Venerability

Frequently, we as amateurs provide an inducement for Mother Nature to find us.  In order to promote good long distance communications, we put our antennas on the top of towers and place the towers so that they protrude above the surrounding buildings or countryside.  While this provides for great signal coverage, it also makes it easier for Mother Nature to find a shorter, conductive path to ground. 

The probability (likelihood) of having your tower struck by lightning is governed primarily by where you are located and the height of the tower.  In 1952, The Weather Bureau compiled a contour map of the US showing the mean number of thunderstorm-days that occur in a year.  The counting process is relatively simple, a thunderstorm-day is one in which one or more claps of thunder are heard.  This type of information gives us a reasonable view of the country with respect to our exposure to lightning.

The other significant factor that affects the probability of your tower being struck is the height of the tower above the average ground level.  As you might suspect, the higher your tower, the higher the probability of being struck.  The graph to the right shows the estimated number of times per year that your tower of a given height would be struck based on the number of thunderstorm days in your area.

Now that you can estimate your approximate exposure, you could have one of several reactions.  First, you could say that the predictions are all wrong — I have never had my 100 foot tower struck since I put it up two years ago.  Maybe you are just lucky, or the law of average probability has yet to catch up with you.  Another reaction you could have is, wow!  This explains what has been happening and I had better do something about this right away. 

In either case, here is what you need to do to protect both life and equipment.  I will break it down into straightforward steps to ensure your probability of success.  Every amateur radio station is different and there is no ‘one size fits all’ solution.  There are however some well grounded (pun intended) principles that must be followed.  A failure to follow the principles will result in the appropriate expenditure of both time and money with no better protection (possibly even worse damage) than if you had done nothing at all.  Please follow each step carefully, and think about the principles involved, and carefully extrapolate the information to your specific installation.