Which of the following most limits an HF mobile installation?
The correct answer is C: Efficiency of the electrically short antenna. What most limits an HF mobile installation is the efficiency of the electrically short antenna. Mobile antennas are physically short, requiring loading (inductive or capacitive), which reduces efficiency. For amateur radio operators, this is the primary limitation of mobile HF operation. Understanding this helps explain mobile HF challenges.
Exam Tip
Most limits HF mobile = efficiency of electrically short antenna. Think 'E'lectrically 'S'hort = 'E'fficiency 'S'uffers. Mobile antennas are physically short, requiring loading that reduces efficiency. Not picket fencing, not wire gauge, not FCC rules - just antenna efficiency.
Memory Aid
"Most limits HF mobile = efficiency of electrically short antenna. Think 'E'lectrically 'S'hort = 'E'fficiency 'S'uffers. Mobile antennas are physically short, requiring loading that reduces efficiency. Primary limitation of mobile HF."
Real-World Application
You operate HF mobile with a short antenna. The antenna requires loading (inductive or capacitive) to resonate, which reduces efficiency. Much of your power is lost as heat in the loading coil rather than radiated. This low efficiency is the primary limitation of mobile HF operation.
Key Concepts
Why Other Options Are Wrong
Option A (Picket fencing): Incorrect. Picket fencing (rapid signal variation) is a problem but not the most limiting factor - antenna efficiency is more fundamental.
Option B: Incorrect. Wire gauge of DC power line isn't the most limiting factor - with proper wiring, power isn't the limitation. Antenna efficiency is more limiting.
Option D: Incorrect. FCC rules don't limit mobile output power on 75 meters - mobile has same power limits as fixed stations. Power limits aren't the issue.
题目解析
The correct answer is C: Efficiency of the electrically short antenna. What most limits an HF mobile installation is the efficiency of the electrically short antenna. Mobile antennas are physically short, requiring loading (inductive or capacitive), which reduces efficiency. For amateur radio operators, this is the primary limitation of mobile HF operation. Understanding this helps explain mobile HF challenges.
考试技巧
Most limits HF mobile = efficiency of electrically short antenna. Think 'E'lectrically 'S'hort = 'E'fficiency 'S'uffers. Mobile antennas are physically short, requiring loading that reduces efficiency. Not picket fencing, not wire gauge, not FCC rules - just antenna efficiency.
记忆口诀
Most limits HF mobile = efficiency of electrically short antenna. Think 'E'lectrically 'S'hort = 'E'fficiency 'S'uffers. Mobile antennas are physically short, requiring loading that reduces efficiency. Primary limitation of mobile HF.
实际应用示例
You operate HF mobile with a short antenna. The antenna requires loading (inductive or capacitive) to resonate, which reduces efficiency. Much of your power is lost as heat in the loading coil rather than radiated. This low efficiency is the primary limitation of mobile HF operation.
错误选项分析
Option A (Picket fencing): Incorrect. Picket fencing (rapid signal variation) is a problem but not the most limiting factor - antenna efficiency is more fundamental. Option B: Incorrect. Wire gauge of DC power line isn't the most limiting factor - with proper wiring, power isn't the limitation. Antenna efficiency is more limiting. Option D: Incorrect. FCC rules don't limit mobile output power on 75 meters - mobile has same power limits as fixed stations. Power limits aren't the issue.
知识点
HF mobile installation, Electrically short antenna, Efficiency, Mobile limitations
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.