Which of the following is a common use for a Smith chart?
The correct answer is A: Determine the length and position of an impedance matching stub. A common use for a Smith chart is to determine the length and position of an impedance matching stub. The chart helps you find where to place the stub and how long it should be.
Smith charts are excellent for designing stub matching networks. You plot the load impedance, then move around the chart to find where a stub should be placed (the position along the transmission line). Then you determine the stub length needed to provide the right reactance to complete the match. The chart shows you the exact lengths and positions needed. This is one of the most common applications of Smith charts in RF engineering - designing matching stubs for antennas and other loads.
Exam Tip
Smith chart common use = Stub matching. Remember: A common use for Smith charts is to determine the length and position of impedance matching stubs - where to place the stub and how long it should be.
Memory Aid
"**S**mith **C**hart **U**se = **S**tub **M**atching (think 'SCU = SM')"
Real-World Application
You need to match a 100-ohm antenna to 50-ohm coax using a stub. You plot the 100-ohm impedance on a Smith chart, then move around the chart to find where a stub should be placed. The chart shows you the stub position (maybe 0.15 wavelengths from the load) and stub length (maybe 0.12 wavelengths) needed to complete the match.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. Smith charts don't determine impedance from physical dimensions. They work with impedances, not physical antenna dimensions.
Option C: Incorrect. Smith charts don't determine antenna gain. They're for impedance and transmission line analysis, not gain calculations.
Option D: Incorrect. Smith charts don't determine transmission line loss from velocity factor and materials. They're for impedance transformations, not loss calculations.
题目解析
The correct answer is A: Determine the length and position of an impedance matching stub. A common use for a Smith chart is to determine the length and position of an impedance matching stub. The chart helps you find where to place the stub and how long it should be. Smith charts are excellent for designing stub matching networks. You plot the load impedance, then move around the chart to find where a stub should be placed (the position along the transmission line). Then you determine the stub length needed to provide the right reactance to complete the match. The chart shows you the exact lengths and positions needed. This is one of the most common applications of Smith charts in RF engineering - designing matching stubs for antennas and other loads.
考试技巧
Smith chart common use = Stub matching. Remember: A common use for Smith charts is to determine the length and position of impedance matching stubs - where to place the stub and how long it should be.
记忆口诀
**S**mith **C**hart **U**se = **S**tub **M**atching (think 'SCU = SM')
实际应用示例
You need to match a 100-ohm antenna to 50-ohm coax using a stub. You plot the 100-ohm impedance on a Smith chart, then move around the chart to find where a stub should be placed. The chart shows you the stub position (maybe 0.15 wavelengths from the load) and stub length (maybe 0.12 wavelengths) needed to complete the match.
错误选项分析
Option B: Incorrect. Smith charts don't determine impedance from physical dimensions. They work with impedances, not physical antenna dimensions. Option C: Incorrect. Smith charts don't determine antenna gain. They're for impedance and transmission line analysis, not gain calculations. Option D: Incorrect. Smith charts don't determine transmission line loss from velocity factor and materials. They're for impedance transformations, not loss calculations.
知识点
Smith chart, Stub matching, Impedance matching, Stub length and position
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.