Question
Which of the following most limits an HF mobile installation?
Answer Options
- A) “Picket fencing”
- B) The wire gauge of the DC power line to the transceiver
- C) Efficiency of the electrically short antenna
- D) FCC rules limiting mobile output power on the 75-meter band
Correct Answer: C
Explanation
The most significant challenge and limiting factor in any HF mobile installation is the compromise forced upon the antenna system. To be practical on a vehicle, the antenna must be physically much shorter than the \frac{1}{4} wavelength required for resonance (especially on 80\text{m} or 40\text{m}).
This physical shortness results in low radiation resistance, necessitating a loading coil to achieve resonance. This process dramatically reduces the efficiency of the electrically short antenna, meaning a significant portion of the transmitter’s power is lost as heat in the loading coil rather than being radiated as an RF signal.
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