(N4KG response to W 5 H V V below)
On Tue, 5 Aug 1997 20:48:34 -0500 w5hvv@aeneas.net (Roderick M.
Fitz-Randolph) writes:
>My first lightning hit here (I've had 3 in 3 years) was off a tip
>end of the driven element on my 40-2CD at 140'. It turned the trap
>on that side of the driven element into a real crispy critter. When
>I reinstalled it (wadda pain) after replacement of the trap and coax,
>I also installed a 10 foot high galvanized tube above the mast that
>held my antennas. This tube has 5 each 18" long (very sharp ended)
>spikes brazed to the top of the tube - one straight up and the rest
>at 45 degrees to the vertical and in the four directions.
>
>I've been hit twice since then but the lightning has hit my "pointy,
>spikey thing" and not my antennas.... for which I am most thankful.
>
>There is no telling if the sharp spikes at the top have bled off
>enough
>charge to prevent any more hits or not. But it sure has caught the
>2nd and 3rd hits and saved me a bunch of money in that I haven't had
>to take down the TH7DX and 40-2CD from off the top of the 130' tower
>to replace any more traps!! For that I am thankful and I am glad I
>put the "charge bleeder/lightning attracter" up there. I don't think
>I'll ever have another tower in my lifetime without one up there, way
>above all the antennas.
>
>Rod, W5HVV
>
>
Thanks for this most relevant testamonial Rod !
I have been biting my tongue on this issue waiting for just such
supportive evidence. I have seen the Van de Graf generator
demonstration by The Wireman (N8UG) and been most impressed
by the audible and visible arc drawn by large conductors and the
imperceptible effects when a bundle of thin wire approaches the
charged sphere.
Some respondents to my LIGHTNING STRIKE SURVEY cited
observed small strikes or charge bleed-off to masts or other
protrusions (one gin pole) with little or no damage.
Another respondent pointed out the effect of local terrain and
ground conductivity in determining lightning strike susceptibility.
With several towers set in ground but without additional ground
rods or radials, I have yet to sustain a damaging strike after
25 years in storm prone Alabama. I attribute part of this to my
local ground conditons (nearby creek and underground water)
and protruding masts above each tower/ antenna.
The POLYPHASOR book dismisses static dissipators as being
worthless and refers to an unnamed NAVY study as corroborating (sp?)
evidence. No title or other reference data was given for the reader
to read the results for himself.
POLYPHASOR seems to take the attitude that if any other devices
are not 100% effective in eliminating a lightning strike, then they
are not worth implementing. They also seem to imply that you
can never have a good enough ground.
The above real life experiences would seem to indicate
that anything which can help reduce charge concentrration
around the tower (Top and Bottom) contributes to reducing
and minimizing lightning damage.
The bottom line is that everyone must ultimately determine
their own cost / benefit comfort level.
de Tom N4KG
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