[TowerTalk] Another Ground Radial Question

[Jim Lux]

-----Original Message-----
>From: Kshaddrick <kshaddrick at jetup.net>
>Sent: May 23, 2011 11:32 AM
>
>Somewhere in the distant past I read that the radials of one antenna cannot overlap those of another. Is this really true? There are some folks who indicate that if the radials are insulated it shouldn't be a problem. My issue is I have an existing vertical installation within radial range of a new tower installation. I plan to shunt feed the tower and if I can't overlap the existing radials from the vertical antenna, that will leave quite a wide area with no radial coverage for the shunt fed antenna (basically from east through south to the west, the vertical sits in the south east and the house covers the rest).
>

If you have overlapping radial systems, inevitably, there's going to be some coupling between them (whether they are insulated or not, or buried or not, or elevated or not).  As such, the "other antenna" becomes a part of the antenna system, and might have an effect on things like feedpoint impedance and pattern.

People who are building phased arrays, especially using some of the ad-hoc feed schemes that are very sensitive to mutual impedances, might notice changes in system performance as the coupling varies (e.g. as soil moisture changes).