nzart-exam-generator/files/N27.TXT

% FILENAME = N27.TXT
% Antennas
% Release version 3, October 2001

%Question: 1
#27.1 <img src = "yagi.gif" align = right width = 291 height = 123> 
<extralines = 4 totallines = 10 >
In this diagram the item U corresponds to the: 

boom 

reflector 

driven element 

director 

% ans 1

%Question: 2
#27.2 <img src = "yagi.gif" align = right width = 291 height = 123> 
<extralines = 4 totallines = 10 >
In this diagram the item V corresponds to the: 

boom 

reflector 

driven element 

director 

% ans 2

%Question: 3
#27.3 <img src = "yagi.gif" align = right width = 291 height = 123> 
<extralines = 4 totallines = 10 >
In this diagram the item X corresponds to the: 

boom 

reflector 

director 

driven element 

% ans 3

%Question: 4
#27.4 <img src = "dipole.gif" align = right width = 400 height = 90> 
<totallines = 10 >
The antenna in this diagram has two equal lengths of wire shown as 'X' forming 
a dipole between insulators. The optimum operating frequency will be when the: 

length X+X equals the signal wavelength 

dimensions are changed with one leg doubled in length 

length X+X is a little shorter than one-half of the signal wavelength 

antenna has one end grounded 

% ans 3

%Question: 5
#27.5 <img src = "dipole.gif" align = right width = 400 height = 90> 
<totallines = 7 >
The antenna in this diagram can be made to operate on several bands if the 
following item is installed at the points shown at 'X' in each wire: 

a capacitor

an inductor 

a fuse 

a parallel-tuned trap 

% ans 4

%Question: 6
#27.6 <img src = "dipole.gif" align = right width = 400 height = 90> 
<totallines = 9 >
The physical length of the antenna shown in this diagram can be shortened and 
the electrical length maintained, if one of the following items is added at the 
points shown at 'X' in each wire: 

an inductor 

a capacitor 

an insulator 

a resistor 

% ans 1

%Question: 7
#27.7 The approximate physical length of a half-wave antenna for a frequency of 
1000 kHz is: 

300 metres 

600 metres 

150 metres 

30 metres 

% ans 3

%Question: 8
#27.8 The wavelength for a frequency of 25 MHz is: 

15 metres 

32 metres 

4 metres 

12 metres 

% ans 4

%Question: 9
#27.9 Magnetic and electric fields about an antenna are: 

parallel to each other 

determined by the type of antenna used 

perpendicular to each other 

variable with the time of day 

% ans 3

%Question: 10
#27.10 Radio wave polarisation is defined by the orientation of the radiated: 

magnetic field 

electric field 

inductive field 

capacitive field 

% ans 2

%Question: 11
#27.11 A half wave dipole antenna is normally fed at the point of: 

maximum voltage 

maximum current 

maximum resistance 

resonance 

% ans 2

%Question: 12
#27.12 An important factor to consider when high angle radiation is desired 
from a horizontal half-wave antenna is the: 

size of the antenna wire 

time of the year 

height of the antenna 

mode of propagation 

% ans 3

%Question: 13
#27.13 An antenna which transmits equally well in all compass directions is a: 

dipole with a reflector only 

quarterwave grounded vertical 

dipole with director only 

half-wave horizontal dipole 

% ans 2

%Question: 14
#27.14 A groundplane antenna emits a: 

horizontally polarised wave 

elliptically polarised wave 

axially polarised wave 

vertically polarised wave 

% ans 4

%Question: 15
#27.15 The impedance at the feed point of a folded dipole antenna is 
approximately: 

300 ohm 

150 ohm 

200 ohm 

100 ohm 

% ans 1

%Question: 16
#27.16 The centre impedance of a 'half-wave' dipole in 'free space' is 
approximately: 

52 ohm 

73 ohm 

100 ohm 

150 ohm 

% ans 2

%Question: 17
#27.17 The effect of adding a series inductance to an antenna is to: 

increase the resonant frequency 

have no change on the resonant frequency 

have little effect 

decrease the resonant frequency 

% ans 4

%Question: 18
#27.18 The purpose of a balun in a transmitting antenna system is to: 

balance harmonic radiation 

reduce unbalanced standing waves 

protect the antenna system from lightning strikes 

match unbalanced and balanced transmission lines 

% ans 4

%Question: 19
#27.19 A dummy antenna: 

attenuates a signal generator to a desirable level 

provides more selectivity when a transmitter is being tuned 

matches an AF generator to the receiver 

duplicates the characteristics of an antenna without radiating signals

% ans 4

%Question: 20
#27.20 A half-wave antenna resonant at 7100 kHz is approximately this long: 

20 metres 

40 metres 

80 metres 

160 metres 

% ans 1

%Question: 21
#27.21 An antenna with 20 metres of wire each side of a centre insulator will 
be resonant at approximately: 

3600 kHz 

3900 kHz 

7050 kHz 

7200 kHz 

% ans 1

%Question: 22
#27.22 A half wave antenna cut for 7 MHz can be used on this band without 
change: 

10 metre 

15 metre 

20 metre 

80 metre 

% ans 2

%Question: 23
#27.23 This property of an antenna broadly defines the range of frequencies to 
which it will be effective: 

bandwidth 

front-to-back ratio 

impedance 

polarisation 

% ans 1

%Question: 24
#27.24 The resonant frequency of an antenna may be increased by: 

shortening the radiating element 

lengthening the radiating element 

increasing the height of the radiating element 

lowering the radiating element 

% ans 1

%Question: 25
#27.25 Insulators are used at the end of suspended antenna wires to: 

increase the effective antenna length 

limit the electrical length of the antenna 

make the antenna look more attractive 

prevent any loss of radio waves by the antenna 

% ans 2

%Question: 26
#27.26 To lower the resonant frequency of an antenna, the operator should: 

lengthen the antenna 

centre feed the antenna with TV ribbon 

shorten the antenna 

ground one end 

% ans 1

%Question: 27
#27.27 A half-wave antenna is often called a: 

bi-polar 

Yagi 

dipole 

beam 

% ans 3

%Question: 28
#27.28 The resonant frequency of a dipole antenna is mainly determined by: 

its height above the ground 

its length 

the output power of the transmitter used 

the length of the transmission line 

% ans 2

%Question: 29
#27.29 A transmitting antenna for 28 MHz for mounting on the roof of a car 
could be a: 

vertical long wire 

quarter wave vertical 

horizontal dipole 

full wave centre fed horizontal 

% ans 2

%Question: 30
#27.30 A vertical antenna which uses a flat conductive surface at its base is 
the: 

vertical dipole 

quarter wave ground plane 

rhombic 

long wire 

% ans 2

%Question: 31
#27.31 The main characteristic of a vertical antenna is that it: 

requires few insulators 

is very sensitive to signals coming from horizontal aerials 

receives signals from all points around it equally well 

is easy to feed with TV ribbon feeder 

% ans 3

%Question: 32
#27.32 At the ends of a half-wave dipole the: 

voltage and current are both high 

voltage is high and current is low 

voltage and current are both low 

voltage low and current is high 

% ans 2

%Question: 33
#27.33 An antenna type commonly used on HF is the: 

parabolic dish 

cubical quad 

13-element Yagi 

helical Yagi 

% ans 2

%Question: 34
#27.34 A Yagi antenna is said to have a power gain over a dipole antenna for 
the same frequency band because: 

it radiates more power than a dipole 

more powerful transmitters can use it 

it concentrates the radiation in one direction 

it can be used for more than one band 

% ans 3

%Question: 35
#27.35 The maximum radiation from a three element Yagi antenna is: 

in the direction of the reflector end of the boom 

in the direction of the director end of the boom 

at right angles to the boom 

parallel to the line of the coaxial feeder 

% ans 2

%Question: 36
#27.36 The reflector and director(s) in a Yagi antenna are called: 

oscillators 

tuning stubs 

parasitic elements 

matching units 

% ans 3

%Question: 37
#27.37 An isotropic antenna is a: 

half wave reference dipole 

infinitely long piece of wire 

dummy load 

hypothetical point source 

% ans 4

%Question: 38
#27.38 The main reason why many VHF base and mobile antennas in amateur use are 
5/8 of a wavelength long is that: 

it is easy to match the antenna to the transmitter 

it is a convenient length on VHF 

the angle of radiation is high giving excellent local coverage 

most of the energy is radiated at a low angle 

% ans 4

%Question: 39
#27.39 A more important consideration when selecting an antenna for working 
stations at great distances is: 

sunspot activity 

angle of radiation 

impedance 

bandwidth 

% ans 2

%Question: 40
#27.40 On VHF and UHF bands, polarisation of the receiving antenna is important 
in relation to the transmitting antenna, but on HF it is relatively unimportant 
because: 

the ionosphere can change the polarisation of the signal from moment to moment 

the ground wave and the sky wave continually shift the polarisation 

anomalies in the earth's magnetic field profoundly affect HF polarisation 

improved selectivity in HF receivers makes changes in polarisation redundant 

% ans 1