[TowerTalk] Rain Induced Voltage

[Bill Turner]

ORIGINAL MESSAGE:

On Fri, 1 Dec 2006 04:47:31 -0800 (PST), Dennis OConnor
 <ad4hk2004 at yahoo.com> wrote:

>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...

------------ REPLY FOLLOWS ------------

I think the static is actually cause by highly charged raindrops
striking the antenna, rather than by dripping off. Snow can do the
same thing. Regardless, you should provide a means to drain off the
static charge from the center conductor of the coax. Even if you never
take a direct lightning hit, the static could theoretically build up
enough to damage the coax. Typical coax is only rated for a few KV and
the static could easily build up much higher than that and cause an
arc. Even though each arc carries only a tiny amount of energy, many
thousands of arcs over a period of time could be a problem. Best to
avoid them in the first place.

One method is to install a 1:1 balun at the feedpoint, and another is
to install a high value resistor (one meg or more) between the coax
center and braid. The balun will be more robust of course whereas the
resistor could easily be damaged by a nearby strike. Either one will
drain the static ok.

Bill, W6WRT