Question
How does the radiation pattern of a horizontally-polarized antenna mounted above a long slope compare with the same antenna mounted above flat ground?
Answer Options
- A) The main lobe takeoff angle increases in the downhill direction
- B) The main lobe takeoff angle decreases in the downhill direction
- C) The horizontal beamwidth decreases in the downhill direction
- D) The horizontal beamwidth increases in the uphill direction
Correct Answer: B
Explanation
The ground reflection used to create the elevation pattern is critically dependent on the geometry of the ground surface. When an antenna is placed near the top of a long, clear slope, the reflected signal path is lengthened, creating highly favorable conditions for low-angle radiation in the downhill direction.
Compared to flat ground, mounting a horizontally-polarized antenna above a long slope causes the main lobe takeoff angle to decrease in the downhill direction. This ‘slope effect’ is an important tool for HF DX operators, as it artificially forces the antenna’s maximum radiation toward the horizon (a lower takeoff angle) without requiring the antenna to be mounted at an impossibly high elevation.
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