Question
What is one disadvantage of using a shortened mobile antenna as opposed to a full-size antenna?
Answer Options
- A) Short antennas are more likely to cause distortion of transmitted signals
- B) Q of the antenna will be very low
- C) Operating bandwidth may be very limited
- D) Harmonic radiation may increase
Correct Answer: C
Explanation
The efficiency of a shortened antenna is achieved by adding a large inductor (loading coil) to counteract the antenna’s capacitive reactance, bringing it to resonance. This loading significantly increases the quality factor (‘Q’) of the antenna system.
However, a high-Q circuit is also a highly selective circuit, meaning it responds only to a very narrow range of frequencies. The practical disadvantage of this is that the operating bandwidth may be very limited, often requiring the operator to re-tune or adjust the loading coil for even a small change in operating frequency within the same band.
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