I've done extensive experimentation with radials on vertical antennas on
160 meters during the past 18 years.
Back in 2001 a MF broadcast engineer friend of mine using professional
broadcast measuring equipment, took near field measurements of the electric
field in V/m RMS. The antenna was a 1/4 wave inverted L with a 64 foot
vertical section and (1/8 wave) 64 foot long radials laying on the ground
surface.
I found the following.
There was little measurable difference between 0 and 4 radials, a small
measurable difference between 4 and 8 radials, a medium measurable
difference between 8-16 radials, a large measurable difference between 16
and 32 radials, a small measurable difference between 32 and 64 and no
discernable measurable difference between 64 and 120 radials.
We then conducted another experiment using conventional (1/4 wave) 128 foot
radials and
found the data to be exactly the same as the 1/8 wave radials. To me this
proved
the theory that the radials need not be any longer than the vertical section
is tall.
I have never had the opportunity to do the experiment with a full 1/4 wave
vertical.
This statement will be controversial. Using a voltage fed electrical 1/2
wave tee antenna with a 64 foot vertical section and three 200 foot long
top hat wires, in the near field we measured only a very small difference
between
1 radial and 64 1/8 wave radials. We measured no difference between 1 radial
and 64 1/4 wave radials.
The ground conductivity was pretty good at the location of the experiment.
It was
a typical Florida hammock swamp that had been filled in but always had black
mucky
soil and a high water table. The conductivity was approximately .03 S/M with
a dielectric
constant of approximately 20.
I've always presumed that the results might be different over ground with
poor conductivity.
- -... ...- -,
Thomas F. Giella, KN4LF
Lakeland, FL, USA
kn4lf@earthlink.net
KN4LF SWL & Amateur Radio Autobiography: http://www.kn4lf.com
New Scientific Evidence for the Existence of God:
http://www.cosmicfingerprints.com/audio/newevidence.htm
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|