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
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