What is the most common impedance of coaxial cables used in amateur radio?
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.
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 Application
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.
Key Concepts
Why Other Options 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.
题目解析
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.
考试技巧
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.
记忆口诀
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.
实际应用示例
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.
错误选项分析
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.
知识点
Coaxial cable impedance, 50 ohms, Feed line standards, Impedance matching
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.