*Question E1D02:
[97.211(b)] Which of the following may transmit encrypted messages?*  

*Correct Answer is  B: Telecommand signals from a space telecommand station*  

### AI Response: (may contain errors)  

In the context of amateur radio, the rules about encryption are quite specific. Let's break down the question and the choices:

### Correct Answer: Telecommand signals from a space telecommand station

1. **Why the correct answer is correct:**
   - According to FCC Part 97.211(b), encryption is permitted for telecommand signals from a space telecommand station. This is because these signals are used to control the operation of spacecraft, and encryption is necessary to ensure the security and integrity of the commands being sent.

### Why the other choices are incorrect:

2. **Telecommand signals to terrestrial repeaters:**
   - Encryption is not allowed for terrestrial repeater control. The FCC requires that amateur communications be open and accessible to all licensed operators, and encryption would violate this principle.

3. **Auxiliary relay links carrying repeater audio:**
   - Similar to terrestrial repeaters, auxiliary relay links must also remain open and accessible. Encryption would prevent other amateur operators from monitoring these communications, which is against FCC rules.

4. **Mesh network backbone nodes:**
   - While mesh networks can be used in amateur radio, the use of encryption on these networks is not permitted. The principle of open communication applies here as well, ensuring that all amateur operators can access and monitor transmissions.

### Useful Rule of Thumb:

- **General Rule:** In amateur radio, communications must be open and accessible to all licensed operators, with very few exceptions. The primary exception is for telecommand signals to control spacecraft, where encryption is allowed to maintain security and integrity.