SUBELEMENT E9 -- ANTENNAS AND FEED LINES
[5 Exam Questions -- 5 Groups]
E9A Isotropic radiators: definition;
used as a standard for
comparison; radiation pattern; basic antenna parameters: radiation
resistance and reactance (including wire dipole, folded dipole), gain,
beamwidth, efficiency
E9A01
(C)
Which
of the following describes an isotropic radiator?
A. A grounded radiator used to measure earth
conductivity
B. A horizontal radiator used to compare Yagi
antennas
C. A theoretical radiator
used to compare other antennas
D. A spacecraft radiator used to direct signals
toward the earth
E9A02
(A)
When is
it useful to refer to an isotropic radiator?
A. When comparing the gains
of directional antennas
B. When testing a transmission line for
standing-wave ratio
C. When directing a transmission toward the
tropical latitudes
D. When using a dummy load to tune a
transmitter
E9A03
(B)
How
much gain does a 1/2-wavelength dipole have over an isotropic radiator?
A. About 1.5 dB
B. About 2.1 dB
C. About 3.0 dB
D. About 6.0 dB
E9A04
(D)
Which
of the following antennas has no gain in any direction?
A. Quarter-wave vertical
B. Yagi
C. Half-wave dipole
D. Isotropic radiator
E9A05
(C)
Which
of the following describes the radiation pattern of an isotropic radiator?
A. A tear drop in the vertical plane
B. A circle in the horizontal plane
C. A sphere with the antenna
in the center
D. Crossed polarized with a spiral shape
E9A06
(A)
Why
would one need to know the radiation resistance of an antenna?
A. To match impedances for
maximum power transfer
B. To measure the near-field radiation density
from a transmitting antenna
C. To calculate the front-to-side ratio of the
antenna
D. To calculate the front-to-back ratio of the
antenna
E9A07
(B)
What
factors determine the radiation resistance of an antenna?
A. Transmission-line length and antenna height
B. Antenna location with
respect to nearby objects and the conductors' length/diameter ratio
C. It is a physical constant and is the same
for all antennas
D. Sunspot activity and time of day
E9A08
(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
E9A09
(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
E9A10
(C)
What is
a folded dipole antenna?
A. A dipole one-quarter wavelength long
B. A type of ground-plane antenna
C. A dipole whose ends are
connected by a one-half wavelength piece of wire
D. A hypothetical antenna used in theoretical
discussions to replace the radiation resistance
E9A11
(A)
What is
meant by antenna gain?
A. The numerical ratio
relating the radiated signal strength of an antenna to that of another antenna
B. The numerical ratio of the signal in the
forward direction to the signal in the back direction
C. The numerical ratio of the amount of power
radiated by an antenna compared to the transmitter output power
D. The final amplifier gain minus the
transmission-line losses (including any phasing lines present)
E9A12
(B)
What is
meant by 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
E9A13
(A)
How can
the approximate beamwidth of a 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
E9A14
(B)
How is
antenna efficiency calculated?
A. (radiation resistance / transmission
resistance) x 100%
B. (radiation resistance /
total resistance) x 100%
C. (total resistance / radiation resistance) x
100%
D. (effective radiated power / transmitter
output) x 100%
E9A15
(A)
How can
the efficiency of an HF grounded vertical antenna be made comparable to that of
a half-wave dipole 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