Which of the following antenna types will be most effective as a near vertical incidence skywave (NVIS) antenna for short-skip communications on 40 meters during the day?
The correct answer is A: A horizontal dipole placed between 1/10 and 1/4 wavelength above the ground. The antenna type that will be most effective as a near vertical incidence skywave (NVIS) antenna for short-skip communications on 40 meters during the day is a horizontal dipole placed between 1/10 and 1/4 wavelength above the ground. NVIS requires high takeoff angles, which horizontal dipoles at low height provide. For amateur radio operators, this is ideal for NVIS operation. Understanding this helps when designing NVIS antennas.
Exam Tip
NVIS antenna = horizontal dipole at 1/10 to 1/4 wavelength height. Think 'N'VIS = 'N'early 'V'ertical = 'H'orizontal 'L'ow height. NVIS requires high takeoff angles, which horizontal dipoles at low height provide. Not vertical, not 1/2 wavelength - just horizontal low height.
Memory Aid
"NVIS antenna = horizontal dipole at 1/10 to 1/4 wavelength height. Think 'N'VIS = 'H'orizontal 'L'ow height. NVIS requires high takeoff angles, which horizontal dipoles at low height provide. Ideal for short-skip communications."
Real-World Application
NVIS operation on 40 meters: A horizontal dipole placed between 1/10 and 1/4 wavelength above ground (e.g., 10-30 feet) provides high takeoff angles, ideal for short-skip communications (50-200 miles). The low height creates nearly vertical radiation, perfect for NVIS. This is the most effective NVIS antenna configuration.
Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. Vertical antenna between 1/4 and 1/2 wavelength doesn't provide high takeoff angles for NVIS - verticals have lower takeoff angles. Vertical isn't ideal for NVIS.
Option C: Incorrect. Horizontal dipole at 1/2 wavelength has lower takeoff angles - NVIS needs high angles, which require lower height. 1/2 wavelength is too high.
Option D: Incorrect. Vertical dipole at 1/2 wavelength doesn't provide high takeoff angles - verticals and higher heights don't work for NVIS. Vertical dipole is wrong.
题目解析
The correct answer is A: A horizontal dipole placed between 1/10 and 1/4 wavelength above the ground. The antenna type that will be most effective as a near vertical incidence skywave (NVIS) antenna for short-skip communications on 40 meters during the day is a horizontal dipole placed between 1/10 and 1/4 wavelength above the ground. NVIS requires high takeoff angles, which horizontal dipoles at low height provide. For amateur radio operators, this is ideal for NVIS operation. Understanding this helps when designing NVIS antennas.
考试技巧
NVIS antenna = horizontal dipole at 1/10 to 1/4 wavelength height. Think 'N'VIS = 'N'early 'V'ertical = 'H'orizontal 'L'ow height. NVIS requires high takeoff angles, which horizontal dipoles at low height provide. Not vertical, not 1/2 wavelength - just horizontal low height.
记忆口诀
NVIS antenna = horizontal dipole at 1/10 to 1/4 wavelength height. Think 'N'VIS = 'H'orizontal 'L'ow height. NVIS requires high takeoff angles, which horizontal dipoles at low height provide. Ideal for short-skip communications.
实际应用示例
NVIS operation on 40 meters: A horizontal dipole placed between 1/10 and 1/4 wavelength above ground (e.g., 10-30 feet) provides high takeoff angles, ideal for short-skip communications (50-200 miles). The low height creates nearly vertical radiation, perfect for NVIS. This is the most effective NVIS antenna configuration.
错误选项分析
Option B: Incorrect. Vertical antenna between 1/4 and 1/2 wavelength doesn't provide high takeoff angles for NVIS - verticals have lower takeoff angles. Vertical isn't ideal for NVIS. Option C: Incorrect. Horizontal dipole at 1/2 wavelength has lower takeoff angles - NVIS needs high angles, which require lower height. 1/2 wavelength is too high. Option D: Incorrect. Vertical dipole at 1/2 wavelength doesn't provide high takeoff angles - verticals and higher heights don't work for NVIS. Vertical dipole is wrong.
知识点
NVIS antenna, Horizontal dipole, 1/10 to 1/4 wavelength height, Short-skip communications
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.