Topband: Tuning elevated radials

[Phil & Ann Duff]

At 01:35 9/16/2005, Ford Peterson wrote:

>There are three elevated radials, each about 1/4wL and each about 
>120 degrees apart.  At resonance, I find that the current was not 
>well balanced between the radials.  So I started trimming.  It turns 
>out that by trimming the highest current radial, the system came 
>into relative balance.
>
>The goal of the process was to minimize pattern skew.  I'm thinking 
>it might be quieter if I achieve a good null at zenith.  Perhaps 
>this is a twisted notion to begin with.  I find that the position of 
>the radials is very important.  The SE radial needs to snake its way 
>through some bushes and repositioning that radial has a significant 
>impact (negative) on the current carried by that radial.
>
>Is this normal for an elevated vertical?  I know I am splitting 
>hairs on this, but I'm trying to understand better what is 
>happening.  Modeling using NEC2 does not seem to predict these behaviors.
>
>Any empirical evidence from others who have experimented with this 
>would be appreciated.

Ford -
Dick Weber K5IU presented a paper in 1995 at the W5 DX Bash that 
included some work Dick had done in the area of elevated radial 
current imbalances with regards to remotely tuned low-band vertical 
ground plane antennas.

K5IU referenced these:
"Understanding Elevated Vertical Antennas" by KJ6GR in Spring 1995 
Communications Quarterly.
This article showed the effect on vertical antenna patterns caused by 
"unbalanced radials" and that <60 degree length radials are desired.
The KJ6GR article referenced "HF Antennas for all Locations" by Les 
Moxon G6XN where Moxon discusses radial current imbalance and 
recommends radials less than .25 wl.

Among the summary conclusions reached by K5IU
.25 wl is worst possible radial length for current imbalance in 
elevated radials.
.125 wl radials fed thru a common radial inductor have much less 
current imbalance vs .25 wl radials with no significant reduction in bandwidth.

YMMV

73 Phil NA4M







.--. .... .. .-..     _. ._ ...._  _ _
Phil Duff NA4M  &  Ann Duff
Georgetown, TX.