[TowerTalk] Bracing, grounding
jimlux at earthlink.net
Mon May 26 09:14:47 EDT 2014
On 5/26/14, 5:49 AM, Mike Reublin NF4L wrote:
> The base for my crank-up tilt-over 70' tower is poured in a 48"
> diameter 10' deep steel culvert. My ground wires are attached to the
> rebar and were also supposed to have been attached to the culvert,
> but were not (long sad story). It would be very very difficult to
> attach them to the culvert now.
> I will drive 2 or 3 rods out from each leg. Should the first one be
> next to the base, or a couple of rod lengths away?
The concrete inside the culvert already gives you a better path to
"earth" than a few rods. A rod driven next to the base would make almost
You'd have to get pretty far away before it would make a difference (the
usual "spacing of the rods" rule of thumb is for rods that are very
thin). By the time you get 20-30 feet away, the series inductance of
the wire going to the rod means that it's not going have much effect.
If you want to reduce "step potential" (the voltage gradient on the
surface), you'd be better off using the money to bury radials, which has
the useful side effect of increasing the apparent soil conductivity for
HF frequencies (and reducing "ground losses" if you operate your tower
as a vertical). If you'll never use your tower as a vertical, then
radials aren't all that useful either.
You've got a great grounding electrode now.
> My raising scheme is a length of 4" diameter pipe embedded 3.5' in
> the concrete a yard behind the tower. Two diagonal braces will run
> from the pipe to the front leg mounts.
> Will 2" water pipe work? Sched 40 or 80? Angle iron?
> 73, Mike NF4L _______________________________________________
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