[TowerTalk] Verticals above chain Link fence

[Jim Brown]

On 10/2/2019 1:09 PM, David Gilbert wrote:
> I've never been much of an advocate for just putting something up and 
> trying to qualitatively decide if it works well enough.  It's a sloppy 
> approach and subject to all sorts of variables we can't easily 
> quantify.  But that changes significantly if there is a reference 
> antenna to compare to that's far enough away to not complicate matters 
> with mutual interaction, for at least you have some indication of 
> relative performance.  In this case, that's probably exactly what I 
> would do.

I agree, sort of. But it also helps to do a bit of studying. Here's a 
study I did several years ago that should shed some light. I certainly 
learned useful stuff from doing the work. The most important takeaway is 
that HF verticals work better if they are not ground-mounted. Raising 
the vertical reduces ground losses, improves the vertical pattern by 
lowering the angle of maximum field strength.

http://k9yc.com/VerticalHeight.pdf

Two VERY important observations. First, use a serious common mode choke 
at the feedpoint. See http://k9yc.com/2018Cookbook.pdf

There are two general types of HF verticals -- 1) those that use radials 
are essentially a "ground plane," with various tuning mechanisms to 
resonate them to a quarter wave on each band, and 2) those that do not 
use radials, with various tuning mechanisms that resonates them as a 
center fed vertical half wave dipole on each band.

Type 1 verticals CAN be electrically connected to a fence, tower, or 
other conductive support, with only "good" modifications to their 
performance to the extent that they have decent radial systems. Modeling 
shows that two elevated radials per band that are slightly shorter than 
a quarter should work pretty well.

When a Type 2 vertical is electrically connected to a fence, tower, or 
other conductive support, GROUNDED OR NOT, that conductive support 
becomes part of the bottom half of the antenna and changes both the 
feedpoint impedance and the vertical pattern.

The applications note about vertical antennas goes into detail about the 
different antenna types and identifies popular models by type.

73, Jim K9YC