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ELE4AI
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1992-01-26
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FCC ADVANCED Exam Question Pool. Subelement 4AI.
Antennas and Feedlines. 5 Questions.
---------------------------------------------------
4AI 1.1 A
What is meant by the term antenna gain?
A. The numerical ratio relating the radiated signal strength of an antenna
to that of another antenna
B. The ratio of the signal in the forward direction to the signal in the
back direction
C. The ratio of the amount of power produced by the antenna compared to the
output power of the transmitter
D. The final amplifier gain minus the transmission line losses (including
any phasing lines present)
4AI 1.2 B
What is the term for a numerical ratio which relates the performance of one
antenna to that of another real or theoretical antenna?
A. Effective radiated power
B. Antenna gain
C. Conversion gain
D. Peak effective power
4AI 1.3 B
What is meant by the term antenna bandwidth?
A. Antenna length divided by the number of elements
B. The frequency range over which an antenna can be expected to perform well
C. The angle between the half-power radiation points
D. The angle formed between two imaginary lines drawn through the ends of
the elements
4AI 1.4 A
How can the approximate beamwidth of a rotatable beam antenna be determined?
A. Note the two points where the signal strength of the antenna is down 3 dB
from the maximum signal point and compute the angular difference
B. Measure the ratio of the signal strengths of the radiated power lobes
from the front and rear of the antenna
C. Draw two imaginary lines through the ends of the elements and measure the
angle between the lines
D. Measure the ratio of the signal strengths of the radiated power lobes
from the front and side of the antenna
4AI 2.1 C
What is a trap antenna?
A. An antenna for rejecting interfering signals
B. A highly sensitive antenna with maximum gain in all directions
C. An antenna capable of being used on more than one band because of the
presence of parallel LC networks
D. An antenna with a large capture area
4AI 2.2 D
What is an advantage of using a trap antenna?
A. It has high directivity in the high-frequency amateur bands
B. It has high gain
C. It minimizes harmonic radiation
D. It may be used for multiband operation
4AI 2.3 A
What is a disadvantage of using a trap antenna?
A. It will radiate harmonics
B. It can only be used for single band operation
C. It is too sharply directional at the lower amateur frequencies
D. It must be neutralized
4AI 2.4 B
What is the principle of a trap antenna?
A. Beamwidth may be controlled by non-linear impedances
B. The traps form a high impedance to isolate parts of the antenna
C. The effective radiated power can be increased if the space around the
antenna "sees" a high impedance
D. The traps increase the antenna gain
4AI 3.1 C
What is a parasitic element of an antenna?
A. An element polarized 90 degrees opposite the driven element
B. An element dependent on the antenna structure for support
C. An element that receives its excitation from mutual coupling rather than
from a transmission line
D. A transmission line that radiates radio-frequency energy
4AI 3.2 D
How does a parasitic element generate an electromagnetic field?
A. By the RF current received from a connected transmission line
B. By interacting with the earth's magnetic field
C. By altering the phase of the current on the driven element
D. By currents induced into the element from a surrounding electric field
4AI 3.3 A
How does the length of the reflector element of a parasitic element beam
antenna compare with that of the driven element?
A. It is about 5% longer
B. It is about 5% shorter
C. It is twice as long
D. It is one-half as long
4AI 3.4 B
How does the length of the director element of a parasitic element beam
antenna compare with that of the driven element?
A. It is about 5% longer
B. It is about 5% shorter
C. It is one-half as long
D. It is twice as long
4AI 4.1 C
What is meant by the term radiation resistance for an antenna?
A. Losses in the antenna elements and feed line
B. The specific impedance of the antenna
C. An equivalent resistance that would dissipate the same amount of power as
that radiated from an antenna
D. The resistance in the trap coils to received signals
4AI 4.2 D
What is the term used for an equivalent resistance which would dissipate the
same amount of energy as that radiated from an antenna?
A. Space resistance
B. Loss resistance
C. Transmission line loss
D. Radiation resistance
4AI 4.3 A
Why is the value of the radiation resistance of an antenna important?
A. Knowing the radiation resistance makes it possible to match impedances
for maximum power transfer
B. Knowing the radiation resistance makes it possible to measure the near-
field radiation density from a transmitting antenna
C. The value of the radiation resistance represents the front-to-side ratio
of the antenna
D. The value of the radiation resistance represents the front-to-back ratio
of the antenna
4AI 4.4 B
What are the factors that determine the radiation resistance of an antenna?
A. Transmission line length and height of antenna
B. The location of the antenna with respect to nearby objects and the
length/diameter ratio of the conductors
C. It is a constant for all antennas since it is a physical constant
D. Sunspot activity and the time of day
4AI 5.1 C
What is a driven element of an antenna?
A. Always the rearmost element
B. Always the forwardmost element
C. The element fed by the transmission line
D. The element connected to the rotator
4AI 5.2 B
What is the usual electrical length of a driven element in an HF beam
antenna?
A. 1/4 wavelength
B. 1/2 wavelength
C. 3/4 wavelength
D. 1 wavelength
4AI 5.3 A
What is the term for an antenna element which is supplied power from a
transmitter through a transmission line?
A. Driven element
B. Director element
C. Reflector element
D. Parasitic element
4AI 6.1 B
What is meant by the term antenna efficiency?
A. Efficiency = ( radiation resistance / transmission resistance ) X 100%
B. Efficiency = ( radiation resistance / total resistance ) X 100%
C. Efficiency = ( total resistance / radiation resistance ) X 100%
D. Efficiency = ( effective radiated power / transmitter output ) X 100%
4AI 6.2 C
What is the term for the ratio of the radiation resistance of an antenna to
the total resistance of the system?
A. Effective radiated power
B. Radiation conversion loss
C. Antenna efficiency
D. Beamwidth
4AI 6.3 D
What is included in the total resistance of an antenna system?
A. Radiation resistance plus space impedance
B. Radiation resistance plus transmission resistance
C. Transmission line resistance plus radiation resistance
D. Radiation resistance plus ohmic resistance
4AI 6.4 A
How can the antenna efficiency of an HF grounded vertical antenna be made
comparable to that of a half-wave antenna?
A. By installing a good ground radial system
B. By isolating the coax shield from ground
C. By shortening the vertical
D. By lengthening the vertical
4AI 6.5 B
Why does a half-wave antenna operate at very high efficiency?
A. Because it is non-resonant
B. Because the conductor resistance is low compared to the radiation
resistance
C. Because earth-induced currents add to its radiated power
D. Because it has less corona from the element ends than other types of
antennas
4AI 7.1 C
What is a folded dipole antenna?
A. A dipole that is one-quarter wavelength long
B. A ground plane antenna
C. A dipole whose ends are connected by another one-half wavelength piece of
wire
D. A fictional antenna used in theoretical discussions to replace the
radiation resistance
4AI 7.2 D
How does the bandwidth of a folded dipole antenna compare with that of a
simple dipole antenna?
A. It is 0.707 times the simple dipole bandwidth
B. It is essentially the same
C. It is less than 50% that of a simple dipole
D. It is greater
4AI 7.3 A
What is the input terminal impedance at the center of a folded dipole
antenna?
A. 300 ohms
B. 72 ohms
C. 50 ohms
D. 450 ohms
4AI 8.1 D
What is the meaning of the term velocity factor of a transmission line?
A. The ratio of the characteristic impedance of the line to the terminating
impedance
B. The index of shielding for coaxial cable
C. The velocity of the wave on the transmission line multiplied by the
velocity of light in a vacuum
D. The velocity of the wave on the transmission line divided by the velocity
of light in a vacuum
4AI 8.2 A
What is the term for the ratio of actual velocity at which a signal travels
through a line to the speed of light in a vacuum?
A. Velocity factor
B. Characteristic impedance
C. Surge impedance
D. Standing wave ratio
4AI 8.3 B
What is the velocity factor for a typical coaxial cable?
A. 2.70
B. 0.66
C. 0.30
D. 0.10
4AI 8.4 C
What determines the velocity factor in a transmission line?
A. The termination impedance
B. The line length
C. Dielectrics in the line
D. The center conductor resistivity
4AI 8.5 B
Why is the physical length of a coaxial cable transmission line shorter than
its electrical length?
A. Skin effect is less pronounced in the coaxial cable
B. RF energy moves slower along the coaxial cable
C. The surge impedance is higher in the parallel feed line
D. The characteristic impedance is higher in the parallel feed line
4AI 9.1 B
What would be the physical length of a typical coaxial transmission line
which is electrically one-quarter wavelength long at 14.1 MHz?
A. 20 meters
B. 3.51 meters
C. 2.33 meters
D. 0.25 meters
4AI 9.2 B
What would be the physical length of a typical coaxial transmission line
which is electrically one-quarter wavelength long at 7.2 MHz?
A. 10.5 meters
B. 6.88 meters
C. 24 meters
D. 50 meters
4AI 9.3 C
What is the physical length of a parallel antenna feedline which is
electrically one-half wavelength long at 14.10 MHz? (assume a velocity
factor of 0.82.)
A. 15 meters
B. 24.3 meters
C. 8.7 meters
D. 70.8 meters
4AI 9.4 A
What is the physical length of a twin lead transmission feedline at 3.65
MHz? (assume a velocity factor of 0.80.)
A. Electrical length times 0.8
B. Electrical length divided by 0.8
C. 80 meters
D. 160 meters
4AI 10.1 A
In a half-wave antenna, where are the current nodes?
A. At the ends
B. At the center
C. Three-quarters of the way from the feed point toward the end
D. One-half of the way from the feed point toward the end
4AI 10.2 B
In a half-wave antenna, where are the voltage nodes?
A. At the ends
B. At the feed point
C. Three-quarters of the way from the feed point toward the end
D. One-half of the way from the feed point toward the end
4AI 10.3 C
At the ends of a half-wave antenna, what values of current and voltage exist
compared to the remainder of the antenna?
A. Equal voltage and current
B. Minimum voltage and maximum current
C. Maximum voltage and minimum current
D. Minimum voltage and minimum current
4AI 10.4 D
At the center of a half-wave antenna, what values of voltage and current
exist compared to the remainder of the antenna?
A. Equal voltage and current
B. Maximum voltage and minimum current
C. Minimum voltage and minimum current
D. Minimum voltage and maximum current
4AI 11.1 A
Why is the inductance required for a base loaded HF mobile antenna less than
that for an inductance placed further up the whip?
A. The capacitance to ground is less farther away from the base
B. The capacitance to ground is greater farther away from the base
C. The current is greater at the top
D. The voltage is less at the top
4AI 11.2 B
What happens to the base feed point of a fixed length HF mobile antenna as
the frequency of operation is lowered?
A. The resistance decreases and the capacitive reactance decreases
B. The resistance decreases and the capacitive reactance increases
C. The resistance increases and the capacitive reactance decreases
D. The resistance increases and the capacitive reactance increases
4AI 11.3 C
Why should an HF mobile antenna loading coil have a high ratio of reactance
to resistance?
A. To swamp out harmonics
B. To maximize losses
C. To minimize losses
D. To minimize the Q
4AI 11.4 D
Why is a loading coil often used with an HF mobile antenna?
A. To improve reception
B. To lower the losses
C. To lower the Q
D. To tune out the capacitive reactance
4AI 12.1 A
For a shortened vertical antenna, where should a loading coil be placed to
minimize losses and produce the most effective performance?
A. Near the center of the vertical radiator
B. As low as possible on the vertical radiator
C. As close to the transmitter as possible
D. At a voltage node
4AI 12.2 B
What happens to the bandwidth of an antenna as it is shortened through the
use of loading coils?
A. It is increased
B. It is decreased
C. No change occurs
D. It becomes flat
4AI 12.3 C
Why are self-resonant antennas popular in amateur stations?
A. They are very broad banded
B. They have high gain in all azimuthal directions
C. They are the most efficient radiators
D. They require no calculations
4AI 12.4 D
What is an advantage of using top loading in a shortened HF vertical
antenna?
A. Lower Q
B. Greater structural strength
C. Higher losses
D. Improved radiation efficiency
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End of Subelement 4AI.