>
> Do you have data contrary to that? Is there anybody who experienced
more
> lightning strikes after putting up bigger antenna installations? Just
> because
> "professionals" did not exprience it (didn't have big antennas) it
can't
> be so?
> Why would you say that? Did you try to do it, or heard of unsuccessful
> event
> like that?
> Or you just "know" better?
anecdotal 'evidence' is just what gets those snake oil salesmen more
sales. If it were true that large horizontal structures on top of
towers didn't get hit then why do power companies spend money trying to
prevent damage from strokes to power lines. HV power lines are larger
than any ham structures, within the same range of heights, and use
conductors that are often bigger in diameter than elements of large
yagis... by your 'experience' they should repel lightning, and yet they
get struck every day by both large and small strokes. In fact we have
many studies and world wide accepted models that show that large
conductive objects like those attract more strokes from the surrounding
area, enough data that I had to build that attractiveness into my
modeling software to properly match the measurements.
The biggest problem with discussing lightning protection is the highly
variable distribution of lightning from year to year. In studies using
the national lightning detection network (which the company I work for
did the initial design and setup of), the number of lightning strokes in
a small area (say 10x10miles) can vary by a factor of 10 or more from
year to year. The typical experience is that a power company has a very
bad year with lightning outages and decides to add arresters or improve
grounding or some other action, then the next year the engineers look
like heros because they have no outages... will if they really looked in
detail they would see they also took no hits and what they had done was
really worthless, if they are lucky they get promoted or move before the
next bad year comes along and shows the truth. Those static brushes are
not the only example of unproven technology in this area, there are
other methods and devices that have also been highly praised over the
years that later prove to be equally ineffective. Even in the area of
designing a ground system to dissipate lightning energy there are lots
of misconceptions and poor practices that have been around for years
that are now being debunked... but that's a whole different thread.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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