*Question E3A02:
What characterizes libration fading of an EME signal?*  

*Correct Answer is  B: A fluttery, irregular fading*  

### AI Response: (may contain errors)  

Libration fading is a phenomenon that occurs in Earth-Moon-Earth (EME) communication, particularly affecting signals reflected off the Moon. Here's a breakdown of the correct answer and the other choices:

### Correct Answer: B - A fluttery, irregular fading

- **Explanation**: Libration fading is caused by the Moon's slight oscillation (libration) as it orbits the Earth. This motion causes variations in the path length of the signal, leading to fluctuations in signal strength. The result is a "fluttery" or irregular fading effect, which can make the signal appear to vary in intensity.

### Why the Other Choices are Incorrect:

- **A: A slow change in the pitch of the CW signal**  
  - This describes a Doppler effect, which is not specific to libration fading. While Doppler shifts can occur in EME communications, they are not characterized by the irregular fading associated with libration.

- **C: A gradual loss of signal as the sun rises**  
  - This refers to the general fading of signals due to the sun's interference, particularly during the daytime when the sun is above the horizon. It is not related to the libration effect, which is specific to the Moon's motion.

- **D: The returning echo is several hertz lower in frequency than the transmitted signal**  
  - This describes a Doppler shift that can occur due to relative motion between the transmitter and the Moon. While it can happen in EME communications, it does not characterize libration fading, which is more about signal strength variations rather than frequency shifts.

### Summary

- Libration fading is characterized by irregular and fluttery changes in signal strength due to the Moon's oscillation.
- The other options describe different phenomena that do not accurately represent libration fading.

Understanding these distinctions will help you recognize the specific characteristics of libration fading in EME communications for your Extra Class exam.