What is the purpose of the series capacitor in a gamma match?
The correct answer is B: To cancel unwanted inductive reactance. The purpose of the series capacitor in a gamma match is to cancel unwanted inductive reactance. The capacitor's capacitive reactance cancels inductive reactance, making the impedance purely resistive and matched.
A gamma match creates an inductive component due to the offset connection and the conductor's inductance. The series capacitor provides capacitive reactance that cancels this inductive reactance. At the design frequency, the capacitor's reactance equals the inductive reactance, they cancel, and the impedance becomes purely resistive (matched to the feed line). The capacitor is adjustable (variable capacitor) to tune the match. Without the capacitor, the gamma match would have a reactive component, causing high SWR.
Exam Tip
Gamma match capacitor = Cancel inductive reactance. Remember: The series capacitor in a gamma match cancels unwanted inductive reactance, making the impedance purely resistive and matched to the feed line.
Memory Aid
"**G**amma **C**apacitor = **C**ancel **I**nductive **R**eactance (think 'GC = CIR')"
Real-World Application
You're tuning a gamma match on your Yagi. The gamma match connection creates some inductive reactance. You adjust the series capacitor - as you change its value, the capacitive reactance changes. When the capacitor's reactance equals the inductive reactance, they cancel, and your SWR drops to 1:1. The capacitor is essential for completing the match.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. While the capacitor provides DC isolation, that's not its primary purpose in a gamma match. The main purpose is to cancel inductive reactance for impedance matching.
Option C: Incorrect. The capacitor doesn't create a rejection notch for harmonics. Its purpose is reactance cancellation, not filtering.
Option D: Incorrect. The capacitor doesn't transform impedance to a higher value. It cancels reactance to make the impedance resistive and matched.
题目解析
The correct answer is B: To cancel unwanted inductive reactance. The purpose of the series capacitor in a gamma match is to cancel unwanted inductive reactance. The capacitor's capacitive reactance cancels inductive reactance, making the impedance purely resistive and matched. A gamma match creates an inductive component due to the offset connection and the conductor's inductance. The series capacitor provides capacitive reactance that cancels this inductive reactance. At the design frequency, the capacitor's reactance equals the inductive reactance, they cancel, and the impedance becomes purely resistive (matched to the feed line). The capacitor is adjustable (variable capacitor) to tune the match. Without the capacitor, the gamma match would have a reactive component, causing high SWR.
考试技巧
Gamma match capacitor = Cancel inductive reactance. Remember: The series capacitor in a gamma match cancels unwanted inductive reactance, making the impedance purely resistive and matched to the feed line.
记忆口诀
**G**amma **C**apacitor = **C**ancel **I**nductive **R**eactance (think 'GC = CIR')
实际应用示例
You're tuning a gamma match on your Yagi. The gamma match connection creates some inductive reactance. You adjust the series capacitor - as you change its value, the capacitive reactance changes. When the capacitor's reactance equals the inductive reactance, they cancel, and your SWR drops to 1:1. The capacitor is essential for completing the match.
错误选项分析
Option A: Incorrect. While the capacitor provides DC isolation, that's not its primary purpose in a gamma match. The main purpose is to cancel inductive reactance for impedance matching. Option C: Incorrect. The capacitor doesn't create a rejection notch for harmonics. Its purpose is reactance cancellation, not filtering. Option D: Incorrect. The capacitor doesn't transform impedance to a higher value. It cancels reactance to make the impedance resistive and matched.
知识点
Gamma match, Series capacitor, Inductive reactance, Impedance matching
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.