*Question G9B07:
How does the feed point impedance of a horizontal 1/2 wave dipole antenna change as the antenna height is reduced to 1/10 wavelength above ground?*  

*Correct Answer is  B: It steadily decreases*  

### AI Response: (may contain errors)  

As the height of a horizontal 1/2 wave dipole antenna is reduced to 1/10 wavelength above ground, the feed point impedance steadily decreases. Here's why:

1. **Correct Answer Explanation (B: It steadily decreases):**
   - The feed point impedance of a dipole antenna is influenced by its height above ground. When the antenna is close to the ground (less than 1/4 wavelength), the ground has a significant effect on the antenna's impedance.
   - At lower heights, the ground causes the antenna to couple more strongly with its image in the ground, which reduces the radiation resistance and thus the feed point impedance.
   - As the height decreases from 1/4 wavelength to 1/10 wavelength, the impedance continues to decrease.

2. **Why Other Choices Are Incorrect:**
   - **A: It steadily increases**: This is incorrect because, as explained, the impedance decreases due to stronger coupling with the ground.
   - **C: It peaks at about 1/8 wavelength above ground**: This is incorrect because there is no peak at 1/8 wavelength; instead, the impedance decreases as the height is reduced below 1/4 wavelength.
   - **D: It is unaffected by the height above ground**: This is incorrect because the height above ground significantly affects the impedance, especially when the antenna is close to the ground.

3. **Useful Rule of Thumb:**
   - For a dipole antenna, the feed point impedance is approximately 73 ohms when it is at a height of 1/2 wavelength above ground. As the height decreases below 1/4 wavelength, the impedance decreases due to ground effects.

Understanding how the height of a dipole affects its impedance is crucial for optimizing antenna performance, especially in low-height installations.