There has been a lot of discussion lately about various types of two
wire parallel transmission line. I am a bit confused about what each
person is actually talking about when using various terms such as ladder
line, open wire feeder, window line, etcetera.
I thought that ladder line was called that, because it is two parallel
wires, with their spacing maintained by insulating rods of ceramic,
polyethylene, paraffin soaked doweling or other plastic material. It
looks like a miniature rope ladder. How does open wire feeder differ
from ladder line? Or is it another name for the same thing?
I thought that window line was essentially jumbo sized TV twinlead, with
rectangular holes punched in the flat polyethylene (or other plastic)
separating dielectric material the maintains the spacing between the two
wires. Is that the correct? Most of what I have seen, that I thought was
called window line, is dark brown or black.
By TV twinlead, I am referring to the 300 ohm flat "ribbon cable" that
was commonly used for TV antennas, before coax became the norm. Often
AM/FM Stereo receivers or tuners would be supplied with a folded dipole
made out of this 300 ohm ribbon cable. It is usually translucent white
or dark brown or black.
I have also seen variations of TV twinlead, which instead of having a
flat section of plastic between the two wires, have a round or
elliptical cross section piece of foam between the wires. What is that
And there is another kind of twinlead, which looks a bit like large zip
cord, or telephone service drop wire. What is that called?
In order to have an intelligent discussion, we need to understand what
we mean by the words we use.
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