Deep Dive: T9B02
The correct answer is B: 50 ohms. The most common impedance of coaxial cables used in amateur radio is 50 ohms. This has become the standard because it provides a good compromise between power handling, loss, and practical considerations. Most amateur transceivers have 50-ohm outputs, and most antennas are designed for 50-ohm feed. For amateur radio operators, 50-ohm cable (like RG-58, RG-8, LMR-400) is the standard. Understanding this helps when selecting feed lines and ensures proper impedance matching throughout the system.
Why Other Answers Are Wrong
Option A (8 ohms): Incorrect. 8 ohms is common for audio speakers, not RF feed lines. Coaxial cables for RF are 50 or 75 ohms. Option C (600 ohms): Incorrect. 600 ohms is used for some audio and telephone systems, not RF coaxial cables. Option D (12 ohms): Incorrect. 12 ohms isn't a standard coaxial cable impedance. Standard RF impedances are 50 and 75 ohms.
Exam Tip
Amateur coax = 50 ohms. Think '5'0 ohms = '5'tandard for amateurs. Most common impedance for amateur radio feed lines. 8 ohms is audio, 600 ohms is telephone, 12 ohms isn't standard.
Memory Aid
Amateur coax = 50 ohms. Think '5'0 ohms = '5'tandard. Most common impedance for amateur radio feed lines. Ensures proper matching with transceivers and antennas.
Real-World Example
Your transceiver has a 50-ohm output, your antenna is designed for 50-ohm feed, and you use 50-ohm coaxial cable (RG-8) to connect them. This 50-ohm standard throughout your system ensures proper impedance matching and maximum power transfer. Using 75-ohm cable (common for TV) would create a mismatch.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T9B
Reference: 2022-2026 Question Pool · T9 - Antennas and feed lines
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T9B topic.