*Question G9B02:
Which of the following is a common way to adjust the feed point impedance of an elevated quarter-wave ground-plane vertical antenna to be approximately 50 ohms?*  

*Correct Answer is  B: Slope the radials downward*  

### AI Response: (may contain errors)  

To adjust the feed point impedance of an elevated quarter-wave ground-plane vertical antenna to be approximately 50 ohms, the correct method is to slope the radials downward.

### Explanation of the Correct Answer:
- **Slope the radials downward**:  
  When the radials are sloped downward, it effectively increases the capacitive reactance of the antenna system. This adjustment helps to lower the feed point impedance closer to the desired 50 ohms. The downward slope allows for better matching with typical coaxial cable impedances.

### Explanation of Incorrect Answers:
- **Slope the radials upward**:  
  Slope the radials upward would increase the inductive reactance, which raises the feed point impedance. This would move the impedance further away from the desired 50 ohms, making it less effective for matching.

- **Lengthen the radials beyond one wavelength**:  
  Lengthening the radials beyond one wavelength can lead to increased impedance, as the antenna may start to behave more like a resonant structure rather than a ground plane. This typically results in a higher feed point impedance, which is not desirable for matching to 50 ohms.

- **Coil the radials**:  
  Coiling the radials introduces additional inductance, which also raises the feed point impedance. This method complicates the antenna's performance and does not help in achieving the desired 50-ohm impedance.

### Useful Rules of Thumb:
- For a quarter-wave ground-plane antenna, the ideal feed point impedance is around 50 ohms when the radials are horizontal or slightly sloped downward.
- Adjusting the angle of the radials can help fine-tune the impedance; downward slopes generally reduce impedance, while upward slopes increase it.

By understanding these principles, you can effectively manage the feed point impedance of your antenna systems.