*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)  

To understand the requirements for a repeater operator when interference occurs with a radiolocation system, let's break down the question and the answer choices.

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

1. **Why the correct answer is correct:**
   - According to FCC regulations, if a repeater is causing harmful interference to a radiolocation system, the operator must take action to resolve the issue. This can include ceasing operation or modifying the repeater's setup (like changing frequency, power, or antenna) to reduce or eliminate the interference. This is crucial to ensure compliance with regulations and to maintain the integrity of critical services like radiolocation.

### Why the other choices are incorrect:

2. **Choice A: Reduce the repeater antenna HAAT (Height Above Average Terrain)**
   - While reducing the height of the antenna could potentially reduce interference, it is not a mandated action. The operator must take effective measures to mitigate interference, which may not necessarily involve changing the antenna height.

3. **Choice B: File an FAA NOTAM (Notice to Air Missions) with the repeater system's ERP, call sign, and six-character grid locator**
   - Filing a NOTAM is not a requirement for addressing interference issues with radiolocation systems. NOTAMs are typically related to aviation and airspace management, not directly to interference resolution for amateur radio operations.

4. **Choice D: All these choices are correct**
   - Since only choice C is correct, this option is also incorrect. The other choices do not fulfill the requirements set by the FCC for handling interference.

### Summary
- The operator must take immediate action to cease operation or modify the repeater to mitigate interference with radiolocation systems, as per FCC regulations. This ensures compliance and protects essential services from disruption. 

This understanding is crucial for the Extra Class exam and for responsible amateur radio operation.