*Question E9H02:
Which is generally true for 160- and 80-meter receiving antennas?*  

*Correct Answer is  A: Atmospheric noise is so high that directivity is much more important than losses*  

### AI Response: (may contain errors)  

The correct answer to the question about 160- and 80-meter receiving antennas is:

**A: Atmospheric noise is so high that directivity is much more important than losses.**

### Explanation of the Correct Answer:
- **Atmospheric Noise**: At lower frequencies like 160 and 80 meters, atmospheric noise (from sources like lightning and other natural phenomena) can be significant. This noise can mask weak signals, making it crucial to have a directional antenna that can focus on the desired signal while rejecting noise from other directions.
- **Directivity vs. Losses**: In this context, having a highly directional antenna (like a Yagi or a loop) can help improve the signal-to-noise ratio (SNR) by picking up signals from a specific direction and minimizing noise from others. This is often more beneficial than minimizing losses in the transmission line or antenna itself.

### Why the Other Choices are Incorrect:
- **B: They must be erected at least 1/2 wavelength above the ground to attain good directivity**: 
  - While height can improve performance, it is not a strict requirement for good directivity. Antennas can still be effective at lower heights, especially if they are designed to be directional. The 1/2 wavelength rule is more about minimizing ground losses than ensuring directivity.
  
- **C: Low loss coax transmission line is essential for good performance**: 
  - While using low-loss coax is beneficial, it is not essential for good performance in all cases. The impact of coax loss is less critical when using highly directional antennas that can effectively reject noise. In many situations, the benefits of directivity outweigh the losses in the coax.

- **D: All these choices are correct**: 
  - Since choices B and C are not universally true, this option cannot be correct.

### Useful Rules of Thumb:
- **Directivity**: A directional antenna can significantly improve reception in noisy environments. The more focused the antenna pattern, the better it can isolate signals from noise.
- **Height Considerations**: While higher antennas generally perform better, especially for low-band frequencies, practical installation constraints often dictate the actual height. 

In summary, for 160- and 80-meter antennas, focusing on directivity is key to overcoming atmospheric noise, making option A the best choice.