*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)  

The feed point impedance at the center of a two-wire half-wave folded dipole antenna is approximately 300 ohms. Here's a breakdown of why this is the correct answer and why the other choices are incorrect.

### Explanation of the Correct Answer (300 ohms):
- A folded dipole antenna consists of two parallel conductors and has a higher impedance than a standard half-wave dipole.
- The standard half-wave dipole has a feed point impedance of about 72 ohms. However, the folding of the dipole effectively increases the impedance due to the additional conductor.
- The formula for the impedance of a folded dipole is given by:

$$
Z_f = n^2 \times Z_d
$$

where:
- $Z_f$ = feed point impedance of the folded dipole
- $Z_d$ = impedance of the standard dipole (approximately 72 ohms)
- $n$ = number of folds (for a half-wave folded dipole, $n = 2$)

Using this, we calculate:

$$
Z_f = 2^2 \times 72 \, \text{ohms} = 4 \times 72 \, \text{ohms} = 288 \, \text{ohms} \approx 300 \, \text{ohms}
$$

### Why the Other Choices are Incorrect:
- **72 ohms (Choice B)**: This is the impedance of a standard half-wave dipole, not a folded dipole.
- **50 ohms (Choice C)**: This is a common impedance for many coaxial cables and some antennas, but it does not apply to a folded dipole.
- **450 ohms (Choice D)**: This value is typical for a long wire or a high-impedance antenna, but it is not representative of a folded dipole's feed point impedance.

### Summary:
- The correct answer is **300 ohms** because the folded dipole's impedance is approximately four times that of a standard half-wave dipole.
- The other choices do not accurately reflect the characteristics of a folded dipole antenna. 

Understanding these concepts will help you in the Extra Class exam and in practical applications of antenna theory.