Practice
Antennas & Feedlines — Practice
Getting power out of the radio and into the air with as little wasted as possible. Untimed topic practice with a full explanation after every question, so a wrong answer becomes a study note rather than a dead end.
Questions
8
Time limit
Untimed
Pass mark
60%
Before you start
- Untimed. The explanation appears as soon as you answer, because the point here is to learn rather than to score.
- Mark an answer as a guess and it enters your review queue even if it happened to be right.
- Every answer moves your ability estimate for that topic and updates your readiness score.
- Retake as often as you like.
Sample questions
Approximately how long is a half-wave dipole for 14.2 MHz?
- 5 metres
- 10 metres
- 20 metres
- 40 metres
Why 10 metres is right: A half-wave dipole is roughly 143 ÷ f(MHz) metres = 143 ÷ 14.2 ≈ 10 metres overall, with each leg about 5 metres. The factor allows for the end effect on real wire.
What is the approximate feedpoint impedance of a half-wave dipole in free space?
- 25 Ω
- 50 Ω
- 73 Ω
- 300 Ω
Why 73 Ω is right: A resonant half-wave dipole presents about 73 Ω at its centre, which is why it feeds reasonably well with either 50 Ω or 75 Ω coaxial cable.
Which antenna is directional and provides gain in one preferred direction?
- Half-wave dipole
- Quarter-wave ground plane
- Yagi-Uda array
- Random wire
Why Yagi-Uda array is right: A Yagi uses a driven element with parasitic reflector and director elements to concentrate radiation in one direction, giving both forward gain and rejection off the back.