SUBELEMENT G9 – ANTENNAS AND FEEDLINES [4 exam questions – 4 groups]
G9A - Antenna
feedlines: characteristic impedance, and attenuation; SWR calculation,
measurement and effects; matching networks
G9A01 (A)
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
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G9A02 (B)
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
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G9A03 (D)
What is the characteristic impedance of flat ribbon TV type twin lead?
A. 50 ohms
B. 75 ohms
C. 100 ohms
D. 300 ohms
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G9A04 (C)
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
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G9A05 (D)
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
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G9A06 (C)
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
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G9A07 (B)
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
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G9A08 (D)
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
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G9A09 (A)
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
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G9A10 (D)
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
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G9A11 (B)
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
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G9A12 (A)
What would be the SWR if you feed a vertical antenna that has a 25-ohm feed-point
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
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G9A13 (C)
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
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G9A14 (B)
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
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G9B - Basic antennas
G9B01 (B)
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
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G9B02 (D)
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
~~
G9B03 (B)
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
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G9B04 (A)
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
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G9B05 (C)
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
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G9B06 (C)
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
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G9B07 (B)
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
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G9B08 (A)
How does the feed-point impedance of a 1/2 wave dipole change as the feed-point
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
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G9B09 (A)
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
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G9B10 (D)
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
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G9B11 (C)
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
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G9B12 (A)
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
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G9C - Directional antennas
G9C01 (A)
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
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G9C02 (B)
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
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G9C03 (B)
Which statement about a three-element 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
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G9C04 (A)
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
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G9C05 (A)
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
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G9C06 (C)
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
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G9C07 (C)
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
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G9C08 (D)
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
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G9C09 (A)
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
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G9C10 (D)
Which of the following is a Yagi antenna design variable that could be adjusted
to optimize forward gain, front-to-back 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
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G9C11 (A)
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
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G9C12 (D)
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
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G9C13 (A)
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
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G9C14 (B)
How does the forward gain of a 2-element 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
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G9C15 (B)
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
~~
G9C16 (D)
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
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G9C17 (B)
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
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G9C18 (D)
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
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G9C19 (C)
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
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G9C20 (A)
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
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G9C21 (D)
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
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G9D - Specialized antennas
G9D01 (D)
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
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G9D02 (B)
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
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G9D03 (D)
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
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G9D04 (B)
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 3-element Yagi?
A. Approximately 1.5 dB higher
B. Approximately 3 dB higher
C. Approximately 6 dB higher
D. Approximately 9 dB higher
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G9D05 (D)
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
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G9D06 (A)
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
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G9D07 (A)
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
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G9D08 (B)
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
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G9D09 (B)
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
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G9D10 (D)
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
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G9D11 (D)
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
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G9D12 (A)
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
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