On Thu, 30 August 2001, "Tom Rauch" wrote:
> The only improvement occurs when multiple drops are so far apart
> zone currents at the base do not overlap each other, which means
> each ground system has to be smaller than optimum.
Basically I agree: there is only improvement with the multiple in-phase
verticals when the original ground system *is* smaller than optimum. That was
implied in the original premise about losses starting out large compared to the
radiation resistance. In fact, as I noted before, there is little to be gained
if the losses had started out low, which means the ground system had to have
been near optimum to begin with. Thus I don't think there is a technical
contradiction here. The issue is whether there are any practical situations
where there would be a benefit. An extreme example would be a vertical with
just a ground rod as a ground system.
Also, I realized my original statement about reduced benefit at larger spacing
is not quite correct. A little analysis shows that the gain can be realized at
larger spacings IF the high loss conditions described above were true.
> One case where this would help is when a driveway would be in the
> middle of an area, and you couldn't cross the driveway with radials.
This is one possible scenario.
>
> This is an advantage for you because you already have a system
> for 80, and can make that system act like a SINGLE vertical the
> same height would behave if placed in the exact middle of your
> array with the same physical area of ground system. That would be
> better than feeding only one element at the edge of the ground
> system.
This is another scenario which may be of interest if an existing short vertical
array was already in place.
73, John W1FV
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