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.
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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