If you read N6LF's work closely (see fig16 in 3/2012 QEX) you will see
that radial height above 5' adds a few 10ths of a db improvement at
most. (8ft =.015 wavelength above ground) Given noise and QSB on 160
hardly worth the effort ..IMO. Ditto on the number of radials more than
4 at a reasonable (8') height buys very little as well. What is actually
more important is soil conductivity Rich farm loam vs sandy Florida
(Fig 15) is worth 5DB !!! I cant imagine trying to keep sixteen 134'
radials 20 feet in the air !
Another good read on elevated radials ( non resonant radials) that
doesn't get much play is by K5IU, "Optimal Elevated Radial Vertical
Antennas" , Communication Qrtly, spring 1997. If Google is not your
friend contact me off list and I will send you a copy.
Dave NR1DX
On 12/3/2022 2:17 PM, Jim Brown wrote:
On 12/3/2022 10:20 AM, Chuck Dietz wrote:
Thanks for the info. I think I am going with 60 radials on the ground. I
want to use the 160 vertical tower to support an 80 meter array
around it.
Elevated radials might make adjustments way more complicated.
It's worth studying N6LF's work on elevated radials. He stresses that
keeping radial currents equal reduces loss, that making them slightly
shorter than resonant helps that, and so does having MORE elevated
radials -- for example, 8 is better than four. From N6BT, I learned
that elevated radials for 160M should be at least 16-20 ft high; I
learned that when I asked him why my 4 ft high radials weren't working
well.
I have a
tractor and a good welder guy to weld a bracket and tube to a single plow
shear to make a radial plow.
Remember that the only virtue of burying radials is to protect them
from damage, or from being a trip hazard. We are NOT trying to couple
the antenna to the earth. The function of radials is to SHIELD the
field produced by the antenna from the lossy earth, and to provide a
low resistance path for the antenna's return current IN PLACE OF THE
LOSSY EARTH.
Radials DO couple to the earth, and the ground loss shows up as series
resistance. But radial current divides by the number of radials, power
loss is I-squared R, so gets smaller in each radial twice as fast as
the number of radials is increased, so more radials reduces loss.
73, Jim K9YC
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