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The short answer is that water won't cause any problem, and even salt
water probably won't (except corrosion). When water bridges across a driven element or to the boom (not by any means the same as the Earth), you've put a high value resistor and capacitor across the driven element or from the element to the boom. Pure water is a good insulator but acts also like a lossy capacitor at RF; rain water on an antenna will have some dissolved minerals so that reduces the shunt R. The feedpoint impedance of a beam is quite low, so all you've done is put a high value of impedance across a low value. The change is therefore very small. This holds for half wave dipoles, quarter wave verticals, and most other common antennas, too. A few antenna types have high impedances at the feedpoint, like an electrically short whip, or a full wavelength dipole. Although I don't know of any rigorous tests, I don't think even these are commonly bothered much by water. Roy Lewallen, W7EL Dan Jacobson wrote: Can one in theory still transmit if rain water creates a bridge across the driven element, or even also to 'ground'? A DC short circuit but not a RF short circuit? Or is it just salt water that is worrisome? |
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