[TowerTalk] re: forked radial systems

[Rick Karlquist]

Regarding the proposal for forked radial systems:  I had considered that a
few years ago but concluded that it is not cost effective unless wire is
extremely expensive and labor for making fork connections is free.  I also
did an electrical test that suggests that you need at least 30 radials
starting at the base for an effective ground screen.  This limits the amount
of forking you can do.

The electrical test was a follows:  install a 1/4 wave ground mounted
vertical over a 230 foot diameter ground screen, and then evaluate various
configurations for connecting the shield of the coax into the ground screen.
I tried just connecting to the nearest wire in the screen, and got 60 ohms
driving point impedance.  I then tried longer and more numerous radials that
went out a certain distance and then had their ends connected into the
ground screen.  To get to 36 ohms driving point impedance, I had to use 60
radials, 25 feet long.  A compromise system was 24 radials, 10 feet long.
That was around 40 ohms.  I also tried 120 radials, 70 feet long, but there
was no difference compared to 60 radials, 25 feet long.  The ground screen
had wires on 3 foot centers with all the crossovers soldered.

Rick Karlquist
N6RK


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