On 2/28/2016 19:36 PM, Hans Hammarquist via TowerTalk wrote:
Does anybody know how the influence would be if I put in wires that run
diametrical instead of radial? What if I put down both radial and diametrical
and connected them together. That would result in a more traditional shield
around the antenna. Just wonder.
Hans - N2JFS
Hans,
A "just wonder" on my list also, particularly since perimeter wires on
top hats make a difference.
So, I built a 40m 1/4wl vertical Pro4 model with 32 buried radials each
0.22wl free space long, 2mm wire, buried 6mm, average ground.
Added a loop (EZNEC function) at the far ends, and then another one
halfway out. 3 models: no loop, loop at ends, and two loops.
Resonance Z was always 55 ohms +/- 1 so no effect on ground loss.
If I buried the wires 10mm then the Z fell to 51 ohms at a lower freq,
for all three cases. The different ground loss for deeper radials seems
a bit like a modeling problem, most likely the wrong Z for the shallower
case.
If Pro4 is to be believed, loop wires on buried radials are a waste of
time and money at 32 radials.
However, there are many anecdotes that ground screens near the base make
a difference. Maybe true when there are few radials, I think unlikely
at 18 and higher. 20 degrees of angle between adjacent radials yields
.034 wl separation at 0.1 wl out on the radial. I've seen posts that
describe ground wire grids for BC stations, maybe there is more insight
there.
YMMV,
Grant KZ1W
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