Am 14.05.2012 21:54, schrieb Hal Murray: > [email protected] said: >> I had the same problem with a GPS antenna at work. Somebody had put the >> manufactures label over the porus plug that should have vented out any >> water... but it didn't so I had too high water-level inside the antenna. > How does water get in? > > I'm not doubting that it does, just trying to understand the mechanism. > Let me try to explain it. The mechanism is as follows:
Air does contain water in form of gas (vapour) which does condense to water when the temperature drops down (eg. at night). The problem is coming up on tight boxes having a pressure leak eg. due to defective sealing, cracks or via non hermetic cable connections. Changing air pressure do always pump in fresh and humid air and the condensed water remain on the bottom inside the box and may as well penetrate into the wire mesh/ braid of coaxial cables. The copper will start "modering" and turn black. The only solutions I think: Apply air pressure tight boxes having a breathing hole an the bottom, mount the box that no rain and water can penetrate from the top or sides. If the hole is big enough, eg. 2mm, no pressure difference is possible and no pumping effect will occur. (If the hole is too wide, small animals may penetrate). Or, when using a pressure tight box, it must be stiff and sealed to withstand under all temperature conditions more then 1 bar/ 100 kPa. Do not forget that all feed throughs must be of real hermetic type, normal coaxial connectors are not tight! Don't route cables directly in, because no cable braid or mesh is vapor tight. I hope this will help, we had never problems that way. Arnold _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
