What is one disadvantage of using a shortened mobile antenna as opposed to a full-size antenna?
The correct answer is C: Operating bandwidth may be very limited. A disadvantage of using a shortened mobile antenna as opposed to a full-size antenna is that operating bandwidth may be very limited. Shortened antennas with loading have high Q (narrow bandwidth), making them sensitive to frequency changes. For amateur radio operators, this requires frequent retuning. Understanding this helps explain shortened antenna limitations.
Exam Tip
Shortened antenna disadvantage = operating bandwidth may be very limited. Think 'S'hortened 'A'ntenna = 'S'lim 'A'perture (narrow bandwidth). Shortened antennas with loading have high Q (narrow bandwidth). Not distortion, not low Q, not harmonics - just limited bandwidth.
Memory Aid
"Shortened antenna disadvantage = operating bandwidth may be very limited. Think 'S'hortened 'A'ntenna = 'S'lim 'A'perture. Shortened antennas with loading have high Q (narrow bandwidth). Requires frequent retuning."
Real-World Application
You use a shortened mobile antenna for 40 meters. The antenna has a narrow bandwidth (e.g., 50 kHz) compared to a full-size antenna (e.g., 200 kHz). As you change frequency, you must retune the antenna. The limited bandwidth is a significant disadvantage of shortened antennas.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Short antennas don't cause signal distortion - distortion comes from other sources. Signal distortion isn't a shortened antenna disadvantage.
Option B: Incorrect. Short antennas don't have very low Q - they have high Q (narrow bandwidth). Low Q would mean wide bandwidth, which isn't the case.
Option D: Incorrect. Short antennas don't increase harmonic radiation - harmonics come from non-linear operation, not antenna length. Harmonic radiation isn't a shortened antenna issue.
题目解析
The correct answer is C: Operating bandwidth may be very limited. A disadvantage of using a shortened mobile antenna as opposed to a full-size antenna is that operating bandwidth may be very limited. Shortened antennas with loading have high Q (narrow bandwidth), making them sensitive to frequency changes. For amateur radio operators, this requires frequent retuning. Understanding this helps explain shortened antenna limitations.
考试技巧
Shortened antenna disadvantage = operating bandwidth may be very limited. Think 'S'hortened 'A'ntenna = 'S'lim 'A'perture (narrow bandwidth). Shortened antennas with loading have high Q (narrow bandwidth). Not distortion, not low Q, not harmonics - just limited bandwidth.
记忆口诀
Shortened antenna disadvantage = operating bandwidth may be very limited. Think 'S'hortened 'A'ntenna = 'S'lim 'A'perture. Shortened antennas with loading have high Q (narrow bandwidth). Requires frequent retuning.
实际应用示例
You use a shortened mobile antenna for 40 meters. The antenna has a narrow bandwidth (e.g., 50 kHz) compared to a full-size antenna (e.g., 200 kHz). As you change frequency, you must retune the antenna. The limited bandwidth is a significant disadvantage of shortened antennas.
错误选项分析
Option A: Incorrect. Short antennas don't cause signal distortion - distortion comes from other sources. Signal distortion isn't a shortened antenna disadvantage. Option B: Incorrect. Short antennas don't have very low Q - they have high Q (narrow bandwidth). Low Q would mean wide bandwidth, which isn't the case. Option D: Incorrect. Short antennas don't increase harmonic radiation - harmonics come from non-linear operation, not antenna length. Harmonic radiation isn't a shortened antenna issue.
知识点
Shortened antenna, Operating bandwidth, Limited bandwidth, Mobile antenna
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.