*Question E9C07:
What is the approximate feed point impedance at the center of a two-wire half-wave folded dipole antenna?*  

*Correct Answer is  A: 300 ohms*  

### AI Response: (may contain errors)  

A two-wire half-wave folded dipole antenna is a variation of the standard half-wave dipole antenna. It consists of two parallel wires, typically spaced a small distance apart, and connected at both ends. This configuration affects the feed point impedance.

### Explanation:

1. **Correct Answer: 300 ohms**

   - The feed point impedance of a standard half-wave dipole is approximately 72 ohms. When you fold the dipole by adding a second parallel wire, the impedance increases. The impedance of a folded dipole is approximately four times that of a standard dipole.
   - Therefore, the feed point impedance of a two-wire half-wave folded dipole is:
     $$ Z_{\text{folded}} = 4 \times Z_{\text{dipole}} = 4 \times 72 \, \text{ohms} = 288 \, \text{ohms} $$
   - This is often rounded to 300 ohms for practical purposes.

2. **Why the Other Choices are Incorrect:**

   - **72 ohms (Choice B):** This is the approximate impedance of a standard half-wave dipole, not a folded dipole.
   - **50 ohms (Choice C):** This is a common impedance for coaxial cables and some antennas, but not for a folded dipole.
   - **450 ohms (Choice D):** This impedance is typical for ladder line or open-wire feed lines, not for a two-wire folded dipole.

### Key Points:

- **Impedance Transformation:** The folding of the dipole increases the impedance by a factor of four.
- **Practical Impedance:** The theoretical 288 ohms is often rounded to 300 ohms for simplicity in design and matching with transmission lines.

Understanding these concepts will help you correctly identify the feed point impedance of a folded dipole antenna on the exam.