I've used shortened elevated radials in a few projects. Made sense to
me - but anyone who knows me will confirm I'm not the sharpest knife in
the drawer.
Started out with radials that were a bit short - 5-10% - forget
exactly. Verts was constructed and radials hung but built a bit long.
Then trimme each radial - one at a time. The VNA was connected between
the fixed vertical and attaching one radial. Measured the resonant
frequency of the first one - which determined the benchmark.
Disconnected that radial, repeated with the next radial, trimming to
length to match the benchmark resonant frequency. Continued with all
radials, one at a time. Then connected 'em all together. The vertical
final trim frequency was made by adjusting the vertical length slightly
(if you use a small coil in series with the vert that makes adjustment
of the frequency a lot easier than raise/lower, repeat).
It was fun and gave me a sense of precision while using my shiny cool
toys. No idea if it really made a big difference as there was no really
good way to do a before/after comparison. The resulting verticals and
4-square arrays "worked" in the classic sense.
There some amount of modeling and discussion of choices out on my web
page under prior antennas (40m 4sq and 80/160m vert) for those looking
for some late night reading.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 8/29/20 10:05 PM, Robert Harmon wrote:
I am very interested in the shortened radials hypothesis. Has there been any
documented testing of full length vs shortened radials done ?
Bob
K6UJ
On Aug 29, 2020, at 7:16 PM, Richard (Rick) Karlquist <richard@karlquist.com>
wrote:
On 8/29/2020 5:44 PM, Dennis W0JX via TowerTalk wrote:
Unequal currents in 1/4 wave radials is to be expected primarily due to three
factors: 1.) varying quality of the ground under each radial; 2.) the effect of
close by objects such as buildings and other towers; and 3.) the variation in
the length of the radial wires depending on type of wire, insulation, and
construction methods. Effect on the actual radiation pattern depends, of
course, on the severity of the current variation and the number of radials
utilized.
Dick Weber, K5IU, wrote a very informative article in the late 90's which was
published in Communications Quarterly. He argued that 1/4 wave long radials
were the poorest length on could use. He strongly recommended radial lengths of
either 60-70 degrees (shortened) or 120 degrees long. These radials are tied
together at a common point and fed either through a coil or a capacitor.
W5UN had a very successful 4 square for 160 meters which used four, 96 foot
long radials fed through a common coil. The radials were about 15 feet off the
ground.
Here at W0JX, I have four, 48 foot radials on my elevated 80 meter ground
plane. The four radials come to a common point below the radiator and are tied
to the coax shield through an inductor of approximately 3.3 uh. A big advantage
of this arrangement is that I can resonate the antenna system by moving the tap
on the radial loading coil. After many years of using full-sized radials, my on
the air results tell me that the shortened radials are working better than the
full size radials did.
73 Dennis W0JXMilan OH
I'm not following the logic here. If various radials have
unequal impedances, I don't see now tying them in parallel
though a coil or capacitor with magically make them have
equal currents. Did Dick actually compare the currents in
the various configurations as built? All I see are anecdotes,
not AB comparisons or measurements.
Now if someone told me to use shortened or lengthened radials
and put individual coils or capacitors in series with each radial, then
I might believe the currents would be forced into equality.
Are you sure you got the story straight about Dick's article?
(I don't have access to it).
73
Rick N6RK
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