[TowerTalk] RADIAL QUESTIONS
T A RUSSELL
Wed, 17 Dec 1997 17:08:38 -0600
QUESTIONS ABOUT RADIALS LAID ON THE GROUND
Are insulated wires laid loosely on the ground essentially non-resonant?
I have always believed that radials laid on the ground were detuned by
their proximity to the ground. A recent experience makes me question
I am installing an 80M quarter wavelength vertical suspended from a
tree branch at 70 ft. When I check "resonance" against a 4 ft ground rod
using an MFJ antenna analyzer, minimum SWR and minimum resistance
occur just below 3.5 MHz. The antenna wire consists of a 140 ft length
number 14 solid copper wire, folded in half and separated by a 2 ft cross
arm at the top with the two halves suspended from the cross arm.
After laying 32 insulated radials and soldering them to a 3 ft diameter
ring of 1/4 inch copper tubing which encircles the base of the tree and
measuring "resonance" against the radials, minimum SWR and
minimum resistance occur around 3.1 MHz. When measured against
one, two, or 4 radials, the minimum readings are even lower in frequency
24 of the 32 radials are approximately 100 ft long while the remaining 8
range from 70 to 80 ft. The shorter radials are from NE to SE and end
at the edge of a creek. The radials are NOT connected to ground.
The ground is soggy and has surface water in several places and tends
to remain this way most of the winter.
An extensive study by Brown et.al. was performed around 1935 showing
that field intensity increased with number and length of BURIED radials.
I do not recall how they matched the antenna or how deep the radials
were buried or even if the radials were bare or insulated wire.
So, for question number two, do I need to tune these insulated radials
laying on top of the ground surface to 1/4 WL at 80M to obtain resonance
at 3.5 MHz?
I refrained from providing the SWR and resistance numbers until I check
the resistance and SWR calibration of this instrument. Presumably the
frequency counter is reasonably accurate. I need to understand what
accounts for the frequency shift between an earth connection and
connection to the insulated radial field laying on the ground.
Your ideas are welcomed!
Thanks for your consideration,
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