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554 lines
8.9 KiB
Plaintext
554 lines
8.9 KiB
Plaintext
% FILENAME = N27.TXT
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% Antennas
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% Release version 3, October 2001
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%Question: 1
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#27.1 <img src = "yagi.gif" align = right width = 291 height = 123>
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<extralines = 4 totallines = 10 >
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In this diagram the item U corresponds to the:
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boom
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reflector
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driven element
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director
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% ans 1
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%Question: 2
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#27.2 <img src = "yagi.gif" align = right width = 291 height = 123>
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<extralines = 4 totallines = 10 >
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In this diagram the item V corresponds to the:
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boom
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reflector
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driven element
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director
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% ans 2
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%Question: 3
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#27.3 <img src = "yagi.gif" align = right width = 291 height = 123>
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<extralines = 4 totallines = 10 >
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In this diagram the item X corresponds to the:
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boom
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reflector
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director
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driven element
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% ans 3
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%Question: 4
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#27.4 <img src = "dipole.gif" align = right width = 400 height = 90>
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<totallines = 10 >
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The antenna in this diagram has two equal lengths of wire shown as 'X' forming
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a dipole between insulators. The optimum operating frequency will be when the:
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length X+X equals the signal wavelength
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dimensions are changed with one leg doubled in length
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length X+X is a little shorter than one-half of the signal wavelength
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antenna has one end grounded
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% ans 3
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%Question: 5
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#27.5 <img src = "dipole.gif" align = right width = 400 height = 90>
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<totallines = 7 >
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The antenna in this diagram can be made to operate on several bands if the
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following item is installed at the points shown at 'X' in each wire:
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a capacitor
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an inductor
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a fuse
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a parallel-tuned trap
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% ans 4
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%Question: 6
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#27.6 <img src = "dipole.gif" align = right width = 400 height = 90>
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<totallines = 9 >
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The physical length of the antenna shown in this diagram can be shortened and
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the electrical length maintained, if one of the following items is added at the
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points shown at 'X' in each wire:
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an inductor
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a capacitor
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an insulator
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a resistor
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% ans 1
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%Question: 7
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#27.7 The approximate physical length of a half-wave antenna for a frequency of
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1000 kHz is:
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300 metres
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600 metres
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150 metres
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30 metres
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% ans 3
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%Question: 8
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#27.8 The wavelength for a frequency of 25 MHz is:
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15 metres
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32 metres
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4 metres
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12 metres
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% ans 4
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%Question: 9
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#27.9 Magnetic and electric fields about an antenna are:
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parallel to each other
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determined by the type of antenna used
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perpendicular to each other
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variable with the time of day
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% ans 3
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%Question: 10
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#27.10 Radio wave polarisation is defined by the orientation of the radiated:
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magnetic field
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electric field
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inductive field
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capacitive field
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% ans 2
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%Question: 11
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#27.11 A half wave dipole antenna is normally fed at the point of:
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maximum voltage
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maximum current
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maximum resistance
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resonance
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% ans 2
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%Question: 12
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#27.12 An important factor to consider when high angle radiation is desired
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from a horizontal half-wave antenna is the:
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size of the antenna wire
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time of the year
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height of the antenna
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mode of propagation
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% ans 3
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%Question: 13
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#27.13 An antenna which transmits equally well in all compass directions is a:
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dipole with a reflector only
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quarterwave grounded vertical
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dipole with director only
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half-wave horizontal dipole
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% ans 2
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%Question: 14
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#27.14 A groundplane antenna emits a:
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horizontally polarised wave
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elliptically polarised wave
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axially polarised wave
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vertically polarised wave
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% ans 4
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%Question: 15
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#27.15 The impedance at the feed point of a folded dipole antenna is
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approximately:
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300 ohm
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150 ohm
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200 ohm
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100 ohm
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% ans 1
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%Question: 16
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#27.16 The centre impedance of a 'half-wave' dipole in 'free space' is
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approximately:
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52 ohm
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73 ohm
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100 ohm
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150 ohm
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% ans 2
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%Question: 17
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#27.17 The effect of adding a series inductance to an antenna is to:
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increase the resonant frequency
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have no change on the resonant frequency
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have little effect
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decrease the resonant frequency
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% ans 4
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%Question: 18
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#27.18 The purpose of a balun in a transmitting antenna system is to:
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balance harmonic radiation
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reduce unbalanced standing waves
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protect the antenna system from lightning strikes
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match unbalanced and balanced transmission lines
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% ans 4
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%Question: 19
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#27.19 A dummy antenna:
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attenuates a signal generator to a desirable level
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provides more selectivity when a transmitter is being tuned
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matches an AF generator to the receiver
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duplicates the characteristics of an antenna without radiating signals
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% ans 4
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%Question: 20
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#27.20 A half-wave antenna resonant at 7100 kHz is approximately this long:
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20 metres
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40 metres
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80 metres
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160 metres
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% ans 1
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%Question: 21
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#27.21 An antenna with 20 metres of wire each side of a centre insulator will
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be resonant at approximately:
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3600 kHz
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3900 kHz
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7050 kHz
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7200 kHz
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% ans 1
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%Question: 22
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#27.22 A half wave antenna cut for 7 MHz can be used on this band without
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change:
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10 metre
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15 metre
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20 metre
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80 metre
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% ans 2
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%Question: 23
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#27.23 This property of an antenna broadly defines the range of frequencies to
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which it will be effective:
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bandwidth
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front-to-back ratio
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impedance
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polarisation
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% ans 1
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%Question: 24
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#27.24 The resonant frequency of an antenna may be increased by:
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shortening the radiating element
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lengthening the radiating element
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increasing the height of the radiating element
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lowering the radiating element
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% ans 1
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%Question: 25
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#27.25 Insulators are used at the end of suspended antenna wires to:
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increase the effective antenna length
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limit the electrical length of the antenna
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make the antenna look more attractive
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prevent any loss of radio waves by the antenna
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% ans 2
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%Question: 26
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#27.26 To lower the resonant frequency of an antenna, the operator should:
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lengthen the antenna
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centre feed the antenna with TV ribbon
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shorten the antenna
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ground one end
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% ans 1
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%Question: 27
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#27.27 A half-wave antenna is often called a:
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bi-polar
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Yagi
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dipole
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beam
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% ans 3
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%Question: 28
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#27.28 The resonant frequency of a dipole antenna is mainly determined by:
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its height above the ground
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its length
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the output power of the transmitter used
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the length of the transmission line
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% ans 2
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%Question: 29
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#27.29 A transmitting antenna for 28 MHz for mounting on the roof of a car
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could be a:
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vertical long wire
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quarter wave vertical
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horizontal dipole
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full wave centre fed horizontal
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% ans 2
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%Question: 30
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#27.30 A vertical antenna which uses a flat conductive surface at its base is
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the:
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vertical dipole
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quarter wave ground plane
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rhombic
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long wire
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% ans 2
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%Question: 31
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#27.31 The main characteristic of a vertical antenna is that it:
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requires few insulators
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is very sensitive to signals coming from horizontal aerials
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receives signals from all points around it equally well
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is easy to feed with TV ribbon feeder
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% ans 3
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%Question: 32
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#27.32 At the ends of a half-wave dipole the:
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voltage and current are both high
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voltage is high and current is low
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voltage and current are both low
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voltage low and current is high
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% ans 2
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%Question: 33
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#27.33 An antenna type commonly used on HF is the:
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parabolic dish
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cubical quad
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13-element Yagi
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helical Yagi
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% ans 2
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%Question: 34
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#27.34 A Yagi antenna is said to have a power gain over a dipole antenna for
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the same frequency band because:
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it radiates more power than a dipole
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more powerful transmitters can use it
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it concentrates the radiation in one direction
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it can be used for more than one band
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% ans 3
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%Question: 35
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#27.35 The maximum radiation from a three element Yagi antenna is:
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in the direction of the reflector end of the boom
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in the direction of the director end of the boom
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at right angles to the boom
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parallel to the line of the coaxial feeder
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% ans 2
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%Question: 36
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#27.36 The reflector and director(s) in a Yagi antenna are called:
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oscillators
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tuning stubs
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parasitic elements
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matching units
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% ans 3
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%Question: 37
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#27.37 An isotropic antenna is a:
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half wave reference dipole
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infinitely long piece of wire
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dummy load
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hypothetical point source
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% ans 4
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%Question: 38
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#27.38 The main reason why many VHF base and mobile antennas in amateur use are
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5/8 of a wavelength long is that:
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it is easy to match the antenna to the transmitter
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it is a convenient length on VHF
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the angle of radiation is high giving excellent local coverage
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most of the energy is radiated at a low angle
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% ans 4
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%Question: 39
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#27.39 A more important consideration when selecting an antenna for working
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stations at great distances is:
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sunspot activity
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angle of radiation
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impedance
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bandwidth
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% ans 2
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%Question: 40
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#27.40 On VHF and UHF bands, polarisation of the receiving antenna is important
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in relation to the transmitting antenna, but on HF it is relatively unimportant
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because:
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the ionosphere can change the polarisation of the signal from moment to moment
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the ground wave and the sky wave continually shift the polarisation
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anomalies in the earth's magnetic field profoundly affect HF polarisation
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improved selectivity in HF receivers makes changes in polarisation redundant
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% ans 1
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