*Question T7C09:
Which of the following causes failure of coaxial cables?*  

*Correct Answer is  A: Moisture contamination*  

### AI Response: (may contain errors)  

Moisture contamination is a significant factor that can lead to the failure of coaxial cables. Here's a breakdown of why this is the correct answer and why the other options are not:

### Correct Answer: A: Moisture contamination
- **Explanation**: Moisture can infiltrate coaxial cables, especially if there are any breaches in the outer jacket. This moisture can cause short circuits, corrosion of the inner conductor, and degradation of the dielectric material, ultimately leading to cable failure. 

### Why the Other Choices are Incorrect:
- **B: Solder flux contamination**: 
  - While solder flux can cause issues in connections, it does not directly lead to the failure of coaxial cables themselves. It may affect solder joints but is not a primary cause of cable failure.

- **C: Rapid fluctuation in transmitter output power**: 
  - Fluctuations in output power can affect performance and may lead to overheating or other issues, but they do not directly cause the physical failure of the coaxial cable. Coaxial cables are designed to handle varying power levels.

- **D: Operation at 100% duty cycle for an extended period**: 
  - Operating at 100% duty cycle can lead to overheating and potential damage to the transmitter or other components, but coaxial cables are typically rated for continuous operation. If properly rated, they should not fail solely due to duty cycle.

### Summary
- **Key Takeaway**: Moisture contamination is the primary concern for coaxial cable integrity, while the other options relate more to operational issues rather than direct causes of cable failure. 

### Rule of Thumb
- Always ensure coaxial cables are properly sealed and protected from moisture, especially in outdoor or humid environments, to maintain their longevity and performance.