Carlos
As I remember it, the original description of an elevated vertical system
appeared in a May 1957 CQ magazine article by Dale Hoppe, W6VSS (now
K6UA) who has one of the first if not the first multi-multi
superstations. This antenna was a parasitic quarter wave vertical array
for 40 meters. By trial and error Dale determined that a height of 10
feet (3 meters) above ground was correct and that the ground losses
appeared to be minimized or absent at this height. Higher did not appear
to improve the antenna. He also found that more than 4 radials were
unneccesary. What he has here you may recognize as a ground plane
antenna, which is much more common at higher frequencies like 10 meters
or at VHF.
I used such an antenna first in the 1960's at the W4BVV multi-multi. We
judged that if 10 feet was good for 40, 20 feet (6 meters) would be good
for 80 and 40 feet (13 meters) would be good for 160. Indeed this is
what we found. Our pair of phased ground planes elevated 6 meters on 80
was a killer antenna for its time on 80. And the 160 meter full sized
vertical elevated 13 meters was very effective into Europe.
These heights above ground were confirmed by antenna modelling on a main
frame computer in the early 1970's. It is interesting that WA3FET who is
one of the people who originally converted the mainframe NEC code into
the MININEC programs we use on PC's to model antennas today gave an
interesting talk on modeling elevated verticals at the Dayton Hamvention
a few years ago. He was unaware of Dale's original article and modeled
the verticals de novo and came out with heights essentially identical to
what had been derived empirically 40 years before.
So you should raise the antenna 10 feet for 40 meters, 20 feet for 80
meters and 40 feet for 160 meters. As a compromise, for an all band
vertical, 20 feet should be a good height for the base. 4 60
foot (20 meter) radials should work well. Of course if you cannot make
the radials that long, make them as long as possible. We drooped them
down toward the ground and secured them to short pieces of wood. You can
make them go to any height at the ends that is convenient and safe for
people walking aroung them.
73 Gene W3ZZ
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