*Question E9H08:
What is the function of a sense antenna?*  

*Correct Answer is  A: It modifies the pattern of a DF antenna to provide a null in only one direction*  

### AI Response: (may contain errors)  

A sense antenna is used in direction finding (DF) systems to help determine the direction of a received signal more accurately. Here's why the correct answer is correct and why the other choices are incorrect:

1. **Correct Answer: A**  
   - **Explanation**: The sense antenna modifies the pattern of a DF antenna to provide a null in only one direction. This is crucial in resolving the 180-degree ambiguity that can occur with some DF systems, such as those using loop antennas. By introducing a sense antenna, the system can distinguish between the front and back of the antenna pattern, allowing for more precise direction finding.

2. **Incorrect Choices**:
   - **B: It increases the sensitivity of a DF antenna array**  
     - **Explanation**: The primary function of a sense antenna is not to increase sensitivity but to resolve directional ambiguities. Sensitivity is generally a function of the main DF antenna system, not the sense antenna.
   
   - **C: It allows DF antennas to receive signals at different vertical angles**  
     - **Explanation**: The sense antenna does not affect the vertical angle of reception. It is used to modify the azimuthal pattern to resolve directional ambiguities.
   
   - **D: It provides diversity reception that cancels multipath signals**  
     - **Explanation**: Diversity reception involves using multiple antennas to improve signal quality by mitigating multipath effects. The sense antenna's role is not related to diversity reception but to pattern modification for direction finding.

In summary, the sense antenna's role is to modify the DF antenna pattern to eliminate directional ambiguity, specifically by providing a null in only one direction. This is essential for accurate direction finding.