Deep Dive: T7C09
The correct answer is A: Moisture contamination. Moisture contamination is a primary cause of coaxial cable failure. Water entering the cable (through damaged jackets, poor connectors, or cracks) causes several problems: it increases losses, can cause short circuits, promotes corrosion of the center conductor, and can freeze and expand, further damaging the cable. For amateur radio operators, preventing moisture ingress is essential for maintaining feed line performance. Proper connector installation, UV-resistant jackets, and sealed connections help prevent moisture problems. Once moisture enters, the cable often needs replacement.
Why Other Answers Are Wrong
Option B: Incorrect. Solder flux contamination can cause problems in connectors but isn't a primary cause of cable failure. Modern cables use crimp connectors that don't require flux. Option C: Incorrect. Rapid power fluctuations don't typically cause cable failure - cables can handle power variations. The problem is usually physical damage or moisture. Option D: Incorrect. Operating at 100% duty cycle (continuous transmission) generates heat but doesn't typically cause cable failure if the cable is properly rated. Heat is a concern, but moisture is the primary failure cause.
Exam Tip
Moisture = primary cause of cable failure. Think 'M'oisture = 'M'ajor problem. Water causes losses, corrosion, and physical damage. Other factors are less common causes of failure.
Memory Aid
Moisture = Major cause of cable failure. Think 'M'oisture = 'M'ajor problem. Water causes losses, corrosion, shorts, and physical damage. Keep cables dry.
Real-World Example
Your feed line develops high losses and poor SWR. Inspection reveals the cable jacket has cracked from UV exposure, allowing water to enter. The moisture has corroded the center conductor and increased losses significantly. The cable needs replacement. Proper installation with UV-resistant cable and sealed connectors would have prevented this. Moisture is the enemy of coaxial cable.
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.