Peter 9V1PC Said: I'm after some advice on lightning protection.
Thomas KN4LF Says: I have been studying and investigating lightning and it's
effects for 35 years, 28 years as a Meteorological Consultant. My
meteorological website is at: Florida Meteorological & Climatic Institute
http://64.176.157.9/sub/fmci.htm
Lightning protection is a two pronged attack. First you need a direct low
resistance path to ground to safely discharge the up to 10 million volts at
500,000 amps +/-. I use #4 solid copper wire to four 10 foot 1/2" copper
pipes. but even this arrangement may not be suitable for all lightning
strikes instances. Higher resistive paths allow the lightning strike to find
multiple alternate grounding paths through your house electrical wiring,
plumbing, etc. creating a fire hazard. Secondly you need to try to reduce
chances of a lightning strike in the first place. This is accomplished by
preventing excessive static electricity building up on your antennas/towers.
I use homebrew copper spline balls/porcupines/bottle brushes which when used
in unison with a good low resistance ground path drain the static
electricity, preventing a buildup that would eventually send a skyward
propagating stepped leader from your antenna/tower, to eventually meet with
a downward propagating stepped leader and blammo lightning strike. A
floating antenna invites a lightning strike, as static electricity is
allowed to build up. The best way to keep lightning out of your shack,
design your station so that all incoming coax, ground and rotator cables,
etc. can be disconnected outside the shack entrance and then grounded,
that's what I do at my QTH.
The bottom line though is that lightning does strange things all the time,
including regularly striking the lowest objects around, so no design is
foolproof. The spline ball is highly used here in Florida by NASA, power,
telephone and cable companies.
73,
Thomas Giella, KN4LF
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