General G9C: Yagi antennas
These are the 11 official questions in group G9C 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.
- G9C01Question 1
Which of the following would increase the bandwidth of a Yagi antenna?
- ALarger-diameter elements Correct
- BCloser element spacing
- CLoading coils in series with the element
- DTapered-diameter elements
Why: Larger-diameter elements widen a Yagi's bandwidth.
- G9C02Question 2
What is the approximate length of the driven element of a Yagi antenna?
- A1/4 wavelength
- B1/2 wavelength Correct
- C3/4 wavelength
- D1 wavelength
Why: A Yagi's driven element is about a half wavelength.
- G9C03Question 3
How do the lengths of a three-element Yagi reflector and director compare to that of the driven element?
- AThe reflector is longer, and the director is shorter Correct
- BThe reflector is shorter, and the director is longer
- CThey are all the same length
- DRelative length depends on the frequency of operation
Why: The reflector is longer and the director shorter than the driven element.
- G9C04Question 4
How does antenna gain in dBi compare to gain stated in dBd for the same antenna?
- AGain in dBi is 2.15 dB lower
- BGain in dBi is 2.15 dB higher Correct
- CGain in dBd is 1.25 dBd lower
- DGain in dBd is 1.25 dBd higher
Why: dBi reads 2.15 dB higher than dBd for the same antenna.
- G9C05Question 5
What is the primary effect of increasing boom length and adding directors to a Yagi antenna?
- AGain increases Correct
- BBeamwidth increases
- CFront-to-back ratio decreases
- DResonant frequency is lower
Why: A longer boom with more directors increases gain.
- G9C07Question 6
What does “front-to-back ratio” mean in reference to a Yagi antenna?
- AThe number of directors versus the number of reflectors
- BThe relative position of the driven element with respect to the reflectors and directors
- CThe power radiated in the major lobe compared to that in the opposite direction Correct
- DThe ratio of forward gain to dipole gain
Why: Front-to-back ratio compares the main lobe's power with the power radiated backward.
- G9C08Question 7
What is meant by the “main lobe” of a directive antenna?
- AThe magnitude of the maximum vertical angle of radiation
- BThe point of maximum current in a radiating antenna element
- CThe maximum voltage standing wave point on a radiating element
- DThe direction of maximum radiated field strength from the antenna Correct
Why: The main lobe is the direction of maximum radiated field strength.
- G9C09Question 8
In free space, how does the gain of two three-element, horizontally polarized Yagi antennas spaced vertically 1/2 wavelength apart typically compare to the gain of a single three-element Yagi?
- AApproximately 1.5 dB higher
- BApproximately 3 dB higher Correct
- CApproximately 6 dB higher
- DApproximately 9 dB higher
Why: Two properly stacked Yagis give about 3 dB more gain.
- G9C10Question 9
Which of the following can be adjusted to optimize forward gain, front-to-back ratio, or SWR bandwidth of a Yagi antenna?
- AThe physical length of the boom
- BThe number of elements on the boom
- CThe spacing of each element along the boom
- DAll these choices are correct Correct
Why: Element lengths, spacing and matching can all be adjusted. All the choices are correct.
- G9C11Question 10
What is a beta or hairpin match?
- AA shorted transmission line stub placed at the feed point of a Yagi antenna to provide impedance matching Correct
- BA 1/4 wavelength section of 75-ohm coax in series with the feed point of a Yagi to provide impedance matching
- CA series capacitor selected to cancel the inductive reactance of a folded dipole antenna
- DA section of 300-ohm twin-lead transmission line used to match a folded dipole antenna
Why: A beta (hairpin) match is a shorted stub at the feed point.
- G9C12Question 11
Which of the following is a characteristic of using a gamma match with a Yagi antenna?
- AIt does not require the driven element to be insulated from the boom Correct
- BIt does not require any inductors or capacitors
- CIt is useful for matching multiband antennas
- DAll these choices are correct
Why: A gamma match doesn't need the driven element insulated from the boom.