*Question E9D04:
Why should antenna loading coils have a high ratio of reactance to resistance?*  

*Correct Answer is  C: To maximize efficiency*  

### AI Response: (may contain errors)  

To understand why antenna loading coils should have a high ratio of reactance to resistance, let's break down the concepts:

### Correct Answer: C: To maximize efficiency

1. **Maximize Efficiency**:  
   - **Reactance ($X$)**: This is the part of the impedance that stores energy temporarily in the magnetic field of the coil.
   - **Resistance ($R$)**: This is the part of the impedance that dissipates energy as heat.
   - **Efficiency**: For an antenna, efficiency is maximized when more energy is radiated and less is lost as heat. This is achieved by having a high reactance-to-resistance ratio ($X/R$), which means the coil stores more energy relative to what it dissipates.

### Why Other Choices Are Incorrect:

2. **A: To swamp out harmonics**:  
   - Harmonics are unwanted frequencies that are multiples of the fundamental frequency. Loading coils are not primarily used to filter out harmonics; instead, they are used to make electrically short antennas resonate at the desired frequency.

3. **B: To lower the radiation angle**:  
   - The radiation angle is more influenced by the physical height and design of the antenna rather than the reactance-to-resistance ratio of loading coils.

4. **D: To minimize the Q**:  
   - **Quality Factor ($Q$)**: This is defined as $Q = \frac{X}{R}$. A high $Q$ indicates a narrow bandwidth and high efficiency. Minimizing $Q$ would mean increasing resistance relative to reactance, which would decrease efficiency, contrary to the goal of maximizing it.

### Useful Formula:

- **Quality Factor ($Q$)**:  
  $$Q = \frac{X}{R}$$  
  A high $Q$ (high $X/R$ ratio) indicates that the coil is efficient at storing energy compared to dissipating it as heat, which is desirable for maximizing antenna efficiency.

In summary, a high reactance-to-resistance ratio in loading coils is crucial for maximizing the efficiency of an antenna by ensuring more energy is stored and radiated rather than lost as heat.