On 9/2/2013 11:18 PM, Matt Moller wrote:
I don't have any experience with 43 ft verticals myself but have heard
a lot about them and have been thinking about building one. I too
would like to learn more.
The reason for my post asking for experience with this antenna and the
Elecraft tuner is that I'm putting together a presentation on 43-ft
verticals for Pacificon next month. So far, I've done a lot of modeling
to understand how a 43-ft vertical behaves on all ham bands, both when
ground-mounted and on the roof of a typical home (with two radials for
each band 40-10M).
A few years ago, AD5X did some excellent work on matching a 43-ft
vertical, with engineering that can best be described as heroic, and
shared it in an fine Power Point that he's done for ham clubs, and that
is on the internet. He's given me permission to include parts of it in
my Pacificon talk. That talk is scheduled for Saturday morning.
The day before, as part of the Antenna Forum, I'm showing a rather
extensive study with the title, "If I Could Put My Multi-Band HF
Vertical On My Roof, Should I?" Except for the 43-ft vertical, nearly
all commercial multi-band verticals are resonant on the bands they
cover, and are either monopoles with radials (a classic ground plane),
or vertical dipoles without radials. Various designs use anything from
traps to a combination of traps, stubs, and matching sections to
resonate the antenna and present a 50 ohm load. .
Both Power Points will be on my website after Pacificon.
As to radials -- some of the best work I've seen is by Rudy Severns,
N6LF, who has done both extensive modeling and significant experimental
work to confirm the models. His work is quite thoughtful, and presented
in a manner that is quite readable (but not light reading). As to
assigning resistance values to a given number and length of radials --
I've seen several published studies, some in the ARRL Handbook and
Antenna Book, that come up with quite conflicting numbers. I suspect
that the primary cause of the conflicting results is the nature of the
soil underneath the radial system. At Pacificon last year I did a talk
about getting on 160M from a residential lot, which is mostly about
antennas, radial systems, and counterpoises. In it, I collected much of
the better work I've seen about radial systems. The Power Point is on
my website. http://k9yc.com/publish.htm
Based on my modeling, and upon an excellent set of measurements by N0AX
and K7LXC of a dozen commercial verticals, if I had limited space and
could not rig horizontal dipoles for the bands I wanted to work, I would
use one of those commercial multi-band antennas configured as a vertical
dipole, and I would put it on my roof.
73, Jim K9YC
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