Which of the following most limits an HF mobile installation?
“Picket fencing”
The wire gauge of the DC power line to the transceiver
Efficiency of the electrically short antenna✓Correct answer
FCC rules limiting mobile output power on the 75-meter band
Explanation
At HF a mobile whip is a small fraction of a wavelength long, so its radiation resistance is only a few ohms while coil, ground and connection losses are of comparable magnitude, and much of the power is dissipated as heat rather than radiated. This efficiency limit dominates over the power wiring and any regulatory consideration.