What do the arcs on a Smith chart represent?
The correct answer is D: Points with constant reactance. The arcs on a Smith chart represent points with constant reactance. Each arc shows all impedances that have the same reactance value (but different resistance values).
The Smith chart has two families of curves: resistance circles and reactance arcs. The arcs are curved lines representing constant reactance. Inductive reactance arcs are in the upper half of the chart (+j values), and capacitive reactance arcs are in the lower half (-j values). All points on a given reactance arc have the same reactance but different resistance values. For example, the +j50-ohm reactance arc contains all impedances with +j50 ohms reactance (like 25+j50, 50+j50, 100+j50, etc.).
Exam Tip
Smith chart arcs = Constant reactance. Remember: The arcs on a Smith chart represent points with constant reactance - inductive arcs in the upper half, capacitive arcs in the lower half.
Memory Aid
"**S**mith **C**hart **A**rcs = **C**onstant **R**eactance (think 'SCA = CR')"
Real-World Application
You look at a Smith chart. You see curved arcs - these are reactance arcs. The +j50-ohm arc (in the upper half) contains all impedances with +j50 ohms reactance: 25+j50, 50+j50, 100+j50, etc. The -j50-ohm arc (in the lower half) contains all impedances with -j50 ohms reactance. Each arc represents constant reactance.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Arcs don't represent frequency. Frequency isn't directly shown on a Smith chart - the chart shows impedance at a given frequency.
Option B: Incorrect. Arcs don't directly represent SWR. SWR is shown by constant-SWR circles, not by the reactance arcs themselves.
Option C: Incorrect. Points with constant resistance are represented by resistance circles, not arcs. Arcs represent constant reactance.
题目解析
The correct answer is D: Points with constant reactance. The arcs on a Smith chart represent points with constant reactance. Each arc shows all impedances that have the same reactance value (but different resistance values). The Smith chart has two families of curves: resistance circles and reactance arcs. The arcs are curved lines representing constant reactance. Inductive reactance arcs are in the upper half of the chart (+j values), and capacitive reactance arcs are in the lower half (-j values). All points on a given reactance arc have the same reactance but different resistance values. For example, the +j50-ohm reactance arc contains all impedances with +j50 ohms reactance (like 25+j50, 50+j50, 100+j50, etc.).
考试技巧
Smith chart arcs = Constant reactance. Remember: The arcs on a Smith chart represent points with constant reactance - inductive arcs in the upper half, capacitive arcs in the lower half.
记忆口诀
**S**mith **C**hart **A**rcs = **C**onstant **R**eactance (think 'SCA = CR')
实际应用示例
You look at a Smith chart. You see curved arcs - these are reactance arcs. The +j50-ohm arc (in the upper half) contains all impedances with +j50 ohms reactance: 25+j50, 50+j50, 100+j50, etc. The -j50-ohm arc (in the lower half) contains all impedances with -j50 ohms reactance. Each arc represents constant reactance.
错误选项分析
Option A: Incorrect. Arcs don't represent frequency. Frequency isn't directly shown on a Smith chart - the chart shows impedance at a given frequency. Option B: Incorrect. Arcs don't directly represent SWR. SWR is shown by constant-SWR circles, not by the reactance arcs themselves. Option C: Incorrect. Points with constant resistance are represented by resistance circles, not arcs. Arcs represent constant reactance.
知识点
Smith chart, Reactance arcs, Constant reactance, Arcs
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.