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

Choices:  
A: Telecommand signals to terrestrial repeaters  
B: Telecommand signals from a space telecommand station  
C: Auxiliary relay links carrying repeater audio  
D: Mesh network backbone nodes    

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

Correct answer: Telecommand signals from a space telecommand station

Why this is correct:
- FCC Part 97.211(b) explicitly permits the use of codes or encryption for telecommand of a space station. A “space telecommand station” is the Earth station that sends those commands. The purpose is to prevent unauthorized access to spacecraft control.

Why the others are incorrect:
- Telecommand signals to terrestrial repeaters: Not allowed to be encrypted. Part 97.113(a)(4) prohibits messages encoded to obscure their meaning, and there is no exception for repeater control. Using DTMF or tones is okay because they are not intended to obscure meaning, but encryption is not.
- Auxiliary relay links carrying repeater audio: Auxiliary stations (97.201) must not use encryption; 97.113(a)(4) applies here as well. Audio or control traffic over aux links must be intelligible to third parties.
- Mesh network backbone nodes: Even on high-speed amateur IP backbones, encryption to obscure meaning is generally prohibited under 97.113(a)(4). Amateur communications must be open and interceptable by third parties, with the spacecraft-control exception only.

Rules of thumb:
- Encryption in Amateur Radio: only for spacecraft telecommand per 97.211(b).
- If it’s not controlling a spacecraft, assume encryption is prohibited by 97.113(a)(4).
- “Codes” like DTMF or standard digital modes are permitted when not intended to obscure meaning; “encryption” that hides meaning is prohibited except for spacecraft control.