*Question E9H11:
What feature of a cardioid pattern antenna makes it useful for direction-finding antennas?*  

*Correct Answer is  B: A single null*  

### AI Response: (may contain errors)  

A cardioid pattern antenna is particularly useful for direction-finding because of its **single null**. Here's why:

1. **Correct Answer: A single null**  
   - A cardioid pattern has a distinct null, or point of minimum reception, in one direction. This null can be used to determine the direction of a signal by rotating the antenna until the signal is minimized. The direction of the null indicates the direction opposite to the source of the signal, making it a valuable tool for direction-finding.

2. **Why the other choices are incorrect:**
   - **A very sharp peak**: While a sharp peak can help in identifying the direction of maximum signal strength, it is not as useful for precise direction-finding as a null. The null provides a more accurate indication of direction by identifying where the signal is weakest.
   - **Broadband response**: This refers to an antenna's ability to operate over a wide range of frequencies. While useful in some contexts, it does not specifically aid in direction-finding.
   - **High radiation angle**: This describes the elevation angle at which the antenna radiates most of its energy. It is not directly related to the ability to find the direction of a signal source.

In summary, the single null of a cardioid pattern is the key feature that makes it effective for direction-finding, as it allows for precise determination of the direction opposite to the signal source.