Topband: Vertical Lightning Protection

Missouri Guy, N0TT n0tt1 at
Wed Jan 5 12:41:59 EST 2005

Hi Phil,

Impressive antenna you have there!

> I have had a large 
> vacuum variable capacitor
> in place to do the job for several years, but lightning took its 
> toll 
> last spring. I thought I had
> ample protection...a 350uh choke across the base insulators to drain 
> off static build-up, 

OK, that's good

> and
> three sets of spark-gap balls; one on each tower leg across the 
> insulators. This worked well
> through many storms. 

I would use *pointed* spark gap hardware vs the round ones.
Electrical charges tend to accumulate where the curvature of a
conductor is greatest.  So, a pointed object would have the
greatest curvature vs a round one....that's why lightning rods 
are shaped the way they are.

> I have another vacuum variable ready to mount; 
> 800pf @ 18 kv, 150 amps.
> Any ideas on how to keep this beauty from falling prey to Mother 
> Nature?

Set the spark gaps as close as you can without arcing under normal
transmitting voltage.  Protect the gaps with a rain hood. 

Other than shorting out the capacitor when it's not in use, there
isn't much else one can do.  Mother Nature does what she wants!  :)

Charlie   N0TT

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