Deep Dive: G9D08
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.
Why Other Answers 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.
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 Example
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.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G9D
Reference: 2023-2027 Question Pool · G9 - Antennas and Feed Lines
Key Concepts
Verified Content
Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G9D topic.