E9C: Wire and phased vertical antennas: beverage antennas; terminated and resonant rhombic antennas; elevation above real ground; ground effects as related to polarization; take-off angles
E9C01:
What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase?
A figure-8 oriented along the axis of the array
A cardioid
Omnidirectional
A figure-8 broadside to the axis of the array
E9C02:
What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase?
A cardioid
A figure-8 end-fire along the axis of the array
A figure-8 broadside to the axis of the array
Omnidirectional
E9C03:
What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase?
A Figure-8 broadside to the axis of the array
Omnidirectional
A cardioid
A Figure-8 end-fire along the axis of the array
E9C04:
Which of the following describes a basic rhombic antenna?
Bidirectional; four-sided, each side one or more wavelengths long; open at the end opposite the transmission line connection
Unidirectional; four-sided, each side one quarter-wavelength long; terminated in a resistance equal to its characteristic impedance
Four-sided; an LC network at each corner except for the transmission connection;
Four-sided, each side of a different physical length
E9C05:
What are the main advantages of a terminated rhombic antenna?
Wide frequency range, high gain and high front-to-back ratio
High front-to-back ratio, compact size and high gain
Unidirectional radiation pattern, high gain and compact size
Bidirectional radiation pattern, high gain and wide frequency range
E9C06:
What are the disadvantages of a terminated rhombic antenna for the HF bands?
The antenna requires a large physical area and 4 separate supports
The antenna has a very narrow operating bandwidth
The antenna produces a circularly polarized signal
The antenna is more sensitive to man-made static than any other type
E9C07:
What is the effect of a terminating resistor on a rhombic antenna?
It changes the radiation pattern from bidirectional to unidirectional
It reflects the standing waves on the antenna elements back to the transmitter
It changes the radiation pattern from horizontal to vertical polarization
It decreases the ground loss
E9C08:
What type of antenna pattern over real ground is shown in Figure E9-2?
Elevation
Azimuth
Radiation resistance
Polarization
E9C09:
What is the elevation angle of peak response in the antenna radiation pattern shown in Figure E9-2?
7.5 degrees
45 degrees
75 degrees
25 degrees
E9C10:
What is the front-to-back ratio of the radiation pattern shown in Figure E9-2?
28 dB
15 dB
3 dB
24 dB
E9C11:
How many elevation lobes appear in the forward direction of the antenna radiation pattern shown in Figure E9-2?
4
3
1
7
E9C12:
How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus rocky ground?
The low-angle radiation increases
The low-angle radiation decreases
The high-angle radiation increases
Both the high- and low-angle radiation decrease
E9C13:
When constructing a Beverage antenna, which of the following factors should be included in the design to achieve good performance at the desired frequency?
It should be one or more wavelengths long
Its overall length must not exceed 1/4 wavelength
It must be mounted more than 1 wavelength above ground
It should be configured as a four-sided loop
E9C14:
How would the electric field be oriented for a Yagi with three elements mounted parallel to the ground?
Horizontally
Vertically
Right-hand elliptically
Left-hand elliptically
E9C15:
What strongly affects the shape of the far-field, low-angle elevation pattern of a vertically polarized antenna?
The conductivity and dielectric constant of the soil in the area of the antenna
The radiation resistance of the antenna and matching network
The SWR on the transmission line
The transmitter output power
E9C17:
What is the main effect of placing a vertical antenna over an imperfect ground?
It reduces low-angle radiation
It causes increased SWR
It changes the impedance angle of the matching network
It reduces losses in the radiating portion of the antenna
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