How does a “screwdriver” mobile antenna adjust its feed point impedance?
The correct answer is B: By varying the base loading inductance. How a 'screwdriver' mobile antenna adjusts its feed point impedance is by varying the base loading inductance. Screwdriver antennas have a motorized loading coil that adjusts inductance, changing the antenna's resonant frequency and impedance. For amateur radio operators, this is how screwdriver antennas work. Understanding this helps when using mobile antennas.
Exam Tip
Screwdriver antenna adjustment = varying base loading inductance. Think 'S'crewdriver = 'S'elects 'L'oading 'I'nductance. Screwdriver antennas have motorized loading coil that adjusts inductance, changing impedance. Not body capacitance, not whip extension, not capacitance hat - just loading inductance.
Memory Aid
"Screwdriver antenna adjustment = varying base loading inductance. Think 'S'crewdriver = 'S'elects 'L'oading. Screwdriver antennas have motorized loading coil that adjusts inductance, changing impedance. How screwdriver antennas work."
Real-World Application
A screwdriver mobile antenna: A motorized loading coil at the base adjusts the inductance. As the coil is adjusted (screwed in/out), the inductance changes, which changes the antenna's resonant frequency and feed point impedance. This allows the antenna to be tuned to different bands. Varying base loading inductance is how screwdriver antennas adjust impedance.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Screwdriver doesn't adjust by varying body capacitance - it adjusts by varying loading inductance. Body capacitance isn't the adjustment.
Option C: Incorrect. Screwdriver doesn't adjust by extending/retracting whip - it adjusts by varying loading inductance. Whip extension isn't the adjustment.
Option D: Incorrect. Screwdriver doesn't adjust by deploying capacitance hat - it adjusts by varying loading inductance. Capacitance hat isn't the adjustment.
题目解析
The correct answer is B: By varying the base loading inductance. How a 'screwdriver' mobile antenna adjusts its feed point impedance is by varying the base loading inductance. Screwdriver antennas have a motorized loading coil that adjusts inductance, changing the antenna's resonant frequency and impedance. For amateur radio operators, this is how screwdriver antennas work. Understanding this helps when using mobile antennas.
考试技巧
Screwdriver antenna adjustment = varying base loading inductance. Think 'S'crewdriver = 'S'elects 'L'oading 'I'nductance. Screwdriver antennas have motorized loading coil that adjusts inductance, changing impedance. Not body capacitance, not whip extension, not capacitance hat - just loading inductance.
记忆口诀
Screwdriver antenna adjustment = varying base loading inductance. Think 'S'crewdriver = 'S'elects 'L'oading. Screwdriver antennas have motorized loading coil that adjusts inductance, changing impedance. How screwdriver antennas work.
实际应用示例
A screwdriver mobile antenna: A motorized loading coil at the base adjusts the inductance. As the coil is adjusted (screwed in/out), the inductance changes, which changes the antenna's resonant frequency and feed point impedance. This allows the antenna to be tuned to different bands. Varying base loading inductance is how screwdriver antennas adjust impedance.
错误选项分析
Option A: Incorrect. Screwdriver doesn't adjust by varying body capacitance - it adjusts by varying loading inductance. Body capacitance isn't the adjustment. Option C: Incorrect. Screwdriver doesn't adjust by extending/retracting whip - it adjusts by varying loading inductance. Whip extension isn't the adjustment. Option D: Incorrect. Screwdriver doesn't adjust by deploying capacitance hat - it adjusts by varying loading inductance. Capacitance hat isn't the adjustment.
知识点
Screwdriver antenna, Feed point impedance, Base loading inductance, Mobile antenna
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.