*Question G9B05:
How does antenna height affect the azimuthal radiation pattern of a horizontal dipole HF antenna at elevation angles higher than about 45 degrees?*  

*Correct Answer is  C: If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional*  

### AI Response: (may contain errors)  

When considering the azimuthal radiation pattern of a horizontal dipole HF antenna, the height of the antenna above ground plays a significant role, especially at elevation angles higher than about 45 degrees.

### Correct Answer: C
- **Explanation**: If the antenna is less than 1/2 wavelength high, the azimuthal pattern tends to be almost omnidirectional. This is because at lower heights, the ground reflection and the direct wave combine in such a way that the pattern becomes more uniform in all directions. The ground has a significant influence on the radiation pattern, causing it to spread out more evenly.

### Why Other Choices Are Incorrect:
- **Choice A**: "If the antenna is too high, the pattern becomes unpredictable"  
  - This is incorrect because while the pattern does change with height, it does not become unpredictable. Instead, it becomes more directional with lobes forming at specific angles as the height increases.

- **Choice B**: "Antenna height has no effect on the pattern"  
  - This is incorrect because antenna height significantly affects the radiation pattern. As the height increases, the pattern becomes more directional with distinct lobes and nulls.

- **Choice D**: "If the antenna is less than 1/2 wavelength high, radiation off the ends of the wire is eliminated"  
  - This is incorrect because radiation off the ends is not eliminated. Instead, the pattern becomes more uniform, but not specifically nullified at the ends.

### Useful Rule of Thumb:
- **Height and Pattern**: 
  - At heights less than 1/2 wavelength, the pattern is more omnidirectional.
  - At heights around 1/2 wavelength or more, the pattern becomes more directional with distinct lobes.

Understanding these principles helps in predicting how an antenna will perform based on its height above ground, which is crucial for optimizing communication effectiveness.