*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)  

The function of a sense antenna in direction finding (DF) systems is to modify the pattern of the main DF antenna, allowing it to create a null in a specific direction. This helps in accurately determining the direction of incoming signals.

### Explanation of the Correct Answer:
- **Correct Answer: A**  
  A sense antenna is used in conjunction with a DF antenna to create a directional pattern that can be adjusted. By modifying the pattern, it can produce a null (a point of minimal reception) in one direction, which is crucial for pinpointing the source of a signal. This is particularly useful in locating the direction of a transmitter.

### Explanation of Incorrect Answers:
- **B: It increases the sensitivity of a DF antenna array**  
  While a sense antenna can help in direction finding, its primary role is not to increase sensitivity but to modify the directional characteristics of the antenna pattern.

- **C: It allows DF antennas to receive signals at different vertical angles**  
  A sense antenna does not primarily function to receive signals at different vertical angles. Instead, it focuses on enhancing the directional capabilities of the main antenna.

- **D: It provides diversity reception that cancels multipath signals**  
  While diversity reception can help mitigate multipath interference, the sense antenna's main purpose is not to cancel these signals but to assist in determining direction by creating a null.

### Summary:
- The sense antenna modifies the DF antenna's pattern to create a null in one direction, aiding in accurate direction finding.
- Other options either misrepresent the function of the sense antenna or focus on aspects that are not its primary purpose.

This understanding is crucial for the Extra Class exam, as it highlights the specific role of antennas in direction finding systems.