*Question G3B12:
Which of the following is typical of the lower HF frequencies during the summer?*  

*Correct Answer is  D: High levels of atmospheric noise or static*  

### AI Response: (may contain errors)  

During the summer, the lower HF frequencies (such as 160 meters and 80 meters) often experience high levels of atmospheric noise or static. This is primarily due to increased thunderstorm activity, which generates a lot of electrical noise that can be picked up by radio receivers.

1. **Correct Answer: D - High levels of atmospheric noise or static**
   - Thunderstorms are more frequent in the summer, leading to increased static and noise on the lower HF bands. This noise is often referred to as "QRN" in amateur radio terminology.

2. **Why the other choices are incorrect:**
   - **A: Poor propagation at any time of day**
     - While there can be poor propagation on lower HF bands during the day due to D-layer absorption, this is not specifically a summer phenomenon. The question asks about what is typical during the summer, which is more about noise levels.
   - **B: World-wide propagation during daylight hours**
     - Lower HF frequencies generally do not support world-wide propagation during daylight hours due to D-layer absorption, which is stronger during the day.
   - **C: Heavy distortion on signals due to photon absorption**
     - Photon absorption is not a term typically used in the context of HF radio propagation. Signal distortion on HF is more commonly due to ionospheric conditions, not photon absorption.

3. **Useful Rules of Thumb:**
   - Lower HF bands are more affected by atmospheric noise, especially in the summer.
   - D-layer absorption is stronger during the day, affecting lower HF bands more significantly.

Understanding these characteristics helps in planning effective communication strategies and choosing the right frequencies for different times and conditions.