*Question E9C10:
Which of the following describes a Zepp antenna?*  

*Correct Answer is  B: An end-fed half-wavelength dipole*  

### AI Response: (may contain errors)  

A Zepp antenna is specifically defined as an end-fed half-wavelength dipole. Let's break down the correct answer and why the other options are incorrect.

### Correct Answer: B - An end-fed half-wavelength dipole
- **Explanation**: 
  - A Zepp antenna is typically a half-wavelength dipole that is fed at one end. This configuration allows it to be used in various setups, especially in portable or temporary installations. The half-wavelength design means that the antenna is resonant at a specific frequency, making it efficient for transmitting and receiving signals.

### Why the Other Choices are Incorrect:
- **A: A horizontal array capable of quickly changing the direction of maximum radiation by changing phasing lines**
  - **Explanation**: This describes a type of phased array antenna, which uses multiple elements and phasing lines to steer the direction of radiation. A Zepp antenna does not have this capability; it is a simple dipole design.

- **C: An omni-directional antenna commonly used for satellite communications**
  - **Explanation**: An omni-directional antenna radiates signals equally in all directions, which is not the case for a Zepp antenna. The Zepp is directional in nature, especially when oriented horizontally, and is not specifically designed for satellite communications.

- **D: A vertical array capable of quickly changing the direction of maximum radiation by changing phasing lines**
  - **Explanation**: Similar to option A, this describes a phased array antenna. A Zepp antenna is not a vertical array and does not utilize phasing lines to change radiation direction.

### Useful Formulas and Rules of Thumb:
- **Half-Wavelength Dipole Length**: The length of a half-wavelength dipole can be calculated using the formula:
  
  $$L = \frac{468}{f}$$

  where:
  - $L$ = length in feet
  - $f$ = frequency in megahertz (MHz)

This formula helps in determining the physical length of the Zepp antenna for a specific operating frequency, ensuring it is resonant and efficient. 

In summary, the Zepp antenna is a specific type of end-fed half-wavelength dipole, while the other options describe different antenna types or configurations that do not apply to the Zepp.