*Question E9D06:
What happens to SWR bandwidth when one or more loading coils are used to resonate an electrically short antenna?*  

*Correct Answer is  B: It is decreased*  

### AI Response: (may contain errors)  

When loading coils are used to resonate an electrically short antenna, the Standing Wave Ratio (SWR) bandwidth is affected. 

### Correct Answer: It is decreased

1. **Why the correct answer is correct:**
   - Loading coils introduce additional reactance to the antenna system. This reactance can narrow the bandwidth over which the antenna remains resonant. As a result, the SWR bandwidth decreases because the range of frequencies where the antenna can operate efficiently (with low SWR) is reduced.

### Incorrect Choices:

2. **Why the other choices are incorrect:**
   - **A: It is increased**  
     This is incorrect because adding loading coils typically narrows the bandwidth rather than broadening it. The additional reactance from the coils makes it harder for the antenna to maintain resonance over a wider frequency range.

   - **C: It is unchanged if the loading coil is located at the feed point**  
     This is incorrect because even if the loading coil is at the feed point, it still adds reactance to the system. This reactance affects the overall impedance and can lead to a decrease in bandwidth.

   - **D: It is unchanged if the loading coil is located at a voltage maximum point**  
     This is also incorrect. While placing the coil at a voltage maximum may optimize the efficiency of the antenna, it does not prevent the loading coil from affecting the bandwidth. The reactance introduced still narrows the SWR bandwidth.

### Useful Formulas or Rules of Thumb:
- The bandwidth of an antenna can be approximated using the formula:
  
  $$BW \approx \frac{f_0}{Q}$$

  where:
  - $BW$ = bandwidth
  - $f_0$ = resonant frequency
  - $Q$ = quality factor of the antenna system

- A higher $Q$ (which can result from the use of loading coils) leads to a narrower bandwidth. Thus, the introduction of loading coils typically increases the $Q$ factor, resulting in decreased bandwidth. 

This understanding is crucial for optimizing antenna performance in amateur radio applications.