Deep Dive: E9F11
The correct answer is C: A capacitive reactance. A 1/8-wavelength transmission line open at the far end presents a capacitive reactance to an RF generator. The line appears as a capacitor. Transmission lines shorter than 1/4 wavelength transform impedances progressively. An open line shorter than 1/4 wavelength appears capacitive. At 1/8 wavelength, the line presents capacitive reactance - it looks like a capacitor. As the line gets longer (approaching 1/4 wavelength), the reactance decreases. At 1/4 wavelength, it becomes very low impedance (short). The 1/8-wavelength open line is useful for providing capacitive reactance in matching networks or filters.
Why Other Answers Are Wrong
Option A: Incorrect. The impedance isn't the same as the characteristic impedance. It's a reactive impedance (capacitive). Option B: Incorrect. An open line shorter than 1/4 wavelength appears capacitive, not inductive. A shorted line appears inductive. Option D: Incorrect. The impedance isn't infinite. At 1/8 wavelength, it's a capacitive reactance with a specific value. Infinite impedance would occur at 1/2 wavelength for an open line.
Exam Tip
1/8λ open line = Capacitive reactance. Remember: A 1/8-wavelength transmission line open at the far end presents a capacitive reactance to the generator. Open lines shorter than 1/4λ appear capacitive.
Memory Aid
**1**/**8**λ **O**pen = **C**apacitive **R**eactance (think '1/8λO = CR')
Real-World Example
You have a 1/8-wavelength piece of transmission line open at the far end. At the input, it appears as a capacitor with capacitive reactance. This can be useful in matching networks where you need capacitive reactance. As you make the line longer (toward 1/4 wavelength), the capacitive reactance decreases.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E9F
Reference: FCC Part 97.3
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E9F topic.