Reg Edwards wrote:
There are also, very common, 2 and 3-wire (3-phase) transmission lines
which have smaller radiation resistances, but radiation resistances
they DO have depending on conductor spacing.

One of the ARRL Antenna Compendiums describes a 4-wire transmission
line whose Z0 is selectable depending on how the wires are connected.
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73, Cecil http://www.qsl.net/w5dxp