Deep Dive: E9C07
The correct answer is A: 300 ohms. The approximate feed point impedance at the center of a two-wire half-wave folded dipole antenna is 300 ohms. This is approximately 4 times the impedance of a standard half-wave dipole. A folded dipole consists of two parallel wires connected at the ends, forming a loop. The folding and the two-wire structure increase the impedance compared to a simple dipole. A standard half-wave dipole has about 72 ohms impedance. A two-wire folded dipole has approximately 4 times that, or about 300 ohms. This higher impedance can be useful for matching to certain feed lines or when you need higher impedance. The exact value depends on the wire spacing and diameter, but 300 ohms is the typical value.
Why Other Answers Are Wrong
Option B: Incorrect. 72 ohms is the impedance of a standard half-wave dipole, not a folded dipole. The folding increases the impedance. Option C: Incorrect. 50 ohms is a common feed line impedance, not the folded dipole impedance. Folded dipoles have higher impedance. Option D: Incorrect. 450 ohms would be too high. A two-wire folded dipole typically has about 300 ohms impedance.
Exam Tip
Folded dipole impedance = 300 ohms. Remember: A two-wire half-wave folded dipole has approximately 300 ohms feed point impedance - about 4 times a standard dipole's 72 ohms.
Memory Aid
**F**olded **D**ipole **I**mpedance = **3**00 ohms (think 'FDI = 300Ω')
Real-World Example
You build a two-wire folded dipole. The two parallel wires are connected at the ends, creating a loop. At the center feed point, you measure approximately 300 ohms impedance. This is much higher than a standard dipole's 72 ohms, which can be useful for matching to 300-ohm twin-lead or when you need higher impedance.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E9C
Reference: FCC Part 97.3
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E9C topic.