*Question G3B01:
What is a characteristic of skywave signals arriving at your location by both short-path and long-path propagation?*  

*Correct Answer is  D: A slightly delayed echo might be heard*  

### AI Response: (may contain errors)  

When a skywave signal arrives at your location via both short-path and long-path propagation, it means the signal has traveled two different routes to reach you. This can result in:

- **Correct Answer: D: A slightly delayed echo might be heard**

### Explanation:
1. **Why the correct answer is correct:**
   - The short-path and long-path routes have different lengths, causing the signal to arrive at slightly different times. This time difference can create an echo effect, where you hear the same signal twice with a slight delay between them.

2. **Why the other choices are incorrect:**
   - **A: Periodic fading approximately every 10 seconds**: This is more characteristic of multipath fading, where signals take multiple paths of similar length, causing interference patterns. The periodicity of 10 seconds is not specifically related to short-path and long-path propagation.
   - **B: Signal strength increased by 3 dB**: An increase in signal strength by 3 dB would imply a doubling of power, which is not a typical result of receiving signals via both short and long paths. The paths can interfere constructively or destructively, but a consistent 3 dB increase is not expected.
   - **C: The signal might be cancelled causing severe attenuation**: While cancellation can occur due to destructive interference, it is not a defining characteristic of short-path and long-path propagation. The key characteristic is the echo effect due to the time delay.

### Useful Concepts:
- **Propagation Paths**: Short-path is the direct route, while long-path is the longer, often opposite direction around the Earth.
- **Echo Effect**: The time delay between the two paths causes the echo, which is the primary characteristic of this phenomenon.