Armin,
there are many ways to proceed. Here is one way to do it that is simple. A
simulation of a 60' vertical with twelve 70' radial wires, 12' above the
ground,
shows that it wil resonate with 64 uH in series with the 60' wire. The
radials appear to be heavily coupled to the ground. The reasoning behind this
statement is that a 60' wire will resonate with 60 uH when fed against perfect
ground. This means to me, that resonating the radials is not a big need with
this
antenna. In some situations, such as my own, series tuning the radials with an
inductor is a good thing.
Now, the input impedance of your antenna is modeled as 7 ohms in NEC-2 using
"average GND." I think it will be closer to 15-20 ohms. If it is 15-20 ohms
it can be fed nicely with a tuner at the shack after adjusting the series
inductor for minimum VSWR, which should be 3 or 4 to 1.
Dave WX7G
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