Deep Dive: G4E05
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.
Why Other Answers 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.
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 Example
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.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G4E
Reference: 2023-2027 Question Pool · G4 - Amateur Radio Practices
Key Concepts
Verified Content
Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G4E topic.