75 lines
3.4 KiB
Markdown
75 lines
3.4 KiB
Markdown
E9D Yagi antennas; parabolic reflectors; feed point impedance and loading of electrically short antennas; antenna Q; RF grounding
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- [[E9D01]] (D)
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How much does the gain of an ideal parabolic reflector antenna increase when the operating frequency is doubled? #card
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- [[A.]] 2 dB
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- [[B.]] 3 dB
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- [[C.]] 4 dB
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- [[D.]] 6 dB
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- [[E9D02]] (C)
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How can two linearly polarized Yagi antennas be used to produce circular polarization? #card
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- [[A.]] Stack two Yagis to form an array with the respective elements in parallel planes fed 90 degrees out of phase
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- [[B.]] Stack two Yagis to form an array with the respective elements in parallel planes fed in phase
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- [[C.]] Arrange two Yagis on the same axis and perpendicular to each other with the driven elements at the same point on the boom and fed 90 degrees out of phase
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- [[D.]] Arrange two Yagis collinear to each other with the driven elements fed 180 degrees out of phase
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- [[E9D03]] (A)
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What is the most efficient location for a loading coil on an electrically short whip? #card
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- [[A.]] Near the center of the vertical radiator
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- [[B.]] As low as possible on the vertical radiator
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- [[C.]] At a voltage maximum
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- [[D.]] At a voltage null
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- [[E9D04]] (C)
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Why should antenna loading coils have a high ratio of reactance to resistance? #card
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- [[A.]] To swamp out harmonics
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- [[B.]] To lower the radiation angle
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- [[C.]] To maximize efficiency
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- [[D.]] To minimize the Q
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- [[E9D05]] (D)
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Approximately how long is a Yagi’s driven element? #card
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- [[A.]] 234 divided by frequency in MHz
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- [[B.]] 1005 divided by frequency in MHz
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- [[C.]] 1/4 wavelength
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- [[D.]] 1/2 wavelength
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- [[E9D06]] (B)
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What happens to SWR bandwidth when one or more loading coils are used to resonate an electrically short antenna? #card
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- [[A.]] It is increased
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- [[B.]] It is decreased
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- [[C.]] It is unchanged if the loading coil is located at the feed point
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- [[D.]] It is unchanged if the loading coil is located at a voltage maximum point
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- [[E9D07]] (D)
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What is an advantage of top loading an electrically short HF vertical antenna? #card
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- [[A.]] Lower Q
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- [[B.]] Greater structural strength
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- [[C.]] Higher losses
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- [[D.]] Improved radiation efficiency
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- [[E9D08]] (B)
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What happens as the Q of an antenna increases? #card
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- [[A.]] SWR bandwidth increases
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- [[B.]] SWR bandwidth decreases
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- [[C.]] Gain is reduced
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- [[D.]] More common-mode current is present on the feed line
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- [[E9D09]] (D)
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What is the function of a loading coil in an electrically short antenna? #card
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- [[A.]] To increase the SWR bandwidth by increasing net reactance
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- [[B.]] To lower the losses
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- [[C.]] To lower the Q
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- [[D.]] To resonate the antenna by cancelling the capacitive reactance
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- [[E9D10]] (B)
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How does radiation resistance of a base-fed whip antenna change below its resonant frequency? #card
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- [[A.]] Radiation resistance increases
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- [[B.]] Radiation resistance decreases
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- [[C.]] Radiation resistance becomes imaginary
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- [[D.]] Radiation resistance does not depend on frequency
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- [[E9D11]] (D)
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Why do most two-element Yagis with normal spacing have a reflector instead of a director? #card
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- [[A.]] Lower SWR
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- [[B.]] Higher receiving directivity factor
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- [[C.]] Greater front-to-side
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- [[D.]] Higher gain
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- [[E9D12]] (C)
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What is the purpose of making a Yagi’s parasitic elements either longer or shorter than resonance? #card
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- [[A.]] Wind torque cancellation
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- [[B.]] Mechanical balance
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- [[C.]] Control of phase shift
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- [[D.]] Minimize losses
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