*Question E1B04:
[97.303(b)] What must the control operator of a repeater operating in the 70-centimeter band do if a radiolocation system experiences interference from that repeater?*  

*Correct Answer is  C: Cease operation or make changes to the repeater that mitigate the interference*  

### AI Response: (may contain errors)  

In the context of amateur radio operations, especially on shared frequency bands like the 70-centimeter band, it is crucial to avoid causing interference to other services. The 70-centimeter band is shared with radiolocation services, which are often used for important applications like radar.

### Explanation:

1. **Correct Answer: C - Cease operation or make changes to the repeater that mitigate the interference**

   - **Reason**: According to FCC rules, if a repeater causes interference to a radiolocation system, the control operator must take immediate action to stop the interference. This can involve ceasing operation or making technical adjustments to the repeater to eliminate the interference. The primary responsibility is to ensure that the repeater does not disrupt the operation of other services.

2. **Why the other choices are incorrect:**

   - **Choice A: Reduce the repeater antenna HAAT**
     - **Reason**: While reducing the antenna height might help in some cases, it is not a guaranteed solution to interference issues. The rule specifically requires ceasing operation or making changes that directly address the interference, not just altering the antenna height.

   - **Choice B: File an FAA NOTAM**
     - **Reason**: Filing a Notice to Air Missions (NOTAM) is not relevant to resolving interference issues with radiolocation systems. NOTAMs are used to inform pilots of potential hazards along a flight route or at a location, not to address radio frequency interference.

   - **Choice D: All these choices are correct**
     - **Reason**: Since only ceasing operation or making changes to mitigate interference is the correct action, this choice is incorrect. The other options do not fulfill the requirement to stop the interference.

### Key Rule:

- **FCC Rule [97.303(b)]**: This rule emphasizes the responsibility of amateur radio operators to avoid causing harmful interference to other services, especially on shared frequency bands. The control operator must take immediate action to resolve any interference issues.

By understanding these responsibilities and the correct actions to take, amateur radio operators can ensure compliance with FCC regulations and maintain harmonious use of the radio spectrum.