General G9D: Special antennas
These are the 12 official questions in group G9D of the 2023–2027 General 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.
- G9D01Question 1
Which of the following antenna types will be most effective as a near vertical incidence skywave (NVIS) antenna for short-skip communications on 40 meters during the day?
- AA horizontal dipole placed between 1/10 and 1/4 wavelength above the ground Correct
- BA vertical antenna placed between 1/4 and 1/2 wavelength above the ground
- CA horizontal dipole placed at approximately 1/2 wavelength above the ground
- DA vertical dipole placed at approximately 1/2 wavelength above the ground
Why: A low horizontal dipole, 1/10 to 1/4 wave high, sends energy nearly straight up for NVIS.
- G9D02Question 2
What is the feed point impedance of an end-fed half-wave antenna?
- AVery low
- BApproximately 50 ohms
- CApproximately 300 ohms
- DVery high Correct
Why: An end-fed half-wave has a very high feed point impedance.
- G9D03Question 3
In which direction is the maximum radiation from a VHF/UHF “halo” antenna?
- ABroadside to the plane of the halo
- BOpposite the feed point
- COmnidirectional in the plane of the halo Correct
- DOn the same side as the feed point
Why: A halo radiates omnidirectionally in its own plane.
- G9D04Question 4
What is the primary function of antenna traps?
- ATo enable multiband operation Correct
- BTo notch spurious frequencies
- CTo provide balanced feed point impedance
- DTo prevent out-of-band operation
Why: Traps let one antenna work on multiple bands.
- G9D05Question 5
What is an advantage of vertically stacking horizontally polarized Yagi antennas?
- AIt allows quick selection of vertical or horizontal polarization
- BIt allows simultaneous vertical and horizontal polarization
- CIt narrows the main lobe in azimuth
- DIt narrows the main lobe in elevation Correct
Why: Vertically stacked Yagis narrow the main lobe in elevation.
- G9D06Question 6
Which of the following is an advantage of a log-periodic antenna?
- AWide bandwidth Correct
- BHigher gain per element than a Yagi antenna
- CHarmonic suppression
- DPolarization diversity
Why: A log-periodic antenna has wide bandwidth.
- G9D07Question 7
Which of the following describes a log-periodic antenna?
- AElement length and spacing vary logarithmically along the boom Correct
- BImpedance varies periodically as a function of frequency
- CGain varies logarithmically as a function of frequency
- DSWR varies periodically as a function of boom length
Why: A log-periodic's element lengths and spacing vary logarithmically along the boom.
- G9D08Question 8
How does a “screwdriver” mobile antenna adjust its feed point impedance?
- ABy varying its body capacitance
- BBy varying the base loading inductance Correct
- CBy extending and retracting the whip
- DBy deploying a capacitance hat
Why: A screwdriver antenna tunes by varying its base loading inductance.
- G9D09Question 9
What is the primary use of a Beverage antenna?
- ADirectional receiving for MF and low HF bands Correct
- BDirectional transmitting for low HF bands
- CPortable direction finding at higher HF frequencies
- DPortable direction finding at lower HF frequencies
Why: A Beverage is for directional receiving on MF and low HF.
- G9D10Question 10
In which direction or directions does an electrically small loop (less than 1/10 wavelength in circumference) have nulls in its radiation pattern?
- AIn the plane of the loop
- BBroadside to the loop Correct
- CBroadside and in the plane of the loop
- DElectrically small loops are omnidirectional
Why: A small loop's nulls are broadside to the loop.
- G9D11Question 11
Which of the following is a disadvantage of multiband antennas?
- AThey present low impedance on all design frequencies
- BThey must be used with an antenna tuner
- CThey must be fed with open wire line
- DThey have poor harmonic rejection Correct
Why: Multiband antennas have poor harmonic rejection.
- G9D12Question 12
What is the common name of a dipole with a single central support?
- AInverted V Correct
- BInverted L
- CSloper
- DLazy H
Why: A dipole hung from one center support is an inverted V.