On Tue, 08 Feb 2005 00:06:25 +0800, 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?

Hi Dan,

Water is an insulator, and a very good dielectric. It would make for
a very good method for building high valued capacitors (displacing
inferior oil), but for one remarkably aggressive characteristic.

Water will disassociate many things (act as a solvent or simply as a
transport). As such it quickly degrades its dielectric characteristic
when in contact with nature. If you were to insert two probes to
measure its initial conductivity (presuming you start with distilled,
de-ionized water), you would find it easily in the megOhms if you
could measure that high in the first place. However, the simple
immersion of the probes (depending on their material and time
immersed) will lead to increasing that conductivity - such is the
aggressive nature of water. Nature is rarely that pristine, so to
dwell on de-ionized rain offers its own comedy of failed expectation.

So, that is the long way of saying you are on the greasy skids of
seeking an all-inclusive answer except to simply offer: don't trust
one. Decades of experience, however, yield practical answers. Look
at insulator materials and construction geometries. Largely, these
two are well tailored to shed water and increase surface area for a
fixed length. If you are worried about salt water, visit a marine
supplier who sells electrical/RF equipment (hard to imagine they would
by shy of examples). These rather simple items reveal how few find
water worrisome after their installation.

Now, if you want the warm snuggly feeling of data to two or three
places, the theory to back it up, and allusions to wave mechanics (be
they water or RF). Time and space will enlarge in this forum to allow
that easily.

73's
Richard Clark, KB7QHC