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Extra-Study/pages/E9D.md
Chris ce979dddb4 Initial checkin
2025-05-01 15:49:18 -05:00

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E9D Yagi antennas; parabolic reflectors; feed point impedance and loading of electrically short antennas; antenna Q; RF grounding

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