Thread: Yagi plans
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Old January 26th 05, 07:33 PM
Richard Harrison
 
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Jim, NN7K wrote:
"When lightning strikes, it is going where ever it wants to, in spite of
the best grounding intentions."

Yes, the trick is to send it to where you would rather it goes. You do
this with your grounding techniques.

The coax itself is important protection against lightning. Opposition
within the coax to lightning is severe. Lightning is a common-mode
phenomenon. Lightning takes the easy path on the outside of the coax.
All coax has a flashover potential which depends on its spacing and the
dielectric of the coax. Once it flashes (not far within the coax) the
voltage is clamped to the sustaining potential of the arc. This is a
steady low potential with a very high conductance in the arc.

Lightning on the outside of the coax must be properly diverted to ground
to avoid damage.
A few twists and turns in the coax increase its opposition to the
lightning (a transient) on the outside of the coax. Such a coil is
advisable between the antenna support and your operating position. Let
the antenna tower carry the lightning to the earth.

Best regards, Richard Harrison, KB5WZI