Transcript G9 - ANTENNAS [4 exam questions - 4 groups]

G9 - ANTENNAS
[4 exam questions - 4 groups]
G9A Antenna feedlines: characteristic impedance, and
attenuation; SWR calculation, measurement and effects;
matching networks
G9B Basic antennas
G9C Directional antennas
G9D Specialized antennas
1
Antennas
Feedlines
2
Antennas
G9A Antenna feedlines
Characteristic impedance and attenuation
•
The distance between the centers of the conductors
and the radius of the conductors help determine the
characteristic impedance of a parallel conductor antenna
feedline
•
The typical characteristic impedance of coaxial
cables used for antenna feelines at amateur
stations is 50 and 75 ohms
3
Antennas
G9A Impedance and attenuation cont’d
•
The characteristic impedance of a flat ribbon TV
type twin lead is 300 ohms
•
The attenuation of coaxial cable increases as the
frequency of the signal it is carrying increases
•
RF feedline losses are usually expressed in dB per 100 ft
4
Antennas
G9A SWR calculations, measurement &
effects
•
•
If the SWR on an antenna feedline is 5 to 1, and a
matching network at the transmitter end of the
feedline is adjusted to 1 to 1 SWR, the resulting SWR
on the feedline will be 5 to 1
A standing-wave-ration of 4:1 will result from the
connection of a 50-ohm feed line to a non-reactive load
having a 200-ohm impedence
•
•
SWR = 200:50 -> 4:1
A SWR of 1:1 will result from the connection of a 50-ohm
feed line to a non-reactive load having 50-ohm
impedance
•
SWR = 50:50 -> 1:1
5
Antennas
G9A SWR cont’d
•
If you feed a vertical antenna that has a 25-ohm
feed-point impedance with 50-ohm coaxial cable
the SWR would be 2:1
•
•
SWR = 50:25 -> 2:1
If you feed a folded dipole antenna that has a 300ohm feed point impedance with 50-ohm coaxial
cable the SWR would be 6:1
•
SWR = 300:50 -> 6:1
6
Antennas
G9A Matching networks
•
•
•
A common reason for the occurrence of reflected
power at the point where a feed line connects to
an antenna is a difference between feedline impedance
and antenna feed point impedance
The antenna feed point impedance must be matched
to the characteristic impedance of the feed line to prevent
standing waves on an antenna feed line
A reason for using an inductively coupled matching
network between the transmitter and parallel
conductor feed line feeding an antenna is to match
the unbalanced transmitter output to the balanced parallel
conductor feed line
7
Antennas
G9A01 Which of the following factors help
determine the characteristic impedance of a
parallel conductor antenna feedline?
A. The distance between the centers of the conductors and
the radius of the conductors
B. The distance between the centers of the conductors and
the length of the line
C. The radius of the conductors and the frequency of the
signal
D. The frequency of the signal and the length of the line
8
Antennas
G9A01 Which of the following factors help
determine the characteristic impedance of a
parallel conductor antenna feedline?
A.
The distance between the centers of the
conductors and the radius of the conductors
B. The distance between the centers of the conductors and
the length of the line
C. The radius of the conductors and the frequency of the
signal
D. The frequency of the signal and the length of the line
9
Antennas
Coax Cable Signal Loss (Attenuation) in dB per 100ft
Loss
RG-174
RG-58
RG-8X RG-213
RG-6
RG-11
9913
LMR-400
1MHz
1.9dB
0.4dB
0.5dB
0.2dB
0.2dB
0.2dB
0.2dB
0.3dB
10MHz
3.3dB
1.4dB
1.0dB
0.6dB
0.6dB
0.4dB
0.4dB
0.5dB
50MHz
6.6dB
3.3dB
2.5dB
1.6dB
1.4dB
1.0dB
0.9dB
0.9dB
100MHz
8.9dB
4.9dB
3.6dB
2.2dB
2.0dB
1.6dB
1.4dB
1.4dB
200MHz
11.9dB
7.3dB
5.4dB
3.3dB
2.8dB
2.3dB
1.8dB
1.8dB
400MHz
17.3dB
11.2dB
7.9dB
4.8dB
4.3dB
3.5dB
2.6dB
2.6dB
700MHz
26.0dB
16.9dB
11.0dB
6.6dB
5.6dB
4.7dB
3.6dB
3.5dB
900MHz
27.9dB
20.1dB
12.6dB
7.7dB
6.0dB
5.4dB
4.2dB
3.9dB
1GHz
32.0dB
21.5dB
13.5dB
8.3dB
6.1dB
5.6dB
4.5dB
4.1dB
Imped
50ohm
50ohm
50ohm
50ohm
75ohm 75ohm 50ohm
50ohm
10
Antennas
G9A02 What is the typical characteristic
impedance of coaxial cables used for
antenna feedlines at amateur stations?
A.
B.
C.
D.
25 and 30 ohms
50 and 75 ohms
80 and 100 ohms
500 and 750 ohms
11
Antennas
G9A02 What is the typical characteristic
impedance of coaxial cables used for
antenna feedlines at amateur stations?
A. 25 and 30 ohms
B.
50 and 75 ohms
C. 80 and 100 ohms
D. 500 and 750 ohms
12
Antennas
G9A03 What is the characteristic impedance
of flat ribbon TV type twin lead?
A.
B.
C.
D.
50 ohms
75 ohms
100 ohms
300 ohms
13
Antennas
G9A03 What is the characteristic impedance
of flat ribbon TV type twin lead?
A. 50 ohms
B. 75 ohms
C. 100 ohms
D.
300 ohms
14
Antennas
Standing Waves
15
Antennas
G9A04 What is a common reason for the
occurrence of reflected power at the point
where a feedline connects to an antenna?
A. Operating an antenna at its resonant frequency
B. Using more transmitter power than the antenna can handle
C. A difference between feedline impedance and antenna feed
point impedance
D. Feeding the antenna with unbalanced feedline
16
Antennas
G9A04 What is a common reason for the
occurrence of reflected power at the point
where a feedline connects to an antenna?
A. Operating an antenna at its resonant frequency
B. Using more transmitter power than the antenna can handle
C.
A difference between feedline impedance and
antenna feed point impedance
D. Feeding the antenna with unbalanced feedline
17
Antennas
G9A05 What must be done to prevent
standing waves on an antenna feedline?
A. The antenna feed point must be at DC ground potential
B. The feedline must be cut to an odd number of electrical
quarter wavelengths long
C. The feedline must be cut to an even number of physical
half wavelengths long
D. The antenna feed point impedance must be matched to the
characteristic impedance of the feedline
18
Antennas
G9A05 What must be done to prevent
standing waves on an antenna feedline?
A. The antenna feed point must be at DC ground potential
B. The feedline must be cut to an odd number of electrical
quarter wavelengths long
C. The feedline must be cut to an even number of physical
half wavelengths long
D.
The antenna feed point impedance must be
matched to the characteristic impedance of the
feedline
19
Antennas
G9A06 Which of the following is a reason for
using an inductively coupled matching
network between the transmitter and
parallel conductor feed line feeding an
antenna?
A. To increase the radiation resistance
B. To reduce spurious emissions
C. To match the unbalanced transmitter output to the
balanced parallel conductor feedline
D. To reduce the feed-point impedance of the antenna
20
Antennas
G9A06 Which of the following is a reason for
using an inductively coupled matching
network between the transmitter and
parallel conductor feed line feeding an
antenna?
A. To increase the radiation resistance
B. To reduce spurious emissions
C.
To match the unbalanced transmitter output to
the balanced parallel conductor feedline
D. To reduce the feed-point impedance of the antenna
21
Antennas
G9A07 How does the attenuation of coaxial
cable change as the frequency of the signal
it is carrying increases?
A.
B.
C.
D.
It
It
It
It
is independent of frequency
increases
decreases
reaches a maximum at approximately 18 MHz
22
Antennas
G9A07 How does the attenuation of coaxial
cable change as the frequency of the signal
it is carrying increases?
A. It is independent of frequency
B.
It increases
C. It decreases
D. It reaches a maximum at approximately 18 MHz
23
Antennas
G9A08 In what values are RF feed line losses
usually expressed?
A.
B.
C.
D.
ohms per 1000 ft
dB per 1000 ft
ohms per 100 ft
dB per 100 ft
24
Antennas
G9A08 In what values are RF feed line losses
usually expressed?
A. ohms per 1000 ft
B. dB per 1000 ft
C. ohms per 100 ft
D.
dB per 100 ft
25
Antennas
G9A09 What standing-wave-ratio will result
from the connection of a 50-ohm feed line to
a non-reactive load having a 200-ohm
impedance?
A.
B.
C.
D.
4:1
1:4
2:1
1:2
26
Antennas
G9A09 What standing-wave-ratio will result
from the connection of a 50-ohm feed line to
a non-reactive load having a 200-ohm
impedance?
A.
4:1
B. 1:4
C. 2:1
D. 1:2
27
Antennas
G9A10 What standing-wave-ratio will result
from the connection of a 50-ohm feed line to
a non-reactive load having a 10-ohm
impedance?
A.
B.
C.
D.
2:1
50:1
1:5
5:1
28
Antennas
G9A10 What standing-wave-ratio will result
from the connection of a 50-ohm feed line to
a non-reactive load having a 10-ohm
impedance?
A. 2:1
B. 50:1
C. 1:5
D.
5:1
29
Antennas
G9A11 What standing-wave-ratio will result
from the connection of a 50-ohm feed line to
a non-reactive load having a 50-ohm
impedance?
A.
B.
C.
D.
2:1
1:1
50:50
0:0
30
Antennas
G9A11 What standing-wave-ratio will result
from the connection of a 50-ohm feed line to
a non-reactive load having a 50-ohm
impedance?
A. 2:1
B.
1:1
C. 50:50
D. 0:0
31
Antennas
G9A12 What would be the SWR if you feed a
vertical antenna that has a 25-ohm feedpoint impedance with 50-ohm coaxial cable?
A.
B.
C.
D.
2:1
2.5:1
1.25:1
You cannot determine SWR from impedance values
32
Antennas
G9A12 What would be the SWR if you feed a
vertical antenna that has a 25-ohm feedpoint impedance with 50-ohm coaxial cable?
A.
2:1
B. 2.5:1
C. 1.25:1
D. You cannot determine SWR from impedance values
33
Antennas
G9A13 What would be the SWR if you feed a
folded dipole antenna that has a 300-ohm
feed-point impedance with 50-ohm coaxial
cable?
A.
B.
C.
D.
1.5:1
3:1
6:1
You cannot determine SWR from impedance values
34
Antennas
G9A13 What would be the SWR if you feed a
folded dipole antenna that has a 300-ohm
feed-point impedance with 50-ohm coaxial
cable?
A. 1.5:1
B. 3:1
C.
6:1
D. You cannot determine SWR from impedance values
35
Antennas
G9A14 If the SWR on an antenna feedline is
5 to 1, and a matching network at the
transmitter end of the feedline is adjusted to
1 to 1 SWR, what is the resulting SWR on
the feedline?
A. 1 to 1
B. 5 to 1
C. Between 1 to 1 and 5 to 1 depending on the characteristic
impedance of the line
D. Between 1 to 1 and 5 to 1 depending on the reflected
power at the transmitter
36
Antennas
G9A14 If the SWR on an antenna feedline is
5 to 1, and a matching network at the
transmitter end of the feedline is adjusted to
1 to 1 SWR, what is the resulting SWR on
the feedline?
A. 1 to 1
B.
5 to 1
C. Between 1 to 1 and 5 to 1 depending on the characteristic
impedance of the line
D. Between 1 to 1 and 5 to 1 depending on the reflected
power at the transmitter
37
Antennas
G9B Basic Antennas
•
Random-wire antenna
•
•
One of the disadvantages of a directly fed random-wire
antenna is you may experience RF burns when touching
metal objects in your station
Groundplane antenna
•
•
An advantage of downward sloping radials on a groundplane antenna is they can be adjusted to bring the geedpoint impedance closer to 50 ohms
The feed-point impedance of a ground-plane antenna
increases when its radials are changed from horizontal to
downward sloping
38
Antennas
G9B Basic Antennas cont’d
•
Vertical antenna
•
•
The radial wire of a ground-mounted vertical antenna
system should be placed on the surface or buried a few
inches below the ground
The approximate length of a ¼ - wave vertical antenna cut
for 28.5 MHz is 8.2 feet
• Length (1/4 – wave Vertical) = 234
= 234/28.5 = 8.2 feet
• In feet
Fx (MHz)
39
Antennas
G9B Antennas (presenter’s note)
** Where did you get 234 in that equation?
Remember these equations
300
Wavelength in meters: f (MHz)
468
Wavelength in feet:
984
f (MHz) ½ wavelength in ft = f (MHz)
234
¼ wavelength in ft = f (MHz)
40
Antennas
G9B Antennas cont’d
•
Dipole
•
The low angle azimuthal radiation pattern of an ideal halfwave dipole antenna installed ½ wavelength high and
parallel to the earth is a figure-eight at right angles to the
antenna
•
The antenna height affects the horizontal (azimuthal)
radiation pattern of a horizontal dipole HF antenna if the
antenna is less than ½ wavelength high and resulting the
azimuthal pattern is almost omnidirectional
41
Antennas
G9B Antennas cont’d
•
Dipole cont’d
•
The feed-point impedance of a ½ wave dipole antenna
steadily:
• Decreases as the antenna is lowered from ¼ wave above ground
• Increases as the feed-point location is moved from the center
toward the ends
•
An advantage of a horizontally polarized as compared to a
vertically polarized HF antenna is lower ground reflection
losses
42
Antennas
G9B Antennas cont’d
•
Dipole cont’
•
•
The approximate length for a ½ wave dipole antenna cut
for 14.250 MHz is 32.8 feet
Length ( ½ wave Dipole) = 468
= 468/14.250= 32.8 ft
fx ( MHz)
The approximate length for a ½ wave dipole antenna cut for
3.550 MHz is 131.8 feet
Length ( ½ wave Dipole ) = 468 = 468/3.550 = 131.8 ft
fx (MHz)
43
Antennas
G9B01 What is one disadvantage of a
directly fed random-wire antenna?
A. It must be longer than 1 wavelength
B. You may experience RF burns when touching metal objects
in your station
C. It produces only vertically polarized radiation
D. It is not effective on the higher HF bands
44
Antennas
G9B01 What is one disadvantage of a
directly fed random-wire antenna?
A. It must be longer than 1 wavelength
B.
You may experience RF burns when touching
metal objects in your station
C. It produces only vertically polarized radiation
D. It is not effective on the higher HF bands
45
Antennas
Vertical Antennas
(Quarter Wavelength Vertical)
Radials
Ground Plane
Ground
Marconi
Ground Plane
300
Wavelength (meters) =
F (MHz)
Quarter wavelength
Meters to inches
¼λ vertical length (inches) = Wavelength / 4 x 39
46
Antennas
Vertical Antenna
Standard ¼ wave vertical
has a feedpoint impedance
of ~35 ohms
Sloping ground radials
downward raises feedpoint
impedance
47
Antennas
G9B02 What is an advantage of downward
sloping radials on a ground-plane antenna?
A.
B.
C.
D.
They lower the radiation angle
They bring the feed-point impedance closer to 300 ohms
They increase the radiation angle
They can be adjusted to bring the feed-point impedance
closer to 50 ohms
48
Antennas
G9B02 What is an advantage of downward
sloping radials on a ground-plane antenna?
A. They lower the radiation angle
B. They bring the feed-point impedance closer to 300 ohms
C. They increase the radiation angle
D.
They can be adjusted to bring the feed-point
impedance closer to 50 ohms
49
Antennas
G9B03 What happens to the feed-point
impedance of a ground-plane antenna when
its radials are changed from horizontal to
downward-sloping?
A.
B.
C.
D.
It
It
It
It
decreases
increases
stays the same
reaches a maximum at an angle of 45 degrees
50
Antennas
G9B03 What happens to the feed-point
impedance of a ground-plane antenna when
its radials are changed from horizontal to
downward-sloping?
A. It decreases
B.
It increases
C. It stays the same
D. It reaches a maximum at an angle of 45 degrees
51
Antennas
G9B04 What is the low angle azimuthal
radiation pattern of an ideal half-wavelength
dipole antenna installed 1/2 wavelength
high and parallel to the earth?
A.
B.
C.
D.
It is a figure-eight at right angles to the antenna
It is a figure-eight off both ends of the antenna
It is a circle (equal radiation in all directions)
It has a pair of lobes on one side of the antenna and a
single lobe on the other side
52
Antennas
G9B04 What is the low angle azimuthal
radiation pattern of an ideal half-wavelength
dipole antenna installed 1/2 wavelength
high and parallel to the earth?
A.
It is a figure-eight at right angles to the
antenna
B. It is a figure-eight off both ends of the antenna
C. It is a circle (equal radiation in all directions)
D. It has a pair of lobes on one side of the antenna and a
single lobe on the other side
53
Antennas
½ λ Dipole Radiation
Radiation pattern for a
dipole placed ½ λ
above ground looking
down from above the
antenna.
Looks like a doughnut
around the wire in 3D
space.
Pattern distorts to
omnidirectional when
placed low to the ground.
54
Antennas
G9B05 How does antenna height affect the
horizontal (azimuthal) radiation pattern of a
horizontal dipole HF antenna?
A. If the antenna is too high, the pattern becomes
unpredictable
B. Antenna height has no effect on the pattern
C. If the antenna is less than 1/2 wavelength high, the
azimuthal pattern is almost omnidirectional
D. If the antenna is less than 1/2 wavelength high, radiation
off the ends of the wire is eliminated
55
Antennas
G9B05 How does antenna height affect the
horizontal (azimuthal) radiation pattern of a
horizontal dipole HF antenna?
A. If the antenna is too high, the pattern becomes
unpredictable
B. Antenna height has no effect on the pattern
C.
If the antenna is less than 1/2 wavelength high,
the azimuthal pattern is almost omnidirectional
D. If the antenna is less than 1/2 wavelength high, radiation
off the ends of the wire is eliminated
56
Antennas
G9B06 Where should the radial wires of a
ground-mounted vertical antenna system be
placed?
A.
B.
C.
D.
As high as possible above the ground
Parallel to the antenna element
On the surface or buried a few inches below the ground
At the top of the antenna
57
Antennas
G9B06 Where should the radial wires of a
ground-mounted vertical antenna system be
placed?
A. As high as possible above the ground
B. Parallel to the antenna element
C.
On the surface or buried a few inches below the
ground
D. At the top of the antenna
58
Antennas
G9B07 How does the feed-point impedance
of a 1/2 wave dipole antenna change as the
antenna is lowered from 1/4 wave above
ground?
A.
B.
C.
D.
It
It
It
It
steadily increases
steadily decreases
peaks at about 1/8 wavelength above ground
is unaffected by the height above ground
59
Antennas
G9B07 How does the feed-point impedance
of a 1/2 wave dipole antenna change as the
antenna is lowered from 1/4 wave above
ground?
A. It steadily increases
B.
It steadily decreases
C. It peaks at about 1/8 wavelength above ground
D. It is unaffected by the height above ground
60
Antennas
G9B08 How does the feed-point impedance
of a 1/2 wave dipole change as the feedpoint location is moved from the center
toward the ends?
A.
B.
C.
D.
It
It
It
It
steadily increases
steadily decreases
peaks at about 1/8 wavelength from the end
is unaffected by the location of the feed-point
61
Antennas
G9B08 How does the feed-point impedance
of a 1/2 wave dipole change as the feedpoint location is moved from the center
toward the ends?
A.
It steadily increases
B. It steadily decreases
C. It peaks at about 1/8 wavelength from the end
D. It is unaffected by the location of the feed-point
62
Antennas
G9B09 Which of the following is an
advantage of a horizontally polarized as
compared to vertically polarized HF
antenna?
A.
B.
C.
D.
Lower ground reflection losses
Lower feed-point impedance
Shorter Radials
Lower radiation resistance
63
Antennas
G9B09 Which of the following is an
advantage of a horizontally polarized as
compared to vertically polarized HF
antenna?
A.
Lower ground reflection losses
B. Lower feed-point impedance
C. Shorter Radials
D. Lower radiation resistance
64
Antennas
G9B10 What is the approximate length for a
1/2-wave dipole antenna cut for 14.250
MHz?
A.
B.
C.
D.
8.2 feet
16.4 feet
24.6 feet
32.8 feet
65
Antennas
G9B10 What is the approximate length for a
1/2-wave dipole antenna cut for 14.250
MHz?
A. 8.2 feet
B. 16.4 feet
C. 24.6 feet
D.
32.8 feet
66
Antennas
G9B11 What is the approximate length for a
1/2-wave dipole antenna cut for 3.550 MHz?
A.
B.
C.
D.
42.2 feet
84.5 feet
131.8 feet
263.6 feet
67
Antennas
G9B11 What is the approximate length for a
1/2-wave dipole antenna cut for 3.550 MHz?
A. 42.2 feet
B. 84.5 feet
C.
131.8 feet
D. 263.6 feet
68
Antennas
G9B12 What is the approximate length for a
1/4-wave vertical antenna cut for 28.5 MHz?
A.
B.
C.
D.
8.2 feet
10.5 feet
16.4 feet
21.0 feet
69
Antennas
G9B12 What is the approximate length for a
1/4-wave vertical antenna cut for 28.5 MHz?
A.
8.2 feet
B. 10.5 feet
C. 16.4 feet
D. 21.0 feet
70
Antennas
The director
acts like a
lens
Director
Boom
Feedline
Reflector
The reflector
acts like a
mirror
Driven Element
Beam Antennas
(Yagi Antenna)
71
Gain
Antennas
Yagi Radiation Pattern
The yagi antenna focuses
RF energy in one direction,
giving the appearance of
getting “free power.”
This free power or
Effective Radiated Power
(ERP) can be expressed as
antenna Gain in Decibels
(dB) over a dipole (dBd) or
isotropic resonator (dBi).
72
Antennas
G9C Directional antennas: Yagi
•
A Yagi antenna consists of a driven element and some
combination of parasitically excited reflector and/or
director elements
•
•
•
•
The director is normally the shortest parasitic element in a
three-element single-band Yagi antenna
The reflector is normally the longest parasitic element in a
Yagi antenna
The SWR bandwidth of a Yagi antenna can be
increased by using larger diameter elements
The approximate length of the driven element of a
Yagi antenna is ½ wavelength
73
Antennas
G9C Yagi cont’s
•
•
•
•
Increasing the boom length and adding directors to
a Yagi antenna will increase Gain
A Yagi is often used for on the 20 meter band
because it helps reduce interference from other stations
to the side or behind the antenna
In a Yagi antenna, “front-to-back ratio” means the
power radiated in the major radiation lobe compared to
the power radiated in exactly the opposite direction
The “main lobe” of a directive antenna is the
direction of maximum radiated field strength from the
antenna
74
Antennas
G9C Yagis cont’d
•
The approximate maximum theoretical forward
gain of a 3 element Yagi antenna is 9.7 dBi
•
All of these Yagi antenna design variables could be
adjusted to optimize forward gain, front-to-back ratio,
or SWR bandwidth:
•
•
•
The physical length of the boom
The number of element on the boom
The spacing of each element along the boom
75
Antennas
G9C Yagi cont’d
•
The purpose of a “gamma match” used with Yagi
antennas is to match the relatively low feed-point
impedance to 50 ohms
•
No insulation is needed for insulating the driven
element of a Yagi antenna from the metal boom when
using a gamma match
76
Antennas
G9C Directional antennas cont’s
•
Quad
•
•
•
•
Each side of a cubical-quad antenna driven element is
approximately ¼ wavelength long
The forward gain of a 2-element cubical–quad antenna is
about the same as the forward gain of a 3 element yagi
Each side of a cubical-quad antenna reflector element is
slightly more than ¼ wavelength
A cubial quad antenna is a directional antenna and is
typically constructed from 2 square loops of wire each
having a circumference of approximately one wavelength
at the operating frequency a separated by approximately
0.2 wavelength
77
Antennas
G9C Quads cont’d
*When the feed-point of a cubical quad antenna is
changed from the center of the lowest horizontal wire to
the center of one of the vertical wires, the polarization of
the radiated signal changes from horizontal to vertical
* In order for the cubical-quad antenna to operate as
a beam antenna, one of the elements is used as a reflector
and the reflector element must be approximately 5 per
cent longer than the driven element
78
Antennas
G9C Directional antennas cont’d
•
Delta-loop
•
The gain of a two element delta-loop beam is about the
same as the gain of a two element cubical quad antenna
•
Each leg of a symmetrical delta-loop antenna Driven
element is approximately 1/3 wavelengths long
79
Antennas
G9C01 How can the SWR bandwidth of a
Yagi antenna be increased?
A.
B.
C.
D.
Use
Use
Use
Use
larger diameter elements
closer element spacing
traps on the elements
tapered-diameter elements
80
Antennas
G9C01 How can the SWR bandwidth of a
Yagi antenna be increased?
A.
Use larger diameter elements
B. Use closer element spacing
C. Use traps on the elements
D. Use tapered-diameter elements
81
Antennas
G9C02 What is the approximate length of
the driven element of a Yagi antenna?
A.
B.
C.
D.
1/4 wavelength
1/2 wavelength
3/4 wavelength
1 wavelength
82
Antennas
G9C02 What is the approximate length of
the driven element of a Yagi antenna?
A. 1/4 wavelength
B.
1/2 wavelength
C. 3/4 wavelength
D. 1 wavelength
83
Antennas
G9C03 Which statement about a threeelement single-band Yagi antenna is true?
A.
B.
C.
D.
The reflector is normally the shortest parasitic element
The director is normally the shortest parasitic element
The driven element is the longest parasitic element
Low feed-point impedance increases bandwidth
84
Antennas
G9C03 Which statement about a threeelement single-band Yagi antenna is true?
A. The reflector is normally the shortest parasitic element
B.
The director is normally the shortest parasitic
element
C. The driven element is the longest parasitic element
D. Low feed-point impedance increases bandwidth
85
Antennas
G9C04 Which statement about a Yagi
antenna is true?
A.
B.
C.
D.
The reflector is normally the longest parasitic element
The director is normally the longest parasitic element
The reflector is normally the shortest parasitic element
All of the elements must be the same length
86
Antennas
G9C04 Which statement about a Yagi
antenna is true?
A.
The reflector is normally the longest parasitic
element
B. The director is normally the longest parasitic element
C. The reflector is normally the shortest parasitic element
D. All of the elements must be the same length
87
Antennas
G9C05 What is one effect of increasing the
boom length and adding directors to a Yagi
antenna?
A.
B.
C.
D.
Gain increases
SWR increases
Weight decreases
Wind load decreases
88
Antennas
G9C05 What is one effect of increasing the
boom length and adding directors to a Yagi
antenna?
A.
Gain increases
B. SWR increases
C. Weight decreases
D. Wind load decreases
89
Antennas
G9C06 Which of the following is a reason
why a Yagi antenna is often used for radio
communications on the 20 meter band?
A. It provides excellent omnidirectional coverage in the
horizontal plane
B. It is smaller, less expensive and easier to erect than a
dipole or vertical antenna
C. It helps reduce interference from other stations to the side
or behind the antenna
D. It provides the highest possible angle of radiation for the
HF bands
90
Antennas
G9C06 Which of the following is a reason
why a Yagi antenna is often used for radio
communications on the 20 meter band?
A. It provides excellent omnidirectional coverage in the
horizontal plane
B. It is smaller, less expensive and easier to erect than a
dipole or vertical antenna
C.
It helps reduce interference from other stations
to the side or behind the antenna
D. It provides the highest possible angle of radiation for the
HF bands
91
Antennas
G9C07 What does "front-to-back ratio" mean
in reference to a Yagi antenna?
A. The number of directors versus the number of reflectors
B. The relative position of the driven element with respect to
the reflectors and directors
C. The power radiated in the major radiation lobe compared
to the power radiated in exactly the opposite direction
D. The ratio of forward gain to dipole gain
92
Antennas
G9C07 What does "front-to-back ratio" mean
in reference to a Yagi antenna?
A. The number of directors versus the number of reflectors
B. The relative position of the driven element with respect to
the reflectors and directors
C.
The power radiated in the major radiation lobe
compared to the power radiated in exactly the
opposite direction
D. The ratio of forward gain to dipole gain
93
Antennas
G9C08 What is meant by the "main lobe" of
a directive antenna?
A. The magnitude of the maximum vertical angle of radiation
B. The point of maximum current in a radiating antenna
element
C. The maximum voltage standing wave point on a radiating
element
D. The direction of maximum radiated field strength from the
antenna
94
Antennas
G9C08 What is meant by the "main lobe" of
a directive antenna?
A. The magnitude of the maximum vertical angle of radiation
B. The point of maximum current in a radiating antenna
element
C. The maximum voltage standing wave point on a radiating
element
D.
The direction of maximum radiated field
strength from the antenna
95
Antennas
G9C09 What is the approximate maximum
theoretical forward gain of a 3 Element Yagi
antenna?
A.
B.
C.
D.
9.7 dBi
7.3 dBd
5.4 times the gain of a dipole
All of these choices are correct
96
Antennas
G9C09 What is the approximate maximum
theoretical forward gain of a 3 Element Yagi
antenna?
A.
9.7 dBi
B. 7.3 dBd
C. 5.4 times the gain of a dipole
D. All of these choices are correct
97
Antennas
G9C10 Which of the following is a Yagi
antenna design variable that could be
adjusted to optimize forward gain, front-toback ratio, or SWR bandwidth?
A.
B.
C.
D.
The physical length of the boom
The number of elements on the boom
The spacing of each element along the boom
All of these choices are correct
98
Antennas
G9C10 Which of the following is a Yagi
antenna design variable that could be
adjusted to optimize forward gain, front-toback ratio, or SWR bandwidth?
A. The physical length of the boom
B. The number of elements on the boom
C. The spacing of each element along the boom
D.
All of these choices are correct
99
Antennas
G9C11 What is the purpose of a "gamma
match" used with Yagi antennas?
A. To match the relatively low feed-point impedance to 50
ohms
B. To match the relatively high feed-point impedance to 50
ohms
C. To increase the front to back ratio
D. To increase the main lobe gain
100
Antennas
G9C11 What is the purpose of a "gamma
match" used with Yagi antennas?
A.
To match the relatively low feed-point
impedance to 50 ohms
B. To match the relatively high feed-point impedance to 50
ohms
C. To increase the front to back ratio
D. To increase the main lobe gain
101
Antennas
G9C12 Which of the following describes a
common method for insulating the driven
element of a Yagi antenna from the metal
boom when using a gamma match?
A. Support the driven element with ceramic standoff
insulators
B. Insert a high impedance transformer at the driven element
C. Insert a high voltage balun at the driven element
D. None of these answers are correct. No insulation is needed
102
Antennas
G9C12 Which of the following describes a
common method for insulating the driven
element of a Yagi antenna from the metal
boom when using a gamma match?
A. Support the driven element with ceramic standoff
insulators
B. Insert a high impedance transformer at the driven element
C. Insert a high voltage balun at the driven element
D.
None of these answers are correct. No
insulation is needed
103
Antennas
Quad antenna
104
Antennas
G9C13 Approximately how long is each side
of a cubical-quad antenna driven element?
A.
B.
C.
D.
1/4 wavelength
1/2 wavelength
3/4 wavelength
1 wavelength
105
Antennas
G9C13 Approximately how long is each side
of a cubical-quad antenna driven element?
A.
1/4 wavelength
B. 1/2 wavelength
C. 3/4 wavelength
D. 1 wavelength
106
Antennas
G9C14 How does the forward gain of a 2element cubical-quad antenna compare to
the forward gain of a 3 element Yagi
antenna?
A.
B.
C.
D.
2/3
About the same
3/2
Twice
107
Antennas
G9C14 How does the forward gain of a 2element cubical-quad antenna compare to
the forward gain of a 3 element Yagi
antenna?
A. 2/3
B.
About the same
C. 3/2
D. Twice
108
Antennas
G9C15 Approximately how long is each side
of a cubical-quad antenna reflector element?
A.
B.
C.
D.
Slightly
Slightly
Slightly
Slightly
less than 1/4 wavelength
more than 1/4 wavelength
less than 1/2 wavelength
more than 1/2 wavelength
109
Antennas
G9C15 Approximately how long is each side
of a cubical-quad antenna reflector element?
A. Slightly less than 1/4 wavelength
B.
Slightly more than 1/4 wavelength
C. Slightly less than 1/2 wavelength
D. Slightly more than 1/2 wavelength
110
Antennas
Delta Loop
111
Antennas
G9C16 How does the gain of a two element
delta-loop beam compare to the gain of a
two element cubical quad antenna?
A.
B.
C.
D.
3 dB higher
3 dB lower
2.54 dB higher
About the same
112
Antennas
G9C16 How does the gain of a two element
delta-loop beam compare to the gain of a
two element cubical quad antenna?
A. 3 dB higher
B. 3 dB lower
C. 2.54 dB higher
D.
About the same
113
Antennas
G9C17 Approximately how long is each leg
of a symmetrical delta-loop antenna Driven
element?
A.
B.
C.
D.
1/4
1/3
1/2
2/3
wavelengths
wavelengths
wavelengths
wavelengths
114
Antennas
G9C17 Approximately how long is each leg
of a symmetrical delta-loop antenna Driven
element?
A. 1/4 wavelengths
B.
1/3 wavelengths
C. 1/2 wavelengths
D. 2/3 wavelengths
115
Antennas
G9C18 Which of the following antenna types
consists of a driven element and some
combination of parasitically excited reflector
and/or director elements?
A.
B.
C.
D.
A
A
A
A
collinear array
rhombic antenna
double-extended Zepp antenna
Yagi antenna
116
Antennas
G9C18 Which of the following antenna types
consists of a driven element and some
combination of parasitically excited reflector
and/or director elements?
A. A collinear array
B. A rhombic antenna
C. A double-extended Zepp antenna
D.
A Yagi antenna
117
Antennas
G9C19 What type of directional antenna is
typically constructed from 2 square loops of
wire each having a circumference of
approximately one wavelength at the
operating frequency and separated by
approximately 0.2 wavelength?
A.
B.
C.
D.
A stacked dipole array
A collinear array
A cubical quad antenna
An Adcock array
118
Antennas
G9C19 What type of directional antenna is
typically constructed from 2 square loops of
wire each having a circumference of
approximately one wavelength at the
operating frequency and separated by
approximately 0.2 wavelength?
A. A stacked dipole array
B. A collinear array
C.
A cubical quad antenna
D. An Adcock array
119
Antennas
G9C20 What happens when the feed-point of
a cubical quad antenna is changed from the
center of the lowest horizontal wire to the
center of one of the vertical wires?
A. The polarization of the radiated signal changes from
horizontal to vertical
B. The polarization of the radiated signal changes from
vertical to horizontal
C. The direction of the main lobe is reversed
D. The radiated signal changes to an omnidirectional pattern
120
Antennas
G9C20 What happens when the feed-point of
a cubical quad antenna is changed from the
center of the lowest horizontal wire to the
center of one of the vertical wires?
A.
The polarization of the radiated signal changes
from horizontal to vertical
B. The polarization of the radiated signal changes from
vertical to horizontal
C. The direction of the main lobe is reversed
D. The radiated signal changes to an omnidirectional pattern
121
Antennas
G9C21 What configuration of the loops of a
cubical-quad antenna must be used for the
antenna to operate as a beam antenna,
assuming one of the elements is used as a
reflector?
A. The driven element must be fed with a balun transformer
B. The driven element must be open-circuited on the side
opposite the feed-point
C. The reflector element must be approximately 5% shorter
than the driven element
D. The reflector element must be approximately 5% longer
than the driven element
122
Antennas
G9C21 What configuration of the loops of a
cubical-quad antenna must be used for the
antenna to operate as a beam antenna,
assuming one of the elements is used as a
reflector?
A. The driven element must be fed with a balun transformer
B. The driven element must be open-circuited on the side
opposite the feed-point
C. The reflector element must be approximately 5% shorter
than the driven element
D.
The reflector element must be approximately
5% longer than the driven element
123
Antennas
G9D Specialized antennas
•
Near Vertical Incidence Skywave (NVIS)
•
•
•
An advantage of a NVIS antenna is the high vertical angle
radiation for short skip during the day
A NVIS antenna is typically installed at a height between
1/10 ¼ wavelength above ground
Horizontally Polarized Yagi
•
•
The gain of a two 3-element horizontally polarized Yagi
antennas spaced vertically ½ wavelength apart from each
other typically is approximately 3 dB higher than the gain
of a single 3-element Yagi
The advantage of vertical stacking of horizontally polarized
Yagi antennas is it narrows the main lobe in elevation
124
Antennas
G9D Specialized antennas cont’d
•
Log Periodic Antenna
•
•
•
An advantage of a log periodic antenna is wide band width
A log periodic antenna is described by the length and
spacing of elements increases logarithmically from one end
of the boom to the other
Beverage Antenna
•
•
•
Generally is not used for transmitting because it has high
losses compared to other types of antennas
One application for a beverage antenna is directional
receiving for low HF bands
It is a very long and low receiving antenna that is highly
directional
125
Antennas
G9D Specialized antennas cont’d
•
Multi-band Antenna
•
•
A disadvantage of multiband antennas is poor harmonic
rejection
The primary purpose of traps installed in antennas is to
permit multiband operation
126
Antennas
G9D01 What does the term "NVIS" mean as
related to antennas?
A.
B.
C.
D.
Nearly Vertical Inductance System
Non-Visible Installation Specification
Non-Varying Impedance Smoothing
Near Vertical Incidence Skywave
127
Antennas
G9D01 What does the term "NVIS" mean as
related to antennas?
A. Nearly Vertical Inductance System
B. Non-Visible Installation Specification
C. Non-Varying Impedance Smoothing
D.
Near Vertical Incidence Skywave
128
Antennas
G9D02 Which of the following is an
advantage of an NVIS antenna?
A.
B.
C.
D.
Low vertical angle radiation for DX work
High vertical angle radiation for short skip during the day
High forward gain
All of these choices are correct
129
Antennas
G9D02 Which of the following is an
advantage of an NVIS antenna?
A. Low vertical angle radiation for DX work
B.
High vertical angle radiation for short skip
during the day
C. High forward gain
D. All of these choices are correct
130
Antennas
G9D03 At what height above ground is an
NVIS antenna typically installed?
A. As close to one-half wave as possible
B. As close to one wavelength as possible
C. Height is not critical as long as significantly more than 1/2
wavelength
D. Between 1/10 and 1/4 wavelength
131
Antennas
G9D03 At what height above ground is an
NVIS antenna typically installed?
A. As close to one-half wave as possible
B. As close to one wavelength as possible
C. Height is not critical as long as significantly more than 1/2
wavelength
D.
Between 1/10 and 1/4 wavelength
132
Antennas
G9D04 How does the gain of two 3-element
horizontally polarized Yagi antennas spaced
vertically 1/2 wave apart from each other
typically compare to the gain of a single 3element Yagi?
A.
B.
C.
D.
Approximately 1.5 dB higher
Approximately 3 dB higher
Approximately 6 dB higher
Approximately 9 dB higher
133
Antennas
G9D04 How does the gain of two 3-element
horizontally polarized Yagi antennas spaced
vertically 1/2 wave apart from each other
typically compare to the gain of a single 3element Yagi?
A. Approximately 1.5 dB higher
B.
Approximately 3 dB higher
C. Approximately 6 dB higher
D. Approximately 9 dB higher
134
Antennas
G9D05 What is the advantage of vertical
stacking of horizontally polarized Yagi
antennas?
A.
B.
C.
D.
Allows quick selection of vertical or horizontal polarization
Allows simultaneous vertical and horizontal polarization
Narrows the main lobe in azimuth
Narrows the main lobe in elevation
135
Antennas
G9D05 What is the advantage of vertical
stacking of horizontally polarized Yagi
antennas?
A. Allows quick selection of vertical or horizontal polarization
B. Allows simultaneous vertical and horizontal polarization
C. Narrows the main lobe in azimuth
D.
Narrows the main lobe in elevation
136
Antennas
G9D06 Which of the following is an
advantage of a log periodic antenna?
A.
B.
C.
D.
Wide bandwidth
Higher gain per element than a Yagi antenna
Harmonic suppression
Polarization diversity
137
Antennas
G9D06 Which of the following is an
advantage of a log periodic antenna?
A.
Wide bandwidth
B. Higher gain per element than a Yagi antenna
C. Harmonic suppression
D. Polarization diversity
138
Antennas
G9D07 Which of the following describes a
log periodic antenna?
A. Length and spacing of the elements increases
logarithmically from one end of the boom to the other
B. Impedance varies periodically as a function of frequency
C. Gain varies logarithmically as a function of frequency
D. SWR varies periodically as a function of boom length
139
Antennas
G9D07 Which of the following describes a
log periodic antenna?
A.
Length and spacing of the elements increases
logarithmically from one end of the boom to the other
B. Impedance varies periodically as a function of frequency
C. Gain varies logarithmically as a function of frequency
D. SWR varies periodically as a function of boom length
140
Antennas
G9D08 Why is a Beverage antenna generally
not used for transmitting?
A.
B.
C.
D.
Its impedance is too low for effective matching
It has high losses compared to other types of antennas
It has poor directivity
All of these choices are correct
141
Antennas
G9D08 Why is a Beverage antenna generally
not used for transmitting?
A. Its impedance is too low for effective matching
B.
It has high losses compared to other types of
antennas
C. It has poor directivity
D. All of these choices are correct
142
Antennas
G9D09 Which of the following is an
application for a Beverage antenna?
A.
B.
C.
D.
Directional transmitting for low HF bands
Directional receiving for low HF bands
Portable Direction finding at higher HF frequencies
Portable Direction finding at lower HF frequencies
143
Antennas
G9D09 Which of the following is an
application for a Beverage antenna?
A. Directional transmitting for low HF bands
B.
Directional receiving for low HF bands
C. Portable Direction finding at higher HF frequencies
D. Portable Direction finding at lower HF frequencies
144
Antennas
G9D10 Which of the following describes a
Beverage antenna?
A.
B.
C.
D.
A vertical antenna constructed from beverage cans
A broad-band mobile antenna
A helical antenna for space reception
A very long and low receiving antenna that is highly
directional
145
Antennas
G9D10 Which of the following describes a
Beverage antenna?
A. A vertical antenna constructed from beverage cans
B. A broad-band mobile antenna
C. A helical antenna for space reception
D.
A very long and low receiving antenna that is
highly directional
146
Antennas
G9D11 Which of the following is a
disadvantage of multiband antennas?
A.
B.
C.
D.
They
They
They
They
present low impedance on all design frequencies
must be used with an antenna tuner
must be fed with open wire line
have poor harmonic rejection
147
Antennas
G9D11 Which of the following is a
disadvantage of multiband antennas?
A. They present low impedance on all design frequencies
B. They must be used with an antenna tuner
C. They must be fed with open wire line
D.
They have poor harmonic rejection
148
Antennas
G9D12 What is the primary purpose of traps
installed in antennas?
A.
B.
C.
D.
To
To
To
To
permit multiband operation
notch spurious frequencies
provide balanced feed-point impedance
prevent out of band operation
149
Antennas
G9D12 What is the primary purpose of traps
installed in antennas?
A.
To permit multiband operation
B. To notch spurious frequencies
C. To provide balanced feed-point impedance
D. To prevent out of band operation
150
Antennas
G9 - ANTENNAS
[4 exam questions - 4 groups]
151
Antennas