Amateur Extra E9D: Loading, Yagis and Q
These are the 12 official questions in group E9D of the 2024–2028 Amateur Extra question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
- E9D01Question 1
How much does the gain of an ideal parabolic reflector antenna increase when the operating frequency is doubled?
- A2 dB
- B3 dB
- C4 dB
- D6 dB Correct
Why: Dish gain rises with frequency squared: double the frequency = +6 dB.
- E9D02Question 2
How can two linearly polarized Yagi antennas be used to produce circular polarization?
- AStack two Yagis to form an array with the respective elements in parallel planes fed 90 degrees out of phase
- BStack two Yagis to form an array with the respective elements in parallel planes fed in phase
- CArrange 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 Correct
- DArrange two Yagis collinear to each other with the driven elements fed 180 degrees out of phase
Why: Two perpendicular Yagis on one axis, fed 90° out of phase, make circular polarization.
- E9D03Question 3
What is the most efficient location for a loading coil on an electrically short whip?
- ANear the center of the vertical radiator Correct
- BAs low as possible on the vertical radiator
- CAt a voltage maximum
- DAt a voltage null
Why: A loading coil is most efficient near the center of the whip.
- E9D04Question 4
Why should antenna loading coils have a high ratio of reactance to resistance?
- ATo swamp out harmonics
- BTo lower the radiation angle
- CTo maximize efficiency Correct
- DTo minimize the Q
Why: A high reactance-to-resistance ratio (high Q) makes the coil efficient.
- E9D05Question 5
Approximately how long is a Yagi’s driven element?
- A234 divided by frequency in MHz
- B1005 divided by frequency in MHz
- C1/4 wavelength
- D1/2 wavelength Correct
Why: A Yagi's driven element is about a half wavelength.
- E9D06Question 6
What happens to SWR bandwidth when one or more loading coils are used to resonate an electrically short antenna?
- AIt is increased
- BIt is decreased Correct
- CIt is unchanged if the loading coil is located at the feed point
- DIt is unchanged if the loading coil is located at a voltage maximum point
Why: Loading coils narrow the SWR bandwidth.
- E9D07Question 7
What is an advantage of top loading an electrically short HF vertical antenna?
- ALower Q
- BGreater structural strength
- CHigher losses
- DImproved radiation efficiency Correct
Why: Top loading improves radiation efficiency.
- E9D08Question 8
What happens as the Q of an antenna increases?
- ASWR bandwidth increases
- BSWR bandwidth decreases Correct
- CGain is reduced
- DMore common-mode current is present on the feed line
Why: Higher Q narrows the SWR bandwidth.
- E9D09Question 9
What is the function of a loading coil in an electrically short antenna?
- ATo increase the SWR bandwidth by increasing net reactance
- BTo lower the losses
- CTo lower the Q
- DTo resonate the antenna by cancelling the capacitive reactance Correct
Why: A loading coil cancels the short antenna's capacitive reactance.
- E9D10Question 10
How does radiation resistance of a base-fed whip antenna change below its resonant frequency?
- ARadiation resistance increases
- BRadiation resistance decreases Correct
- CRadiation resistance becomes imaginary
- DRadiation resistance does not depend on frequency
Why: Below resonance, a whip's radiation resistance drops.
- E9D11Question 11
Why do most two-element Yagis with normal spacing have a reflector instead of a director?
- ALower SWR
- BHigher receiving directivity factor
- CGreater front-to-side
- DHigher gain Correct
Why: A reflector gives more gain in a two-element Yagi.
- E9D12Question 12
What is the purpose of making a Yagi’s parasitic elements either longer or shorter than resonance?
- AWind torque cancellation
- BMechanical balance
- CControl of phase shift Correct
- DMinimize losses
Why: Detuning parasitic elements controls their phase shift.