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Cortana Stati-Cats Protect, Serve
by Mark Persons 
Radio World Article
December 22, 1999

Lightning happens almost anywhere.  The difference between one location and another is the frequency of lightning strikes per year.  Florida gets the highest number.  I, and most of my clients, are in Minnesota.  We are a long ways from Florida.  However, that doesn't exempt this area from lightning damage.

At least twice each summer, I am called to repair lightning damage.  Each time, financial damage to a facility starts at $500.00 and goes up from there.   One of our clients suffered $18,000.00 damage from a single lightning strike this summer.  That station would have spent four days off the air if there had not been a backup transmitter available.  

Most lightning damage occurs at facilities where there is no lightning protection.  You are mistaken if you think a lightning rod at the top of a tower is lightning protection.  The rod usually provides a convenient place for lightning to strike and protects the tower beacon light next to it. 

In the case of the station with $18,000.00 damage, there was a lightning rod at the top of the tower.  The station had major damage to an exciter, high voltage rectifier stacks, low voltage rectifier stacks, remote control, and audio processing equipment.

You probably know that lightning strikes are the result of a high voltage buildup between two places.  There is cloud to cloud lightning that doesn't do any more than annoy us.  Then there is cloud to ground lighting.  Lightning can actually strike from a cloud down to the ground or from the ground up to a cloud depending on the polarity of the electric charge at those two locations. 

What can Cortana Static Cats do to prevent the problem or reduce the severity of a lightning strike?  Static Cat technology is not magic, but is based on physics.  Static Cats have hundreds of sharp points, which bleed off static charges.  That bleeding action is a flow of electrons, like through a resistor, to reduce the potential or voltage between cloud and ground.   The result is that the number of lightning strikes is reduced and the severity of the lighting hits is less.  Some problem prone stations have reported their lightning problems have been virtually eliminated using Static Cats. 

If sharp points are all that is required, why can't I build my own?  Because tower maintenance is expensive, the best answer is to purchase a commercially produced product with a long expected life.  Cortana uses stainless steel rods that have been sharpened to a fine point.  Those rods are mounted in aluminum bars with a high strength adhesive.  They are not something I can imagine the average person making.   Even with stainless steel points, a static cat may not last forever.  High discharge rates actually heat the points making them dull at the ends after years of faithful service.  Static Cats should be inspected annually and repaired or replaced as necessary.  If you need to spend some money repairing a Static Cat, you know it has been working hard for you.

With a Cortana Static Cat, you get professional advice on how many stainless steel points would be right for your situation.  That advice is worth as much as the product itself.  

I recommend Cortana Static Cats for all installations.  There are even some small inexpensive ones for STL towers.   As far as I am concerned, they are cheap at twice the price.  Cortana is now out of business...replaced by Nott Ltd. 

BIO of Mark Persons:

Mark Persons, ham W0MH, is certified by the Society of Broadcast Engineers as a Professional Broadcast Engineer with more than 30 years experience. He has written numerous articles for Radio World over the years. His Web site is

     Questions?  Email Mark Persons:       

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