*Question G1A06:
[97.303] Which of the following applies when the FCC rules designate the amateur service as a secondary user on a band?*  

*Correct Answer is  C: Amateur stations must not cause harmful interference to primary users and must accept interference from primary users*  

### AI Response: (may contain errors)  

In the context of the FCC rules, when the amateur service is designated as a secondary user on a band, it means that amateur radio operators have limited rights compared to primary users. Here's a breakdown of the correct answer and why the other choices are incorrect:

1. **Correct Answer: C**  
   - **Explanation**: As secondary users, amateur stations must not cause harmful interference to primary users. This means that if a primary user is operating on the frequency, amateurs must either avoid using that frequency or ensure their operations do not interfere with the primary user. Additionally, amateurs must accept any interference they receive from primary users, as primary users have priority access to the band.

2. **Why Other Choices Are Incorrect**:
   - **Choice A**: Amateur stations are not required to record the call sign of the primary service station. The focus is on avoiding interference, not on documentation of primary users.
   - **Choice B**: The use of the band is not restricted to emergencies. Amateurs can use the band under normal conditions as long as they do not interfere with primary users.
   - **Choice D**: There are no specific hours during which amateurs can operate. The restriction is based on interference, not time of day.

3. **Useful Rule of Thumb**:
   - **Primary vs. Secondary**: Always remember that primary users have priority. Secondary users must ensure their operations do not interfere with primary users and must tolerate any interference from them. This is a fundamental principle when operating as a secondary user on any band.