Deep Dive: E9C14
The correct answer is B: The main lobe takeoff angle decreases in the downhill direction. A horizontally-polarized antenna mounted above a long slope compared to flat ground has decreased main lobe takeoff angle in the downhill direction. The slope acts like the antenna is higher in that direction, creating a lower take-off angle. When mounted on a slope, the effective height is different in different directions. In the downhill direction, the ground is effectively further away (the antenna appears higher relative to the ground in that direction), which creates a lower take-off angle. This is similar to raising the antenna - lower take-off angles are better for long-distance communications. The slope effectively tilts the elevation pattern, with better low-angle radiation in the downhill direction.
Why Other Answers Are Wrong
Option A: Incorrect. The takeoff angle doesn't increase downhill - it decreases. The slope makes the antenna effectively higher in the downhill direction. Option C: Incorrect. The takeoff angle doesn't increase uphill. The question specifically asks about the downhill direction. Option D: Incorrect. The takeoff angle doesn't decrease uphill. The improvement is in the downhill direction where the antenna is effectively higher.
Exam Tip
Horizontal on slope = Lower take-off angle downhill. Remember: A horizontally-polarized antenna on a slope has decreased main lobe takeoff angle in the downhill direction, where the antenna is effectively higher.
Memory Aid
**H**orizontal **S**lope = **L**ower **A**ngle **D**ownhill (think 'HS = LAD')
Real-World Example
You install a horizontal dipole on a hillside, with the antenna running along the slope. In the downhill direction, the ground is effectively further away (the antenna appears higher), creating a lower take-off angle. This lower angle improves long-distance performance in the downhill direction. The slope effectively tilts your elevation pattern.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E9C
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 E9C topic.