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NEETS > Neets 10 ch 2,3,4 > Flashcards

Neets 10 ch 2,3,4 Flashcards

1
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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2
Q

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

A

Induction field.

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3
Q

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

A

Radiation field.

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4
Q

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

A

Fundamental frequency

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5
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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6
Q

Q6. 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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7
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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8
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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9
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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10
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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11
Q

What are the three layers of the atmosphere?

A

Troposphere, stratosphere, and ionosphere.

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12
Q

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

A

Stratosphere.

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13
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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14
Q

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

A

Sea water.

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15
Q

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

A

. Radio horizon is about 1/3 farther.

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16
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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17
Q

What causes ionization to occur in the ionosphere?

A

High energy ultraviolet light waves from the sun

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18
Q

How are the four distinct layers of the ionosphere designated?

A

D, E, F1, and F2 layers.

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19
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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20
Q

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

A

Thickness of ionized layer.

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21
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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22
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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23
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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24
Q

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

A

Where ionization density is greatest.

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25
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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26
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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27
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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28
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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29
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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30
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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31
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

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32
Q

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

A

. Regular and irregular variations

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33
Q

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

A

Regular variations can be predicted but irregular variations are unpredictable.

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34
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.

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35
Q

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

A

Sporadic E, sudden disturbances, and ionospheric storms.

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36
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

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37
Q

When is muf at its highest and why?

A

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

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38
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

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39
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

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40
Q

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

A

. Frequent signal fading and dropouts

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41
Q

What is fot?

A

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

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42
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.

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43
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.

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44
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.

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45
Q

List the five types of transmission lines in use today.

A

. Parallel two-wire, twisted pair, shielded pair, coaxial line and waveguide.

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46
Q

Name two of the three described uses of a two-wire open line.

A

Power lines, rural telephone lines, and telegraph lines

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47
Q

What are the two primary disadvantages of a two-wire open line?

A

. High radiation losses and noise pickup

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48
Q

What type of transmission line is often used to connect a television set to its antenna?

A

. Twin lead.

49
Q

What is the primary advantage of the shielded pair?

A

The conductors are balanced to ground

50
Q

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

A

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

51
Q

What is the chief advantage of the air coaxial line?

A

The ability to minimize radiation losses

52
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

53
Q

List the two common types of waveguides in use today.

A

Cylindrical and rectangular.

54
Q

What are the three types of line losses associated with transmission lines?

A

Copper, dielectric, and radiation.

55
Q

Losses caused by skin effect and the I squared R (power) loss are classified as what type of loss?

A

Copper losses.

56
Q

What types of losses cause the dielectric material between the conductors to be heated?

A

Dielectric losses

57
Q

What must the physical length of a transmission line be if it will be operated at 15,000,000 Hz?
Use the formula: waveform lenght(y)=v divided by f

A

. _ ____PHWHUV_

58
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

59
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.

60
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

61
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.

62
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

63
Q

What is the range of the characteristic impedance of lines used in actual practice?

A

. Between 50 and 600 ohms.

64
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.

65
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

66
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.

67
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.

68
Q

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

A

YHQ_TXDUWHU_ZDYH_SRLQWV_____ ___ _____ __HWF___

69
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.

70
Q

What is the square of the voltage standing-wave ratio called?

A

Power standing-wave ratio (pswr).

71
Q

What does vswr measure?

A

. The existence of voltage variations on a line.

72
Q

What are the two basic classifications of antennas?

A

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

73
Q

What are the three parts of a complete antenna system?

A

Coupling device, feeder, and antenna.

74
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

75
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.

76
Q

What is the term used to identify the points of high current and high voltage on an antenna?

A

. Current and voltage loops.

77
Q

What is the term used to identify the points of minimum current and minimum voltage on an
antenna?

A

Current and voltage nodes.

78
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.

79
Q

The direction of what field is used to designate the polarization of a wave?

A

Electric (E) field.

80
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

81
Q

What type of polarization should be used at medium and low frequencies?

A

Vertical polarization.

82
Q

What is an advantage of using horizontal polarization at high frequencies?

A

Less interference is experienced by man-made noise sources.

83
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.

84
Q

What is the radiation resistance of a half-wave antenna in free space?

A

. 73 ohms

85
Q

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

A

Anisotropic radiator.

86
Q

A radiating source that radiates energy equally in all directions is known as what type of
radiator?

A

Isotropic radiator.

87
Q

A flashlight is an example of what type of radiator?

A

Anisotropic radiator

88
Q

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

A

Dipole, doublet and Hertz.

89
Q

If a basic half-wave antenna is mounted vertically, what type of radiation pattern will be
produced?

A

Nondirectional.

90
Q

In which plane will the half-wave antenna be operating if it is mounted horizontally?

A

Vertical plane.

91
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.

92
Q

What is the simplest method of feeding power to the half-wave antenna?

A

connect one end through a capacitor to the final output stage of the transmitter.

93
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.

94
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

95
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

96
Q

Which has a wider frequency range, a simple dipole or a folded dipole?

A

Folded dipole.

97
Q

What is the purpose of antenna stubs?

A

To produce desired phase relationship between connected elements.

98
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

99
Q

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

A

. Four.

100
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.

101
Q

How can the frequency range of a collinear array be increased?

A

By increasing the lengths of the elements of the array.

102
Q

How is directivity of a collinear array affected when the number of elements is increased?

A

Directivity increases.

103
Q

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

A

Lower radiation resistance

104
Q

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

A

Parallel and in the same plane.

105
Q

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

A

They sharpen

106
Q

What are some disadvantages of the end-fire array?

A

. Extremely low radiation resistance, confined to one frequency, and affected by atmospheric
conditions.

107
Q

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

A

. Along the major axis

108
Q

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

A

Symmetrically.

109
Q

What two factors determine the directivity pattern of the parasitic array?

A

Length of the parasitic element (tuning) and spacing between the parasitic and driven elements

110
Q

What two main advantages of a parasitic array can be obtained by combining a reflector and a
director with the driven element?

A

Increased gain and directivity

111
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.

112
Q

What are the disadvantages of the parasitic array?

A

Their adjustment is critical and they do not operate over a wide frequency range

113
Q

What is the advantage of adding parasitic elements to a Yagi array?

A

Increased gain.

114
Q

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

A

Multielement parasitic array.

115
Q

To radiate power efficiently, a long-wire antenna must have what minimum overall length?

A

One-half wavelength

116
Q

What is another name for the Beverage antenna?

A

. Wave antenna.

117
Q

What is the polarity of the currents that feed the V antenna?

A

Opposite

118
Q

What is the main disadvantage of the rhombic antenna?

A

It requires a large antenna site.

119
Q

What is the primary reason for the development of the turnstile antenna?

A

For omnidirectional vhf communications.

NEETS (11 decks)

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