When wires are used in very moist environments, such as near the ocean, moisture is an ever-present concern. Some cables can deteriorate after only a few years of operation because moisture enters either the cable itself or the connector. Shields and conductors can suffer from corrosion when the cables are not properly cleaned. There are several modifications you must make to your cables to guard them against moisture.
The Moisture Threat
Even when corrosion does not develop on a military cable, moisture in the connector will change the characteristic impedance of the cable. When there is a change in impedance, there is an increase in the signal reflection. This can lead to a sensitive system becoming unreliable or even failing.
In some cases, you may have a difficult time identifying why a component is being exposed to moisture. For example, an antenna can become exposed to moisture as a result of a swing in temperature. A drop in cabin pressure can create a vacuum in and around the connector, which can draw in moisture.
One way around this problem is to use solid-dielectric cables. However, these types of cables are not completely immune to the effects of moisture, even if they are not as absorbent. Also, solid cables weigh more than more porous cables. Because cables are stiffer, they will have a greater bend radius requirement. As a result, they might have different routing requirements when being installed.
Another concern is that the construction of the device that uses the cables makes it impractical for moisture to be drained from the cable. The moisture might wick back into the cable through a capillary action. Because of this problem, you must try to stop the flow of moisture to the military cable in the first place whenever possible.
One way to block the passage of moisture into the connectors is to use water-sealing connectors. However, it is not known how well the connectors will seal against moisture in the long-term. Plastic connectors are not able to entirely seal out moisture, but they can stop water from condensing. Heat-shrink tubing can help with strain relief.
If you want to completely stop the passage of moisture, you will need a hermetic seal. Because this is impractical, you will need to use a variety of the other options available to make sure that you can minimize the amount of moisture that will negatively impact your cables.