Deep Dive: T7C05
The correct answer is A: To protect the output amplifier transistors. Most solid-state transmitters reduce output power as SWR increases beyond a certain level to protect the output amplifier transistors. High SWR causes reflected power to return to the transmitter, which can damage or destroy the output transistors. The protection circuit detects high SWR and automatically reduces power to prevent damage. For amateur radio operators, this is a safety feature that protects expensive equipment. Understanding this helps explain why your transmitter power drops when SWR is high, and emphasizes the importance of proper antenna tuning.
Why Other Answers Are Wrong
Option B: Incorrect. While FCC rules require spectral purity, the power reduction is for equipment protection, not specifically for compliance. The protection circuit prevents damage, not violations. Option C: Incorrect. Power supplies can typically supply enough current - the limitation is the output transistors' ability to handle reflected power, not power supply capacity. Option D: Incorrect. Reducing power doesn't lower SWR - SWR is determined by impedance mismatch, not power level. The protection reduces power to prevent damage, not to fix SWR.
Exam Tip
High SWR = power reduction to protect transistors. Think 'H'igh 'S'WR = 'H'armful to 'S'olid-state transistors. The protection circuit reduces power to prevent damage from reflected power. It's equipment protection, not for compliance or fixing SWR.
Memory Aid
High SWR = power reduction to protect transistors. Think 'H'igh 'S'WR = 'H'armful, so 'S'ave transistors by reducing power. Protection circuit prevents damage from reflected power.
Real-World Example
Your antenna develops a problem and SWR rises to 5:1. Your transmitter's protection circuit detects this and automatically reduces power from 100 watts to 20 watts. This prevents the reflected power from damaging your expensive output transistors. Once you fix the antenna and SWR returns to normal, the transmitter automatically returns to full power. This protection saves your equipment from expensive repairs.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T7C
Reference: 2022-2026 Question Pool · T7 - Practical circuits
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T7C topic.