Topband: Lightning Protection

[Tom Rauch]

I replied to KN4LF off the reflector, and he requoted me here. So I 
guess I'll respond here on the reflector.

> Thomas KN4LF Says:  Yes it's the large voltage gradient between the
> earth and the charged moisture in the air, in other words a cloud or
> cumulonimbus. You can remove the built up charge potential between
> cloud and earth with a path, in other words a lightning bolt!

That's right. The little whiskers do absolutely nothing to discharge 
the cloud.  
  
> Thomas KN4LF Says: A spline ball drains excessive voltage buildup on
> the object it's attached to and the immediate atmosphere near the
> object within a few feet but not the earth itself. 

A spiked ball can not do that. The fact it is a conductor and is tied 
to earth means any charges that leave are immediately replenished 
from the vast reserve of the earth. In order to reduce voltage 
gradient, you MUST discharge the cloud. That is where the 
problem is.

> Tom W8JI Said: An airplane (where the idea came from) is different. In
> the case of an airplane the movement of the plane through the charged
> area "leaks charges off" and makes the plane come closer to the
> potential of the air (and moisture) around the plane. It looks like
> part of the sky around the airplane, so far as charges go.
> 
> Thomas KN4LF Says: They were not trying to reduce or prevent a
> lightning strike to an aircraft but trying to reduce St. Elmo's Fire
> or plasma or voltage buildup which creates a constant hiss of QRN on
> receivers and can also damage static sensitive microchips in
> electronic equipment.

The spikes and whiskers do exactly the opposite. They encourage 
corona discharge.  That is how they function.

The end-effect of these little spiked balls is they simply make a 
small ion cloud around the area of the ball if the wind is not 
dispersing the cloud. While that can reduce voltage gradient around 
the area of the cloud, it does not affect anything outside of that 
small area. It also "blunts" the structure's sharp points by adding 
corona discharge and of course with that discharge comes noise!  

If you want to eliminate hissing noise from corona, you need a 
large rounded smooth ball. That is the primary function of the 
smooth round balls on mobile whips and car radio antennas. This 
is also what quad has less corona than a yagi, all other things 
equal (the quad element has four "blunt" sides, the yagi has two 
sharp points per element stick out into the air that encourages 
corona). 

If you replaced the smooth round ball on a mobile whip with a 
bunch of sharp whiskers, corona would increase.....not decrease. 
You might as well put a stop sign on a tower as a spiked ball.
73, Tom W8JI
W8JI@contesting.com