G9B: Basic antennas
G9B01:
What is one disadvantage of a directly fed random-wire antenna?
You may experience RF burns when touching metal objects in your station
It must be longer than 1 wavelength
It produces only vertically polarized radiation
It is not effective on the higher HF bands
G9B02:
What is an advantage of downward sloping radials on a ground-plane antenna?
They can be adjusted to bring the feed-point impedance closer to 50 ohms
They lower the radiation angle
They bring the feed-point impedance closer to 300 ohms
They increase the radiation angle
G9B03:
What happens to the feed-point impedance of a ground-plane antenna when its radials are changed from horizontal to downward-sloping?
It increases
It decreases
It stays the same
It reaches a maximum at an angle of 45 degrees
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?
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
G9B05:
How does antenna height affect the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna?
If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional
If the antenna is too high, the pattern becomes unpredictable
Antenna height has no effect on the pattern
If the antenna is less than 1/2 wavelength high, radiation off the ends of the wire is eliminated
G9B06:
Where should the radial wires of a ground-mounted vertical antenna system be placed?
On the surface or buried a few inches below the ground
As high as possible above the ground
Parallel to the antenna element
At the top of the antenna
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?
It steadily decreases
It steadily increases
It peaks at about 1/8 wavelength above ground
It is unaffected by the height above ground
G9B08:
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?
It steadily increases
It steadily decreases
It peaks at about 1/8 wavelength from the end
It is unaffected by the location of the feed-point
G9B09:
Which of the following is an advantage of a horizontally polarized as compared to vertically polarized HF antenna?
Lower ground reflection losses
Lower feed-point impedance
Shorter Radials
Lower radiation resistance
G9B10:
What is the approximate length for a 1/2-wave dipole antenna cut for 14.250 MHz?
32.8 feet
8.2 feet
16.4 feet
24.6 feet
G9B11:
What is the approximate length for a 1/2-wave dipole antenna cut for 3.550 MHz?
131.8 feet
42.2 feet
84.5 feet
263.6 feet
G9B12:
What is the approximate length for a 1/4-wave vertical antenna cut for 28.5 MHz?
8.2 feet
10.5 feet
16.4 feet
21.0 feet
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