[TowerTalk] Corona Electromagnetic Interference

[Kipton Moravec]

On Sun, 2011-04-24 at 01:59 -0400, Fuqua, Bill L wrote:
> If you have not had a problem in 4 years and now you do you may look into other electrical hardware on the tower.
> It may me lighting systems that have started to arc when there is heavy rain or some other electrical problems caused
> by rain or wind. 
> If it is particularly cold it could be ice on the antenna which detunes it. Water has a very high dielectric constant.
> Unlikely corona. 
> 
> 73
> bill wa4lav
> 

When we inspected the system yesterday, we noticed none of the antennas
were properly grounded to the tower where they clamped onto the upright
of the railing around the top of the tower. 

The railing has a heavy coat of paint, and I guess that we assumed that
the U-Bolts would crush the paint and make contact. If they do not then
that is like a capacitor. In the next couple of weeks we are going back
and adding a short #8 or #10 ground wire from the antenna to a
self-tapping screw into the post where we are certain we will be making
good electrical contact. 

We have lightning arrestors where the coax goes into the the tower, and
there is a big copper grounding plate. 

About halfway down there is a grounding strap from the coax shield to
one of the water tank ground wires. 

At the bottom, the coax shield is grounded again to a big single point
ground near the repeater cabinets. 

So we have identified one potential problem area. But it still baffles
me why we have not had a problem until this spring. And it is bad when a
storm comes through and clears up quickly when it passes. Not very good
for a Skywarn repeater. But that tells us that it is not a moisture
problem, because it would take a long time to dry out. That is not the
case.

Our "lightning arrestor" experts tell us that the lightning arrestor
will fail in a short between the center and coax shield, so it is not
the lightning arrestor. That seems a little odd to me, but he works on
commercial antenna sites as his job, and is very knowledgeable. So I
have to believe he knows what he is talking about. 

We are in North Texas, and do not currently have any ice to worry about.
We do get ice storms for a couple of days in the year, but not now.

Thanks for the suggestions everybody.

Kip
-- 
Kipton Moravec AE5IB .- . ..... .. -...

"Always do right; this will gratify some people and astonish the rest."
--Mark Twain