
Q

A transmission line is said to have distributed
constants of inductance, capacitance, and resistance
along the line. What units of measurement are used to
express these constants?

A

Inductance is expressed in microhenrys per unit length,
capacitance is expressed in picofarads per unit length,
and resistance is expressed in ohms per unit length

101
Q

Describe the leakage current in a transmission line

and in what unit it is expressed.

A

The small amount of current that flows through the

dielectric between two wires of a transmission line and is expressed in micromhos per unit length

102
Q

All the power sent down a transmission line from a

transmitter can be transferred to an antenna under what optimum conditions?

A

When the characteristic impedance of the transmission

line and the load impedance are equal.

103
Q

What symbol is used to designate the characteristic
impedance of a line, and what two variables does it
compare?

A

Z0 and it is the ratio of E to I at every point along the line.

104
Q

What is the range of the characteristic impedance

of lines used in actual practice?

A

Between 50 and 600 ohms.

105
Q

Two types of waves are formed on a transmission line. What names are given to these waves?

A

Incident waves from generator to load. Reflected waves from load back to generator.

106
Q

In figure 3-27, which waveforms on the left have a
resultant wave of zero, and what is indicated by these
waves?

A

2 and 6 have zero resultant wave and they indicate that
the incident and reflected waves are 180
degrees out of phase at all parts

107
Q

On an open-ended transmission line, the voltage is always zero at what distance from each end of the line?

A

One-fourth the distance from each end of the line.

108
Q

A nonresonant line is a line that has no standing

waves of current and voltage on it and is considered to be flat. Why is this true?

A

The load impedance of such a line is equal to Z0.

109
Q

On an open line, the voltage and impedance are maximum at what points on the line?

A

Even quarter-wave points(1/2λ,1λ,3/2λ, etc)

110
Q

At what point on an open-circuited rf line do voltage

peaks occur?

A

At 1/2 wavelength from the end and at every 1/2

wavelength along the line.

111
Q

What is the square of the voltage standing-wave

ratio called?

A

Power standing-wave ratio (pswr).

112
Q

What does vswr measure?

A

The existence of voltage variations on a line

113
Q

What are the two basic classifications of antennas?

A

Half-wave (Hertz) and quarter-wave (Marconi).

114
Q

What are the three parts of a complete antenna system?

A

Coupling device, feeder, and antenna.

115
Q

What three factors determine the type, size, and shape of an antenna?

A

Frequency of operation of the transmitter, amount of
power to be radiated, and general direction of the
receiving set

116
Q

If a wave travels exactly the length of an antenna

from one end to the other and back during the period of 1 cycle, what is the length of the antenna?

A

One-half the wavelength.

117
Q

What is the term used to identify the points of high

current and high voltage on an antenna?

A

Current and voltage loops.

118
Q

What is the term used to identify the points of

minimum current and minimum voltage on an antenna?

A

Current and voltage nodes.

119
Q

The various properties of a transmitting antenna can
apply equally to the same antenna when it is used as a
receiving antenna. What term is used for this property?

A

Reciprocity of antennas.

120
Q

The direction of what field is used to designate the

polarization of a wave?

A

Electric (E) field.

121
Q

If a wave’s electric lines of force rotate through
360 degrees with every cycle of rf energy, what is
the polarization of this wave?

A

Circular polarization.

122
Q

What type of polarization should be used at medium

and low frequencies?

A

Vertical polarization.

123
Q

What is an advantage of using horizontal

polarization at high frequencies?

A

Less interference is experienced by man-made noise sources.

124
Q

What type of polarization should be used if an

antenna is mounted on a moving vehicle at frequencies below 50 megahertz?

A

Vertical polarization.

125
Q

What is the radiation resistance of a half-wave

antenna in free space?

A

73 ohms.

126
Q

A radiating source that radiates energy stronger in
one direction than another is known as what type of
radiator?

A

Anisotropic radiator

127
Q

A radiating source that radiates energy equally in

all directions is known as what type of radiator?

A

Isotropic radiator.

128
Q

A flashlight is an example of what type of radiator?

A

Anisotropic radiator.

129
Q

What terms are often used to describe basic half-wave antennas?

A

Dipole, doublet and Hertz.

130
Q

If a basic half-wave antenna is mounted vertically,

what type of radiation pattern will be produced?

A

Nondirectional.

131
Q

In which plane will the half-wave antenna be

operating if it is mounted horizontally?

A

Vertical plane.

132
Q

Since the radiation pattern of a dipole is similar
to that of a doublet, what will happen to the pattern
if the length of the doublet is increased?

A

The pattern would flatten.

133
Q

What is the simplest method of feeding power to the

half-wave antenna?

A

To connect one end through a capacitor to the final

output stage of the transmitter.

134
Q

What is the radiation pattern of a quarter-wave

antenna?

A

A circular radiation pattern in the horizontal plane,

or same as a half wave

135
Q

Describe the physical arrangement of a ground

screen.

A

It is composed of a series of conductors arranged in a
radial pattern and buried 1 to 2 feet below
the ground.

136
Q

What is the difference in the amount of impedance

between a three-wire dipole and a simple center-fed dipole?

A

Nine times the feed-point impedance.

137
Q

Which has a wider frequency range, a simple dipole

or a folded dipole?

A

Folded dipole.

138
Q

What is the purpose of antenna stubs?

A

To produce desired phase relationship between connected elements.

139
Q

What is the primary difference between the major and minor lobes of a radiation pattern?

A

Major lobes have the greatest amount of radiation

140
Q

What is the maximum number of elements ordinarily used in a collinear array?

A

Four.

141
Q

Why is the number of elements used in a collinear

array limited?

A

As more elements are added, an unbalanced condition in the system occurs which impairs efficiency

142
Q

How can the frequency range of a collinear array be

increased?

A

By increasing the lengths of the elements of the array.

Property of

143
Q

How is directivity of a collinear array affected

when the number of elements is increased?

A

Directivity increases.

144
Q

What is the primary cause of broadside arrays losing
efficiency when not operating at their designed
frequency?

A

Lower radiation resistance

145
Q

When more than two elements are used in a broadside array, how are the elements arranged?

A

Parallel and in the same plane.

146
Q

As the spacing between elements in a broadside array increases, what is the effect on the major lobes?

A

They sharpen.

147
Q

What are some disadvantages of the end-fire array?

A

Extremely low radiation resistance, confined to one

frequency, and affected by atmospheric conditions.

148
Q

Where does the major lobe in the end-fire array occur?

A

Along the major axis

149
Q

To maintain the required balance of phase
relationships and critical feeding, how must the
end-fire array be constructed?

A

Symmetrically.

150
Q

What two factors determine the directivity pattern

of the parasitic array?

A

What two factors determine the directivity pattern

of the parasitic array?

151
Q

What two factors determine the directivity pattern

of the parasitic array?

A

What two factors determine the directivity pattern

of the parasitic array?

152
Q

The parasitic array can be rotated to receive or

transmit in different directions. What is the name given to such an antenna?

A

Rotary array

153
Q

What are the disadvantages of the parasitic array?

A

Their adjustment is critical and they do not operate

over a wide frequency range.

154
Q

What is the advantage of adding parasitic elements

to a Yagi array?

A

Increased gain.

155
Q

The Yagi antenna is an example of what type of array?

A

Multielement parasitic array.

156
Q

To radiate power efficiently, a long-wire antenna

must have what minimum overall length?

A

One-half wavelength

157
Q

What is an other name for the Beverage antenna?

A

Wave antenna.

158
Q

What is the polarity of the currents that feed the

V antenna?

A

Opposite.

159
Q

What is the main disadvantage of the rhombic

antenna?

A

It requires a large antenna site.

160
Q

What is the primary reason for the development of

the turnstile antenna?

A

For omnidirectional vhf communications

LOOKS FAM (6 decks)

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