Amateur Extra E9E: Matching systems
These are the 10 official questions in group E9E 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.
- E9E01Question 1
Which matching system for Yagi antennas requires the driven element to be insulated from the boom?
- AGamma
- BBeta or hairpin Correct
- CShunt-fed
- DT-match
Why: A beta (hairpin) match needs the driven element insulated from the boom.
- E9E02Question 2
What antenna matching system matches coaxial cable to an antenna by connecting the shield to the center of the antenna and the conductor a fraction of a wavelength to one side?
- AGamma match Correct
- BDelta match
- CT-match
- DStub match
Why: A gamma match connects the shield at center and the conductor a short way out.
- E9E03Question 3
What matching system uses a short length of transmission line connected in parallel with the feed line at or near the feed point?
- AGamma match
- BDelta match
- CT-match
- DStub match Correct
Why: A stub match uses a short line in parallel with the feed line.
- E9E04Question 4
What is the purpose of the series capacitor in a gamma match?
- ATo provide DC isolation between the feed line and the antenna
- BTo cancel unwanted inductive reactance Correct
- CTo provide a rejection notch that prevents the radiation of harmonics
- DTo transform the antenna impedance to a higher value
Why: The gamma's series capacitor cancels inductive reactance.
- E9E05Question 5
What Yagi driven element feed point impedance is required to use a beta or hairpin matching system?
- ACapacitive (driven element electrically shorter than 1/2 wavelength) Correct
- BInductive (driven element electrically longer than 1/2 wavelength)
- CPurely resistive
- DPurely reactive
Why: A hairpin needs a capacitive driven element, slightly shorter than a half wave.
- E9E06Question 6
Which of these transmission line impedances would be suitable for constructing a quarter-wave Q-section for matching a 100-ohm feed point impedance to a 50-ohm transmission line?
- A50 ohms
- B62 ohms
- C75 ohms Correct
- D90 ohms
Why: √(100 × 50) ≈ 71 Ω, so 75 Ω line works.
- E9E07Question 7
What parameter describes the interaction of a load and transmission line?
- ACharacteristic impedance
- BReflection coefficient Correct
- CVelocity factor
- DDielectric constant
Why: The reflection coefficient describes how a load interacts with the line.
- E9E08Question 8
What is a use for a Wilkinson divider?
- ATo divide the operating frequency of a transmitter signal so it can be used on a lower frequency band
- BTo feed high-impedance antennas from a low-impedance source
- CTo divide power equally between two 50-ohm loads while maintaining 50-ohm input impedance Correct
- DTo divide the frequency of the input to a counter to increase its frequency range
Why: A Wilkinson divider splits power equally into two 50 Ω loads with a 50 Ω input.
- E9E09Question 9
Which of the following is used to shunt feed a grounded tower at its base?
- ADouble-bazooka match
- BBeta or hairpin match
- CGamma match Correct
- DAll these choices are correct
Why: A gamma match can shunt-feed a grounded tower.
- E9E11Question 10
What is the purpose of using multiple driven elements connected through phasing lines?
- ATo control the antenna’s radiation pattern Correct
- BTo prevent harmonic radiation from the transmitter
- CTo allow single-band antennas to operate on other bands
- DTo create a low-angle radiation pattern
Why: Phasing lines between driven elements control the radiation pattern.