Reg, have made a lot of progress in developing a NEC 4 model
of a 100 radial system. Just have to iron out a few bugs. When
this
is completed I can try some high frequency models.

Frank
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Frank, don't forget to use a 1/4-wave vertical when calculating
efficiency.

I assume you always include the power in the ground wave in the total
power radiated when calculating efficiency.

I think radial length intervals of 0.5 metres will be OK for 100 or
more radials.
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Reg.