Which of the following causes failure of coaxial cables?

Moisture contamination is a significant factor that can lead to the failure of coaxial cables. Coaxial cables are designed to protect the inner conductor from external elements, but if moisture penetrates the cable due to physical damage, faulty connectors, or improper sealing, it can cause several issues.

When moisture enters the cable, it can lead to corrosion of the inner conductor or the dielectric material, which can increase attenuation and result in signal loss. Furthermore, moisture can lead to arcing at high frequencies, which can severely damage the cable's performance.

In contrast, solder flux contamination typically affects connections and solder joints but does not directly impact the cable's integrity in the same pervasive way as moisture. Rapid fluctuations in transmitter output power can create issues related to signal fidelity but are less likely to physically damage the cable itself. Lastly, while operating at 100% duty cycle for an extended period may cause overheating and potentially affect performance, it does not usually lead to immediate failure in the way that moisture can.