ANTENNAS AND FEED LINES
Subelement T9
Section T9A
Antennas: vertical and horizontal polarization, concept of antenna gain, definition and types of beam antennas, antenna loading, common portable and mobile antennas, relationships between resonant length and frequency, dipole pattern
What is a beam antenna?
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An antenna built from square aluminum beams
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An omnidirectional antenna invented by Clarence Beam
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Correct AnswerAn antenna that concentrates signals in one direction
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An antenna that focuses the signal into two intense rays
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Which of the following describes a type of antenna loading?
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Correct AnswerElectrically lengthening by inserting inductors in radiating elements
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Inserting a resistor in the radiating portion of the antenna to make it resonant
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Installing a spring in the base of a mobile vertical antenna to make it more flexible
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Strengthening the radiating elements of a beam antenna to better resist wind damage
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How is the polarization of an antenna described?
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By the shape of the driven element
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Correct AnswerBy the orientation of the electric field
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By the orientation of the magnetic field
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By the direction of radiation
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What is a disadvantage of a handheld radio transceiver’s short flexible antenna compared to a full-sized quarter-wave antenna?
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Correct AnswerIt has low efficiency
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It transmits only circularly polarized signals
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It is more susceptible to receiver desensitization
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It only works on analog signals, not digital ones
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Which of the following increases the resonant frequency of a dipole antenna?
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Lengthening it
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Inserting coils in series with radiating wires
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Correct AnswerShortening it
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Adding capacitive loading to the ends of the radiating wires
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Which of the following types of antennas offers the greatest gain?
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5/8 wave vertical
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Isotropic
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J pole
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Correct AnswerYagi
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What is a potential drawback of using a handheld VHF transceiver inside a vehicle that lacks an externally mounted antenna?
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Correct AnswerSignal strength is reduced due to the shielding effect of the vehicle
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The bandwidth of the antenna will decrease, increasing SWR
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The SWR might decrease, decreasing the signal strength
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The handheld will overheat due to reflected power in the vehicle
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Why is a 19-inch-long vertical antenna often used on 2 meters?
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It has high gain
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It is a resonant half-wave
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Correct AnswerIt is a resonant quarter-wave
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It has low RF radiation exposure
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What is an advantage of a 5/8-wavelength whip antenna for VHF or UHF mobile service compared to a 1/4-wave antenna?
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Correct AnswerIt has more gain
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It radiates at a higher angle
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It has lower SWR
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It has lower impedance
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In which direction does a half-wave dipole antenna radiate the strongest signal?
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Equally in all directions
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Off the ends of the antenna
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In the direction of the feed line
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Correct AnswerBroadside to the antenna
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What is antenna gain?
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The additional power that is added to the transmitter power
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The additional power that is required in the antenna when transmitting on a higher frequency
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Correct AnswerThe increase in signal strength in a specified direction compared to a reference antenna
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The increase in impedance on receive or transmit compared to a reference antenna
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