Deep Dive: G5C07
The correct answer is A: 3.5 to 1. The transformer turns ratio that matches an antenna's 600-ohm feed point impedance to a 50-ohm coaxial cable is 3.5 to 1. Impedance ratio = 600/50 = 12:1. Turns ratio = √(impedance ratio) = √12 = 3.46 ≈ 3.5:1. For amateur radio operators, this is how impedance matching transformers work. Understanding this helps when matching antennas.
Why Other Answers Are Wrong
Option B (12 to 1): Incorrect. 12:1 is the impedance ratio, not the turns ratio. Turns ratio = √(impedance ratio) = √12 = 3.5:1. Option C (24 to 1): Incorrect. 24:1 is too high - that would be √576, not √12. Calculation error. Option D (144 to 1): Incorrect. 144:1 is way too high - that would be √20,736, not √12. Calculation error.
Exam Tip
Impedance matching transformer: Impedance ratio = 600/50 = 12:1, Turns ratio = √12 = 3.5:1. Think 'I'mpedance 'M'atching = 'I'mpedance ratio, 'M'ultiply by √. Turns ratio = √(impedance ratio). Not 12:1 (impedance ratio), not 24:1, not 144:1 - just 3.5:1.
Memory Aid
Impedance matching transformer: Turns ratio = √(impedance ratio) = √12 = 3.5:1. Think 'I'mpedance 'M'atching = 'I'mpedance ratio, 'M'ultiply by √. Turns ratio = √(impedance ratio). Standard impedance matching calculation.
Real-World Example
You need to match a 600-ohm antenna to 50-ohm coax. Impedance ratio = 600/50 = 12:1. Turns ratio = √12 = 3.46 ≈ 3.5:1. A transformer with 3.5:1 turns ratio will match 600Ω to 50Ω. The square root relationship comes from impedance being proportional to turns squared.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G5C
Reference: 2023-2027 Question Pool · G5 - Electrical Principles
Key Concepts
Verified Content
Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G5C topic.