Deep Dive: E9F01
The correct answer is D: The velocity of a wave in the transmission line divided by the velocity of light in a vacuum. The velocity factor of a transmission line is the velocity of a wave in the transmission line divided by the velocity of light in a vacuum. It's a ratio, typically between 0.5 and 1.0. The velocity factor (VF) tells you how fast signals travel in the transmission line compared to the speed of light. VF = v_line / c, where v_line is the wave velocity in the line and c is the speed of light. For example, if VF = 0.66, signals travel at 66% of the speed of light. The velocity factor depends on the dielectric material - air-insulated lines have VF ≈ 0.95-1.0, while solid dielectric coax might have VF ≈ 0.66. The velocity factor is important for calculating electrical length from physical length.
Why Other Answers Are Wrong
Option A: Incorrect. Velocity factor isn't about impedance ratios. It's about wave velocity, not impedance relationships. Option B: Incorrect. This is the inverse of the correct relationship. Velocity factor is line velocity divided by light speed, not the other way around. Option C: Incorrect. Velocity factor isn't multiplied by light speed - it's divided by light speed. Signals in transmission lines travel slower than light, so VF < 1.
Exam Tip
Velocity factor = Line velocity / Light speed. Remember: Velocity factor = velocity in transmission line / velocity of light in vacuum. It's typically 0.5-1.0 (signals travel slower than light).
Memory Aid
**V**elocity **F**actor = **L**ine **V**elocity / **L**ight **S**peed (think 'VF = LV/LS')
Real-World Example
You have coaxial cable with velocity factor 0.66. This means signals travel at 66% of the speed of light in this cable. If you need a 1/4-wavelength section at 14 MHz, the physical length is shorter than the free-space length because of the velocity factor. The velocity factor accounts for the slower wave propagation in the cable's dielectric.
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.