A little more about snake oil. About the only thing you can do to
control where lightning is going to strike is to attract it, more or
less. A lightning rod or one of these dissipation brushes produce a corona
which produces a great deal of ozone and free electrons. If the path of the
lightning come near enough to this cloud of charges it may take that path
back to the lightning rod or brush and then to "ground". One thing you
can do on a tower is to have a lightning rod with its own very heavy
ground conductor to perhaps encourage the lightning to hit it rather than
your antennas. The induced currents and paths for currents are another matter.
I had a direct hit on a TA33 once. It did not hurt anything in the
house but it did interesting damage to the antenna.
About on inch away from the end of the reflector there was a 1/4 inch
hole in the aluminum tube. The hole was almost circular and there was a
large "frozen" drop of aluminum hanging down inside of tube from the edge
of the hole. The plastic cap on the end of the element was not melted or
effected in any way. This seemed very strange but that was how I found it.
The traps survived by the way.
73
Bill wa4lav
>Talk about "snake oil" this dissipation brush thing is nuts. A bunch of
>sharp wires on the top of an tower is supposed to prevent lightning? If
>there is a high potential between these wires and the clouds it will cause
>field ionization of the atoms and molecules at the sharp tips of the wire.
>This will not dissipate the charge ( lots of coulombs stored between earth
>and clouds) at all unless
>there is a tremendous discharge ( lightning).
> Where the lightning goes depends where the random paths of the
> cosmic rays that strike the atmosphere. The cosmic rays ( very high
> energy particles) leave ionization trails that cross each other and when
> these paths happen to make a connection between the clouds and earth
> there is a discharge. That is why lightning seems to be a bunch of
> connected straight lines.
> The guys that sell the dissipation brushes put these on top of a
> little Van de Graaff generators and then show that they get a much
> smaller arc off the dome than without the "brush". However, the charge on
> the dome of the Van de Graaff is very small and the rate at which it can
> be charged (current) is limited by the amount of charge the little rubber
> belt can carry from the grounded base to the dome. The field ionization
> at the tips of the wires produces a corona that discharges the dome of
> the Van de Graaff and in effect reduces its voltage. We use corona
> loading to regulate the dome (high voltage terminal) voltage on our large
> Van de Graaff accelerator. And when it discharges at 5 or 6 MV it makes
> quite a noise. Lightning involves many more coulombs of charge than the
> salesman would have you think.
>
>
>73
>Bill wa4lav
>
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