[TowerTalk] Rooftop vertical grounding
Fri, 11 Feb 2000 08:39:39 EST
<< My name is Jeff and I'm a new ham. I received my general class
license approximately two weeks ago....snip...My first antenna is going to
be a vertical. The Butternut HF9V to be exact. I'm planning on mounting it
the roof of my house with the counterpoise kit on a tripod. The antenna is
about 26 feet in height.
I'm trying to figure out the best way to ground this thing in
case Mother Nature decides to zap it....snip >>
Welcome to amateur radio and to TowerTalk! I must agree with others that it
seems you have been reading through the archives, which are a powerful
resource, especially with the search engine.
I'm no expert myself, but have learned tremendously from reading here. On
the note of sufficient grounding for lightning, you have good reason for
concern: a single ground rod has limited capacity to dissipate lightning
strike energy before the earth immediately surrounding it becomes saturated.
Any remaining energy goes hunting for other (undesirable) places to go.
The minimum recommended number of ground rods for a tower, for instance, is
6, and they are spaced no closer than 2 times their depth. This provides a
substantially larger volume of earth to 'sink' the charge.
I would consider using at least three rods in your downlead or strap from
the roof: one at the point where it first reaches ground level, one along
the line going toward the service ground, and one in the opposite direction
from the service ground, all connected with the same gauge conductor as the
downlead. Space the two additional rods according to the rule above (2 x
their depth). Then, tie in to the service ground as previously recommended.
This keeps the shortest conductor path from the downlead to all rods.
As for homebrew entrance panels, there is a description of one you can build
in the December '99 archive that provides the disconnection scheme also
previously recommended to you. The grounding plate/panel can be as simple as
a flattened 3/4" or 1" copper water pipe, for limited space.
Have fun! The sunspots are still rising!
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