> To a first order, you have 3 dipole elements with
> impedance of 72 ohms, in parallel.
I don't think so Jim. If that were the case there would be
no F/B and the current would not be binomial.
The three element Yagi works so well for F/B because
elements have a 1:2:1 current ratio and differing phase,
which means they clearly cannot be treated or thought of as
three 72 ohm dipoles in parallel.
It's all about the complex mutual coupling and that coupling
can move the impedance of the driven element around with
quite a variation in actual amount.
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