Which matching system for Yagi antennas requires the driven element to be insulated from the boom?
The correct answer is B: Beta or hairpin match. The Beta or hairpin matching system for Yagi antennas requires the driven element to be insulated from the boom. This is because the beta/hairpin match works with a capacitively reactive feed point, which requires the element to be electrically isolated.
The beta (or hairpin) match uses a U-shaped conductor (the 'hairpin') connected across the driven element. This match works when the driven element is slightly shorter than resonance (capacitive). The element must be insulated from the boom so it can have the proper reactive impedance. If the element were connected to the boom (grounded), the impedance characteristics would be different, and the beta match wouldn't work properly. Other matching systems like gamma match can work with the element connected to the boom.
Exam Tip
Beta/hairpin match = Insulated element. Remember: Beta or hairpin matching requires the Yagi driven element to be insulated from the boom because it works with a capacitively reactive feed point that needs electrical isolation.
Memory Aid
"**B**eta/**H**airpin **M**atch = **I**nsulated **E**lement (think 'BHM = IE')"
Real-World Application
You're building a Yagi and want to use a beta (hairpin) match. You must insulate the driven element from the boom - maybe using plastic insulators. The beta match works with a capacitive feed point impedance, which requires the element to be electrically isolated. If you grounded the element to the boom, the beta match wouldn't work properly.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Gamma match can work with the element connected to the boom. It doesn't require insulation.
Option C: Incorrect. Shunt-fed matching doesn't specifically require the element to be insulated from the boom.
Option D: Incorrect. T-match doesn't require the element to be insulated from the boom. Beta/hairpin match is the one that requires insulation.
题目解析
The correct answer is B: Beta or hairpin match. The Beta or hairpin matching system for Yagi antennas requires the driven element to be insulated from the boom. This is because the beta/hairpin match works with a capacitively reactive feed point, which requires the element to be electrically isolated. The beta (or hairpin) match uses a U-shaped conductor (the 'hairpin') connected across the driven element. This match works when the driven element is slightly shorter than resonance (capacitive). The element must be insulated from the boom so it can have the proper reactive impedance. If the element were connected to the boom (grounded), the impedance characteristics would be different, and the beta match wouldn't work properly. Other matching systems like gamma match can work with the element connected to the boom.
考试技巧
Beta/hairpin match = Insulated element. Remember: Beta or hairpin matching requires the Yagi driven element to be insulated from the boom because it works with a capacitively reactive feed point that needs electrical isolation.
记忆口诀
**B**eta/**H**airpin **M**atch = **I**nsulated **E**lement (think 'BHM = IE')
实际应用示例
You're building a Yagi and want to use a beta (hairpin) match. You must insulate the driven element from the boom - maybe using plastic insulators. The beta match works with a capacitive feed point impedance, which requires the element to be electrically isolated. If you grounded the element to the boom, the beta match wouldn't work properly.
错误选项分析
Option A: Incorrect. Gamma match can work with the element connected to the boom. It doesn't require insulation. Option C: Incorrect. Shunt-fed matching doesn't specifically require the element to be insulated from the boom. Option D: Incorrect. T-match doesn't require the element to be insulated from the boom. Beta/hairpin match is the one that requires insulation.
知识点
Beta match, Hairpin match, Yagi matching, Insulated driven element
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.