Question
Why should antenna loading coils have a high ratio of reactance to resistance?
Answer Options
- A) To swamp out harmonics
- B) To lower the radiation angle
- C) To maximize efficiency
- D) To minimize the Q
Correct Answer: C
Explanation
Antenna loading coils are required to resonate electrically short antennas, but they introduce loss resistance (R_{Loss}) that directly compromises the antenna’s radiation efficiency (\eta = R_{Rad} / R_{Total}). The goal is to use a coil that introduces the required reactance with the absolute minimum possible loss resistance.
The ratio of a coil’s inductive reactance (X_L) to its series loss resistance (R_{Loss}) is its Quality factor, or Q = X_L / R_{Loss}. A high Q coil minimizes R_{Loss} and thereby maximizes efficiency. Therefore, antenna loading coils should have a high ratio of reactance to resistance (high Q) to ensure most of the input power is radiated rather than dissipated as heat in the coil.
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