Topband: Evaluating shunt fed tower ground system

[Michael Tope]

----- Original Message ----- 
From: <nl7z at mtaonline.net>


> At the current time, there is only 22 radials connected - which I plan to
> increase to about 100 radials.
> 
> My question is mainly, what impedance should I be seeing with this
> electrical length antenna?


Kevin,

If you are shunt feeding your tower, then the feedpoint 
impedance in all likelihood won't bear any reseamblance to 
the base impedance. The shunt arm forms an impedance 
transformer. By changing the tap point and shunt arm 
spacing you can vary the resistive component of the feedpoint 
impedance over a whole range of values. I think 60 radials 
over average soil is considered the point of dimensioning 
returns. If you have really good soil, you might get by with 
less. If it were me, I would go with 40 to 60 depending on 
how hard it is to put them down. 

73 de Mike, W4EF.................................