What is the purpose of a capacitance hat on a mobile antenna?
The correct answer is C: To electrically lengthen a physically short antenna. The purpose of a capacitance hat on a mobile antenna is to electrically lengthen a physically short antenna. A capacitance hat adds capacitance at the top, which electrically lengthens the antenna, improving its performance. For amateur radio operators, this helps mobile antennas work better on lower frequencies. Understanding this helps when using mobile antennas.
Exam Tip
Capacitance hat purpose = electrically lengthen physically short antenna. Think 'C'apacitance 'H'at = 'C'apacitance 'H'elps lengthen. Adds capacitance at top, electrically lengthening antenna. Not power handling, not resistance reduction, not radiation angle - just electrical lengthening.
Memory Aid
"Capacitance hat purpose = electrically lengthen physically short antenna. Think 'C'apacitance 'H'at = 'C'apacitance 'H'elps lengthen. Adds capacitance at top, electrically lengthening antenna. Improves mobile antenna performance."
Real-World Application
You have a physically short mobile antenna for 40 meters. You add a capacitance hat (metal disk or wires at the top). The capacitance hat adds capacitance, which electrically lengthens the antenna, making it resonate better on 40 meters. This improves the antenna's performance without making it physically longer.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Capacitance hats don't increase power handling - that's about antenna construction, not capacitance hats. Power handling isn't the purpose.
Option B: Incorrect. Capacitance hats don't reduce radiation resistance - they help match impedance, not reduce resistance. Resistance reduction isn't the purpose.
Option D: Incorrect. Capacitance hats don't lower the radiation angle - that's about antenna height and design, not capacitance hats. Radiation angle isn't affected.
题目解析
The correct answer is C: To electrically lengthen a physically short antenna. The purpose of a capacitance hat on a mobile antenna is to electrically lengthen a physically short antenna. A capacitance hat adds capacitance at the top, which electrically lengthens the antenna, improving its performance. For amateur radio operators, this helps mobile antennas work better on lower frequencies. Understanding this helps when using mobile antennas.
考试技巧
Capacitance hat purpose = electrically lengthen physically short antenna. Think 'C'apacitance 'H'at = 'C'apacitance 'H'elps lengthen. Adds capacitance at top, electrically lengthening antenna. Not power handling, not resistance reduction, not radiation angle - just electrical lengthening.
记忆口诀
Capacitance hat purpose = electrically lengthen physically short antenna. Think 'C'apacitance 'H'at = 'C'apacitance 'H'elps lengthen. Adds capacitance at top, electrically lengthening antenna. Improves mobile antenna performance.
实际应用示例
You have a physically short mobile antenna for 40 meters. You add a capacitance hat (metal disk or wires at the top). The capacitance hat adds capacitance, which electrically lengthens the antenna, making it resonate better on 40 meters. This improves the antenna's performance without making it physically longer.
错误选项分析
Option A: Incorrect. Capacitance hats don't increase power handling - that's about antenna construction, not capacitance hats. Power handling isn't the purpose. Option B: Incorrect. Capacitance hats don't reduce radiation resistance - they help match impedance, not reduce resistance. Resistance reduction isn't the purpose. Option D: Incorrect. Capacitance hats don't lower the radiation angle - that's about antenna height and design, not capacitance hats. Radiation angle isn't affected.
知识点
Capacitance hat, Mobile antenna, Electrical lengthening, Antenna loading
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.