Deep Dive: E9F06
The correct answer is C: 10.6 meters. For an air-insulated, parallel conductor transmission line that is electrically 1/2 wavelength long at 14.10 MHz, the approximate physical length is 10.6 meters. Air-insulated lines have velocity factor ≈ 0.95-1.0, so physical length is close to electrical length. Calculation: Wavelength at 14.10 MHz = 300 / 14.10 = 21.28 meters. Half-wavelength = 10.64 meters. For air-insulated line (VF ≈ 0.95-1.0), physical length ≈ electrical length, so about 10.6 meters. Air-insulated parallel line (like ladder line) has high velocity factor because air is the dielectric, so the physical length is very close to the free-space half-wavelength. This is why open-wire feed lines are popular - they have high velocity factors and low loss.
Why Other Answers Are Wrong
Option A: Incorrect. 7.0 meters would be too short. That's about 1/3 wavelength, not 1/2 wavelength. Option B: Incorrect. 8.5 meters is still too short. The half-wavelength at 14.10 MHz is about 10.6 meters. Option D: Incorrect. 13.3 meters would be too long - that's closer to 3/4 wavelength. The half-wavelength is about 10.6 meters.
Exam Tip
1/2λ at 14.10 MHz = 10.6 meters (air-insulated). Remember: Half-wavelength at 14.10 MHz = 300/(2×14.10) = 10.64 meters. For air-insulated line (VF≈1.0), physical length ≈ 10.6 meters.
Memory Aid
**1**/**2**λ **1**4.**1**0 **M**Hz = **1**0.**6** **m**eters (think '1/2λ 14.10MHz = 10.6m')
Real-World Example
You need a 1/2-wavelength section of air-insulated parallel line at 14.10 MHz. The free-space half-wavelength is 10.64 meters. Since air-insulated line has velocity factor close to 1.0, the physical length is about 10.6 meters. You cut your ladder line to this length for the matching section.
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.