At 04:47 AM 12/1/2006, Dennis OConnor wrote:
>This morning in Michigan we are having a mix of sleet and freezing
>rain... I was up early so I wandered out to the shack about 5AM to
>see if any Pacific DX was coming in on 80 or 160... When I
>energized the antenna switch I was greeted by the sound of a
>frying/popping noise at about 4-5 cycles per second and an S-meter
>completely pinned to the right... I know that sound quite well and
>instantly cut the power to the antenna switching box... I unscrewed
>the coax to the one antenna that is not link coupled - meaning I
>have a DC connection to the actual antenna - a 160 meter
>dipole... Using the tip of my pocket knife I can draw an arc
>between the shell and the center pin on the PL-259... The VOM reads
>from 5 to 7 volts DC across the connector continuous into a 1 megohm
>load... There is no convective activity in the area, no thunder or
>lightning, and no thunder storms predicted... The voltage appears
>to be induced by the rain drops dripping off the antenna wire removing
> electrons and leaving a static charge with the ungrounded side of
> the antenna <coax center pin) left positively charged...
The mechanism you propose (or one similar to it) is very likely
what's going on.
Check out the Kelvin Water Dropper electrostatic generator.
http://en.wikipedia.org/wiki/Kelvin_water_dropper
FWIW, the raindrops probably are charged, even without a thunderstorm
around. One of the mechanisms by which that charging occurs has to
do with the transition between water and ice. And, there's always an
electric field of around 1kV/meter (fair weather field). But, as you
have a dipole, both sides of it would be expected to charge equally
(at least at the antenna). Then, as you note, one side is grounded,
the other not.
And, a related phenomenon, P-static, occurs in planes just flying
through rain, without the need for thunderstorms.
>I know we have genteely discussed this before <called a scrum in
>some circles>, but since it is fresh in my mind, I thought I would
>bring it up again <also known as stirring the pot>...
>
>denny / k8do
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