*Question E3B11:
At what time of day is sporadic-E propagation most likely to occur?*  

*Correct Answer is  D: Between sunrise and sunset*  

### AI Response: (may contain errors)  

Sporadic-E propagation is a type of radio wave propagation that occurs in the E layer of the ionosphere, typically characterized by short-lived openings that can enhance communication over long distances, especially on VHF and UHF frequencies.

### Correct Answer: Between sunrise and sunset

1. **Why the correct answer is correct:**
   - Sporadic-E propagation is most likely to occur during the daytime, particularly from sunrise to sunset. This is due to the increased solar radiation during the day, which ionizes the E layer of the ionosphere. The ionization creates irregularities that can reflect radio waves, allowing for long-distance communication.

2. **Why the other choices are incorrect:**
   - **A: Between midnight and sunrise**  
     - During this time, the ionosphere is less ionized due to the absence of solar radiation, making sporadic-E propagation unlikely.
   - **B: Between sunset and midnight**  
     - Similar to choice A, the lack of solar energy leads to decreased ionization, reducing the chances of sporadic-E propagation.
   - **C: Between sunset and sunrise**  
     - This option encompasses both A and B, where the ionosphere is not sufficiently energized to support sporadic-E propagation.

### Useful Rules of Thumb:
- **Daytime Propagation:** Sporadic-E is primarily a daytime phenomenon due to solar activity.
- **Frequency Range:** It is most effective on VHF (30 MHz to 300 MHz) and UHF (300 MHz to 3 GHz) bands.

Understanding these factors will help you recognize the conditions under which sporadic-E propagation is most likely to occur, aiding in your exam preparation.