*Question E2D06:
Which of the following is a method for establishing EME contacts?*  

*Correct Answer is  A: Time-synchronous transmissions alternating between stations*  

### AI Response: (may contain errors)  

To establish Earth-Moon-Earth (EME) contacts, the correct method is:

**Correct Answer: A: Time-synchronous transmissions alternating between stations**

### Explanation:

1. **Why the correct answer is correct:**
   - **Time-synchronous transmissions** involve coordinating the timing of transmissions and receptions between two stations. This is crucial for EME because the signals travel a long distance (to the moon and back), and precise timing helps ensure that both stations are listening and transmitting at the right times. Typically, one station transmits for a set period (e.g., 2 minutes), then listens while the other station transmits.

2. **Why the other choices are incorrect:**
   - **B: Storing and forwarding digital messages**: This method is not applicable to EME contacts. EME requires real-time communication due to the nature of the signal path and the need for immediate reception and response.
   - **C: Judging optimum transmission times by monitoring beacons reflected from the moon**: While monitoring beacons can help determine conditions, it is not a method for establishing contacts. It is more of a preparatory step rather than a communication method.
   - **D: High-speed CW identification to avoid fading**: High-speed CW (Continuous Wave) can be used in EME, but it is not specifically a method to avoid fading. Fading is a natural part of EME due to the long path and reflections, and timing synchronization is more critical for successful communication.

### Useful Concepts:

- **Round-trip time**: The time it takes for a signal to travel to the moon and back is approximately 2.5 seconds. This delay must be accounted for in time-synchronous operations.
- **Doppler shift**: The relative motion of the Earth and Moon can cause frequency shifts, which must be considered when setting up EME communications.

Understanding these concepts and the importance of timing will help you successfully establish EME contacts.