Extra-Study/logseq/bak/pages/E9D/2025-05-01T20_36_29.901Z.Desktop.md

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?
  • A. 2 dB
  • B. 3 dB
  • C. 4 dB

  • D. 6 dB

• E9D02 (C) How can two linearly polarized Yagi antennas be used to produce circular polarization?
  • 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?
  • 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?
  • 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?
  • 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?
  • 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?
  • 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?
  • 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?
  • 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?
  • 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?
  • 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?
  • A. Wind torque cancellation
  • B. Mechanical balance
  • C. Control of phase shift
  • D. Minimize losses