<> It can be quite tedious to build one's own ladder line. Wire size and
<> spacing between wires is a critical factor in determining the resulting
<> impedance of the line. Maintaining consistent spacing between wires
<> is difficult.
All of this is quite true. But let me play devil's advocate. I maintain
that keeping a constant impedance (and hence spacing) is not at all
important. The impedance of the line could vary over a wide range (200 to
600 ohms, to pick some numbers) along the length of the line and the most
important characteristics would still be conserved. 1) The line would still
be low loss. 2) At any given point along the line current balance would
still be maintained, even if the spacing was different than at another
point.
Most of us do NOT depend on the characteristic impedance of the ladder line
to do an exact impedance transformation from the antenna to the rig.
Rather, we use a tuning network at the transmitter end of the ladder line to
do the needed impedance transformation. All a variable spacing on the
ladder line means, in pragmatic terms, is a slightly different setting of
the antenna tuner.
I've built only one ladder line recently and the construction technique
resulted in perhaps a +/- 20% variance in the spacing along the line. It
works just fine.
73
... Craig AC0DS
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