Topband: 160M Short Verticals

[John Kaufmann]

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