Ham Radio Technician Test Antennas & Feedlines 2 — Questions and Answers
Question 1: What is the approximate length of a quarter-wave vertical antenna for the 2-meter band (146 MHz)?
- 19 inches (Correct answer)
- 38 inches
- 9.5 inches
- 75 inches
Correct answer: 19 inches
A quarter-wave vertical at 146 MHz is approximately 19 inches (about 48 cm).
Question 2: Which feedline type has the lowest loss per unit length at VHF frequencies?
- Hardline (rigid coax)
- RG-58
- RG-8X
- Open-wire ladder line (Correct answer)
Correct answer: Open-wire ladder line
Open-wire ladder line has very low loss at VHF because of its air dielectric and wide conductor spacing.
Question 3: What does a balun do in an antenna system?
- It matches balanced to unbalanced transmission lines (Correct answer)
- It amplifies the signal before transmission
- It filters harmonic frequencies
- It measures antenna SWR
Correct answer: It matches balanced to unbalanced transmission lines
A balun (BALanced-UNbalanced) transitions between balanced antenna elements and unbalanced coax feedline.
Question 4: What is the radiation pattern of a vertical quarter-wave antenna over a perfect ground plane?
- Omnidirectional in the horizontal plane (Correct answer)
- Bidirectional like a figure-eight
- Highly directional toward one end
- Circular in the vertical plane only
Correct answer: Omnidirectional in the horizontal plane
A vertical quarter-wave antenna radiates equally in all horizontal directions, making it omnidirectional in azimuth.
Question 5: What is the effect of increasing coaxial cable diameter on signal loss?
- Loss decreases (Correct answer)
- Loss increases
- Loss is unaffected by diameter
- Loss only changes above 1 GHz
Correct answer: Loss decreases
Larger-diameter coax has lower loss because of reduced resistance and better power-handling capability.
Question 6: A 5/8-wave vertical antenna is often preferred over a quarter-wave vertical for VHF because it has:
- A lower radiation angle and slight gain over a quarter-wave (Correct answer)
- Higher SWR that boosts power
- A broader bandwidth
- Less susceptibility to lightning
Correct answer: A lower radiation angle and slight gain over a quarter-wave
The 5/8-wave vertical has a lower radiation angle than the quarter-wave, providing a few dB of gain toward the horizon.
Question 7: What is the purpose of a ground plane on a vertical antenna?
- It acts as the other half of the antenna and provides a return path for RF current (Correct answer)
- It shields the antenna from static buildup
- It increases the antenna's resonant frequency
- It prevents lightning from striking the antenna
Correct answer: It acts as the other half of the antenna and provides a return path for RF current
The ground plane (radials) completes the antenna system by providing a low-impedance RF return path, simulating actual earth ground.
Ham Radio Technician Test Antennas & Feedlines 2
What is the approximate length of a quarter-wave vertical antenna for the 2-meter band (146 MHz)?